objective heat transfer.docx

7/28/2019 objective heat transfer.docx

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1. Unit of thermal conductivity in M.K.S units is

(a) Kcal/kg m2 oC (b) kcal m/hr m2 oC (c) W/m oK (d) kcal /hr m2 oC

2. Unit of thermal conductivity in S.I units is

(a) Kcal/kg m2 oC (b) J/m oK sec (c) W/m oK (d) both b & c

3. Heat transfer take place as per

(a) Zeroth law of thermodynamics (b) First law of thermodynamics

(c)Second law of thermodynamics (d) Stefan’s law

4. When heat is transfer from one particle of hot body to another by actual motion of the

heated particles, it is referred to as heat transfer by

(a) Conduction (b) Convection

(c) Radiation (d) Conduction & convection

5. When heat is transfer from hot body to cold body, in a straight line, without affecting

the intervening medium, it is referred to as heat transfer by



6. When heat is transferred by molecular collision, it is referred to as heat transfer by



7. Heat transfer in liquid and gases take place by



8. Which of the following is the case of heat transfer by radiation

(a) Blast furnace (b) Heating of building

(c) Cooling of parts in furnace (d) heat received by a person from fireplace



9. Heat is closely related with

(a) Liquid (b) Energy

(c) Temperature (d) Entropy

10. Metal are good conductors of heat because

(a) Their atoms collide frequently

(b) Their atoms are relatively far apart

(c) They contain free electrons

(d) All of the above

11. Which of the following is a case of steady state heat transfer

(a) IC engine (b) Air preheaters

(c) All of the above (d) None of the above

12. Heat flow from one body to other when they have

(a) Different heat content

(b) Different specific heat

(c) Different atomic structure

(d) Different temperature

13. The concept of overall coefficient of heat transfer is used in heat transfer problems of

(a) Conduction (b)Convection

(c)Radiation (d) Conduction and convection

14. The amount of heat flow through a body by conduction is

(a) Directly proportional to surface area, temperature difference, thermal conductivity

and inversely proportional to thickness of body

(b) ) Directly proportional to surface area,(c) Directly proportional to temperature difference

(d) Both a & b

15. Which of the following has least value of thermal conductivity

(a) Glass (b) Water (c) Plastic (d) Air

16. Which of the following has expected highest value of thermal conductivity

(a) Steam (b) Water (c) Solid ice (d) Air

17. Heat transfer by radiation mainly depends upon

(a) Its temperature (b) Nature of the body

(c) None of the above (d) both a & b

18. Thermal diffusivity is

(a) Dimensionless parameter

(b) Function of temperature





28. Heat is transferred by all three modes of transfer, viz , conduction, convection and

radiation in

(a) Electric heater (b) Steam condenser

(c) Refrigerator condenser coil (d) Boiler

29. The heat flow rate through parallel wall of thickness L1, L2 and L3 and having surface

area A1, A2 and A3, Thermal conductivity k 1, k 2 and k 3 , respectively and first and last

wall maintained at temperature t 1 and t 2 will be

(a)

33

3

22

2

11

1

21

k A

L

k A

L

k A

L

t t

(b)

3

33

2

22

1

11

21

A

k L

A

k L

A

k L

t t

(c)

33

3

22

2

11

1

21

L A

k

L A

k

L A

k

t t

(d) Both a & b

30.kA

dxthis term called as

(a) Thermal conductance (b) Temperature gradient

(c) Thermal conduction resistance (d) Thermal convection resistance

31. Calculate the rate of heat transfer through a copper plate having area 5 m2 and 45 mm

thickness, whose one face is maintained at 300 oC and the other face at 50 oC. Take

thermal conductivity of copper as 37 W/m oC.

(a) 102.77×106 W (b) 1.0277×106 J/sec m2

(c) ) 1.0277×106 J/sec (d) 10.277×106 W

32. The following data : thickness of wall 82.5 mm, thermal conductivity of wall insulation

0.044 W/m oC, Temperature on inside of the wall 175 oC, energy dissipated by the

electrical coil within the oven and outside temperature does not exceed 75 oC.

Determine the area of wall surface.

(a) 0.759 m (b) 0.759 cm2 (c) 8.169 ft2 (d) 8.169 m2

33. A hot plate 3.28 ft × 4.92 ft is maintained at 300 oC. Air at 20 oC below over the plate.

If the convective heat transfer coefficient is 20 W/m2 oC, calculate the rate of heat

transfer.

(a) 8400 J/sec (b)8.4 W (c) 90.370×103 W (d)Both a & b



34. The 420 W heat transfer from 15 ft2 area calculate how much heat transfer from unit

area ?

(a) 301.28 W/m2 (b) 28 W/m2 (c) 280 W/m (d) 301.28 W

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objective heat transfer.docx