C D B 2 0 2 3 : P r o c e s s H e a t T r a n s f e r : A s s i g n m e n t 2 P a g e | 1

CDB 2023: Process Heat Transfer, Semester Jan 2015

Assignment 2

Deadline for Submission: 8 April 2015, Wednesday, before

5pm. (Total marks = 40 %)

Answer ALL questions:

1. A furnace has a 40 cm x 40 cm glass window can be considered to be a

blackbody at 1200 K. If the transmissivity of the glass is 0.7 for radiation at

wavelengths less that 3 µm and zero for radiation at wavelengths greater than

3 µm, determine the fraction and rate of radiation coming from the furnace and

transmitted through the window.

[5 marks]

2. Cylindrical stainless steel rods are heated to a uniform temperature at 700 ºC

and then quenched in water at 1 atm. The rods are 25 cm in length, 25 mm in

diameter and their surface have an emissivity of 0.3. Determine the convection

heat transfer coefficient and the total rate of heat removed from a rod at the

instant it is submerged in the water during quenching.

[10 marks]

C D B 2 0 2 3 : P r o c e s s H e a t T r a n s f e r : A s s i g n m e n t 2 P a g e | 2

3. Saturated steam at 100°C condenses on a 2 m x 2 m plate that is tilted 40° form

the vertical. The plate is maintained at 80°C by cooling it from the other side.

Determine the rate of condensation of the steam over the entire plate. Assume

wavy flow, is this a good assumption?

[10 marks]

4. In a parallel flow heat exchanger, hot fluid enters the heat exchanger at a

temperature of 150 ºC and a mass flow rate of 3 kg/s. The cooling medium enters

the heat exchanger at a temperature of 30 ºC with a mass flow rate of 0.5 kg/s

and leaves at a temperature of 70 ºC. The specific heat capacities of the hot and

cold fluids are 1150 J/kg·K and 4180 J/kg·K, respectively. The convection heat

transfer coefficient on the inner and outer side of the thin-walled tube is

300 W/m2·K and 800 W/m2·K, respectively. For a fouling factor of 0.0003 m2·K/W

on the tube side and 0.0001 m2·K/W on the shell side, determine:

a. the overall heat transfer coefficient

[5 marks]

b. the exit temperature of the hot fluid

[5 marks]

c. surface area of the heat exchanger

[5 marks]

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