Liquid-Liquid Heat Transfer in Spray Column

LIQUID-LIQUID HEAT TRANSFER IN A SPRAY COLUMN THESIS Submitted by SUDHANYA KARMAKAR Class Roll No- 001310302001 Exam Roll No-M4CHE15-01 Registration No-124698 of 2013- 2014 Under the Guidance of Prof. (Dr.) Avijit Bhowal in partial fulfillment for the award of the degree of MASTER OF ENGINEERING IN CHEMICAL ENGINEERING DEPARTMENT OF CHEMICAL ENGINEERING JADAVPUR UNIVERSITY Jadavpur, Kolkata-700032 MAY 2015

Declaration of Originality and Compliance of Academic Ethics

I hereby declare that this thesis contains literature survey and original research work by

the undersigned candidate, as part of his Master of Engineering in Chemical

Engineering studies.

All information in this document have been obtained and presented in accordance with

academic rules and ethical conduct.

I also declare that, as required by these rules and conduct, I have fully cited and

referenced all material and results that are not original to this work.

Name: Sudhanya Karmakar

Class Roll No-001310302001

Exam Roll No- M4CHE15-01

Registration No- 124698 of 2013- 2014

Thesis Title : LIQUID LIQUID HEAT TRANSFER IN A SPRAY COLUMN

Date: Sudhanya Karmakar

FACULTY OF ENGINEERING AND TECHNOLOGY

DEPARTMENT OF CHEMICAL ENGINEERING

JADAVPUR UNIVERSITY

CERTIFICATE OF RECOMMENDATION

This is to certify that Ms. Sudhanya Karmakar, final year student of Master of

Engineering in Chemical Engineering, Jadavpur University, has completed the Project

work titled Liquid Liquid Heat Transfer in a Spray Column under the guidance of

Prof. Dr. Avijit Bhowal during his Masters Curriculum. This work has not been reported

earlier anywhere and can be approved for submission in partial fulfillment of the course

work.

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Dr . Avijit Bhowal

Project Supervisor

Professor

Department of Chemical Engineering

Jadavpur University , Kolkata 32

Approval

The following thesis is hereby approved as a credible study of a Engineering subject and

presented in a manner satisfactory to warrant its acceptance as a perquisite to the degree

for which it has been submitted. It is to be understood that by this approval, the

undersigned do not necessarily endorse or approve any statement made, opinion

expressed or conclusion drawn there in, but approve the thesis only for thr purpose for

which it has been submitted.

Department of Chemical Engineering

Jadavpur University

--------------------------------------------------

HOD (Department of Chemical Engineering)

---------------------------------------------------

Dean (FET)

Committee of final examination for evaluation of thesis

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ACKNOWLEDGEMENT

Though the following project is an individual work, I could never have reached the

heights or explored the depths without the help, support, guidance and efforts of a lot of

people. Firstly, I would like to thank my Project Guide, Prof. Dr. Avijit Bhowal

(Chemical Engineering) for instilling in me the qualities of being a good researcher. His

infectious enthusiasm and unlimited zeal have been major driving forces through my post

graduate career at the Jadavpur University, Kolkata. I would also like to thank my

laboratory co-researcher Aritra Das for her support during the project work. I would like

to take this opportunity to thank Mr. Jayant Modak , for his constant encouragement and

helpful advice. I also extend my gratitude to Ms. Chandana Das for her support. My very

special thanks to my parents whom I owe everything I am today, my father Mr. Subodh

Karmakar and my mother Mrs. Tapashi Karmakar. Their unwavering faith and

confidence in my abilities and in me is what has shaped me to be the person I am today.

Thank you for everything. Finally, I would like to take the opportunity to thank all my

teachers and support staff of the Chemical Engineering Department, Jadavpur University,

Kolkata.

Sudhanya Karmakar

22st May, 2013

Contents Chapter No Topics/Subtopics Page No 1. Introduction 1-26 1.1 Cooling Tower 3 1.2 Evaporator 4 1.3 Heat Exchanger 4-23 1.3.1 Classification according to 9-17 contact type 1.3.2 Classification according to 18-19 flow type 1.3.3 Classification according to 19-23 construction type 1.3.4 Classification according to 23 number of fluids 1.3.5 Classification according to 23 surface compactness 1.4 Spray Column 24-26 2. Literature Review 27-36 3. Aim & Objective 37-39 4. Experimental Section 40-44 4.1 Experimental Setup 41-42

4.2 Experimental Procedure 42-43 5. Results & Discussion 45-65 5.1 Study of heat loss in counter-flow 46-48 Spray-Column 5.2 Calculation of thermal efficiency 49 5.3 Calculation of heat transfer coeff 49 -icient 5.4 Effect of water flow rate on h & 50-55 5.5 Effect of variation in water inlet 56-58 temperature on h & 5.5 Effect of variation in column height 59-61 on h & 5.5 Effect of variation in phase ratio on 62-65 6. Conclusion 66-67 NOMENCLATURE 68 REFFERENCES 69-70

List of Figures Fig No. Figure Name Page No. Fig 1.1 Classification of heat exchangers 8 Fig 1.2 Shell and tube heat exchanger 9

Fig 1.3 Plate and Frame heat exchanger 10

Fig 1.4 Turbulent pipe contact 13

Fig 1.5 Typical mechanically agitated towers 14

Fig 1.6 Baffle tray column 15

Fig 1.7 A possible configuration of a packed bed condenser 15

Fig 1.8 Schematics of a Spray Column 16

Fig 1.9 Schematic of a sieve tray column 17

Fig 1.10 Schematic of a Parallel flow & a Counter Flow Heat Exchanger 18

Fig 1.11 Schematic of a Cross Flow Heat Exchanger 19

Fig1.12 Tubular Heat Exchanger 19

Fig1.13 Plate-Type Heat Exchanger 20

Fig1.14 Extended Surface Heat Exchanger 21

Fig1.15 Regenerator 22

Fig1.16 Typical countercurrent-flow spray tower 26

Fig 1.17 Crosscurrent-flow spray tower 26

Fig 4.1 Overall Experimental Set Up 43

Fig 4.2 Schematic of experimental set up 44

Fig 5.1 Effect of water flow rate on thermal efficiency at water 51

bath temperature550C & Column Height 105cm

Fig 5.2 Effect of water flow rate on thermal efficiency 51

at water bath temperature 640C & Column Height 105cm


at water bath temperature550C & Column Height 80cm


at water bath temperature640C & Column Height 80cm

Fig 5.5 Effect of water flow rate on heat transfer coefficient 54

at water bath temperature 550C & column height 105cm

Fig No. Figure Name Page No.







Fig 5.9 Effect on thermal efficiency with change in water 57

bath temperature at a height 105cm

Fig 5.10 Effect on thermal efficiency with change in water 57


Fig 5.11 Effect on heat transfer coefficient with change in water 58


Fig 5.12 Effect on heat transfer coefficient with change in water 58


Fig 5.13 Effect on thermal efficiency with change in column height 60

at a water bath temperature 550C

Fig 5.14 Effect on thermal efficiency with change in column height 60

at a water bath temperature 640C

Fig 5.15 Effect on overall heat transfer coefficient with change in 61

height at a water bath temperature 550C


height at a water bath temperature 640C

Fig 5.17 Effect on Thermal Efficiency with change in phase ratio at 63

a Column Height 105cm

Fig 5.18 Effect on Thermal Efficiency with change in phase ratio at 63



phase ratio at a Column Height 105cm



Fig 5.21 Effect on Kerosene Outlet temperature with change in 65


Fig 5.22 Effect on Kerosene Outlet temperature with change in 65


List of Tables Table No. Table Name Page No

Table1 Heat loss at Water Bath Temperature-55 0C & 46

Column Height- 105 cm

Table2 Heat Loss at Water Bath Temperature- 64 0C & 47


Table3 Heat Loss at Water Bath Temperature- 55 0C & 47


Table4 Heat loss at Water Bath Temperature- 64 0C & 48


1

Chapter 1 IntroductIon

2

Most of the industries use water for their production and this water often requires

particular properties such as solubility, transportability and heat exchanging potential.

Water in industry is used for boiler make up, processing, product treatment and cleaning,

cooling etc. The quantity of water consumption differs between types of industries. The steel,

chemical, oil, petrochemical, pulp and paper industries are major users of large quantities

of water per unit price of products because they use fresh water for cooling, cleaning and

product processing. Cooling water comprise the majority of consumption of industrial

water. Due to huge water consumption in each plant, cooling water is generally reused in

order to save the acquisition cost & the water resource.

So, a huge amount of water is necessary to re-circulate in many industries such as:

thermal power plant, oil industries, petrochemical industries etc. In thermal power plant,

large amount of superheated steam is produced by using soft water. This steam is used to

rotate the impeller of the turbine so that it can generate power. This used steam is

condensed by passing it through a condenser. For this purpose, a water stream is passed

through the condenser coil to transfer the heat energy from steam to water. Therefore, the

water temperature rises. The temperature of the water must be reduced to make the water

fit for recycling.

