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The objectives of this experiment are to evaluate and study the heat load and head
balance, LMTD and overall heat transfer coefficient, to calculate the Reynolds numbers at the
shell and tubes sides and to measure and determine the shell and tube sides pressure drop.
This experiment consists of five runs. For each of the run, three sets of data are obtained. A set
of data from each of the run is selected based on the best convergence of QC and QH (the ratio
of QC/QH is nearest to 1.0). From the selected set, the heat load and head balance, LMTD and
overall heat transfer coefficient, Reynolds numbers and pressure drop are determined. From
the results obtained, an ideal set to choose based on the ratio is majorly from set 3.
Introduction
A heat exchanger can be defined as any device that transfers heat from one fluid to another or
from or to a fluid and the environment. There are several types of shell and tube heat
exchanger:
Figure 1: Heat exchanger with fixed tube plates (four tubes, one shell-pass)
Figure 2: Heat exchanger with floating head (two tube-pass, one shell pass)
Figure 3: Heat exchanger with hairpin tubes
Basic Considerations in Choosing a Mechanical Arrangement of Heat Exchanger
There are four basic considerations in choosing a mechanical arrangement that provides for
efficient heat transfer between the two fluids or vapors, while taking care of such practical
matters as preventing leakage from one into the other. They are:
Consideration for differential thermal expansion of tube and shell
Means of directing fluid through the tubes
Methods of controlling fluid flow through the shell
Consideration for ease of maintenance and servicing
Advantages of Heat Exchanger
The main advantages of shell-and-tube heat exchangers are:
Condensation or boiling heat transfer can be accommodated in either the tubes or the
shell, and the orientation can be horizontal or vertical.
The pressures and pressure drops can be varied over a wide range.
Thermal stresses can be accommodated inexpensively.
There is substantial flexibility regarding materials of construction to accommodate
corrosion and other concerns. The shell and the tubes can be made of different
materials.
Extended heat transfer surfaces (fins) can be used to enhance heat transfer.
Cleaning and repair are relatively straightforward, because the equipment can be
dismantled for this purpose.
Applications of Heat Exchanger
Shell and tube heat exchangers represent the most widely used vehicle for the transfer of heat
in industrial process applications. They are frequently selected for such duties as:
Process liquid or gas cooling
Process or refrigerant vapor or steam condensing
Process liquid, steam or refrigerant evaporation
Process heat removal and preheating of feed water
Thermal energy conservation efforts, heat recovery
Compressor, turbine and engine cooling, oil and jacket water
Hydraulic and lube oil cooling
Many other industrial applications
Shell and tube heat exchangers have the ability to transfer large amounts of heat in relatively
low cost, serviceable designs. They can provide large amounts of effective tube surface while
minimizing the requirements of floor space, liquid volume and weight.
Aims/Objectives
To evaluate and study the heat load and head balance, LMTD and overall heat transfer
coefficient.
To calculate the Reynolds numbers at the shell and tubes sides.
To measure and determine the shell and tube sides pressure drop.
Theory
Heat load and heat balance
This part of the calculation is to use the data in Table 1 to check the heat load QH and QC and
to select the set of values where QC is closest toQH .
Hot water flow rate (HW )
QH = FH×CpH×(t1−t2 )
Hot water flow rate (CW )
QC = FC×CpC×(T 2−T1 )
Where:
QH = Heat load for hot water flow rate
QC = Heat load for cold water flow rate
FH= Hot water mass flow rate
FC=Cold water mass flow rate
t1= Hot water inlet temperature
t2= Hot water outlet temperature
T 1=Cold water inlet temperature
T 2= Cold water outlet temperature
LMTD
Calculations of log mean temperature difference (LMTD).
LMTD=( t1−T 2 )−( t2−T1 )
ln( t1−T 2)( t2−T 1)
Where, all variables are same with the above section:
R=−( t1−T 2)−( t2−t1 )
S=−( t2−t1 )−(T1−t1)
Both equations would determine the value of correction factorFT . Practically, FT value
obtained from the graph with respect to R and S value. In this case, the correction factor
would apply to enhance the LMTD value. So, equation below show the corrected LMTD can be
determined.
LMTD=FT×LMTD
Overall heat transfer coefficient, U
Overall heat transfer coefficient at which equivalent to U D can be calculated by using equation
below. In this case, the value of total heat transfer area A has been given and equal to 31.0 ft2
U= QA×LMTD×FT
Where:
Q= Heat rate with respect to the average head load
FT=Correction factor
Reynolds Number Calculation
Shell-side Re( s )for CW
Re( s )=De .Gsμ
Where:
De=de12
de=4 (1/2PT×0 .86 PT−1 /2 π .
do4
2
)
1/2π .do
At which:
PT=Pitch = 0.81inch
do=Tube outside diameter, inch
μ= Viscosity, taken at average fluid temperature in the shell, lbmft-1hr-1
Gs=WsAs (lbmft-2hr-1)
Ws= Flow rate in (lbmhr-1)
As= 0.029 ft2
Tube-side Re( t ) for HW
Re( t )=D .Gtμ
Where:
D= Tube ID = 0.04125 ft
μ= Viscosity, taken at average fluid temperature in the tube, lbmft-1hr-1
Gt=WtAt (lbmft-2hr-1)
Wt= Flow rate in lbmhr-1
At= 0.02139 ft2
Pressure drop
This part would determine the following:
HW : The measured tube-inside pressure drop DP (tube) which will be corrected and is
expected to be more than calculated tube-side pressure drop.
CW : The measured shell-inside pressure drop DP (shell) which will be corrected and is
expected to be more than calculated tube-side pressure drop.
