Roll Number: __________________________
Thapar Institute of Engineering and Technology Patiala
Department of Chemical Engineering
B. E. (Second Year): Semester-IV Course Code: UCH402
(Chemical Engineering) Course Name: Heat Transfer
End Semester Exam; May 23, 2024 Thursday, 9:00 AM
Time: 3 Hours, M. Marks: 50 Name of Faculty: Dr. J. P. Kushwaha
Note: Attempt any five questions.
Assume missing data, if any, suitably.
Q. No. Question Marks CO BL
Q1 (a) Hot oil (Cp = 2200 J/kg · °C) is to be cooled by water (Cp = 4180 J/kg · °C) 6 CO2 L3
in a 2-shell-pass and 12-tube-pass heat exchanger. The tubes are thin-walled
and are made of copper with a diameter of 1.8 cm. The length of each tube
pass in the heat exchanger is 3 m, and the overall heat transfer coefficient is
340 W/m2 · °C. Water flows through the tubes at a total rate of 0.1 kg/s, and
the oil through the shell at a rate of 0.2 kg/s. The water and the oil enter at
temperatures 18°C and 160°C, respectively. Determine the rate of heat
transfer in the heat exchanger and the outlet temperatures of the water and
the oil. Consider the effectiveness of this exchanger as Ꜫ = 0.61
Q1 (b) What is the role of the baffles in a shell-and-tube heat exchanger? How does 4 CO2 L2
the presence of baffles affect the heat transfer and the pumping power
requirements? Explain.
Q2 (a) Draw the boiling curve and identify the different boiling regimes. Also, 5 CO1 L2
explain the characteristics of each regime.
Q2 (b) A single effect evaporator is used to concentrate cane sugar juice from 10% 5 CO3 L4
to 40% concentration at a rate of 2000 kg/h. Inlet temp. of feed is 30 C and
pressure 0.33 kg /cm2 is maintained in vapour space. Liquid is boiling at
75C at this pressure. Saturated steam (latent heat = 529.5 kcal/kg) is
supplied at 115 C. Calculate the steam required and number of tubes used
(OD= 0.025 m, ID= 0.021 m), if height of tubes is 1.6 m.
Given: Specific heat of feed = 0.946 kcal/kg C; Latent heat of steam (at
0.33 kg/cm2) =556.5 kcal/kg); Overall heat transfer coefficient = 2150
kcal/h m2 C.
Q3 (a) Explain the difference in working of Falling-film-type evaporator and 5 CO3 L1
agitated-film-type evaporator.
Q3 (b) Steam in the condenser of a steam power plant is to be condensed at a 5 CO3 L3
temperature of 50 °C (latent heat = 2305 kJ/kg) with cooling water (Cp =
4180 J/kg · °C) from a nearby lake, which enters the tubes of the condenser
at 18 °C and leaves at 27 °C. The surface area of the tubes is 58 m2, and the
overall heat transfer coefficient is 2400 W/m2 · °C. Determine the mass flow
rate of the cooling water needed and the rate of condensation of the steam in
the condenser considering counter flow arrangement.
PTO
Q4 (a) Water (Cp = 4180 J/kg · °C) enters the 2.5-cm internal-diameter tube of a 5 CO2 L3
double-pipe counter-flow heat exchanger at 17 °C at a rate of 3 kg/s. It is
heated by steam condensing at 120 °C (hfg = 2203 kJ/kg) in the shell. If the
overall heat transfer coefficient of the heat exchanger is 1500 W/m2 · °C,
determine the length of the tube required in order to heat the water to 80 °C.
Q4 (b) With neat sketch, compare the working of low level and high level counter 5 CO3 L2
flow jet condensers.
Q5 (a) A copper wire of 5.2 mm diameter is insulated with PVC (polyvinyl chloride) 4 CO1 L3
of thermal conductivity Kc = 0.43 W/m ⁰C. The wire carries current and its
temperature is 60 ⁰C. The film coefficient at the outer surface of the
insulation is 11.35 W/m2 ⁰C. Calculate the critical insulation thickness.
Q5 (b) A shell-and-tube heat exchanger (counterflow arrangement) with 2-shell 6 CO2 L3
passes and 8-tube passes is used to heat ethyl alcohol (Cp = 2670 J/kg · °C)
in the tubes from 25 °C to 70 °C at a rate of 2.1 kg/s. The heating is to be
done by water (Cp = 4190 J/kg · °C) that enters the shell side at 95 °C and
leaves at 45 °C. If the overall heat transfer coefficient is 950 W/m2 · °C,
determine the heat transfer surface area of the heat exchanger.
Fig. 1. Correction factor for Two-shell passes and 4, 8, 12, etc. tube passes
Q6 (a) How is the intensity of emitted radiation defined? For a diffused surface, how 5 CO1 L2
is the emissive power related to the intensity of emitted radiation?
Q6 (b) A 20 cm diameter spherical ball (assume black body) is at 800 K. Determine 5 CO1 L3
(a) the total blackbody emissive power, (b) the total amount of radiation
emitted by the ball in 5 min, and (c) the spectral blackbody emissive power
at a wavelength of 3 μm.
Stefan-Boltzmann constant (σ) = 5.67 x10-8 W/m2K4
Monochromatic emissive power is given by the following relation:
Marks Distribution
Bloom's level-wise marks Course outcome-wise marks distribution
distribution 36
8.33 35
8.33 35
34 33.33
31.67
51.66 33
32 31.67
31
L1 8.33 L2 31.67 30
L3 51.66 L4 8.33 CO1 CO2 CO3
