Sathyabama University 2008 B.Tech Chemical Engineering Heat Transfer - Question Paper
SATHYABAMA UNIVERSITY
(Established under section 3 of UGC Act, 1956)
Course & Branch: B. Tech Chemical (Part Time)
Title of the paper: Heat Transfer
Semester: III Max. Marks: 80
Sub.Code: 619PT303 (2007 JAN) Time: 3 Hours
Date: 27-04-2008 Session: FN
PART A (10 x 2 = 20)
Answer All the Questions
1. State the assumptions involved in the Fourier law of conduction?
2. What is transient heat condition?
3. What is Sieder-Tate relation and how is it different from Dittus-Boelter equation?
4. Distinguish between natural and forced convection heat transfer.
5. What is Wilsons plot?
6. What are the advantages of a plate heat exchanger?
7. What is Kirchoffs identity? When does it apply?
8. Define Radiation Intensity and Radiation shape factor
9. Define capacity and economy of an evaporator.
10. State any two advantages of vapor compression evaporation.
PART B (5 x 12 = 60)
Answer All the Questions
11. (a) Derive one dimensional heat transfer
equation for a hollow
sphere by conduction.
(b) A furnace walk is constructed of three layers of different materials. 22cm of A inside, 7.5cm of B in the middle and 11cm of C outside. The inside temperature is 870C and the outside temperature is 30C. The thermal conductivities of A, B and C are 1, 0.12 and 0.75kcal/hr.m.C respectively. What is the heat loss in kcal/hr.m2.?
(or)
12. (a) Derive the expression for optimum insulation thickness.
(b) Determine the temperature at the
mid plane of a wall whose
faces are at 1200C and 400C. The wall is 500mm
thick
and the thermal conductivity of the material at temperature TC is given by K = 0.8 (1+0.0005T)W/mC. Also determine
the heat flow by conduction.
13. (a) Discuss about drop wise and film type condensation. (4)
(b) Air at 2atm and 200C is heated as it flows through a tube
with a diameter of 2.54cm at a velocity of 10m/s. Calculate
the heat transfer per unit length of tube if a constant heat flux condition is
maintained at the wall and the wall temperature is 20C above the air temperature, all along the length of the tube. How much
would the bulk temperature increase over a 3m length of the tube? (8)
(or)
14. (a) Differentiate between nucleate and film boiling. (4)
(b) Water at 60C enters a tube of 2.54cm diameter at a mean
velocity of 2cm/s. Calculate the exit water temperature is constant at 80C. The properties of water at 60C are as follows:
r = 985 kg/m3; m = 4.71 x 10-4kg/m.s;
k = 0.651 W.mC Cp = 4.18kJ/kg.C (8)
15. (a) If in a condenser you have non
condensable gases present
how would it affect the operation? State the reasons. (4)
(b) A 1-2 shell and tube counter flow heat exchanger is used for heating cold water from 37.8C to 54.5C. Cold water is flowing inside the tube. On the shell side hot water is used as the heating fluid. The inlet temperature of the hot water is 93.3C. The flow rate of cold water is 3.78kg/s. The flow rate of hot water is 1.89kg/s. The overall heat transfer coefficient is 1420W/m2C. The average water velocity inside the tube is 0.366 m/s. Tubes of 1.9cm diameter are used. Because of the space limitations the tube length must not be longer than 2.4m. Calculate the number of tubes required. (8)
(or)
16. (a) What is LMTD? (4)
(b) 60000kg/hr of nitrobenzene is to be
cooled from 160C to
125C using benzene which is heated from 35C to 85C.
For this steel pipes of 6m length are available. The inner and outer diameter
of inner pipe are 7.8cm and 8.9cm respectively. The inner and outer diameter of
outer pipe are 10.2cm and 11.5cm respectively. Calculate the heat exchanger
area. Physical properties of the liquids are as follows: (8)
|
Property |
Nitrobenzene |
Benzene |
|
K in W/m.C |
0.18 |
0.185 |
|
r in kg/m3 |
1200 |
880 |
|
m in kg/m.s |
0.3 x 10-3 |
0.28 x 10-3 |
|
Cp in J/kg.C |
1884 |
2596 |
17. (a) Define (i) emissivity (ii) absorptivity (iii) reflectivity
(b) Two large parallel planes having
emissivities of 0.3 and 0.5
are maintained at temperature of 800K and 400K respectively. A radiation shield
(e = 0.05 on both sides) is placed between the two
planes. Calculate the heat transfer with and without the shield temperature.
(or)
18. (a) Show that the emissive power of a black
body with diffuse
radiation is p times the intensity of radiation. (4)
(b) Calculate the fractional reduction in radiant energy transfer when a thin polished copper plate of emissivity 0.4 is introduced as a shield between parallel plates of dull steel of emissivity 0.8. Derive the necessary equation also. (8)
19. An aqueous solution is to be concentrated from 8% to 45% solids in a single effect evaporator. Steam is available at 3kg/cm2 (abs). A pressure of 15cm Hg (abs) is to be maintained at the vapor space. Feed rate is 20000kg/hr and it enters at 28C. The overall heat transfer coefficient is 2350kCal/hr.m2C. The solution has no boiling point elevation. The specific heats of the feed and concentrated solution are 0.85 and 0.65cal/gm.C respectively. Calculate the heating area and steam consuming no radiation losses.
(or)
20. (a) When is backward feed evaporator
preferred over a forward
feed evaporator? (3)
(b) With a neat diagram explain a long vertical tube evaporator. (6)
(c) Explain briefly the liquid characteristics that affect evaporation. (3)
| Earning: Approval pending. |