Notice that, both calculated pressure and also measured pressure are considered in unit
mmH2O. In this case, since calculated pressure drop in both of shell and tube side have been
obtained during the experiment, so it’s only required conversion factor to change the value into
unit of mmH2O.
Conversion factor: x .bar×1×105Pa
1bar×
1mmH 2O
(9 . 81)Pa .
Where x is the calculated pressure value in unit bar.
Apparatus
HE 12: SHELL AND TUBE HEAT EXCHANGER PLANT
Experimental procedure
Step i)
1. All the pump suction valves (for PH, PC1, and PC2) are checked so that they are fully
opened all the time.
2. BVC2 is opened fully but CV2 is closed fully so that PC2 shall operate as a back-mixing
pump for tank T2 in the next experiment. Both CV1 and BVC1 are opened fully. Only PC1
shall be used here to pump CW into the Heat Exchanger in the next experiment. Do not
switch on any CW pumps (PC1, PC2) yet.
3. HV is closed fully but BVH is opened fully.
4. Pump PH for HW is started to circulate around tank T1 via only BVH.
5. The heaters are started and TlC5 is noted. When the HW in tank T1 is almost 70 C/158 ͦF (see TlC5), HV is opened fully. The HW flowrate is quickly adjusted ͦto about 25 USGPM by regulating its by-pass valve BVH.6. Both the CW pumps, PC1 and PC2 are switched on. The CW flowrate is quickly adjusted to about 10 USGPM by regulating the by-pass valve BVC1.7. The DP Selector Switch is switched to the DP (Shell) position.
Step ii)
a) The first set of temperature and flowrate readings are taken.
CW: Temperature - inlet/outlet, T13*(T1), T14*(T2):
Flowrate FC at FI(C*)
HW: Temperature - inlet/outlet, TI1*(T1), T12*(T2):
Flowrate FH at FI(H*)
Note that the CW inlet temperature (T1) is increasing gradually. The CW outlet temperature
(T2) varies together with the HW inlet/outlet temperatures t1/t2. It is important that all the
temperature and flowrate readings be taken almost simultaneously.
These readings are recorded appropriately in Table 1.
Also the respective inlet pressure and inlet pressure drop of the CW and HW flow
streams are recorded. For the pressure drop readings, DP (shell), DP (tube) at the panel
amount DPI*, use the DP signal Selector Switch appropriately as explained below:
CW: PG-C; DPI* for DP (shell) with the DP Selector Switch at the DP (shell) position.
HW: PG-H; DPI* for DP (tube) with the DP Selector Switch at the DP (tube) position.
To take the DP readings at DPI*, they are waited till they are fairly steady.
The DP reading is then taken at its highest reading (i.e. peak reading) just when it starts to
decrease.
b) The second and third sets of the above readings for RUN 1 are continued and taken
consecutively. The last set of temperature readings should be taken when all the
temperatures are fairly steady.
Step iii)
1. RUN 1 is completed, with three sets of the above readings.
2. All the CW pumps PC1 and PC2 are stopped.
3. The heaters are kept on for the next RUN.
4. With the HW pump PH still running, the discharge valve HV is closed fully but the by-
pass valve BVH is opened fully.
5. The DP Selector Switch is switched to the equalizing (vertical or “0”) position.
Step iv)
1. RUN 2, 3, 4 and 5 are repeated at different recommended nominal flowrate of CW (i.e.
FC) and HW (i.e. FH) using the following procedures check-list.
To continue with the next run
The HW pump PH is checked so that it is running with BVH fully opened and HV
fully closed.
With the heaters ON, the HW in tank T1is heated till it almost 70 C/150 F (seeͦ ͦ TlC5). HV is fully opened. The HW flowrate is adjusted until FH at Fl (H*) is almost at the recommended nominal flowrate for the RUN. This is done by regulating the by-pass valve BVH with HV fully opened. (However, if the flowrate is still too high even when its by-pass valve is fully open, its discharge valve, HV is gradually closed to get the required HW flowrate). The CW pumps PC1 and PC2 are started with CV1/BVC1/BVC2 are fully opened but CV2 is fully closed. FC at Fl(C*) is noted. FC is adjusted to the recommended nominal flowrate for the RUN by regulating the by-pass valve BVC1 with CV1 fully opened. (However if the CW flowrate (FC) from PC1 is still inadequate even when its by-pass valve BVC1 is fully closed, use the second CW pump (PC2) by gradually opening CV2 and simultaneously closing BVC2 to get the required CW flowrate). The DP Selector Switch is switched to the DP (shell) position.
The various readings for the RUN are taken.
To end a RUN after getting 3 sets of readings
All the CW pumps, PC1 and PC2 are stopped.
The DP Selector Switch is switched to the equalizing (vertical or “0”) position.
With the HW pump PH and the heaters stillON, HV is closed fully nut BVH is
opened fully.
PLANT SHUT-DOWN
1. The heaters are switched OFF.
2. All the pumps (PH, PC1 and PC2) are checked so that they are switched OFF.
3. The DP Selector Switch is switched to the equalizing (vertical or “0”) position.
4. The main power supply to the plant at the front of the panel/cubical is switched OFF. All
the pumps suction valves, discharge valves (HV, CV1 and CV2) and by-pass valves (BVH,
NAME : NURFARAHIMA BINTI IBRAHIM MATRIC NO. : 2010389697GROUP : GROUP 2/EH2203AEXPERIMENT : EXPERIMENT 3 (SHELL AND TUBE HEAT EXCHANGER)DATE PERFORMED : 20 MARCH 2012SEMESTER : 3PROGRAMME / CODE :EH220SUBMIT TO :MADAM RABIATUL ADAWIYAH BT. ABDU AZIZ
13 Supervisor’s grading 10 TOTAL MARKS 100
Remarks:
Checked by:
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Date:
UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA