1. Identify the wrong statement
a) The process of heat transfer is an irreversible process
b) Heat flow doesn’t depend on temperature
c) For heat exchange, a temperature gradient must exist
d) A material medium is not necessary for heat transmission
Explanation: Heat flows from higher to lower temperature.
2. Which statement is true regarding steady state condition?
a) There is a variation in temperature in the course of time
b) It is a function of space and time coordinates
c) Heat exchange is constant
d) Internal energy of the system changes
Explanation: Heat influx is always equal to heat efflux. It is a function of space coordinates only.
3. A radiator in a domestic heating system operates at a surface temperature of 60 degree Celsius. Calculate the heat flux at the surface of the radiator if it behaves as a black body
a) 697.2 W/m2
b) 786.9 W/m2
c) 324.7 W/m2
d) 592.1 W/m2
Explanation: As, q = Q/A = 5.67 * 10-8 (273+60)4 = 697.2.
4. An oil cooler in a high performance engine has an outside surface area 0.12 m2 and a surface temperature of 65 degree Celsius. At any intermediate time air moves over the surface of the cooler at a temperature of 30 degree Celsius and gives rise to a surface coefficient equal to 45.4 W/ m2 K. Find out the heat transfer rate?
a) 238.43 W
b) 543.67 W
c) 190.68 W
d) 675.98 W
Explanation: Q = (T2 – T1) A h = 0.12 (65-30) 45.4 = 190.68 W.
5. Most unsteady heat flow occurs
a) Through the walls of the refrigerator
b) Through the walls of the furnace
c) Through lagged pipe carrying steam
d) During annealing of castings
Explanation: Under steady state condition, with time there is a change in temperature i.e. temperature field is a function of space and time.
6. Regarding one dimensional heat transfer, choose the correct statement.
a) Steady – f (x), Unsteady – f (x, t)
b) Steady – f (x, t), Unsteady – f (x)
c) Steady – f (x, y, t), Unsteady – f (x)
d) Steady – f (y, z), Unsteady – f (y)
Explanation: In case of one dimensional heat flow steady state is a function of x coordinate only while unsteady state is a function of x coordinate and time only.
7. Heat transfer takes place according to which law?
a) Newton’s law of cooling
b) Second law of thermodynamics
c) Newton’s second law of motion
d) First law of thermodynamics
Explanation: Second law states about heat transfer between source and sink.
8. During a cold winter season, a person prefers to sit near a fire. Which of the following modes of heat transfer provides him the maximum heat?
a) Conduction from the fire
b) If it is near the fire, convection sounds good
c) Convection and radiation together
d) Radiation will provide quick warmth
Explanation: Heat transfer by radiation can occur between two bodies even when they are separated by a medium colder than both of them.
9. Heat transfer in a long, hollow cylinder which is maintained at uniform but different temperatures on its inner and outer surfaces may be assumed to be taking place in which direction?
a) Axial only
b) Unpredictable
c) Radial only
d) No heat transfer takes place
Explanation: Ambient temperature is uniform on the periphery of cylinder and temperature is uniform. So it takes place in the radial direction only.
10. The appropriate rate equation for convective heat transfer between a surface and adjacent fluid is prescribed by
a) Newton’s first law
b) Wein’s displacement law
c) Kirchhoff’s law
d) Newton’s law of cooling
Explanation: The rate equation used to describe the mechanism of convection is called Newton’s law of cooling when the solid surface is cooled by the fluid.