Heat Exchangers

Saturday, April 8, 2023Saturday, April 8, 2023 11

Heat ExchangersHeat Exchangers

B K KumbharB K Kumbhar


Presentation pointsPresentation points

Importance & ClassificationImportance & Classification Types of Heat Exchangers in Dairy & Food Types of Heat Exchangers in Dairy & Food

IndustryIndustry Selection of Heat ExchangersSelection of Heat Exchangers Indirect Contact Type Heat Indirect Contact Type Heat Direct Contact Type Heat Direct Contact Type Heat


Heat ExchangerHeat Exchanger Heating and/or cooling of the process streams during Heating and/or cooling of the process streams during

processing processing Heat transfer between two fluids through a separating wall Heat transfer between two fluids through a separating wall

or by direct contact with each otheror by direct contact with each other Classification based onClassification based on

Degree of heat transfer surface compactness Degree of heat transfer surface compactness Construction features Construction features

Flow arrangementsFlow arrangementsNumber of fluids Number of fluids Heat transfer mechanismsHeat transfer mechanisms


In Dairy and Food IndustriesIn Dairy and Food Industries

Direct ContactDirect Contact

Steam InjectionSteam Injection

Steam infusionSteam infusion

Indirect ContactIndirect Contact

TubularTubular

PlatePlate

Jacketed KettleJacketed Kettle


Selection of Heat ExchangersSelection of Heat Exchangers

Flow Rate of Both the Fluids Flow Rate of Both the Fluids Heat SensitivityHeat Sensitivity Terminal TemperaturesTerminal Temperatures Types of Fluids Types of Fluids Properties of Both FluidsProperties of Both Fluids Flow ArrangementFlow Arrangement Operating Pressure and TemperatureOperating Pressure and Temperature Pressure DropPressure Drop

Contd


Selection of Heat Exchangers ----contdSelection of Heat Exchangers ----contd

Heat Recovery Heat Recovery FoulingFouling Ease of Inspection, Cleaning, Repair & Ease of Inspection, Cleaning, Repair &

MaintenanceMaintenance Materials of ConstructionMaterials of Construction Cost of Heat ExchangerCost of Heat Exchanger


Flow Rate of Both the FluidsFlow Rate of Both the Fluids

SizeSizeLengthLengthWidthWidthHeightHeightWeightWeight

Site RequirementSite RequirementLifting and Servicing capabilitiesLifting and Servicing capabilitiesInventory ConsiderationsInventory Considerations

Sizing of the Heat ExchangerSizing of the Heat ExchangerMinimum Pressure DropMinimum Pressure DropFlow RatioFlow Ratio


Heat SensitivityHeat Sensitivity

Low Hold-up VolumeLow Hold-up Volume Low Residence TimeLow Residence Time Low Surface Temperature Low Surface Temperature

RequirementsRequirements Good Flow DistributionGood Flow Distribution High Heat Transfer CoefficientHigh Heat Transfer Coefficient Small Channel VolumeSmall Channel Volume


Terminal TemperaturesTerminal Temperatures Performance of Heat Exchanger depends on terminal Performance of Heat Exchanger depends on terminal

temperaturestemperatures

Heat Transfer Units (HTU) defined asHeat Transfer Units (HTU) defined asRatio ofRatio of

* Temperature of one fluid* Temperature of one fluid * Mean temperature difference between the fluids * Mean temperature difference between the fluids

Plate heat exchanger > Tubular Heat Exchanger Plate heat exchanger > Tubular Heat Exchanger Up to 4 HTU in case of Plate heat exchanger Up to 4 HTU in case of Plate heat exchanger


Types of FluidsTypes of Fluids

LiquidsLiquids GasesGases

Tubular heat exchanger suitable for condensable Tubular heat exchanger suitable for condensable gases (steam)gases (steam)

Plate heat exchanger suitable for liquids with less Plate heat exchanger suitable for liquids with less than 50000 cPthan 50000 cP


Properties of Both FluidsProperties of Both Fluids

Heat Transfer CalculationsHeat Transfer Calculations Pumping CalculationsPumping Calculations

ViscosityViscosityLow viscosity- Low viscosity- Plate heat exchanger Plate heat exchanger

High viscosity- High viscosity- Scraped surface heat exchanger Scraped surface heat exchanger Thermal conductivityThermal conductivity DensityDensity Specific heatSpecific heat Thermal diffusivityThermal diffusivity


Flow ArrangementFlow Arrangement

ConcurrentConcurrent – – Flow in same directionFlow in same direction Thermodynamically poorThermodynamically poor High thermal stresses since large temperature difference at inletHigh thermal stresses since large temperature difference at inlet Heat sensitive materialsHeat sensitive materials

