study of heat transfer coefficient in a double pipe heat exchanger
DESCRIPTION
The objectives of this experiment were to study a double pipe heat exchanger and hence to obtain individual and overall heat transfer coefficients. Also the variation of heat transfer coefficient with Reynolds number and fluid velocity and also the experimental and theoretical heat transfer coefficient was compared. In this experiment, steam was used as the hot fluid while water was used as the cold fluid. Water was passed through the pipe and steam was passed through the annulus. Steam pressure was controlled by the valve opening. The inlet and outlet water temperature was recorded. This same process was done for several steam pressures of 5, 10 and 15 psig and different flow rate of water. Then by proper mathematical operation, heat transfer coefficient was determined. In this experiment, the overall theoretical heat transfer coefficient was found to be varied from 674.1697 W/m2.oC to 1501.875 W/m2.oC while the experimental values varied from 763.644 W/m2.oC to 1644.788 W/m2.oC. And, the individual steam side heat transfer coefficient was in the range of 7979.871 W/m2.oC to 8377.854 W/m2.oC while waterside heat transfer coefficient was from 987.6382 W/m2.oC to 1981.433 W/m2.oC. Graph of Nusselt number vs. Reynolds number, heat transfer coefficient vs. velocity and Wilson plot was drawn. The possible discrepancies are discussed at the end of the report.TRANSCRIPT
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ChE 304
Chemical engineering laboratory - III Experiment No. 1 Group No. 03 (A2)
Name of the experiment:
Study of heat transfer coefficient in a
double pipe heat exchanger
Submitted by:
Md. Hasib Al Mahbub
Student Id: 0902045
Level: 3; Term: 2
Section: A2
Date of performance: 04/03/2014
Date of submission: 14/03/2014
Partners Student Id. 0902041
0902042
0902043
0902044
Department of Chemical Engineering.
Bangladesh University of engineering and technology, Dhaka.
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1
Summary
The objectives of this experiment were to study a double pipe heat exchanger and hence to
obtain individual and overall heat transfer coefficients. Also the variation of heat transfer
coefficient with Reynolds number and fluid velocity and also the experimental and theoretical
heat transfer coefficient was compared. In this experiment, steam was used as the hot fluid
while water was used as the cold fluid. Water was passed through the pipe and steam was
passed through the annulus. Steam pressure was controlled by the valve opening. The inlet and
outlet water temperature was recorded. This same process was done for several steam pressures
of 5, 10 and 15 psig and different flow rate of water. Then by proper mathematical operation,
heat transfer coefficient was determined. In this experiment, the overall theoretical heat transfer
coefficient was found to be varied from 674.1697 W/m2.oC to 1501.875 W/m2.oC while the
experimental values varied from 763.644 W/m2.oC to 1644.788 W/m2.oC. And, the individual
steam side heat transfer coefficient was in the range of 7979.871 W/m2.oC to 8377.854 W/m2.oC
while waterside heat transfer coefficient was from 987.6382 W/m2.oC to 1981.433 W/m2.oC.
Graph of Nusselt number vs. Reynolds number, heat transfer coefficient vs. velocity and
Wilson plot was drawn. The possible discrepancies are discussed at the end of the report.
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2
Experimental Setup
Figure 1: Experimental setup of a double pipe heat exchanger.
Saturated
steam inlet
Pressure
Gauge
Outlet
Temperature
Water
Outlet
Steam
Trap
Water
Inlet
Inlet
Temperature
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3
Observed data
Tube Length = 7 feet 4 inch
Inner Tube: Nominal Diameter 1 inch; Schedule 40
Table 1: Observed data for double pipe heat exchanger.
Steam
Pressure,
P (psig)
Obs.
No.
