Assignment - IV

Department of Chemical Engineering, NITK
Heat Transfer (CH250)

Assignment – IV
Due date : 27-03-2024
1. An oil cooler, of the concentric tube type is used for cooling oil at 65.6°C to
54.4 °C with water at 26.7 °C with a temperature rise of 11.1 °C. Assuming an overall
heat transfer coefficient of 738 W/m²K based on the outside area of the tubes
determine the heat transfer surface area required for a design heat load of 190.5
kW for a single pass (a) parallel flow mode and (b) counter flow mode.
2. A heat exchanger is to be designed to cool air from 500°C to 350°C by an

equal flow rate of air entering at 90°C. The heat transfer coefficient on the hot
side is 60 W/m2K and on the cold side 30 W/m2K. Calculate the heat transfer area
required for (i) parallel flow, and (ii) counter flow. Take the flow rate of air to be 5
kg/s and the specific heat of air to be 1.02 kJ/kg K.
3. A heat exchanger is required to cool 55.000 kg/h of alcohol from 66°C to 40°C
using 40,000 kg/h of water entering at 5°C. Calculate the surface area required for
(a) parallel flow mode and (b) counter flow mode. Take U = 580 W/m²K, CP for water
= 4180 J/kg.K and CP for alcohol = 3760 J/kg.K.
4. A heat exchanger of total outside surface area of 17.5 m² is to be used for

cooling oil at 200°C with a mass flow rate of 2.77 kg/s having a specific heat of 1.9
kJ/kg K. Water at a flow rate of 0.83 kg/s is available at 20°C as a cooling agent.
Calculate the exit temperature of the oil if the heat exchanger is operated in a (1)
parallel flow mode, (2) counter flow mode. Take U = 300 W/m²K.
5. In a concentric tube counter flow heat exchanger water flows through the
inner tube (D = 25 mm) at a rate of 12 kg/min while an oil flows through the outer
annulus (D = 45 mm) at a rate of 6 kg/min. The inlet temperatures of oil and water
are 100°C and 30°C respectively. What should be the length of the exchanger for an
oil outlet temperature of 60°C. Take Ui = 37.8 W/m²K. CP (oil) = 2130 J/kgK, and CP
(water) = 4178 J/kg K.
6. Find the surface area required in a counter-flow steam superheater in which
the steam enters at 180°C in a dry, saturated state and leaves at 250°C with an
increase in enthalpy of 159 kJ/kg. The hot combustion gases (CP = 1.05 kJ/kg K)
enter the superheater at 510°C. The steam flow rate is 1000 kg/h, the hot gas flow
rate is 2000 kg/h and the overall heat transfer coefficient is 26 W/m2K.
7. 3000 kg/h of furnace oil is to be heated from 10°C in a shell-and-tube type

heat exchanger. The oil is to flow inside the tubes while steam at 120°C is flowing
through the shell. If the tube size is 1.9 cm O.D. and 1.65 m. I.D. determine the
number of passes, number of tubes per pass and the length of each tube.
8. Calculate the area of a single pass cross-flow heat exchanger (both fluids
unmixed) given the following data: Thi = 65.2°C, The = 46.3°C, Tci = 35.1°C, Tce = 54.1°C,
ṁh = 100 kg/h, Cph = 1.00 kJ/kg.K, U = 46.5 W/m2K.
9. In a shell-and-tube heat exchanger with 8 tube passes through the shell, hot
engine oil available at 160°C flows through the shell and water through the tubes.
Water at the rate of 2.5 kg/s is heated from 15°C to 85°C and there are ten tubes
per pass. The diameter of each tube is 2.5 cm and the average convection coefficient
ho = 400 W/m2 K. Determine the flow rate of oil if its exit temperature is to be
100°C. Also compute the length of the tubes.
10. A single pass crossflow intercooler is used to cool 2.142 kg/s of air (CP = 1017
J/Kg.K), at 105°C with water flowing through tubes at a rate of 2.083 kg/s. The
water enters at 25°C and the overall heat transfer coefficient is 150 W/m2K based
on the outer tube surface area of 20.45 m2. Using the NTU method estimate the
exit temperature of air.
11. In a heat exchanger, dry air passing through the shell side is heated from
38°C to 280°C in cooling the converter gases from 455°C to 205°C. The exchanger
is designed for a duty of 102000 kcal/hr using 5 meters long 38 mm OD, 2 mm thick
alloy steel tubes arranged in a double pass. Assuming heat transfer coefficient
(overall) 5 kcal/hr.m2°C, estimate the number of tubes required and the internal
diameter of the shell. The tubes are laid down on a triangular pitch of 4.78 cm.
12. Given Thi = 60°C, The = 48°C, Tei = 35°C and Tee = 44°C, calculate the mean
temperature difference for (i) parallel flow; (ii) counter flow; (iii) single pass cross
flow (both fluids unmixed); (iv) single pass cross flow (fluid in the hot side mixed,
fluid in the cold side unmixed); and (v) single pass cross flow (fluid in the hot side
unmixed, fluid in the cold side mixed). Also calculate the effectiveness.
13. A process fluid having a specific heat of 3500 J/kg-K and flowing at 2 kg/s is
to be cooled from 80°C to 50°C with chilled water, which is supplied at a temperature
of 15°C and a flow rate of 2.5 kg/s. Assuming an overall heat transfer coefficient of
2000 W/m².K, calculate the required heat transfer areas for following exchanger
configurations: (a) parallel flow, (b) counterflow, (c) shell-and-tube, one shell pass
and two tube passes, and (d) cross-flow, single pass, both fluids unmixed.
14. A double-pipe heat exchanger is constructed of copper and operated in a