In oil and petroleum industries, steam is used to raise the temperature of oil and

petroleum product to maintain the flowability. For this reason a huge steam is used in

steam jacket in storage tanks, process lines, columns, reboilers etc. in all over the process.

That steam passed through the condenser where water recirculation is necessary. Besides

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condenser there are many heat exchanger equipments in those industries where water is

used as coolant. There also water recycling process is essential. Again, it should also be

noted that for the environmental friendly discharging of the waste water in some

industries the temperature of the water should be brought down or else it may have

several effects on the aquatic or marine life by causing abnormal increase in the

temperature of the water body. The sharp increase in water temperature inhibits the

growth of microorganisms which are very essential for the maintenance of aquatic

symbiosis. So cooling of process hot water stream is an important operation in process

industries. There are various equipment used for cooling hot water such as heat

exchanger, cooling towers, evaporators etc. The different equipment used for cooling

water is:

1.1 Cooling Tower

When warm liquid is brought into contact with unsaturated gas, part of the liquid

evaporates and the liquid temperature drops. The most important application of this

principle is in the use of cooling towers to lower the temperature of recirculated water

used for condensers and heat exchangers in chemical plants, power plants. Cooling

towers are large-diameter columns with special type of packing designed to give good

gas-liquid contact with low pressure drop. Warm water is distributed over the packing by

spray nozzles or a grid of notched troughs or pipes. Air is passed through the packing by

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forced-draft or induced-draft fan or in some designs it is drawn through by natural

convection.

1.2 Evaporator

An evaporator is a device used to turn the liquid form of a chemical into its

gaseous form. The liquid is evaporated, or vaporized, into a gas. It is used in air

conditioning system to evaporate gas from liquid while absorbing heat in the process. It

can also be used to remove water or other liquids from mixtures. In the concentration

process, the main objective of evaporation is to vaporize most of the water from a

solution which contains the desired product. The general types of evaporator used in

todays world are open kettle or pan evaporator, agitated film evaporator, pan solar

evaporator, natural circulation type and forced circulation type. Natural circulation type

evaporators are classified into horizontal tube evaporator, vertical short tube or calandria

evaporator, long tube vertical rising film type, long tube vertical falling film type. Open

kettle or pan evaporators are the simplest evaporator consists of an open kettle in which

the liquid is boiled. The heat supplied by condensation of steam in a jacket in the liquid.

these are inexpensive and simple to operate but the steam economy is very poor.

1.3 Heat Exchanger

A heat exchanger is a device that is used to transfer thermal energy (enthalpy)

between two or more fluids, between a solid surface and a fluid, or between solid

5

particulates and a fluid, at different temperatures and in thermal contact. In heat

exchangers, there are usually no external heat and work interactions.

Heat exchangers are commonly used in practice in a wide range of applications,

from heating and air-conditioning systems in a household, to chemical processing and

power production in large plants. Heat exchangers differ from mixing chambers in that

they do not allow the two fluids involved to mix. In a car radiator, for example, heat is

transferred from the hot water flowing through the radiator tubes to the air flowing

through the closely spaced thin plates outside attached to the tubes.

Heat transfer in a heat exchanger usually involves convection in each fluid and

conduction through the wall separating the two fluids. In the analysis of heat exchangers,

it is convenient to work with an overall heat transfer coefficient U that accounts for the

contribution of all these effects on heat transfer. The rate of heat transfer between the two

fluids at a location in a heat exchanger depends on the magnitude of the temperature

difference at that location, which varies along the heat exchanger. In the analysis of heat

exchangers, it is usually convenient to work with the logarithmic mean temperature

difference LMTD, which is an equivalent mean temperature difference between the two

fluids for the entire heat exchanger.

In a few heat exchangers, the fluids exchanging heat are in direct contact. In most

heat exchangers, heat transfer between fluids takes place through a separating wall or into

6

and out of a wall in a transient manner. In many heat exchangers, the fluids are not

separated by a heat transfer surface, and ideally they do not mix or leak. Such exchangers

are referred to as direct transfer type, or simply recuperators. In contrast, exchangers in

which there is intermittent heat exchange between the hot and cold fluidsvia thermal

energy storage and release through the exchanger surface or matrix are referred to as

indirect transfer type, or simply regenerators. Such exchangers usually have fluid leakage

from one fluid stream to the other, due to pressure differences and matrix rotation/valve

switching. Common examples of heat exchangers are shell-and tube exchangers,

automobile radiators, condensers, air preheaters. If no phase change occurs in any of the

fluids in the exchanger, it is sometimes referred to as a sensible heat exchanger. There

could be internal thermal energy sources in the exchangers, such as in electric heaters and

nuclear fuel elements. Combustion and chemical reaction may take place within the

exchanger, such as in boilers, fired heaters, and fluidized-bed exchangers. Mechanical

devices may be used in some exchangers such as in scraped surface exchangers, agitated

vessels, and stirred tank reactors. Heat transfer in the separating wall of a recuperator

generally takes place by conduction. However, in a heat pipe heat exchanger, the heat

pipe not only acts as a separating wall, but also facilitates the transfer of heat by

condensation, evaporation, and conduction of the working fluid inside the heat pipe. In

general, if the fluids are immiscible, the separating wall may be eliminated, and the

7

interface between the fluids replaces a heat transfer surface, as in a direct-contact heat

exchanger. There are different types of heat exchangers as follows.

8

Fig 1.1: Classification of Heat Exchangers

9

1.3.1 Classification according to contact type:

1.3.1(a) Indirect contact heat exchanger involves heat transfer between hot and cold

streams of two phases in the presence of a separating solid wall.

Shell and tube heat exchangers:

As shown in fig.1.2 shell and tube heat exchanger has two sides. One is tube side

and another is shell side. Tube side has series of tubes called tube bundle. Tube bundle

can be made of different types of tubes: plain, longitudinally finned, etc .The fluid

contains tube side can be heated or cooled by transferring heat with shell side fluid. The

shell and tube heat exchanger can be used at temperature >2500 C and pressure at>30 bar.

Fig.1.2: Shell and tube heat exchanger.

10

Plate and Frame heat exchanger:

For many applications at moderate temperature and pressure, an alternative to the

shell and tube exchanger is the gasketed plate exchanger (fig.1.3), which consists of

many corrugated stainless-steel sheets separated by polymer gaskets and clamped in a

steel frame. Inlet portals and slots in the gaskets direct the hot and cold fluid to alternate

spaces between the plates. The corrugation induces turbulence for improved heat transfer

and each plate is supported by multiple contacts with adjoining plates, which have a

different pattern or angle of corrugation. The space between plates is equal to the depth of

the corrugations and is usually 2 to 5 mm.

Fig.1.3: Plate and Frame heat exchanger

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1.3.1(b) Direct Contact Heat Exchanger

In a direct-contact exchanger, two fluid streams come into direct contact,

exchange heat, and are then separated. Common applications of a direct-contact

exchanger involve mass transfer in addition to heat transfer, such as in evaporative

cooling and rectification; applications involving only sensible heat transfer are rare. The

enthalpy of phase change in such an exchanger generally represents a significant portion

of the total energy transfer. The phase change generally enhances the heat transfer rate.

Advantages and Disadvantages in Utilizing Direct Contactors

The exchange of heat between two fluid streams can, in general, be accomplished

using either direct contact or surface-type heat exchangers. There are, however, several

limitations to the use of direct contactors. First, if two fluid streams are placed in direct

contact, they will mix, unless the streams are immiscible. Thus, stream contamination

will occur depending on the degree of miscibility. The two streams must also be at the

same pressure in a direct contactor, which could lead to additional costs. The advantages

in utilizing a direct contactor include the lack of surfaces to corrode or foul, or otherwise

degrade the heat transfer performance. Other advantages include the potentially superior

heat transfer for a given volume of heat exchanger due to the larger heat transfer surface

area achievable and the ability to transfer heat at much lower temperature differences

between the two streams. Still another advantage is the much lower pressure drop

12

associated with direct contactors as compared to their tubular counterparts. A final

advantage is the much lower capital cost as direct contact heat exchangers can be

constructed out of little more than a pressure vessel, inlet nozzles for the fluid streams,

and exit ports. Of course, it is sometimes advantageous to provide internals,

Varieties of Direct Contact Heat Exchangers

A typical direct contactor provides heat transfer between two fluid streams. The

processes include the simple heating or cooling of one fluid by the other; cooling with the

vaporization of the coolant; cooling of a gas-vapor mixture with partial condensation;

cooling of a vapor or vapor mixture with total condensation; and cooling of a liquid with

partial or complete solidification. Most of the direct-contact applications can be

accomplished with the following devices: a) Spray columns, b) Baffle tray columns, c)

Sieve tray or bubble tray columns, d) Packed columns, e) Pipeline contactors, and f)

Mechanically agitated contactors. There are also some other direct contactors like

evaporator, cooling tower , bubble column reactor.