Water temperature
(C)
Water Condensate
Inlet Outlet Volume(L) Time(s) Weight(kg) Time(s)
5 01 28 61 1.0 10.19 0.25 60
02 28 59 1.0 8.8 0.3 60
03 28 49 1.0 4.15 0.65 60
04 28 43 1.0 2.94 0.95 60
10 05 28 64 1.0 10.03 0.45 60
06 28 57 1.0 6.78 0.55 60
07 28 50 1.0 4.56 0.65 60
08 28 46 1.0 3.44 0.75 60
15 09 28 68 1.0 12.47 0.35 60
10 28 58 1.0 6.87 0.45 60
11 28 53.5 1.0 5.25 0.55 60
12 28 49.5 1.0 4.06 0.65 60
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4
Calculated data
Length of the pipe, L= 7 ft 4 inch = 7.33 ft. = 2.234184 m.
Outer diameter of the pipe, Do=1.32 inch. = 0.033528 m. (Donald Q. Kern, Process Heat
Transfer, page: 843.)
Outside surface area, Ao = D0L = 0.2344 m2.
Table 2: Data for experimental overall heat transfer coefficients.
Obs. No.
Steam
Pressure
(psig)
Saturation
temperature,
TS (oC)
Heat of
condensation,
S (kJ/kg)
Wt. of
condensate,
WC (kg)
Mass flow
rate of
condensate,
Mc
(kg/s)
1
5
108.39
2234.347
0.25 0.0042
2 0.3 0.005
3 0.65 0.0108
4 0.95 0.0158
5
10
115.21
2215.612
0.45 0.0075
6 0.55 0.0092
7 0.65 0.0108
8 0.75 0.0125
9
15
120.97
2199.242
0.35 0.0058
10 0.45 0.0075
11 0.55 0.0092
12 0.65 0.0108
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5
Table 3: Data for properties of water at mean temperature.
Obs.
No.
Mean
temperature
of water, TM
(oC)
Tube wall
temperature
on steam
side,Tw
(oC)
Density,
M
(kg/m3)
Mass Flow
rate of
Water
(kg/s)
Viscosity,
M
(kg/m.s)
Prandtl
No.
Pr
1 44.5 76.445 990.42447 0.097195728 0.000585 3.7295
2 43.5 75.945 990.83579 0.112594976 0.000596 3.8043
3 38.5 73.445 992.7838 0.239225012 0.000654 4.2178
4 35.5 71.945 993.8621 0.338048333 0.000694 4.5018
5 46 80.605 989.7944 0.09868339 0.00057 3.6217
6 42.5 78.855 991.24 0.14620059 0.000607 3.8816
7 39 77.105 992.5973 0.217674846 0.000648 4.1733
8 37 76.105 993.3316 0.288759186 0.000673 4.3561
9 48 84.485 988.9303 0.079304755 0.00055 3.4857
10 43 81.985 991.0388 0.144256012 0.000601 3.8426
11 40.75 80.86 991.93 0.188939048 0.000627 4.0232
12 38.75 79.86 992.6908 0.244505123 0.000651 4.1954
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6
Table 4: Data for properties at mean temperature (Contd)
Obs.No.
Velocity of
Water,
V
(m/s)
Reynolds
No.
Re
Nusselt
No.
Nu
Water side
heat
transfer
coefficients,
hi
(W/m2.oC)
hio
(W/m2.oC)
Film
temperature,
Tf
(oC)
1 0.175932999 7.94E+03 46.99696 1124.823 893.8938 84.43125
2 0.203722416 9.03E+03 52.45477 1253.147 995.8725 84.05625
3 0.431989701 1.75E+04 92.06636 2178.535 1731.276 82.18125
4 0.609781381 2.33E+04 118.3597 2783.741 2212.231 81.05625
5 0.178739508 8.28E+03 48.12093 1154.83 917.74 89.25625
6 0.264418475 1.15E+04 64.13742 1529.407 1215.415 87.94375
7 0.393148522 1.61E+04 85.72424 2030.458 1613.599 86.63125
8 0.521150366 2.05E+04 105.6861 2493.319 1981.433 85.88125
9 0.143765618 6.89E+03 41.01053 987.6382 784.8731 93.60625
10 0.260954478 1.15E+04 63.70505 1520.507 1208.342 91.73125
11 0.341477573 1.44E+04 77.64805 1845.46 1466.581 90.8875
12 0.441565828 1.80E+04 93.88314 2222.617 1766.307 90.1375
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Table 5: Data for properties at film temperature.