counterflow mode. It is designed to heat 0.76 kg/s of water from 10°C to 79.4°C.
The water flows through the inner pipe. The heating is accomplished by condensing
steam in the outer pipe at a temperature of 250°F. The water-side heat-transfer
coefficient is 1420 W/m²°C. Assume a reasonable value for the steam-side
coefficient and then calculate the area of the heat exchanger. Estimate the exit
water temperature would be if the water flow rate were reduced by 60 percent for
this exchanger.
15. A shell-and-tube heat exchanger is to be designed for heating water from

25°C to 50°C with the help of steam condensing at 1 atmospheric pressure. The water
flows through the tubes (2.5 cm ID, 2.9 cm OD and 2 m long) and the steam
condenses on the outside. Calculate the number of tubes required if the water flow
rate is 500 kg/min and the individual coefficients of heat transfer on the steam and
water side are 8000 and 3000 W/m2K. Neglect all other resistances.
16. The feed water heater for a steam boiler is a shell-and-tube heat exchanger
in which the raw feed water flowing through the tubes is heated by condensing steam
on the shell side. The water flow rate is 9000 kg/h and it is heated from 16°C to
60°C. The steam is at 1.30 bar (saturation temperature 107°C). Calculate the surface
area of the heat exchanger if the overall heat transfer coefficient is 2150 W/m2K.
17. It is proposed to cool 1000 kg/h of oil from 150°C to 50°C in a heat exchanger
using 1666.7 kg/h of water at an inlet temperature of 30°C. Calculate the surface
area required assuming a single pass cross flow arrangement in which the oil is mixed
and the water unmixed. Assume CV for oil = 2.087 kJ/kg.K and the overall heat
transfer coefficient = 550 W/m2K. (Do the problem by the mean temperature
difference method as well as the effectiveness-NTU method.)
18. A single pass cross-flow (both fluids unmixed) heat exchanger is used for
heating 2000 kg/h of air from 25°C to 40°C with hot water entering at 85°C. The
overall heat transfer coefficient is 175 W/m2K and the heat exchange area is 2 m2•
Calculate the mass flow rate of water and the exit water temperature.
19. A concentric tube heat exchanger operates in the counter flow mode. The
fluid flowing in the annular space enters at 20°C and leaves at 70°C, while the fluid
flowing through the inner tube enters at 110°C and leaves at 65°C. The length of the
heat exchanger is 30 m. It is desired to increase the outlet temperature of the cold
fluid to 80°C by increasing only the length while maintaining the same mass flow
rates, inlet temperatures and tube diameters. Make any justifiable assumption and
calculate the new length.
20. (a) The following data are given for a heat exchanger: ṁh = 4 kg/min, ṁc = 8
kg/min, Cp,h = 4 .20 kJ/kg.K, Cp,c = 2.52 kJ/kg.K, Thi = 100°C, Tci = 20°C. What is the
maximum possible effectiveness if the arrangement is (i) parallel flow, and (ii)
counter flow?
(b) The following data is for a counter-flow heat exchanger: ṁh = 3 kg/s, ṁc
= 0. 75 kg/s, Cp,h = 1.05 kJ/kg.K, Cp,c = 4.2 kJ/kg.K, Thi = 500°C, Tce = 85°C, U = 450
W/m2K, A = 1 m2. Calculate The and Tci.

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Department of Chemical Engineering, NITK

Heat Transfer (CH250)

2. A heat exchanger is to be designed to cool air from 500°C to 350°C by an

4. A heat exchanger of total outside surface area of 17.5 m² is to be used for

7. 3000 kg/h of furnace oil is to be heated from 10°C in a shell-and-tube type

14. A double-pipe heat exchanger is constructed of copper and operated in a

15. A shell-and-tube heat exchanger is to be designed for heating water from

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