Counter currentCounter current- - flow opposite to each otherflow opposite to each other Thermodynamically superiorThermodynamically superior Minimum thermal stressesMinimum thermal stresses Maximum heat recoveryMaximum heat recovery Least heat transfer area Least heat transfer area

Cross flowCross flow- - Flow perpendicular to each otherFlow perpendicular to each other In between the aboveIn between the above Design of headers require less spaceDesign of headers require less space Space is important Space is important



Operating Pressure and TemperatureOperating Pressure and TemperatureMechanical DesignMechanical Design Operating PressureOperating Pressure Operating TemperatureOperating Temperature

Problems of high operating temperature and pressureProblems of high operating temperature and pressure VibrationVibration FatigueFatigue Thermal stresses, etc.Thermal stresses, etc.

Plate heat exchanger free from such problems however plate Plate heat exchanger free from such problems however plate thickness and gasket material limit its applicationthickness and gasket material limit its application


Maximum Operating ConditionsMaximum Operating Conditions

Heat ExchangerHeat Exchanger T, T, 00CC P, kg/cm²P, kg/cm² Q, l/hQ, l/h

Plate heat exchangerPlate heat exchanger 260260 21 21 50,00,0050,00,00 Double pipeDouble pipe 540540 70 70 no limitno limit Shell and tubeShell and tube 540540 105105 no limitno limit Scraped surfaceScraped surface 250 250 35 35 27,0027,00 KettleKettle 260260 5 5 - -


Pressure DropPressure Drop

Important forImportant for Pumping CostPumping Cost - - proportional to pressure dropproportional to pressure drop

Heat Transfer RateHeat Transfer Rate - - proportional to pressure dropproportional to pressure drop

Specific pressure drop defined asSpecific pressure drop defined as Pressure drop per unit HTUPressure drop per unit HTU Used to compare the performance of different heat exchangersUsed to compare the performance of different heat exchangers


Heat RecoveryHeat Recovery

Conservation of energy- very important Conservation of energy- very important Recovery of heat from used/waste process streamsRecovery of heat from used/waste process streams

Less than 50% in tubular heat exchangersLess than 50% in tubular heat exchangers Up to 95% in plate heat exchangerUp to 95% in plate heat exchanger


FoulingFoulingDeposition of solid material-Deposition of solid material- poor conductor of heat poor conductor of heat

* * Decreases heat transferDecreases heat transfer* Decreases flow rate* Decreases flow rate* Lead to corrosion* Lead to corrosion* Loss of valuable materials* Loss of valuable materials* Affects the design and size of the unit* Affects the design and size of the unit* Affects the production runs * Affects the production runs

Factors affecting foulingFactors affecting fouling Velocity- Velocity- High velocity less foulingHigh velocity less fouling

* Shearing force* Shearing force * Turbulence* Turbulence* Laminar layer thickness* Laminar layer thickness * Residence time* Residence time

Surface temperatureSurface temperature – important for heat sensitive liquids – important for heat sensitive liquids

- small temperature difference required- small temperature difference required Bulk fluid temperatureBulk fluid temperature – more fouling in less bulk temperature – more fouling in less bulk temperature

CompositionComposition


Ease of Inspection, Cleaning, Repair & MaintenanceEase of Inspection, Cleaning, Repair & Maintenance

Requirement Requirement PHE PHE DPDP STST SS SS Kettle Kettle Inspection for foulingInspection for fouling Product side Product side a a b b a a a a a a Media side Media side a a b b b/d b/d d d c/dc/d

Inspection for leakageInspection for leakage Product side Product side a a b/c b/c b/d d b/d d c/d c/d Media side Media side a a a a a b a b aa

Inspection for corrosionInspection for corrosion Product side Product side a a a/b a/b a/d a/d a a a a Media side Media side a a b/d b/d a/dc a/dc c c b/cb/c

a: Very good b: Acceptable c: Poor d: Impossible a: Very good b: Acceptable c: Poor d: Impossible PHE- Plate heat exchanger DP- double pipe ST- shell and tube SS- scraped PHE- Plate heat exchanger DP- double pipe ST- shell and tube SS- scraped

surface surface


Ease of Inspection, Cleaning, Repair & Maintenance Ease of Inspection, Cleaning, Repair & Maintenance ------contd------contd

Chemical cleaningChemical cleaning Product side Product side a a a a b/c a b/c a a a Media side Media side a a a a a a a a aa

Manual cleaningManual cleaning Product side Product side a a b b a a a a a a Media side Media side a a c/d c/d a/d a/d d d c/dc/d