Obs. No. Density, f
(kg/m3)
Viscosity, f104
(kg/m.s)
Thermal
conductivity,
kf (W/m.oC)
Condensation
heat transfer
coefficients, ho
(W/m2.oC)
1 968 3.28 0.67285 8377.854
2 969 3.29 0.67262 8334.933
3 970 3.37 0.67145 8130.011
4 971 3.42 0.67072 8013.865
5 965 3.10 0.67565 8323.548
6 966 3.14 0.67492 8187.492
7 967 3.19 0.67417 8057.763
8 967 3.22 0.67373 7986.179
9 962 2.95 0.67793 8308.74
10 963 3.01 0.67698 8126.193
11 964 3.04 0.67654 8047.844
12 964 3.07 0.67613 7979.871
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8
Table 6: Data for experimental heat transfer coefficients.
Observation
No.
Rate of heat
taken-up by
water,
Qw(J/s)
Rate of heat
given-up by
steam,
Qc (J/s)
Mean rate of
heat
transfer,
Qm(J/s)
Log mean
temperature
difference,
Tlm (oC)
Experimental
overall heat
transfer
Coefficient,
UOE
(W/m2 oC)
1 13044.73587 9309.779167 11177.25752 62.4434 763.6442362
2 14195.63681 11171.735 12683.6859 63.6365 850.318422
3 20431.4906 24205.42583 22318.45822 69.36097 1372.749895
4 20627.7093 35377.16083 28002.43507 72.63203 1644.788241
5 14444.87987 16617.09 15530.98493 67.62034 979.8600024
6 17243.33618 20309.77667 18776.55642 71.73568 1116.665483
7 19476.23921 24002.46333 21739.35127 75.67779 1225.520398
8 21144.10264 27695.15 24419.62632 77.86355 1337.972592
9 12898.12542 12828.91167 12863.51854 71.10465 771.7989638
10 17609.33134 16494.315 17051.82317 76.99841 944.7816707
11 19594.58522 20159.71833 19877.15178 79.5399 1066.133263
12 21384.90708 23825.12167 22605.01437 81.74934 1179.676555
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9
Table 7: Data for calculation of theoretical heat transfer coefficients
Obs. No.
Theoretical
Overall heat
transfer
coefficients,
UOT (W/m2.oC)
OTU
1
OEU
1 8.0
1
MV
1 753.6054 0.001327 0.00131 4.015338
2 824.378 0.001213 0.001176 3.570828
3 1266.447 0.00079 0.000728 1.957137
4 1501.857 0.000666 0.000608 1.485459
5 770.0179 0.001299 0.001021 3.964821
6 967.2557 0.001034 0.000896 2.898455
7 1200.727 0.000833 0.000816 2.110351
8 1390.981 0.000719 0.000747 1.684339
9 674.1697 0.001483 0.001296 4.719282
10 961.9187 0.00104 0.001058 2.929194
11 1117.201 0.000895 0.000938 2.362165
12 1281.277 0.00078 0.000848 1.923108
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10
Table 8: Data for the heat loss calculation and % of heat loss calculation.
Observation No.
