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Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
ME SEMESTER-1 EXAMINATION WINTER 2018
Subject Code: 3711609 Date: 02/01/2019
Subject Name: COMPUTER AIDED DESIGN IN HEAT TRANSFER
Time: 02:30 PM To 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full mark.
Q.1 Discuss general design method for shell tube heat exchanger. 07
Calculation of shell side and tube side pressure drop for no phase change fluid. 07
Q.2 Discuss Delaware method for design of baffled shell tube heat exchanger. 07
With a neat sketch discuss the different types of baffles used in shell and tube heat
exchanger. Discuss the functions of baffles also.
07
OR
Discuss the advantages and disadvantages of U-tube heat exchanger over Floating head
heat exchanger.
07
Q.3 Design shell tube horizontal condensor for condensation of 22593 kg/hr n-propanol
at 0.3 kgf/cm2g by cooling water at 32 0C. The condensing temp. at this pressure is 85.2
0C. The dirt factors of both shell tube side is 2500 kcal/hr m2C. Assume that allowable
pressure drop on both the side is within limit. Assume the tube length of 2500 mm, tube
o.d. of 19.05 mm and 23.81 mm triangular pitch. Tube wall thickness to be taken as 1.65
mm. Assume isothermal condensation and U 400 kcal/hr m2 0C.
Properties for n-propanol:
Latent heat of condensation: 158 kcal/kg
Thermal conductivity 0.14 kcal/hr m C
Liquid density 800 kg/m3 Liquid viscosity: 0.62 cP Vapor viscosity: 0.01 cP
Thermal conductivity of tube metal 39 kcal/hr m C.
Condensation coefficient is to be calculated as:
6
3

0.95





R
c
c c v
c c N
g
h k


kcal/hrm2C
Where, kc condensate thermal conductivity, kcal/hrmC
condensate density, kg/m3
vapor density, kg/m3
condensate viscosity, kg/m-s
tube loading, condensate flow per unit length
of tube, kg/m-s
NR of maximum tubes in central row.
Water side coefficient is calculated as:
0.86
4200(1.35 0.02 0.8
0.2 u x
d
t
h t
i
i

kcal/hr m2C
t water side average temperature, 0C
di inside diameter of tube, mm
ut tube side velocity, m/sec
For triangular pitch, constants for bundle diameter are as:
No of passes 1 2 4 6 8
k1 0.319 0.249 0.175 0.0743 0.0365
n1 2.142 2.207 2.285 2.499 2.675
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2
OR
Q.3
Discuss the steps for process design of kettle type reboiler.
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Q.4
Discuss the steps for process design of Vertical Thermosyphon Reboiler.
14
OR
Q.4
Design the box type heat exchanger for cooling air for the following data:
Outside:
Fluid Air
Flow rate 1546 CFM (at NTP)
Temp. in/out 45 0C 12 0C
Operating pressure 500 mm H2O g
Sp. Heat of air 0.25 kcal/kg C
Viscosity of air 0.02 cP
Thermal conductivity of air 0.02575 kcal/hr m C
Dirt coefficient 2000 kcal/hr m2C
Take condensation load as 120% of sensible load.
Tube side:
Fluid Chilled Water
Temp. in/out 6 0C 9 0C
Tube length 1200 mm
Tube o.d. /i.d. 19.05 15.748 mm
Tube wall thickness: 1.651 mm
Fin i.d. 19.05 mm
Fin o.d. 38.1 mm
Fins/inch 7
Tube pitch 43 mm
Dirt coefficient 4000 kcal/hr m2C
Thermal conductivity of fin metal 205.87 kcal/hr m C
Pr 0.699
jf= (0.04536 x NRE)0.699
hf jf x kcal/hr m2 C
Efficiency of fin 0.97
For air side pressure drop, f (435352461 x NRE)-0.19123 x 144
Calculate: LMTD
Area required, m2
Area provided, m2
Pressure drop on Air side
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Q.5
Discuss the advantages and disadvantages of Plate type heat exchangers over Shell and tube heat exchangers. Also discuss the step by step procedure for process design of plate type heat exchanger.
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OR
Q.5
Discuss in detail about multi component condensation. With a typical example, explain the design of condenser for multi component, process for finding dew point and bubble point, weighted average temperature difference and use of K values.
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