Extension Extension a a b/d b/d d d d d dd

Repair Repair a a b/c b/c b b a a aa


Materials of ConstructionMaterials of ConstructionMaterial of construction depends onMaterial of construction depends on Properties of the fluids such as heat sensitivity, fouling, corrosivity, Properties of the fluids such as heat sensitivity, fouling, corrosivity, Operating temperature and pressureOperating temperature and pressure Welding easeWelding ease AvailabilityAvailability Conformance to all applicable laws, codes and insurance Conformance to all applicable laws, codes and insurance

requirementsrequirements CostCost

MaterialsMaterialsStainless steelStainless steel Carbon steelCarbon steel GraphiteGraphiteAluminumAluminum TitaniumTitanium HastalloyHastalloy

GasketsGasketsNitryl rubberNitryl rubber Butyl rubberButyl rubberTeflonTeflon Compressed asbestos fibersCompressed asbestos fibers


Cost of Heat ExchangerCost of Heat Exchanger

Optimization based on cost considerationOptimization based on cost consideration Consider all above factorsConsider all above factors


Indirect Contact Type Heat ExchangersIndirect Contact Type Heat Exchangers

Plate heat exchangerPlate heat exchanger Tubular heat exchangersTubular heat exchangers

Double pipe heat exchangerDouble pipe heat exchanger Scraped surface heat exchanger (SSHE)Scraped surface heat exchanger (SSHE) Spiral tube heat exchangerSpiral tube heat exchanger Shell and tube heat exchangerShell and tube heat exchanger

Jacketed kettleJacketed kettle


Plate Heat ExchangerPlate Heat Exchanger Consists of rectangular thin corrugated plates Consists of rectangular thin corrugated plates

stacked in a frame.stacked in a frame. Plates pressed against each other between the Plates pressed against each other between the

stationary frame plate and movable pressure plate stationary frame plate and movable pressure plate with compression bolt to form narrow flow with compression bolt to form narrow flow channels.channels.

Hot and cold streams flow in alternate channels.Hot and cold streams flow in alternate channels. Corner openings termed as portsCorner openings termed as ports

Flow portFlow port Transfer portTransfer port

Fluid flow may be diagonal or verticalFluid flow may be diagonal or vertical


Plate Heat ExchangersPlate Heat Exchangers ConstructionConstruction PortsPorts CorrugationsCorrugations Flow arrangementsFlow arrangements AdvantagesAdvantages LimitationsLimitations


Parts of Plate heat exchangerParts of Plate heat exchanger Thin corrugated platesThin corrugated plates Stationary frame plateStationary frame plate Movable pressure plateMovable pressure plate Plate carrying barPlate carrying bar Plate guide barPlate guide bar Compression boltCompression bolt Connecting plateConnecting plate GasketGasket Inlet and outlet nozzles for each streamInlet and outlet nozzles for each stream


Plate Heat ExchangerPlate Heat Exchanger

Movable pressure plate

Connecting plate

Stationary frame platePlate carrying bar

Plate carrying bar

Hot water in

Hot water out

Milk out

Milk in

Compression nut & bolt



Flow Path in Plate Heat ExchangerFlow Path in Plate Heat Exchanger

Hot Water in Hot Water out

Milk inMilk Out

First pass

Second passFour pass of milk

Two pass of hot water


GasketsGaskets Prevent leakage of liquidsPrevent leakage of liquids Eliminate possibility of mixingEliminate possibility of mixing

Criteria for gasket materialsCriteria for gasket materials Thermal stabilityThermal stability Resistance to assuming permanent deformationResistance to assuming permanent deformation Good ageing characteristicsGood ageing characteristics Low compression setLow compression set Selection depends on the chemical composition of the Selection depends on the chemical composition of the

process streams and operating temperature.process streams and operating temperature.


Type of PortsType of Ports

Flow PortFlow Port Transfer PortTransfer Port


CorrugationsCorrugations Inducing turbulence in the process streamInducing turbulence in the process stream Providing reinforcementProviding reinforcement Plate support points to maintain interplate Plate support points to maintain interplate

separation and increasing heat transfer surface separation and increasing heat transfer surface area.area.

PatternsPatterns Trough typeTrough type Chevron or herringbone typeChevron or herringbone type


Flow arrangementFlow arrangement Series – low flow rates and large temp. changeSeries – low flow rates and large temp. change Looped – large flow rates and small Looped – large flow rates and small

temperature changetemperature change Complex – intermediate cases of flow and Complex – intermediate cases of flow and

temperature changetemperature change

Looped flow

Series Flow

Looped flow

Series Flow

Looped flow

Series Flow

Looped flow

Series Flow


Series flowSeries flow

Looped flow

Series Flow

Looped flow

Series Flow


Looped Flow PatternLooped Flow Pattern

Looped flow

Series Flow

Looped flow

Series Flow


Parts of a PlateParts of a Plate

Flow portTransfer port

Gasket

Flow portTransfer port

Corrugations

Flow distribution triangles

Gasket


Herringbone (Chevron type, 3D)Herringbone (Chevron type, 3D)


Flow patternFlow pattern

Looped flow

Series Flow


Overall heat transfer coefficient higherOverall heat transfer coefficient higher Effective mean temp difference usually higherEffective mean temp difference usually higher Less costLess cost Occupies less floor and head space – low hold-up Occupies less floor and head space – low hold-up

volume gives quicker start up and faster response to volume gives quicker start up and faster response to control function changes.control function changes.

