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 1 P a g e | 1

CDB 2023: Process Heat Transfer, Semester Jan 2015

Assignment 1

Deadline for Submission: 4 March 2015, Wednesday, before

5pm. (Total marks = 40 %)

Answer ALL questions:

1. Consider a 5-m high, 8-m long , and 0.22 m thick wall whose representative

cross section is as given in the figure. The thermal conductivities of various

materials used, in W/m·K, are kA= kF=2, kB=8, kC=20,kD=15,and kE=35. The left

and right surfaces of the wall are maintained at uniform temperatures of 300oC

and 100oC, respectively. Assuming heat transfer through the wall to be one-

dimensional, determine:

a. The rate of heat transfer through the wall.

[7 marks]

b. The temperature drop across the section F.

[3 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 1 P a g e | 2

2. Superheated steam at an average temperature 200oC is transport through a steel

pipe (k=50W/m·K, Do = 8.0 cm, Di =6 cm, and L = 20 m). The pipe is insulated

with a 4-cm thick layer of gypsum plaster (k=0.5 W/m·K). The insulated pipe is

placed horizontally inside a ware house where the average air temperature is

10oC. The steam and the air heat transfer coefficients are estimated to be 800

and 200 W/m2·K, respectively. Calculate:

a. The daily rate of heat transfer from the superheated steam

[7 marks]

b. The temperature on the outside surface of the gypsum plaster insulation.

[3 marks]

3. Air is to be heated by passing it over a bank of 3 m long tubes inside which

steam is condensing at 100 ºC. Air approaches the tube bank in the normal

direction at 20 ºC and 1 atm with a mean velocity of 5.2 m/s, The outer diameter

of the tubes is 1.6 cm, and the tubes are arranged in-line with longitudinal and

trancerse pitches of SL=ST=4cm. There are 20 row in the flow direction with 10

tubes in each row. Determine the rate of heat transfer by assuming that the mean

temperature is 35 ºC.

[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 1 P a g e | 3

4. Consider the flow of oil at 10 ºC in a 40 cm diameter pipeline at an average

velocity of 0.5 m/s. A 1500 m long section of pipeline passes through icy waters

of a lake at 0 ºC. Measurement indicate that the surface temperature of the pipe

is very nealy 0 ºC. Disregarding the thermal resistance of the pipe material,

determine:

a. The temperature of the oil when the pipe leaves the lake.

[5 marks]

b. The rate of heat transfer from the oil.

[5 marks]

---END---