Rate of heat
taken-up by
water,
Qw(J/s)
Rate of heat
given-up by
steam,
Qc (J/s)
Heat loss
QL (J/s)
% of heat loss
1 13044.73587 9309.779167 -3734.96 -40.11863911
2 14195.63681 11171.735 -3023.9 -27.06743229
3 20431.4906 24205.42583 3773.935 15.59127799
4 20627.7093 35377.16083 14749.45 41.69201594
5 14444.87987 16617.09 2172.21 13.07214518
6 17243.33618 20309.77667 3066.44 15.09834664
7 19476.23921 24002.46333 4526.224 18.85733166
8 21144.10264 27695.15 6551.047 23.65413208
9 12898.12542 12828.91167 -69.2138 -0.539513838
10 17609.33134 16494.315 -1115.02 -6.760003926
11 19594.58522 20159.71833 565.1331 2.803278816
12 21384.90708 23825.12167 2440.215 10.2421915
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Sample Calculation
For observation No. 10:
Inlet water temperature, T1 =28oC
Outlet water temperature, T2 =58oC
Volume of water collected, V1 =0.001m3
Time for water collection, tw = 6.87 s
Weight of condensate collected, WC = 0.45 Kg
Time for condensation, tc = 60s
Density of water at 37 oC = 991.0388 Kg/m3
Weight of water collected, Ww = 0.001 991.0388
= 0.9910388 Kg
Mass flow rate of water, Mw = Ww/tw = (0.99103886.87) Kg/s
= 0.1442560116 Kg/s
Mass flow rate of condensate, Mc = WC/tc
= (0.45 60) kg/s
= 0.0075 kg/s
Mean temperature of water, Tm = (T1+ T2)/2 = (58+28)/2 =43 oC
Heat capacity of water at 43 oC, Cp = 4069 J/kg. oC
Rate of heat taken by water, Qw = Mw Cp (T2-T1)
=0.1442560116 4069 (58-28)
= 17609.33134 J/s
Heat of condensation of steam at 15 psig (29.7 psia), s =2199.242 KJ/kg
(Ref: Richard M. Felder, Ronald W. Rousseau, Element Principles of Chemical Processes,
3rd ed.)
Rate of heat given by steam,
QC = MC s = (0.0075 2199242) J/s =16494.315 J/s
Mean rate of heat flow,
Qm = 2
CW QQ = 2
315.16494 417609.3313 = 17051.82317 J/s
Saturation temperature of steam at 15 psig (29.7 psia), Ts = 120.97 oC
(Ref: Richard M. Felder, Ronald W. Rousseau, Element Principles of Chemical Processes,
3rd ed.)
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12
Temperature difference at inlet,
T1 = Ts - T1 = (120.97 28) oC = 92.97 oC
Temperature difference at outlet,
T2 = Ts - T2 = (120.97 58) oC =62.97 oC
Log mean temperature difference,
Tlm =
2
1
21
lnT
T
TT
=
97.62
97.92ln
97.6297.92 oC =77 oC
The outside surface per linear feet = 0.344 ft2/ft
Inside diameter (ID) of the pipe, Di = 1.049 in. = 0.02665 m. (Donald Q. Kern, Process
Heat Transfer, page: 843.)
Outside diameter (OD) of the pipe, Do = 1.32 in. = 0.033528 m. (Donald Q. Kern, Process
Heat Transfer, page: 843.)
Tube length = 7 ft. 4 in. = 88 in. = 7.33 ft.
Outside area available for heat transfer, Ao = 0.3447.33 ft2 = 0.2344 m2.