Less massive foundationLess massive foundation Less foulingLess fouling Disassembled easilyDisassembled easily Variety of ways for assemblingVariety of ways for assembling Multiple duties like heating, cooling, regeneration etc.Multiple duties like heating, cooling, regeneration etc. Intermixing prevented by double gasket.Intermixing prevented by double gasket. Over 90 % heat recovery.Over 90 % heat recovery.

ADVANTAGESADVANTAGES


LimitationsLimitations

Cannot withstand operating pressures much in Cannot withstand operating pressures much in excess of 21 kg/cmexcess of 21 kg/cm22 (300 psi) (300 psi)

Gaskets should be elastomeric. So, maximum Gaskets should be elastomeric. So, maximum operating temp. usually limited to 260operating temp. usually limited to 26000C.C.

For mild steel construction, plate heat For mild steel construction, plate heat exchangers are costlier.exchangers are costlier.

Moderate pressure loss required to produce Moderate pressure loss required to produce economic designs to handle large quantities of economic designs to handle large quantities of low density fluids such as vapors and gases.low density fluids such as vapors and gases.


Tubular Heat ExchangersTubular Heat Exchangers

Double/triple pipeDouble/triple pipe Shell and tubeShell and tube Spiral tubeSpiral tube Scraped surface heat exchangers (SSHE)Scraped surface heat exchangers (SSHE)

• Common factor among former three is that tube of Common factor among former three is that tube of relatively smaller diameter housed in shell.relatively smaller diameter housed in shell.

• SSHE is basically large double pipe heat SSHE is basically large double pipe heat exchanger with scraper inside the inner tube exchanger with scraper inside the inner tube


Double Pipe Heat ExchangersDouble Pipe Heat Exchangers Simplest Type of Heat ExchangerSimplest Type of Heat Exchanger Pair of single lengths of pipe Pair of single lengths of pipe smaller diameter pipe -within another pipe smaller diameter pipe -within another pipe from a number of lengths arranged in a vertical row from a number of lengths arranged in a vertical row Welding of the outer jacket to the inner pipe is done Welding of the outer jacket to the inner pipe is done

oror A packed stuffing box -permit differential A packed stuffing box -permit differential

movement - removal of inner pipe for cleaning or movement - removal of inner pipe for cleaning or maintenance purpose. maintenance purpose.

5-10 cm pipe size shells5-10 cm pipe size shells 1.9-6.35 cm inner tubes 1.9-6.35 cm inner tubes


Application of Double Pipe HEApplication of Double Pipe HE

Can be used for liquid-liquid or steam/gas-Can be used for liquid-liquid or steam/gas-liquid duties with high liquid duties with high μμ

Suitable for low flow rates Suitable for low flow rates high temp. ranges high temp. ranges withstand high pressurewithstand high pressure Difficult to inspect for fouling or leakage.Difficult to inspect for fouling or leakage.


Low flow rates Low flow rates High temperature range High temperature range High pressure because of small diameter pipes High pressure because of small diameter pipes Space requirement - high as compared to plate Space requirement - high as compared to plate

heat exchangerheat exchanger Ceiling or wall mounted thereby taking up no floor Ceiling or wall mounted thereby taking up no floor

space. space. Flow distribution is no problemFlow distribution is no problem In-place-cleaning - very easilyIn-place-cleaning - very easily

Most difficult to inspect for fouling orMost difficult to inspect for fouling or leakage. leakage.


Repair - not difficult Repair - not difficult very close temperature approaches- true very close temperature approaches- true

counter current flow counter current flow Sometimes three tubes - concentrically - triple Sometimes three tubes - concentrically - triple

pipe heat exchangerpipe heat exchanger annuals between the innermost and annuals between the innermost and

intermediate tubes intermediate tubes concurrently or counter currently concurrently or counter currently to preheat the liquid food material before to preheat the liquid food material before

evaporation or spray drying evaporation or spray drying


Space requirement normally highSpace requirement normally high No problem in flow distribution and in-place No problem in flow distribution and in-place

cleaning, repair no problem.cleaning, repair no problem. Three tubes mounted concentrically to form triple Three tubes mounted concentrically to form triple

pipe heat exchanger.pipe heat exchanger. Velocity in heater is high and excellent heat Velocity in heater is high and excellent heat

transfer rates possible.transfer rates possible. In double pipe type, heat recovery or regeneration In double pipe type, heat recovery or regeneration

not possible, while the triple tube arrangement not possible, while the triple tube arrangement makes possible the use of efficient and compact makes possible the use of efficient and compact regenerative hook-up.regenerative hook-up.