Fig1.4 to 1.9 - illustrate the general configurations of a) through f), respectively.

Except for the turbulent pipe contactor, all of the devices are countercurrent devices and

depend upon the relative buoyancy of the dispersed phase through a continuous phase.

While the figures illustrate a less-dense dispersed phase being introduced at the bottom of

13

the column, it is possible for the dispersed phase to be denser and introduced at the top,

with the configuration internals appropriately revised.

The turbulent pipe contactor is a parallel-flow device and has the limits of

efficiency of all such systems, whether they be direct contact or surface-type heat

exchangers. That is, the maximum temperature

achieved by the cool stream is that of the

mixing cup temperature. The size of the

turbulent pipe contactor is dictated by the

relative mass flow rate and the nature of the

turbulence.Turbulence promoters can be Fig 1.4: Turbulent pipe contactor

installed to enhance the turbulence and, thereby, reduce the length of contactor necessary

to essentially obtain the mixing cup temperature. If separation of the streams is desired,

the contactor must be followed by a separation device such as a settler, a cyclone

separator, or other mechanisms. While the turbulent pipe conductor is very inexpensive,

if separation is desired, the cost of the settler will in all probability dictate the economics

of the process.The remaining apparatus all have the heat transfer take place between a

continuous phase and a clearly defined disperse phase in the form of drops, bubbles, jets,

sheets, or thin supported films in the case of packed beds.

14

Heat exchangers with

mechanical agitators (Fig 1.5),

while often superior as heat or

mass transfer equipment, are more

difficult to design as the dispersed

phase may have a wide range or Fig 1.5: Typical mechanically agitated towers

drop or bubble sizes. Thus, empirical data from the manufacturer to establish

performance is necessary.Further, problems may result in seals at the penetration point of

the drive shafts. Special designs may therefore be necessary.

Baffle tray columns may have similar problems in defining the nature of the

curtain of the dispersed phase. Depending on flow rates and battle design, the dispersed

phase may be a sheet, a series of rivulets or defined streams, which can break up into

drops. If the baffles are, in fact, trays with serrated or notched rims, the dispersed phase

can be designed to be a series of well-defined streams and the heat transfer is more easily

analyzed. The baffles/trays then result in mixing of the dispersed phase and enhance the

internal-to-the-dispersed phase mixing.

15

Fig 1.6: Baffle tray column

Fig1.7: A possible configuration of a packed bed condenser

16

The spray column shown in Fig 1.8 is an open column whose only internals are

the inlet nozzles for the dispersed and continuous

phase. Ideally, such columns are capable of pure

counter flow operation, with the dispersed phase made

up of nearly uniform diameter drops. While it is

possible to design the dispersed phase inlet nozzle to

achieve the desired characteristics, providing a Fig1.8: Schematics of a Spray Column

uniform flow in the continuous phase is more difficult. Great care must be taken or

maldistribution of the continuous phase may lead to diminished heat transfer. Thus, the

design of continuous phase inlet nozzles is sometimes proprietary, or patented.

The bubble column or sieve tray column (see Fig 1.9) enhances the internal heat

transfer coefficient by repeatedly reforming the drops at each tray. Proper tray or baffle

design can lead to shorter columns, and potentially small heat exchanger volume for the

same service. Their major disadvantage is fouling, corrosion or blockage of some of the

holes in the sieve tray.

17

Fig 1.9: Schematic of a sieve tray column

A liquid to liquid heat exchanger designed for highly efficient heat transfer

covering a wide variety of liquid types. The heavy duty design makes it ideal for

demanding commercial, industrial and residential applications where high performance

and low maintenance are important. Here transfer coefficients are greater than

conventional shell and tube or plate exchangers because of the enhanced heat exchange

surface and counter flow design.

18

1.3.2 Classification according to flow type:

1.3.2(a) Parallel flow Heat Exchanger The hot and cold fluids enter the same end,

flow in the same direction and leave at the same end.

Fig 1.10: Schematic of a Parallel flow & a Counter Flow Heat Exchanger

1.3.2(b) Counter flow Heat Exchanger The hot and cold fluids enter at opposite ends,

flow in opposite direction and leave at opposite ends.

1.3.2(c) Cross flow heat exchanger The flow of one fluid is perpendicular to the other

fluid.

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Fig 1.11: Schematic of a Cross Flow Heat Exchanger

1.3.3 Classification according to Construction Type

1.3.3(a) Tubular Heat Exchangers-

These exchangers are generally built of

circular tubes, although elliptical,

rectangular, or round/flat twisted tubes

have also been used in some

Fig1.12: Tubular Heat Exchanger applications. There is considerable flexibility in

the design because the core geometry can be varied easily by changing the tube diameter,

length, and arrangement. Tubular exchangers can be designed for high pressures relative

to the environment and high-pressure differences between the fluids. Tubular exchangers

are used primarily for liquid-to-liquid and liquid-to-phase change (condensing or

evaporating) heat transfer applications. They are used for gas-to-liquid and gas-to-gas

20

heat transfer applications primarily when the operating temperature and/ or pressure is

very high or fouling is a severe problem on at least one fluid side and no other types of

exchangers would work. These exchangers may be classified as shell-and tube, double-

pipe, and spiral tube exchangers. They are all prime surface exchangers except for

exchangers having fins outside/inside tubes.

1.3.3(b) Plate-Type Heat Exchangers-Plate-type

heat exchangers are usually built of thin plates (all

prime surface). The plates are either smooth or have

some form of corrugation, and they are either flat or

wound in an exchanger. Generally, these

exchangers cannot accommodate very high

pressures, temperatures, or pressure and Fig1.13 Plate-Type Heat Exchanger

temperature differences. Plate heat exchangers (PHEs){ can be classified as gasketed,

welded (one or both fluid passages), or brazed, depending on the leak tightness required.

Other plate-type exchangers are spiral plate, lamella, and platecoil exchangers.

21

1.3.3(c) Extended Surface Heat

Exchangers- The tubular and

plate-type exchangers described

previously are all prime surface

heat exchangers, except for a shell-

and-tube exchanger with low

finned tubing. Their heat

exchanger effectiveness is usually Fig1.14: Extended Surface Heat Exchanger

60% or below, and the heat transfer surface area density is usually less than 700 m2 /m3

(213 ft2 /ft3). In some applications, much higher (up to about 98%) exchanger

effectiveness is essential, and the box volume and mass are limited so that a much more

compact surface is mandated. Also, in a heat exchanger with gases or some liquids, the

heat transfer coefficient is quite low on one or both fluid sides. This results in a large heat

transfer surface area requirement. One of the most common methods to increase the

surface area and exchanger compactness is to add the extended surface (fins) and use fins

with the fin density ( fin frequency, fins/m or fins/in.) as high as possible on one or both

fluid sides, depending on the design requirement. Addition of fins can increase the

surface area by 5 to 12 times the primary surface area in general, depending on the

design. The resulting exchanger is referred to as an extended surface exchanger. Flow

22

area is increased by the use of thin gauge material and sizing the core properly. The heat

transfer coefficient on extended surfaces may be higher or lower than that on unfinned

surfaces. For example, interrupted (strip, louver, etc.) fins provide both an increased area

and increased heat transfer coefficient, while internal fins in a tube increase the tube-side

surface area but may result in a slight reduction in the heat transfer coefficient, depending

on the fin spacing. Generally, increasing the fin density reduces the heat transfer

coefficient associated with fins. Flow interruptions (as in offset strip fins, louvered fins,

etc.) may increase the heat transfer coefficient two to four times that for the

corresponding plain (uncut) fin surface. Plate-fin and tube-fin geometries are the two

most common types of extended surface heat exchangers.

1.3.3(d) Regenerators- The

regenerator is a storage-type heat

exchanger, as described earlier.

The heat transfer surface or

elements are usually referred to

as a matrix in the regenerator. Fig1.15:Regenerator

To have continuous operation, either the matrix must be moved periodically into and out

of the fixed streams of gases, as in a rotary regenerator , or the gas flows must be

diverted through valves to and from the fixed matrices as in a fixedmatrix regenerator.

23

The latter is also sometimes referred to as a periodic-flow regenerator, a swing

regenerator, or a reversible heat accumulator.

1.3.4 Classification According to Number of Fluids

Most processes of heating, cooling, heat recovery, and heat rejection involve transfer of

heat between two fluids. Hence, two-fluid heat exchangers are the most common. Three-

fluid heat exchangers are widely used in cryogenics and some chemical processes (e.g.,

air separation systems, a heliumair separation unit, purification and liquefaction of

hydrogen, ammonia gas synthesis). Heat exchangers with as many as 12 fluid streams

have been used in some chemical process applications.