Experimental overall heat transfer coefficient, UOE = 0.AT
Q
lm
m
= 2344.077
717051.8231
W/m2.oC
= 944.78167 W/m2.oC
Tube wall temperature on steam side,
Tw = 2
mS TT oC = 2
4397.120 oC =81.985 oC
Properties at mean temperature, Tm= 43 oC
Density of water, m =991.0338 kg/m3
Viscosity of water, m =0.00060102 kg/m.s
Prandtl no. of water,Pr = 3.8426
Thermal conductivity of water, km = 0.63608 W/m.oC (Ref: J P Holman, Suvik Bhattacharyya,
Heat Transfer, page no.: 609)
Inner flow area, Ai = 0.0005576 m2
Velocity of water, vm = im
W
A
M
=
0005576.00338.991
160.14425601
m/s = 0.260954478 m/s
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13
Reynolds no. of water,
Re = m
mmi vD
.. =
00060102.0
260954478.00338.99102665.0 = 11468.05
Water side heat transfer coefficient for turbulent flow
Using Dittus-Boelter equation, hi = 0.023 i
m
D
k (Re)
0.8 (Pr)1/3
= 0.02302665.0
63608.0 (11468.05)0.8 (3.8426)1/3
= 1520.507 W/m2.oC
Film temperature,
Tf = Ts-0.75 (Ts-Tw)
= 120.97- 0.75 (120.97- 81.985) oC
= 91.73125 C
Properties of condensate at film temperature, Tf = 97.73125 C
Density, f =963.21 kg/m3
Viscosity of condensate, f = 0.00030103 kg/m.s
Thermal conductivity of condensate, kf = 0.67698 W/m.oC (Ref: J P Holman, Suvik
Bhattacharyya, Heat Transfer, page no.: 609)
Steam side heat transfer coefficient using Nusselt equation for film type condensation,
ho = 25.0
0
23
])(
...[725.0
fWS
Sff
TTD
gk
=25.0
23
]00030103.0)985.8197.120(033528.0
2199.242 81.9)21.963()67698.0([725.0
W/m2.oC
= 8126.193 W/m2.oC
Now, xw= mDD i .003439.0
2
02665.0033528.0
2
0
Carbon-steel metals thermal conductivity, KM = 43 W/m.oC
Log-mean diameter, Dlm =
i
i
D
D
DD
0
0
ln
= m.03.0
02665.0
033528.0ln
02665.0033528.0
Theoretical overall heat transfer coefficient,
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14
UOT = 100
0
).
.
.
1(
lmm
W
ii DK
Dx
hD
D
h
= 1)03.043
033528.0003439.0
1520.50702665.0
033528.0
8126.193
1(
W/m2.oC
= 961.9187 W/m2.oC
Now, 0.001058944.78167
11
OEUm2.oC/W
0.00104961.9187
11
OTU m2.oC/W
2.929194)750.26095447(
118.08.0
v (s/m)0.8
Heat loss, QL = Qc-Qw = 1649.315- 17609.331341 = -1115.02 J/s
% of heat loss = (Qc-Qw)*100/Qc = -6.76%
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15
Graphs
Figure 2: Log-log plot of Nusselt number vs. Reynolds number plot for 10 psig steam
pressure.
Figure 3: Log-log plot of Nusselt number vs. Reynolds number for 5 psig steam pressure.
y = 0.019x0.8686
10
100
1000
7000
Nuss
elt
Num
ber
,Nu
Reynolds Number,Re
10 psig
Power (10 psig)
y = 0.0214x0.8569
10
100
1000
6000
Nuss
elt
Num
ber
,Nu
Reynolds Number, Re
5 psig
Power (5 psig)
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16
Figure 4: Log-log plot of Nusselt number vs. Reynolds number for 15 psig pressure steam.
Figure 5: Log-log plot of water side head transfer coefficient vs. velocity for 5 psig steam
pressure
y = 0.0197x0.8646
10
100
5000
Nuss
elt
Num
ber
,Nu
Reynolds Number, Re
15 psig
Power (15 psig)
y = 3842.6x + 469.57
100
1000
10000
0.1 1
Wat
er s
ide
hea
t tr
ansf
er c
oef
fici
ent,
hi
W/m
2.
C
Velocity of water, v(m/s)
5 psig
Linear (5 psig)
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17
Figure 6: Log-log plot of water side head transfer coefficient vs. velocity for 10 psig steam
pressure.
Figure 7: Log-log plot of water side head transfer coefficient vs. velocity for 15 psig steam
pressure.
y = 3894.8x + 480.24
100
1000
10000
0.1 1Velocity of water,v (m/s)
10 psig
Linear (10 psig)
y = 4147x + 412.63
100
1000
10000
0.1 1
Wat
er s
ide
hea
t tr
ansf
er c
oef
fici
ent,
hi
(W/m
2.C)
Velocity of water,v (m/s)
15 psig
Linear (15 psig)
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18
Figure 8: (1/U) vs. (1/V)0.8 plot for Wilson plot at 5 psig steam pressure.