Typical application – dairy and food industryTypical application – dairy and food industry To preheat the liquid food material before evaporation or To preheat the liquid food material before evaporation or

spray drying.spray drying.



Scraped surface heat exchanger (SSHE)Scraped surface heat exchanger (SSHE)

Also called votator or swept surface heat Also called votator or swept surface heat exchanger.exchanger.

Two concentric scraper fitted cylinders with two Two concentric scraper fitted cylinders with two or more scraper blades.or more scraper blades.

Outer cylinder covered with insulating materialOuter cylinder covered with insulating material Stainless steel sheet used to cover the insulation to Stainless steel sheet used to cover the insulation to

protect from mechanical damage.protect from mechanical damage. Inner cylinder made of SS or MS lined with Inner cylinder made of SS or MS lined with

chrome-nickel plating.chrome-nickel plating.


Scraped Surface Heat ExchangerScraped Surface Heat Exchanger


Scraped Surface Heat ExchangerScraped Surface Heat Exchanger


Scraped Surface Heat ExchangerScraped Surface Heat Exchanger Fixed-clearance scrapersFixed-clearance scrapers

small clearance between the blades and the heat transfer small clearance between the blades and the heat transfer surface highly abrasive products such as sugar/fat surface highly abrasive products such as sugar/fat

mixturesmixtures Variable-clearance scraper- floating bladesVariable-clearance scraper- floating blades

• Forced toward the wall by, springs, centrifugal force, and hydrodynamic Forced toward the wall by, springs, centrifugal force, and hydrodynamic action of the fluid scrape, sweep, or cut the product film -minimum fouling action of the fluid scrape, sweep, or cut the product film -minimum fouling and burn on takes place and burn on takes place

Heat transfer rate increases Heat transfer rate increases mechanically-induced turbulence, film removal, product mixingmechanically-induced turbulence, film removal, product mixing HTC compare very well with those of plate heat exchangerHTC compare very well with those of plate heat exchanger

Product velocity at the heat transfer surface Product velocity at the heat transfer surface speed of the scraper, number of rows of blades. It does speed of the scraper, number of rows of blades. It does not not depend on the product flow ratedepend on the product flow rate

The product requires whipping and aerating - ice-cream The product requires whipping and aerating - ice-cream freezers - beatersfreezers - beaters


OperationsOperations

Liquid-full operationLiquid-full operation

filled completely with liquid productfilled completely with liquid product

sensible heat transfersensible heat transfer Thin-film operationThin-film operation

does not run full does not run full

phase changephase change


Diameters 7.5-25 cms Diameters 7.5-25 cms And lengths 120-180 cms And lengths 120-180 cms Viscosity up to 100000 cp Viscosity up to 100000 cp Solids contents upto 75 per centSolids contents upto 75 per cent Temperatures -180 to 30 C Temperatures -180 to 30 C


Ice cream, condensed milk, baby foods, etc. Or for Ice cream, condensed milk, baby foods, etc. Or for pasteurization or sterilizationpasteurization or sterilization

Space requirement Space requirement -high or low depending upon the type of unit. -high or low depending upon the type of unit.

Vertical installation Vertical installation -less floor area- difficult to inspect for cleaning-less floor area- difficult to inspect for cleaning

Horizontal installationHorizontal installation needs double unit size for removal of rotor shaft if floor mounted -easy needs double unit size for removal of rotor shaft if floor mounted -easy

to lower down for inspection. to lower down for inspection.

. .


Costliest among all heat exchangers Costliest among all heat exchangers Moving parts, seals and blades -proper Moving parts, seals and blades -proper

maintenance maintenance Lubrication -manufacturers instructions. Lubrication -manufacturers instructions. Blades - sharpened as they get worn. Blades - sharpened as they get worn.


ScrapersScrapers• Scrape the film continuously.Scrape the film continuously.• More heat transfer rate.More heat transfer rate.• Minimum fouling and burningMinimum fouling and burning

Fixed clearance scrapersFixed clearance scrapers Used for highly abrasive products (sugar/fat Used for highly abrasive products (sugar/fat

mixtures)mixtures) Variable clearance scrapersVariable clearance scrapers

Floating blades forced towards wall by springs, Floating blades forced towards wall by springs, centrifugal force, hydrodynamic action of the centrifugal force, hydrodynamic action of the fluid or combination of these factorsfluid or combination of these factors..