1.3.5 Classification According to Surface Compactness-

Compared to shell-and-tube exchangers, compact heat exchangers are characterized by a

large heat transfer surface area per unit volume of the exchanger, resulting in reduced

space, weight, support structure and footprint, energy requirements and cost, as well as

improved process design and plant layout and processing conditions, together with low

fluid inventory. A gas-to-fluid exchanger is referred to as a compact heat exchanger if it

incorporates a heat transfer surface having a surface area density greater than about 700

m2 /m3. In case of heat transfer surface having a surface area density less than about 700

m2/m3 then it is called non-compact heat exchanger.

24

1.4 Spray Column

1.4.1 Spray Column

In this study of liquid liquid heat transfer Spray Column is used as a heat

exchange equipment. A Spray Column is a two phase contactor used to achieve the mass

& heat transfer between a continuous phase & a dispersed phase. It consists of empty

cylindrical vessel made of steel or plastic & nozzles that spray liquid in the vessel. The

light phase usually enters the bottom of the tower and moves upward while the heavy

phase moves downward.

A spray is a dynamic collection of drops dispersed in a gas. The process of

forming a spray is known as atomization. A spray nozzle is the device used to generate a

spray. The two main uses of sprays are to distribute material over a cross-section and to

generate liquid surface area. There are thousands of applications in which sprays allow

material to be used most efficiently. The spray characteristics required must be

understood in order to select the most appropriate technology, optimal device and size.

It is mainly considered as a gas liquid contactor. But it also works on liquid-liquid

contact. The common design consists of an empty cylindrical shell through which the gas

flows upwards against a downflowing spray of the absorbing liquid .Here the gas is the

continuous phase & the liquid is the dispersed phase. The liquid is dispersed in the form

of fine droplets near the top by forcing it through spray nozzles. Spraying should be

uniform over the cross-section of the vessel for the sake of better gas liquid contact. The

liquid droplets have a distribution of size. The contact time between the droplets & the

gas has also a distribution. A fraction of the droplets unavoidably strike the wall of the

tower and the liquid flows down as a film. Backmixing of the gas remains small in a

25

spray tower. The raining droplets are collected at the bottom and liquid leaves through a

nozzle. A demister is invariably used to prevent entrainment of droplets in the exit gases.

The Spray tower can handle a large volumetric gas flow rate at a low pressure drop. The

HTU is substantially large. Pumping the liquid at a high pressure to the spray nozzles

involves substantial power consumption. The absence of any moving parts is also an

advantage of the spray Column. The device is particularly suitable for a. corrosive liquids

& gases, b. liquids containing suspended solid, c. gas streams may contain dust, d. low

gas pressure drop application, e. scrubbing various waste gas stream, f. liquid-liquid

extraction.

1.4.2 Spray formation

Spray atomization can be formed by several methods. The most common method

is through a spray nozzle which typically has a fluid passage that is acted upon by

different mechanical forces that atomize the liquid. The first atomization nozzle was

invented by Thomas A. DeVilbiss of Toledo, Ohio in the late 1800s His invention was

bulb atomizer that used pressure to impinge upon a liquid, breaking the liquid into a fine

mist. Spray formation has taken on several forms, the most common being, pressure

sprayers, centrifugal, electrostatic and ultrasonic nozzle.

26

1.4.3 Flow Patterns in a Spray Column

Fig 1.16: Typical countercurrent-flow spray tower

Fig1.17: Crosscurrent-flow spray tower

27

Chapter-2 Literature review

28

Letan & Kehat (1967) studied the mechanics of a Spray Column. Local & average

hold up & drop size distribution as function of flow rates which were measured for

kerosene drops and water in a counter current , 15cm I.D., 160cm long Spray Column.

The range of flow rates was 5 to 40 liters/min of kerosene & 0 to 50 liters/min of water.

At the same pairs of flow rates of the dispersed and the continuous phases in spray

columns, three modes of drop packing can be obtained. These are termed, in order of

increasing average hold up and increasing regularity of flow patterns, dispersed,

restrained, and dense packing. For dispersed packing, at low flow rates of the two phases,

the hold up and the drop size are constant along the column. At high flow rates the drop

size increases from bottom to top of the column & hold up increases from top to bottom

of the column. The range of flow rates for the operation of a spray column is extended by

use of a conical entry section (Elgin design) at the bottom of the column, by the

formation of an equilibrium region in the conical section. The average hold up increases

with flow rates of both phases for dispersed & restrained packing, and restrained packing

and with decreased flow rates of both phases for dense packing. The best definitions of

flooding in a spray column are either the point of maximum average specific area of the

drops, which corresponds to the onset of coalescence in the column, or the start of

rejection of drops from the column proper.

Siqueiros & Bonilla (1999) did an experimental study of a three-phase, direct-

contact heat exchanger. An experimental pilot scale three-phase, direct-contact heat

exchanger was constructed and tested. The DCHE (Direct Contact Heat Exchanger) is a

spray column of 0.61 m (24 in) nominal diameter carbon steel, 3.3 m height with two

distributors. The water (continuous phase) distributor is on the top of the column. The

29

pentane (discontinuous phase) distributor is on the bottom of the column. It has six

viewing windows along its length. The column has two flanges. On the upper flange the

pentane vapour exit and the security valve were installed. On the lower flange the cool

brine exit and the liquid pentane inlet were installed. Steady-state conditions were

reached between 30 and 60 min after the pentane was fed into the column. The main

parameters of control for each experimental test were the pentane and water mass flow-

rates. The inlet water temperatures ranged from 75 C to 88C, and the inlet pentane

temperatures varied from 23 C to 38C. The volumetric heat transfer coefficient, hold-up

and heat flow-rate are functions of pentane mass flow-rate. For high pentane/water

volumetric flow ratios flooding was reached. Before reaching flooding conditions,

accumulation of liquid pentane at the top of the active volume was found. The volumetric

heat transfer coefficient was achieved in between 4.5-8 KW m 1 K 1 .

Peng et.al, (2001) studied heat transfer in gasliquidliquid three-phase direct-

contact exchanger. The heat transfer to dispersed droplets in an immiscible continuous

phase is studied for the n-pentanewater system. The gasliquidliquid three-phase

section of the exchanger is divided into two stages, where the volumetric heat transfer

coefficients are developed, respectively. These models take into account the evaporation

of continuous phase water into the dispersed phase and the two-phase droplets break-up.

The calculated results showed good agreement with the experimental values. This paper

studies the heat transfer in a parallel flow exchanger and discusses the effects of some

operational parameters on the volumetric heat transfer coefficient. Some expressions take

account of the possible coalescence and break-up of the droplets. The expressions may

improve our insight into the dependencies of the total heat transfer performance of

30

exchangers on individual operational parameters and, indirectly, on the exchanger design.

The exchanger is made of plexiglass with an inside diameter of 90mm and a length of

2000 mm. On both sides of the exchanger there are 20 holes with a diameter of 8mm each

and which are used for measuring the temperature and pressure. n-Pentane is used as the

dispersed fluid. It is injected into the exchanger from a distributor located at the bottom

of the exchanger. Hot water is supplied to the exchanger from the bottom when it is

heated to the given temperature in the heater. The water flow rate is measured by using a

rotameter. A volumetric heat transfer coefficient was achieved in between the range of

20-120 KW m 3 K 1 for variation in column elevations (0-2m) at different flow rates of

dispersed & continuous phase.

Pierce et.al (1959) studied heat transfer and fluid dynamics in mercury-water

spray columns. Heat transfer and fluid dynamics were studied in columns in which hot

mercury was sprayed into a rising stream of water. Volumetric and area heat transfer

coefficients are presented which were found to be lower than those reported for heat

transfer from fixed spheres. It was observed that considerable water bypassed the stream

of drops, while some surrounding the drops flowed downward. This behavior resulted in

water temperatures at the base of the column which were considerably higher than the

inlet water temperatures. Consequently the outlet mercury temperature did not approach

the inlet water temperature as a limit. The very unconventional flow pattern of the water

was unexpected and is believed to be an important factor in spray-column heat transfer

and mass transfer kinetics. Six different columns were used, but the same steel end

assemblies were used with each. The columns were fabricated from 1- and 2-in. I.D.

Pyrex pipe. The enlarged ends of the columns were 6 in. I.D. to accommodate the end

31

assemblies. Measurements of temperatures, mercury flow rate, water flow rate, drop

sizes, drop velocities, water phase movements were measured & varied during the

experiment. The volumetric heat transfer coefficient observed in between the range of

19.3*103 B.T.U/hr-cubic ft-0F to 48.3*103 B.T.U/hr-cubic ft-0F for a column of 1 inch

diameter, 13.25 inch length where water flow rate were maintained at 54.8 to 109.8

gal/min-sq ft & mercury flow rate were maintained at 2000 to 5000 lb/min-sq ft.

