PTU Punjab Technical University B-Tech May 2019 Question Papers 6th Semester Mechanical Engineering (MECH)
Total No. of Pages : 03
Total No. of Questions : 09
B.Tech.(ME) (E-I 2011 Onwards) (Sem.?6)
HEAT EXCHANGER DESIGN
Subject Code : DE/ME-1.7
M.Code : 71249
Time : 3 Hrs. Max. Marks : 60
INSTRUCTION TO CANDIDATES :
1.
SECTION-A is COMPULSORY consisting of TEN questions carrying T WO marks
each.
2.
SECTION-B contains FIVE questions carrying FIVE marks each and students
have to attempt any FOUR questions.
3.
SECTION-C contains T HREE questions carrying T EN marks each and students
have to attempt any T WO questions.
SECTION-A
1.
Write short notes on :
a. Differentiate between recuperative and regenerative type of heat exchanger.
b. What is the purpose of using baffles in a heat exchanger?
c. Differentiate between LMTD and NTU approach for design of heat exchanger.
d. Draw the schematic of a two shell and four tube pass heat exchanger.
e. What is fouling factor and how do the temperature and velocity affect it?
f. Write a short note on multiple effect evaporators.
g. What do you mean by liquid chillers?
h. Write down the names of various methods for enhancement of heat transfer.
i. Differentiate between thermosyphen and forced circulation reboilers.
j. Why fouling fluids are not used in compact heat exchanger?
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SECTION-B
2.
Derive an expression for logarithmic mean temperature difference (LMTD) in counter
flow heat exchanger.
3.
Exhaust gases (Cp =1.12 KJ/Kg-deg) flowing through a tubular heat exchanger at the rate
of 1200 Kg/hr are cooled from 400?C to 120?C. The cooling is affected by water
(Cp = 4.18 KJ/Kg K) that enters the system at 10?C at the rate of 1500Kg/hr. If the
overall heat transfer coefficient is 500 KJ/m2-hr-deg. What heat exchanger area is
required to handle the load for :
(a) Parallel flow arrangement
(b) Counter flow arrangement.
4.
When one of the two fluids undergoes phase change, show that effectiveness values for
both parallel flow and counter flow heat exchanger are equal and given by = 1- exp
(-NTU).
5.
A chemical having a specific heat of 3.3 KJ/Kg K flowing at the rate of 20,000Kg/h
enters a parallel flow heat exchanger at 120?C. The flow rate of cooling water is 50,000
Kg/h with an inlet temperature of 20?C. The transfer area is 10m2 and overall heat
transfer coefficient is 1200 W/m2 ?C. Taking specifications heat of water as 4.186KJ/Kg
K, find
a) Effectiveness of the heat exchanger
b) Outlet temperature of water and chemical.
6.
Explain the methods for performance evaluation of heat transfer enhancement techniques.
SECTION-C
7.
n a counter flow double pipe heat exchanger, water is heated from 25?C to 65?C by an oil
with a specific heat of 1.45KJ/Kg K and mass flow rate of 0.9Kg/s. The oil is cooled
from 230?C to 160?C. If the overall heat transfer coefficient is 420W/m2 ?C, calculate the
following :
(a) The rate of heat transfer
(b) The mass flow rate of water
(c) The surface area of heat exchanger
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8.
In a double pipe parallel flow heat exchanger, the hot water is cooled by colder water
flowing inside the tube. The results obtained from experiments are as follows :
Mass flow rate
Inlet Temp.?C
Outlet
Specific heat
Kg/s
Temp.?C
J/Kg K
Hot Water
50
90
60
4180
Cold Water
500
25
-
4180
Overall heat transfer coefficient, U = 2400W/m2K. Find :
a) Heat transfer area needed
b) Effectiveness of heat exchanger
9.
Explain the following :
a) Criteria for selection of material for heat exchanger.
b) Discuss the phenomena of two phase boiling flow.
NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any
page of Answer Sheet will lead to UMC against the Student.
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This post was last modified on 04 November 2019