SSHE can be used for two modes of operationsSSHE can be used for two modes of operations Liquid-full operationLiquid-full operation

Vessel completely filled with productVessel completely filled with product Almost always sensible heat transferAlmost always sensible heat transfer

Thin-film operationThin-film operation Does not run full, but liquid flows in a thin film down Does not run full, but liquid flows in a thin film down

the vessel devicethe vessel device Sensible + latent heat transferSensible + latent heat transfer


Spiral tube heat exchangerSpiral tube heat exchanger One or more spirally wound tubesOne or more spirally wound tubes Heat transfer higherHeat transfer higher Turbulence induced is more due to higher velocityTurbulence induced is more due to higher velocity Natural scrubbing of the tubeNatural scrubbing of the tube Production cycle extended for a longer time.Production cycle extended for a longer time. Fewer cleaning cycles required.Fewer cleaning cycles required. Large amount of space accommodated.Large amount of space accommodated. Used for aseptic production of liquid and semi-Used for aseptic production of liquid and semi-

solid food productssolid food products @ 75 – 15000 lit/hr@ 75 – 15000 lit/hr


• Diameters 7.5 to 25 cm, lengths 120 to 180 cmDiameters 7.5 to 25 cm, lengths 120 to 180 cm• Continuous heating or freezing (Continuous heating or freezing (μμ = 1,00,000 cP = 1,00,000 cP

and solid content up to 75 %)and solid content up to 75 %)• Temperature range 180Temperature range 18000 to -30 to -3000CC• Manufacturing of ice cream, condensed milk, baby Manufacturing of ice cream, condensed milk, baby

foods etc.foods etc.• Space requirement high or low depending upon Space requirement high or low depending upon

type of unittype of unit• Costliest among all othersCostliest among all others


Considerable amount of surface can be Considerable amount of surface can be accommodated in a given space by spiraling. accommodated in a given space by spiraling. Thermal expansion -not a problemThermal expansion -not a problem

Cleaning of the outer surface of the tube is Cleaning of the outer surface of the tube is difficult. difficult.

Used for aseptic production of liquid and semi-Used for aseptic production of liquid and semi-solid food productssolid food products


Spiral Tube Heat ExchangerSpiral Tube Heat Exchanger


Shell and Tube Heat ExchangersShell and Tube Heat ExchangersRound tubes housed in a cylindrical shell Round tubes housed in a cylindrical shell One fluid flows inside the tube while the other fluid flows One fluid flows inside the tube while the other fluid flows

across and along the tubesacross and along the tubes Major components- Major components-

Tubes Tubes ShellShell BafflesBaffles Tube sheetsTube sheets Pass divider Pass divider Channel coverChannel cover Tube side and shell side nozzles Tube side and shell side nozzles

The tubes The tubes Arranged on a square pitch- easily cleanedArranged on a square pitch- easily cleaned Triangular pitch pattern -more number of tubesTriangular pitch pattern -more number of tubes


Shell and tube heat exchangersShell and tube heat exchangers Tubes arranged on square or triangular pitch patternTubes arranged on square or triangular pitch pattern

Square pattern – easy cleaningSquare pattern – easy cleaning Triangular pattern – more no. of tubes to a given shell Triangular pattern – more no. of tubes to a given shell

diameterdiameter.. Material – usually low carbon steel, low alloy steel. Material – usually low carbon steel, low alloy steel.

SS, Cu etc.SS, Cu etc. BafflesBaffles

Support tubes, prevent vibration and guide shell side Support tubes, prevent vibration and guide shell side fluid back and forthfluid back and forth

Increase in velocity, turbulences, degree of mixing Increase in velocity, turbulences, degree of mixing and high heat transfer coefficient.and high heat transfer coefficient.


Shell and tube heat exchanger -widely used in process Shell and tube heat exchanger -widely used in process industries - relatively easy construction -wide range of industries - relatively easy construction -wide range of duties-mechanically rugged -withstand normal shop duties-mechanically rugged -withstand normal shop fabrication stresses, shipping and field erection stresses fabrication stresses, shipping and field erection stresses and normal operating conditionsand normal operating conditions

Can be reasonably easily cleanedCan be reasonably easily cleaned Gaskets and tubes, which are most subject to failure, can Gaskets and tubes, which are most subject to failure, can

be replaced easilybe replaced easily Low solids content and viscosities normally less than Low solids content and viscosities normally less than