Hanna et.al presented investigation deals with experimental and theoretical

phenomenological study of three phase direct-contact heat exchanger, for n-pentane

water system. The test section consisted of a cylindrical perspex column 17.2cm I.D. and

1m long, in which, distilled water, was to be confined. Liquid n-pentane drops were

injected into the hot water filled column, through a special design of two distributors. A

study of speed and high resolution camera films taken during the heat transfer process

rendered information regarding the bubble shape, bubble size, and evaporation rates of n-

pentane drops evaporating in hot water. The study was devoted to express the effect of

process variables on heat transfer coefficient, and volumetric heat transfer coefficient and

effectiveness. From this parametric analysis of this countercurrent column it was found

that The volumetric heat transfer coefficient values fall with an increase in the inlet

temperature of water. Small-diameter nozzles associated with faster nozzle velocities, and

smaller droplets, yield higher volumetric heat transfer coefficient, and larger heat transfer

coefficients gave higher values of volumetric heat transfer coefficient .It was found that

volumetric heat transfer coefficient varied in between 0.5 KW/m3 0C to 4 KW/m3 0C for

the water flow rate 5 cm3/s to 55 cm3/s and n-pentane flow rate 0.8 cm3/s to 2 cm3/s.

32

Mahood & Sharif et. Al (2013) developed a model for temperature distribution of

a spray column, three-phase direct contact heat exchanger. This study is for the relative

velocity and the drag coefficient of the evaporation swarm of drops in an immiscible

liquid, using a convective heat transfer coefficient of those drops. They assume a constant

holdup ratio (range 0.14 to 0.165) along the direct contact column. From this study it is

been evaluated that the variation of dispersed and continuous phase temperatures and the

spray column height at different initial phases temperatures and flow rates, with an initial

drop radius equal to 2mm and 1.6mm. At the phases entrance, at the fist zone where the

temperature difference is at its maximum between the phases. In this region a high

increase in dispersed temperature occurs, while nearly a constant temperature in the

continuous phase. This zone covers a very short length of the column (about 1m), and it

seems independent of the operational column parameters. In the second zone, a slow heat

exchange occurs between the phases and this region cover a wide range of the column

height. At the final zone the temperature difference decreases to minimum. The results

have shown that the rate of heat transfer increases with decreasing drops size. And the

heat exchange is influenced by the vaporization ratio.

Letan & Kehat(1968) studied the mechanism of heat transfer in a Spray Column

Heat Exchanger. Temperature profiles of water in a Spray Column Heat Exchanger 15cm

in diameter and 150cm long operating with a dense packing of kerosene drops were

measured. The range of superficial velocities was 0 to 0.8 cm/s for water and 0.5 to 1.7

cm/s of kerosene. The bottom of the dense packing was either slightly above or 15 cm

below the bottom of the column proper. The mathematical equations for dispersed

packing of drops were modified to take into the account of the reduction of wake size at

33

the interface of the two packings and the difference in the mixing patterns at the top of

the column.This operation was controlled by the fluid mechanics of the system and not

by the resistance to heat transfer inside or at the surface of the drops. The thermal

performance of the small diameter column was reduced significantly by the effect of

bypassing and was also reduced if the bottom of the dense packing of drops was

maintained within the conical bottom entry section.

Sathiyan (2011) et.al studied heat transfer for water-diesel two-phase system in a

Spiral Heat Exchanger. In this study, the main objective was to evolve a correlation to

predict liquid-liquid two-phase heat transfer coefficients in a spiral plate heat exchanger.

Experimental studies were conducted in a spiral plate heat exchanger using the liquid-

liquid two-phase system of water-diesel in different volume fractions and flow rates as

the cold fluid. Experiments were conducted by varying the volumetric flow rate and

temperature, keeping the volumetric flow rate of hot fluid constant. The two-phase heat

transfer coefficients were correlated with Reynolds number, Prandtl number and volume

fraction in the form Nu = a (Re) b (Pr) c () d. The data obtained from fresh experiments

were compared with the predictions of the obtained correlation. The predicted

coefficients showed a spread of 12 % in the laminar range, indicating the potential use

for practical applications. For 40% water + 60% diesel mixture it was found that the

overall heat transfer coefficient varied in the range of 162.22 - 766.06 W/m2K.

Zabulok et.al studied experimental investigation of direct contact heat transfer in

Isopentane-water system. The test section consisted of a cylindrical perspex column, in

which distilled water was to be confined. Liquid isopentane drops were injected into the

hot water filled column through special distributors located at the bottom of the column.

34

Various operating and design parameters were investigated and their effects on the

overall performance of the heat transfer process were deduced. The experimental runs

were planned using the central composite rotatable design method. It has been found that

the volumetric heat transfer coefficient values fall with an increase in the inlet

temperature of water, also small-diameter nozzles associated with faster nozzle velocities,

and smaller droplets, yield higher volumetric heat transfer coefficient. In addition, iso-

pentane was found to yield a slightly higher volumetric heat transfer coefficient

compared with n pentane. The inlet water temperature was maintained in between 300C

to 380C & the volumetric flow rate of water & Iso pentane was maintained in between

9.8-49 cm3/s and 0.96 to 1.92 cm3/s, respectively. The volumetric heat transfer coefficient

varies in the range between 3-7 KW/m3 0C.

Ming Yeh (2010) performed an analysis of heat transfer in the heat exchangers of

cocurrent and countercurrent flows with external recycle. It has been carried out by heat-

transfer theory. Considerable improvement is achievable by recycle operation if the

increase in heat-transfer coefficient by applying the recycle effect to enhance the fluid

velocity can compensate for the decrease in the driving force (temperature difference) of

heat transfer due to the remixing of inlet fluid. As expected, the heat-transfer rate

obtained in the countercurrent-flow heat exchangers with or without recycle is superior to

those in the cocurrent-flow devices. However, the space for the improvement in

performance by recycle in the countercurrent-flow device is smaller than that in the

cocurrent-flow one.

35

Terasaka and Tsuge (Terasaka & Tsuge, 1993) studied the bubble volumes and

shapes formed from a constant-flow nozzle submerged in a liquid. They photographed

the bubble shapes during bubble formation with a high-speed video camera, using

different liquids in N2 gas such as tap water and 68 Wt % glycerol.

Sideman et al. (1965) investigated the spray column with fixed dispersed phase

flow rates and different diameters of orifices using the n-pentane / sea water system. The

results show that the smaller the droplets, the smaller the optimal volume, and the larger

the volumetric heat transfer coefficient.

Sideman and Gat. (1966) measured the volumetric heat transfer coefficient and

column heights required to vaporize pentane in water. Volumetric heat transfer

coefficients were in the range of 8,000 to 20,000 kJ/m hr. C, and the results show that the

coefficients decrease with increasing driving force.

Brickman and Boehm (1994) studied the liquid-liquid direct-contact heat

exchangers for the purpose of finding the design that brings the temperature difference

between the two fluids to as a small value as possible, using oil-water system. They

confirmed that a longer column and smaller droplet size yield an increase in

effectiveness.

Shahidi & Ozbelge et. Al (1995) investigated direct contact heat transfer between

water and a heat transfer oil under non-boiling conditions in co-current turbulent flow

through a horizontal concentric annulus. The ratio of the inner pipe diameter to the outer

pipe diameter (aspect ratio) K = 0.730-0.816; total liquid velocity (mixture velocity) =

0.42 1.1 m/s; inlet oil temperature = 38 94C; oil volume fraction in the flowing

mixture = 0.25 0.75 were varied and their effects on the overall volumetric heat

36

transfer coefficient were determined at constant interfacial tension of 48 dynes/cm. It

was found that, in each concentric pipe set, the overall volumetric heat transfer

coefficient increased with increasing dispersed phase volume fraction at each constant

mixture velocity and reached a maximum at around = 0.5. The maximum U v

values increased with increasing total liquid velocity and decreasing aspect ratio of the

annulus. The volumetric heat transfer coefficient was also found to increase with

increasing inlet oil temperature and increasing total liquid velocity but to decrease with

length along the test section keeping all other parameters constant. Empirical expressions

for the volumetric heat transfer coefficient were obtained within the ranges of the

experimental parameters.

Mori (1991) studied the evaporation of drops of a volatile liquid sprayed upward

in an immiscible liquid flowing down in a vertical column, and derived an expression for

the volumetric heat transfer coefficient in a counter flow spray column. The expression of

the volumetric heat transfer coefficient was used to predict its values under some

particular column operating conditions, which were then compared with relevant

experimental data found in the literature.

Rasheed (1999) studied the direct-contact evaporation of a drop moving in a

stagnant column of an immiscible liquids, using n-pentane-water, 2-methyl pentane-

water, and n-pentane/2-methyl pentane-water systems. A theoretical analysis of

evaporating droplets in an immiscible liquid was developed by solving the governing

equations of the motion and heat transfer numerically by Runge-Kutta method, assuming

a spherical drop in a column of stagnant immiscible liquid at uniform temperature.

37

Chapter 3 Aim & objectives

38

It reveals from the literature survey that Direct Contact Heat Exchangers (such as

Spray Column, Mechanically agitated Column, Packed Column etc.) between two

immiscible fluids have shown many advantages because of higher effective heat transfer

coefficients, a relatively simple design that provides cost effective performance and

absence of surface scaling.