Figure 9: (1/U) vs. (1/V)0.8 plot for Wilson plot at 10 psig steam pressure.
0.0005
0.0008
0.0011
0.0014
1.48 2.184 2.888 3.592 4.296 5
1/U
1/v.8
Experimental
Theoretical
Power (Experimental)
Power (Theoretical)
Dirt factor = 0.0006658- 0.000608= 0.0000578
0.0006
0.0009
0.0012
0.0015
1.68 2.344 3.008 3.672 4.336 5
1/U
1/v0.8
Experimental
Theoretical
Power (Experimental)
Power (Theoretical)
Dirt Factor = 0.000747-0.000719= 0.000028
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19
Figure 10: (1/U) vs. (1/V)0.8 plot for Wilson plot at 15 psig steam pressure.
0.0006
0.0009
0.0012
0.0015
0.0018
1.92 2.536 3.152 3.768 4.384 5
1/U
1/v0.8
Experimental
Theoretical
Power (Experimental)
Power (Theoretical)
Dirt Factor =0.000848-0.00078= 0.000068
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20
Results and Discussions
Range of the Theoretical Overall Heat Transfer Coefficient (UOT), 674.1697 W/m2.oC to
1501.875 W/m2.oC
Range of the Experimental Overall Heat Transfer Coefficient (UOE), 763.644 W/m2.oC to
1644.788 W/m2.oC
Ranges of individual steam side heat transfer coefficient - 7979.871 W/m2.oC to 8377.854
W/m2.oC
Ranges of waterside heat transfer coefficient - 987.6382 W/m2.oC to 1981.433 W/m2.oC
Slope of the straight line Nusselt number Vs. Reynolds number Plots are-
For 5 psig pressure - 0.8569
For 10 psig pressure - 0.8686
For 15 psig pressure - 0.8646
The theoretical value of Nusselt number Vs. Reynolds number Plots are 0.8
When the values of Nusselt no. is plotted against the values of corresponding Reynolds
no. in a logarithmic plot a straight line with a slope of 0.8569 0.8686 is obtained. According
to Dittus-Boelter equation, the slope should be 0.8. This curve also conforms to Dittus-Boelter
equation. Therefore, this finding is highly satisfactory.
The dirt factor from the 1/U vs. 1/v0.8 plot ranges from 0.000028 to 0.000068.
Nusselt no. vs. Reynolds and water side heat transfer coefficient (hi) vs. velocity (v) plots for
different pressure shows straight lines in log-log coordinate. But 1/U vs. 1/v0.8 plots for
different pressure for both theoretical and experimental overall heat transfer coefficients show
straight lines in normal coordinate. As the experimental findings of overall heat transfer
coefficients were generally lower than the theoretical ones, the 1/U curve for theoretical values
was in below the curve for experimental values.
The possible reasons of the discrepancies of theoretical and experimental values are mentioned
bellow
At the times of calculating the theoretical overall heat transfer coefficients the
resistance due to the formation of scale or dirt was not taken into consideration. Hence,
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21
Fouling or other factors are left from the calculation. In reality, the performance and
efficiency of any heat exchanger are subject to these factors and this is why industrial
exchangers are dismantled routinely after operating a certain period for cleaning dirts
that are deposited on the wall. The double pipe heat exchanger used in this experiment
is very old and may not undergo overhauling for a long period. The scale deposited in
the meantime is sufficient to deviate the theoretical values from the experimental ones
especially when dirt formation is neglected in calculation.
Malfunctioning of the stream trap is one of the reason for the heat loss becoming
negative.
The steam pressure was considered constant during the experiment. But in practical it
was not constant throughout the experiment.
Heat lost during the experiment due to convection and conduction were not considered.
Could be the unsteady nature of condensate flow caused some error in the determination
of corresponding condensate for a given flow of water.
Some assumptions were made in determination of steam side heat transfer coefficient
determination; such as the vapor pressure was neglected and the condensation was
considered to be laminar and film type. But in practical could not satisfy those
assumptions.
1245678