10000 cps10000 cps Often used for non-food processing steps such as chilling Often used for non-food processing steps such as chilling

the brine for refrigeration or as hot water heatersthe brine for refrigeration or as hot water heaters Tubular evaporators - shell and tube heat exchanger Tubular evaporators - shell and tube heat exchanger


Shell and Tube Heat ExchangerShell and Tube Heat Exchanger



ShellShell Roundness of the shell -important for inserting and Roundness of the shell -important for inserting and

fixing the baffles of maximum diameter impingement fixing the baffles of maximum diameter impingement baffle -below the shell-side inlet nozzle- prevent the baffle -below the shell-side inlet nozzle- prevent the impact of fluid on the tubes, which may lead to erosion, impact of fluid on the tubes, which may lead to erosion, cavitation, and/or vibration of tubes cavitation, and/or vibration of tubes

Tube bundle- tubes, tube sheets and baffles from the Tube bundle- tubes, tube sheets and baffles from the shell for inspection and cleaningshell for inspection and cleaning

Tube-side channels and nozzles control - tube-side fluid Tube-side channels and nozzles control - tube-side fluid into and out of the tubes into and out of the tubes

Channel cover -round plate fitted to the channel flanges Channel cover -round plate fitted to the channel flanges - removed for tube inspection - removed for tube inspection


BafflesBafflesTo support the tubes in proper position during assembly and To support the tubes in proper position during assembly and

operation operation To prevent vibration of the tubes caused by flow induced To prevent vibration of the tubes caused by flow induced

eddies eddies To guide the shell side fluid back and forth across the tube To guide the shell side fluid back and forth across the tube

field field Increase in velocity, turbulences, degree of mixing and heat Increase in velocity, turbulences, degree of mixing and heat

transfer coefficient transfer coefficient Types of BafflesTypes of Baffles Transverse baffles are placed along the length of tubesTransverse baffles are placed along the length of tubes Longitudinal bafflesLongitudinal bafflesMinimum spacing between baffles -one-fifth of the shell diameterMinimum spacing between baffles -one-fifth of the shell diameter


A pass divider A pass divider Plate fitted into one or both the channel Plate fitted into one or both the channel Pass dividers - fitted tightly to prevent the leakage of Pass dividers - fitted tightly to prevent the leakage of

fluid from one pass to anotherfluid from one pass to another Tube side passes – may be moreTube side passes – may be more

Shell side passes – restricted to one- twoShell side passes – restricted to one- two Sometimes more than two.Sometimes more than two.


Fluid choiceFluid choice

Fouling and corrosion characteristics of the fluid, Fouling and corrosion characteristics of the fluid, permissible pressure drop across the heat permissible pressure drop across the heat exchanger, constructional cost, etc. exchanger, constructional cost, etc.

Corrosive and more susceptible for fouling fluids - Corrosive and more susceptible for fouling fluids - tubes tubes

In shell-side fluid -more pressure drop In shell-side fluid -more pressure drop


Types of baffles:Types of baffles:• TransverseTransverse• LongitudinalLongitudinal Minimum spacing between baffles 1/5 th of shell Minimum spacing between baffles 1/5 th of shell

diameter, but not less than 5 cm.diameter, but not less than 5 cm.

Choice of fluid depends on:Choice of fluid depends on: Fouling and corrosion characteristicsFouling and corrosion characteristics Permissible pressure dropPermissible pressure drop Constructional cost etc.Constructional cost etc. Corrosive and fouling producing fluids in tubesCorrosive and fouling producing fluids in tubes


Jacketed KettleJacketed Kettle Semispherical container and a jacket Semispherical container and a jacket cylindrical container with jacket - jacketed vat. cylindrical container with jacket - jacketed vat. The steam or hot water may be used as a heating mediumThe steam or hot water may be used as a heating medium Hot water- spray- more efficient- rapidly moving thin filmHot water- spray- more efficient- rapidly moving thin film Flooded into the heating/cooling medium passageFlooded into the heating/cooling medium passage 40 percent saving in heating time by spray method 40 percent saving in heating time by spray method

agitator or scraper- uniform heating and increase rate of heat agitator or scraper- uniform heating and increase rate of heat transfertransfer

small capacity plant small capacity plant production of small quantities of material in large capacity plantsproduction of small quantities of material in large capacity plants not efficient as compared to other types of heat exchangersnot efficient as compared to other types of heat exchangers the initial cost of the exchanger is low. the initial cost of the exchanger is low. Operation and maintenance are easyOperation and maintenance are easy No skilled worker is needed. No skilled worker is needed. energy consumption of the heat exchanger is moreenergy consumption of the heat exchanger is more


JACKETED KETTLEJACKETED KETTLE

Spray or flooded typeSpray or flooded type 40 % saving in heating time in spray40 % saving in heating time in spray Agitator for uniform heatingAgitator for uniform heating Scraper when concentration of liquid doneScraper when concentration of liquid done Operation and maintenance easier.Operation and maintenance easier. Not efficient as compared to othersNot efficient as compared to others Initial cost is lowInitial cost is low Volume /heat transfer area highVolume /heat transfer area high Area/volume lowArea/volume low


Agitator or scraper- uniform heating and increase rate of Agitator or scraper- uniform heating and increase rate of heat transferheat transfer

Cylindrical container with jacket - jacketed vat. Cylindrical container with jacket - jacketed vat. Small capacity plant Small capacity plant Production of small quantities of material in large capacity Production of small quantities of material in large capacity

plantsplants Not efficient as compared to other types of heat exchangersNot efficient as compared to other types of heat exchangers The initial cost of the exchanger is lowThe initial cost of the exchanger is low Operation and maintenance are easyOperation and maintenance are easy Energy consumption of the heat exchanger is moreEnergy consumption of the heat exchanger is more


DIRECT CONTACT TYPE HEAT DIRECT CONTACT TYPE HEAT EXCHANGERSEXCHANGERS

Steam injectionSteam injection Steam into process fluidSteam into process fluid

Steam infusionSteam infusion Process fluid spread into vessel with steam Process fluid spread into vessel with steam

atmosphereatmosphere Employed in dairy industry for UHT processingEmployed in dairy industry for UHT processing Temp. rises very rapidly to 135-150Temp. rises very rapidly to 135-15000C.C. Heat transfer mainly due to condensation of Heat transfer mainly due to condensation of

steam resulting in 10 % dilution of the product.steam resulting in 10 % dilution of the product.


Advantages of Direct contact HEAdvantages of Direct contact HE

Very rapid heating and coolingVery rapid heating and cooling Less scaling permits longer production runsLess scaling permits longer production runs Low oxygen content of final productLow oxygen content of final product


Limitations/disadvantages of Direct Contact Limitations/disadvantages of Direct Contact HEHE

Direct heating more complexDirect heating more complex RequiresRequires

more plant components, more plant components, additional controls and additional controls and high quality steam (culinary steam)high quality steam (culinary steam)

Relatively expensive in Relatively expensive in initial and initial and operating costoperating cost

No regenerative heating above the temperature at No regenerative heating above the temperature at which steam is mixedwhich steam is mixed


Direct Contact TypeDirect Contact Type Steam injection - steam -suitable nozzle -liquidSteam injection - steam -suitable nozzle -liquid Steam infusion heat exchangers - spread into a Steam infusion heat exchangers - spread into a

vessel with steam atmospherevessel with steam atmosphere Raises the temperature very rapidly to 135 - 150. Raises the temperature very rapidly to 135 - 150. Heat transfer - condensation of steam Heat transfer - condensation of steam 10% dilution of the product10% dilution of the product Vacuum chamber- evaporatively cooled and the Vacuum chamber- evaporatively cooled and the

condensed water is flushed off. Adjustment of the condensed water is flushed off. Adjustment of the vacuum - necessary removal of water and vacuum - necessary removal of water and simultaneously controls the dry matter content of simultaneously controls the dry matter content of the final produce. the final produce.


Advantages of Direct Contact HEAdvantages of Direct Contact HE

Very rapid heating and cooling and consequently a low total temperature load on the product.

Less scaling in the equipment as compared to indirect heating which also permits longer production runs because of less frequent cleaning cycles.

Low oxygen content of the final product. Expansion cooling does not only remove water but also dissolved air (02) resulting in an oxygen content of the final product (milk) of about or less than 0.1 ppm.


It is not possible to use regenerative heating It is not possible to use regenerative heating above the temperature at which steam is above the temperature at which steam is mixed with the product. mixed with the product.


Steam Injection SystemSteam Injection System

Injection requires steam pressures higher Injection requires steam pressures higher than those of the product in the infuser.than those of the product in the infuser.


Steam Infusion SystemSteam Infusion System

With infuser, any pool of product in the With infuser, any pool of product in the bottom of heating vessel contributes much bottom of heating vessel contributes much of the holding period needed for sterilizing of the holding period needed for sterilizing effect. effect.

Very close control of product level at this Very close control of product level at this point is necessary if the process is not to be point is necessary if the process is not to be variablevariable


Temperature-Time Profile in Temperature-Time Profile in UHT ProcessUHT Process


Temperature-Time ProfileTemperature-Time Profile

Heat Exchangers

Documents

heat exchangersb

heat transfer area

processing heat transfer

plate heat exchanger

case of plate heat exchanger

inlet heat sensitive

fluids flow arrangement

flow ratiosaturday