Ming Yeh (2010) in his study reported that heat-transfer rates obtained in the

countercurrent-flow heat exchangers with or without recycle, are superior to those in the

cocurrent-flow device, the space for the improvement by recycle in the countercurrent-

flow device is also smaller than that in the cocurrent-flow one. This fact will be more

obvious when the devices are operated under higher temperature difference and/or low

flow rate and/or smaller reflux ratio

With respect to liquid/liquid countercurrent studies in these devices, Letan and

Kehat (1967) gave a theoretical model in which heat transfer in a spray column is

controlled by the fluid dynamics of the system, and not by the resistance to heat transfer

inside or at the surface of the drops. Siqueiros & Bonilla(1999) did an experimental study

of heat transfer in a countercurrent Spray Column. The experimental study resulted in

enhancement of heat transfer coefficient, thermal efficiency etc. The volumetric heat

transfer coefficient found to be in the range of 4.5-8 KW m 1 K 1 . Again from the heat

transfer study in between mercurywater in a counter-current spray column done by

Pierce et.al (1959) desirable heat transfer effects were found. Mercury flow rate, water

flow rate, drop sizes, drop velocities, water phase movements were measured & varied

during the experiment. The volumetric heat transfer coefficient observed in between the

range of 19.3x103 B.T.U/hr-cubic ft-0F to 48.3x103 B.T.U/hr-cubic ft-0F for a column of 1

39

inch diameter, 13.25 inch length where water flow rate were maintained at 54.8 to 109.8

gal/min-sq ft & mercury flow rate were maintained at 2000 to 5000 lb/min-sq ft.

Extremely rapid heat transfer was experienced between the dispersed phases in the

mercury-water columns. The major heat transfer resistance was within the bulk of the

water phase. Heat transfer results did not vary appreciably with minor change in column

design nor between 1 and 2 inch diameter columns, but the column efficiencies decreased

markedly with increased column length. This study has illustrated that flow patterns can

greatly limit the efficiency of liquid-liquid spray columns.

Because of the disadvantages reported in cross flow heat exchanger as stated above and the

positive aspects of counter flow Spray Column reported by Pierce et al. ( 1959 ), project aims

liquid to liquid heat transfer in a counter flow Spray Column. By the application of this

contactor, the performance is expected to enhance the heat transfer coefficient with reduced

heat loss. Therefore a project aimed to study heat transfer performance of spray column with

water-kerosene system.

The objectives of the proposed project include:

1. To determine the heat transfer coefficient in a counter flow Spray Column.

2. To study the effect of water & kerosene flow rate on heat transfer characteristics

& thermal efficiency.

3. To reduce the heat loss.

40

Chapter 4 ExpErimEntal sEction

41

4.1 Experimental set up

A schematic diagram of apparatus is given in Fig 4.2. It consists of a stainless

steel oil tank, a spray column, oil & water pump, a stainless steel water bath equipped

with a 400V electrical heater, an electrical stirrer & a thermocouple connected to the

digital temperature controller to keep the inlet water temperature constant at the desired

value.

The heat transfer section is a vertical column made up of stainless steel and has a

provision to change its height. A stationary distributor of 76 mm diameter, located at the

bottom of column, consisting of number of 1 mm diameter holes on its surface was used

to spray kerosene around the heat transfer zone. The casing on which the unit along with

the distributor is installed was cylindrical in shape, with a diameter of 80 mm and axial

length of 120 cm. For another column this height was 95 cm.

A magnetic pump is used to feed warm water from a storage tank of capacity

around 100 liters, maintained at a constant temperature to the heat transfer unit. Kerosene

is sprayed against the vertically down flowing hot water, in the cylindrical column and

flow vertically upward. There is a by pass system in the storage tank to maintain uniform

temperature of the water bath, also there are two stirrers in the water tank to maintain

constant mixing. Kerosene used for cooling the warm water was fed to the column, by a

pump, in the reverse direction of gravity or in the upward direction. One control valve is

provided at the water outlet for maintaining the water level in the column. The spray

column provides a counter-flow contact of kerosene and warm water.

42

The water and kerosene flow rates were measured by previously calibrated

rotameter of capacity 0.1-1 LPM and 0.2-2 LPM respectively. The temperature of the

water entering and leaving the column was measured by thermocouple connected to a

digital display. Also, the entering and exit kerosene temperature was measured by

thermocouple connected to the digital display. Flow rates of liquids were controlled by

the valves on the bypass line of the pumps and adjusting the indivisual rotameters.

To reduce the heat loss the total heat transfer unit was covered with two layers of nylon

rope .

4.2 Experimental Procedure

Distilled water was heated in a constant temperature bath with the temperature

fixed at 55 C. After the temperature reaches to 55 C, the stirrers along with the

recirculation in the bath was switched on to maintain complete mixing and uniform

temperature of the water bath. In the mean time the water pump was switched on with the

water flow rate fixed at the desired value, made to pass through the column for 5-7 min

so that a steady state is attained. The water flow rates used are 0.2, 0.3, 0.4, 0.5 LPM. The

water level was fixed in the column by adjusting the control valve at the water outlet.

The kerosene flow rate is switched on now and the desired flow rate is maintained by the

rotameter. The kerosene flow rates used are 0.2, 0.3, 0.4, 0.5 LPM. The hot water flows

downward & kerosene was sprayed at the bottom & flows in the upward direction.

Now keeping the water flow rate, kerosene flow rate fixed it is allowed to reach a

steady state. Subsequently after reaching the steady state in 7 to 8 minutes, few sets of

reading for inlet water temperature, outlet water temperature, inlet kerosene temperature,

outlet kerosene temperature, was noted down at a regular interval of 4 minutes for 20 to

43

24 minutes and the most steady state of the readings is reported among those noted. Also

the actual water & kerosene outlet flow rate were noted. Then the water bath temperature

was increased to 64 0C and the above procedure was repeated with the same kerosene and

water flow rate.

The whole experimental procedure was performed by varying the height of the

column from 80 cm to 105 cm. Each set of run last for about approximately 40 min. After

each set of run the machine was given rest for around 1 hr. In the entire set of run for the

two sets of height the kerosene inlet temperature was found to vary from 26.5 C to 32.9

C.

Fig 4.1: Overall Experimental Set Up

44

Fig 4.2: Schematic of Experimental Set Up

A-Water Bath, B-Valve, C-Magnetic Pump, D- Gear Pump, E-Rotameter, F-

Kerosene Bath, G-Spray Column, H-Water Inlet, I-Water Outlet, J-Kerosene

Inlet, K-Kerosene Outlet, L- Stirrer, M-Heating Coil

45

Chapter 5

Results & Discussion

46

As stated earlier, this heat transfer study was performed for two column heights in

counter flow mode between two liquid phases i.e. water and kerosene.

Value/Range of Operating Parameters in the study

qw=0.2LPM-0.5LPM ,

qk =0.2LPM-0.5LPM

Water bath Temperature- 550C -650 C

H=95cm-120cm, d= 8cm, t=2mm

w = 988.1 Kg/m3 at 550C, 983.2 Kg/m3 at 640C

k = 800 Kg/m3

C pw= 4.1806 KJ/ Kg-K at 550C, 4.1843 KJ/Kg-K at 640C

C kw= 2.01 KJ/ Kg-K

5.1 Study of Heat Loss in counter-flow Spray Column

Preliminary experimentation for calculation of heat loss in the equipment was conducted

in the beginning so as to consider it during the calculations of heat transfer coefficient for

accuracy purpose. The data for heat loss in Spray Column in Watt is as given below

Table1: Heat loss at Water Bath Temperature-55 0C & Column Height- 105 cm

Water Flow Rate (LPM) 0.2 0.3 0.4 0.5

Kerosene Flow Rate (LPM)

0.2 19.12 16.47 10.10 19.62

0.3 10.76 5.88 8.74 16.21

0.4 6.33 14.29 17.75 5.58

0.5 15 18.4 11.58 4.98

47

Table2: Heat Loss at Water Bath Temperature- 64 0C & Column Height- 105 cm

Water Flow

Rate (LPM) 0.2 0.3 0.4 0.5

Kerosene Flow

Rate(LPM)

0.2 20.87 21.71 26.05 26.33

0.3 2.30 18.53 24.94 16.6

0.4 1.4 14.1 22.8 16.96

0.5 2.61 17.93 8.76 8.67

Table3: Heat Loss at Water Bath Temperature- 55 0C & Column Height- 80 cm

Water Flow

Rate (LPM) 0.2 0.3 0.4 0.5

Kerosene Flow

Rate (LPM)

0.2 14.14 2.34 25.72 0.62

0.3 0.74 6.96 2.49 0.63

0.4 22.20 25.10 10.81 7.99

0.5 29.22 23.86 14.70 5.71

48

Table4: Heat loss at Water Bath Temperature- 64 0C & Column Height- 80 cm

Water Flow

Rate (LPM) 0.2 0.3 0.4 0.5

Kerosene Flow

Rate (LPM)

0.2 26.98 4.37 1.60 0.98

0.3 49.38 29.45 4.28 23.25

0.4 33.98 27.46 28.44 14.17

0.5 12.48 29.45 5.89 0.94

It can be seen a certain amount of heat loss in each of the cases does exists. So,

the heat loss term, being considerable, was added in heat transfer coefficient calculations

for the sake of accuracy in the governing equation.The amount of kerosene coming out

from water outlet is negligible. 1 L of kerosene content in a 50 L of water bucket was

measured.

From the above experimental data thermal efficiency & overall heat transfer coefficient

of the column were determined.

49

5.2 Calculation of Thermal Efficiency

Thermal efficiency for both height of the column & varying water bath

temperature were determined. The simultaneous heat transfer of the spray Column was

presented in terms of thermal efficiency defined as

= Actual heat transfer/ Maximum possible heat transfer

= TTTT

KIWI

WOWI

The effectiveness lies in between 0 to 1.

5.3 Calculation of Heat Transfer Coefficient

To calculate the overall heat transfer co-efficient (h) a model equation is

developed and represented as

lQ

lATTh

dxdT

kowoaw

pwwcm.

)(

50

5.4 Effect of Water flow rate on h & Fig 5.1 and Fig 5.2 illustrates the variation of thermal efficiency with water flow

rate, at kerosene flow rates of 0.2, 0.3, 0.4 & 0.5 LPM for water bath temperature 55 0C

& 640 C respectively and the column height of 105 cm. It can be seen that the thermal

efficiency increased as the water flow rate decreased & increased with increase in the

kerosene flow rates. For example, at a constant kerosene flow rate of 0.2 LPM, the

thermal efficiency for the column decreased from 0.21 to 0.10 with an increase in water

flow rate from 0.2 LPM to 0.5 LPM for water bath temperature 55 0C, whereas in case of

constant water flow rate of 0.2 LPM thermal efficiency increases from 0.21 to 0.43 with

an increase in kerosene flow rate from 0.2 LPM to 0.5 LPM for water bath temperature

64 0C.

Fig 5.3 and Fig 5.4 plots the variation of thermal efficiency with water flow rate

for kerosene flow rates of 0.2, 0.3, 0.4 & 0.5 LPM, water bath temperature 550C & 640C

and the column height 80 cm. It was found that the thermal efficiency decreased as the

water flow rate increased & increased with increase in the kerosene flow rates which are

quite clear from the plots. For example, at a constant kerosene flow rate of 0.2 LPM, the

thermal efficiency for the column decreased from 0.21 to 0.11 with an increase in water

flow rate from 0.2 LPM to 0.5 LPM for water bath temperature 55 0C. Where as in case

of constant water flow rate of 0.2 LPM thermal efficiency increases from 0.22 to 0.39

with an increase in kerosene flow rate from 0.2 LPM to 0.5 LPM for water bath

temperature of 64 0C.

51

Fig 5.1: Effect of water flow rate on thermal efficiency at water bath

temperature 55 0C & Column Height 105 cm



00.050.1

0.150.2

0.250.3

0.350.4

0.450.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Qw(LPM)

Ther

mal

Effi

cien

cy

Qk=0.2LPMQk=0.3LPMQk=0.4LPMQk=0.5LPM

0

0.050.1

0.15

0.20.25

0.3

0.350.4

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Qw(LPM)

Ther

mal

Effi

cien

cy Qk=0.2LPMQk=0.3LPMQk=0.4LPMQk=0.5LPM

52





00.05

0.10.15

0.20.25

0.30.35

0.40.45

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Qw(LPM)

Ther

mal

Effi

cien

cy


0

0.050.1

0.15

0.20.25

0.3

0.350.4

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Qw(LPM)

Ther

mal

Effi

cien

cy


53

Fig 5.5 and Fig 5.6 depicts the variation of heat transfer coefficient with water

flow rate for kerosene flow rates of 0.2, 0.3, 0.4 & 0.5 LPM, water bath temperature 550C

& 640 C and the column height of 105 cm. It was found that the heat transfer coefficient

increased as the water flow rate increased & decreased with increase in the kerosene

flow. For example, at a constant kerosene flow rate of 0.2 LPM, the heat transfer

coefficient for the column increased from 360 to 730 W/m2K with an increase in water

flow rate from 0.2 LPM to 0.5 LPM for water bath temperature 55 0C. Where as in case

of constant water flow rate of 0.2 LPM heat transfer coefficient decreases from 442 to

232 W/m2K with an increase in kerosene flow rate from 0.2 LPM to 0.5 LPM for water

bath temperature 64 0C.

Fig 5.7 and Fig 5.8 plots the variation of heat transfer coefficient with water flow

rate, at kerosene flow rates of 0.2, 0.3, 0.4 & 0.5 LPM for water bath temperature 550C &

640 C respectively and the column height is 80 cm. It can be seen from figures that the

heat transfer coefficient increased as the water flow rate increased & decreased with

increase in the kerosene flow rates. For example, at a constant kerosene flow rate of 0.2

LPM, the heat transfer coefficient for the column increased from 465 to 775 W/m2K with

an increase in water flow rate from 0.2 LPM to 0.5 LPM for water bath temperature

550C. Whereas in case of constant water flow rate of 0.2 LPM, heat transfer coefficient

decreases from 478 to 295 W/m2K with an increase in kerosene flow rate from 0.2 LPM

to 0.5 LPM for constant water bath temperature of 640C.

54

Fig 5.5: Effect of water flow rate on heat transfer coefficient at water bath

temperature 550C & column height 105cm



0

100

200

300

400

500

600

700

800

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Qw(LPM)

Heat

Tra

nsfe

r Coe

ffici

ent(W

/m2 K

)


0

100

200300

400

500

600700

800

900

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Qw(LPM)

Heat

Tra

nsfe

r Co

effic

ient

(W/m

2 K)


55





0

100200

300400

500600

700800

900

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Qw(LPM)

Heat

Tra

nsfe

r Coe

ffici

ent(W

/m2 K

)


0100200300400500600700800900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Qw(LPM)

Hea

t Tra

nsfe

r Coe

ffici

ent(W

/m2 K

)


56

5.5 Effect of variation in Water Inlet Temperature on h & Fig 5.9 & 5.10 shows the variation of thermal efficiency with change in the water

inlet temperature at constant water flow rate and kerosene flow rates which are

maintained in between the range of 0.2 to 0.5 LPM for column height of 105 cm & 80 cm

respectively . Water bath temperature was maintained at 550C & 640C. It was found that

there is not much variation in thermal efficiency with change in temperature. It remains

almost same. In some cases thermal efficiency decreased as the water bath temperature

increased. For example, at a constant kerosene flow rate of 0.3 LPM and 0.2 LPM water

flow rate, the thermal efficiency for the column at 550C is 0.27 decreased to 0.25 at 640C

for the column height 105 cm.

Fig 5.11 & 5.12 plots the variation of heat transfer coefficient with water flow

rate, at kerosene flow rates of 0.2, 0.3, 0.4 & 0.5 LPM for water bath temperature 550C

& 640C for the column height is 105 cm & 80cm respectively . It was found that the heat

transfer coefficient increased as the water bath temperature increased which is revealed

by the plots. For example, at a constant kerosene flow rate of 0.2 LPM & 0.2LPM water

flow rate, the heat transfer coefficient for the column at 550C is 360W/m2K increased to

408 W/m2K at 640C for 105 cm column height.

57

Fig 5.9: Effect on thermal efficiency with change in water bath temperature at

a height 105cm

Fig 5.10: Effect on thermal efficiency with change in water bath temperature at

a height 80cm

00.050.1

0.150.2

0.250.3

0.350.4

0.450.5

0 0.2 0.4 0.6 0.8 1

Qw(LPM)

Ther

mal

Effi

cien

cyQk=0.2LPM, Temp=55CQk=0.3LPM, Temp=55CQk=0.4LPM, Temp=55CQk=0.5LPM, Temp=55CQk=0.2LPM, Temp=64CQk=0.3LPM,Temp=64CQk=0.4LPM,Temp=64CQk=0.5LPM,Temp=64C

0

0.05

0.10.15

0.2

0.25

0.30.35

0.4

0.45

0 0.2 0.4 0.6 0.8 1

Qw(LPM)

Ther

mal

Effi

cien

cy

Qk=0.2LPM,Temp=55CQk=0.3LPM, Temp=55CQk=0.4LPM, Temp=55CQk=0.5LPM, Temp=55CQk=0.2LPM, Temp=64CQk=0.3LPM, Temp=64CQk=0.4LPM, Temp=64CQk=0.5LPM, Temp=64C

58

Fig 5.11: Effect on heat transfer coefficient with change in water bath

temperature at a height 105cm

Fig 5.12: Effect on heat transfer coefficient with change in water bath

temperature at a height 105cm

0

100200

300

400500

600

700800

900

0 0.2 0.4 0.6 0.8 1

Qw(LPM)

Heat

Tra

nsfe

r Coe

ffici

ent(W

/m2 K

)

Qk=0.2LPM, Temp=55CQk=0.3LPM, Temp=55CQk=0.4LPM, Temp=55CQk=0.5LPM, Temp=55CQk=0.2LPM, Temp=64CQk=0.3LPM,Temp=64CQk=0.4LPM,Temp=64CQk=0.5LPM,Temp=64C

0100200300400500600700800900

1000

0 0.2 0.4 0.6 0.8 1

Qw(LPM)

Heat

Tra

nsfe

r Coe

ffici

ent(W

/m2 K

)

Qk=0.2LPM,Temp=55CQk=0.3LPM, Temp=55CQk=0.4LPM, Temp=55CQk=0.5LPM, Temp=55CQk=0.2LPM, Temp=64CQk=0.3LPM, Temp=64CQk=0.4LPM, Temp=64CQk=0.5LPM, Temp=64C

59

5.5 Effect of Variation in Column Height

Fig 5.13 & 5.14 present the variation of thermal efficiency with water flow rate, at

kerosene flow rates of 0.2, 0.3, 0.4 & 0.5 LPM for column height 105 cm & 8 0cm for

water bath temperature 550C & 640C respectively. It was found that the thermal

efficiency increased as the column height decreased. For example, at a constant

kerosene flow rate of 0.2 LPM & 0.4 LPM water flow rate, the thermal efficiency for the

column height 105 cm at 550C is 0.10 increased to 0.12 at 550C for the 80 cm height. But

in most of the cases thermal efficiency does not vary too much with column height.

Fig 5.15 & 5.16 plots the variation of heat transfer coefficient with water flow

rate, at kerosene flow rates of 0.2, 0.3, 0.4 & 0.5 LPM for column height 105 cm & 80

cm for water bath temperature 550C & 640C respectively. It was found that the overall

heat transfer coefficient increased as the column height decreased. For example, at a

constant kerosene flow rate of 0.3LPM & 0.3LPM water flow rate, the heat transfer

coefficient for the column height 105 cm at 550C is 403 W/m2K increased to 440 W/m2K

at 550C for the 80 cm height.

60

Fig 5.13: Effect on Thermal Efficiency with change in height at a water bath

temperature 550C

Fig 5.14: Effect on Thermal efficiency with change in height at a water bath

temperature 640C

00.050.1

0.150.2

0.250.3

0.350.4

0.450.5

0 0.2 0.4 0.6 0.8 1

Qw(LPM)

Ther

mal

Effi

cien

cyQk=0.2LPM,H=105cmQk=0.3LPM,H=105cmQk=0.4LPM,H=105cmQk=0.5LPM,H=105cmQk=0.2LPM,H=80cmQk=0.3LPM,H=80cmQk=0.4LPM,H=80cmQk=0.5LPM,H=80cm

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.4 0.6 0.8 1

Qw(LPM)

Ther

mal

Effi

cien

cy

Qk=0.2LPM,H=105cmQk=0.3LPM,H=105cmQk=0.4LPM,H=105cmQk=0.5LPM,H=105cmQk=0.2LPM,H=80cmQk=0.3LPM,H=80cmQk=0.4LPM,H=80cmQk=0.5LPM,H=80cm

61

Fig 5.15: Effect on overall heat transfer coefficient with change in height at a

water bath temperature 550C

Fig 5.16: Effect on overall heat transfer coefficient with change in height at a

water bath temperature 640C

0

100200

300

400500

600

700800

900

0 0.2 0.4 0.6 0.8 1

Qw(LPM)

Heat

Tra

nsfe

r Coe

ffici

ent(W

/m2K

)Qk=0.2LPM,H=105cmQk=0.3LPM,H=105cmQk=0.4LPM,H=105cmQk=0.5LPM,H=105cmQk=0.2LPM,H=80cmQk=0.3LPM,H=80cmQk=0.4LPM,H=80cmQk=0.5LPM,H=80cm

0100200300400500600700800900

1000

0 0.2 0.4 0.6 0.8 1

Qw(LPM)

Heat

Tra

nsfe

r Coe

ffici

ent(W

/m2K

)

Qk=0.2LPM,H=105cmQk=0.3LPM,H=105cmQk=0.4LPM,H=105cmQk=0.5LPM,H=105cmQk=0.2LPM,H=80cmQk=0.3LPM,H=80cmQk=0.4LPM,H=80cmQk=0.5LPM,H=80cm

62

5.6 Effect of Phase Ratio

Fig 5.17 & 5.18 shows the variation of heat transfer coefficient with variation in

kerosene-water phase ratio for column height 105 cm & 80 cm and water bath

temperature 550C & 640C respectively at different water flow rates. It was found that the

thermal efficiency increased as the phase ratio increased which means that increase in the

kerosene mass flow rate is a result of increasing thermal efficiency.

Fig 5.19 & 5.20 indicates the variation of heat transfer coefficient with variation

in kerosene-water phase ratio for column height 105 cm & 80 cm varying water bath

temperature 550C & 640C respectively at different water flow rate. It was found that the

overall heat transfer coefficient decreased as the phase ratio increased.

Fig 5.21 & 5.22 shows change in kerosene outlet temperatures with the change in

phase ratio for two different column heights varying the water bath temperature. It was

found that with increasing phase ratio the kerosene outlet temperature marginally varied.

But with increasing water inlet temperature it markedly changed.

63

Fig 5.17: Effect on Thermal Efficiency with change in phase ratio at a Column

Height 105cm

Fig 5.18: Effect on Thermal Efficiency with change in phase ratio at a Column

Height 80cm

00.050.1

0.150.2

0.250.3

0.350.4

0.450.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Phase Ratio

Ther

mal

Effi

cien

cy

Temp=55CTemp=64C

0

0.05

0.10.15

0.2

0.25

0.30.35

0.4

0.45

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Phase Ratio

Ther

mal

Effi

cien

cy

Temp=55CTemp=64C

64

Fig 5.19: Effect on overall heat transfer coefficient with change in phase ratio

at a Column Height 105cm

Fig 5.20: Effect on overall heat transfer coefficient with change in phase ratio

at a Column Height 80cm

0

100200

300

400500

600

700800

900

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Phase ratio

Heat

Tra

nsfe

r Coe

ffici

ent(W

/m2 K

)

Temp=55CTemp=64C

0100200300400500600700800900

1000

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Phase Ratio

Heat

tran

sfer

coe

ffici

ent(W

/m2K

)

Temp=55CTemp=64C

65

Fig 5.21: Effect on Kerosene Outlet temperature with change in phase ratio at


Fig 5.22: Effect on Kerosene Outlet temperature with change in phase ratio at


0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Phase Ratio

T ko(

0 C)

Temp=55 Ctemp=64C

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Phase Ratio

T ko(0 C

) Temp=55CTemp=64C

66

Chapter 6 ConClusion

67

The performance of a Spray Column at two different column heights of 105 cm & 80 cm

were studied for heat transfer in between Kerosene-Water. The heat loss in the counter

flow Spray Column found, were not small enough to be negligible. So, a term consisting

of heat loss was added to the governing equation for the calculation of heat transfer

coefficient. The thermal efficiency of the 80 cm column height varied in the range of 0.78

to 0.96 and found to be higher by maximum of 6 % than that of 105 cm column height.

So, it can be said that variation in column characteristics does not affect thermal

efficiency. The value of overall heat transfer coefficient (h) reported in the range of 200

W/m2K to 900 W/m2K. It increased as the water flow rate was varied from 0.2 LPM to

0.5 LPM and decreased with increase in kerosene flow rate to 0.5 LPM. This could be

because as the water working here as a warm liquid so at higher flow rate the amount of

heat flow in the column increases thus providing higher amount of heat to be transferred.

It was also found that h increases markedly with increase in water bath temperature &

decrease in column height.

The volumetric heat transfer coefficient reported in mechanically agitated column at

similar operating conditions varied between 150 W/m2K to 600 W/m2K. Thus it can be

concluded that due to improved heat transfer coefficient along with less heat loss, counter

flow Spray Column can be used as a replacement of mechanically agitated column.

Further work can be performed by changing the column diameter, increasing or

decreasing the nozzle diameter of the kerosene distributor or by changing the no of holes

or nozzles in the kerosene distributor.

68

Nomenclature

mw= mass flow rate of water

mk= mass flow rate of kerosene

qw = volumetric flow rate of water

qk =volumetric flow rate of kerosene

Cpw= specific heat of water

w = Density of water

k= Density of Kerosene

C kw= Specific heat of Kerosene

dTw= Temperature change in water flow

ha= heat transfer coefficient

Two= Water outlet temperature

Tko= Kerosene outlet temperature

T

Liquid-Liquid Heat Transfer in Spray Column

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