Q.1

The total radiation from a black body per second per unit area is __________ fourth power of the absolute temperature. This statement is known as Stefan-Boltzmann law.

  • equal to
  • directly proportional to
  • inversely proportional to
Q.2

For ammonia refrigerating systems, the tubes of a shell and tube condenser are made of

  • copper
  • aluminium
  • steel
  • brass
Q.3

The optimum effective temperature for human comfort is

  • higher in winter than in summer
  • lower in winter than in summer
  • same in winter and summer
  • not dependent on season
Q.4

The highest thermal diffusivity is of

  • iron
  • lead
  • concrete
  • wood
Q.5

The heat transfer by conduction through a thick sphere is same as through a thick cylinder.

  • True
  • False
Q.6

The optimum effective temperature for human comfort is

  • higher in winter than in summer
  • lower in winter than in summer
  • same in winter and summer
  • not dependent on season
Q.7

The heat transfer by conduction through a thick sphere is same as through a thick cylinder.

  • True
  • False
Q.8

The wet bulb temperature during sensible heating of air

  • remains constant
  • increases
  • decreases
Q.9

Which of the following statement is wrong?

  • The heat transfer in liquid and gases takes place according to convection.
  • The amount of heat flow through a body is dependent upon the material of the body.
  • The thermal conductivity of solid metals increases with rise in temperature,
  • Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.
Q.10

Which of the following statement is wrong?

  • The heat transfer in liquid and gases takes place according to convection.
  • The amount of heat flow through a body is dependent upon the material of the body.
  • The thermal conductivity of solid metals increases with rise in temperature,
  • Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.
Q.11

In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

  • Reynold's number
  • Grashoff's number
  • Reynold's number, Grashoff's number
  • Prandtl number, Grashoff's number
Q.12

In a refrigerating machine, heat rejected is __________ heat absorbed.

  • equal to
  • less than
  • greater than
Q.13

Which of the following refrigerant has the highest freezing point.

  • Ammonia
  • Carbon dioxide
  • Sulphur dioxide
  • R-12
Q.14

The sensible heat gain is due to the __________ difference between the fresh air and the air in space.

  • temperature
  • humidity
Q.15

Air conditioning means

  • cooling
  • heating
  • dehumidifying
  • all of these
Q.16

During cooling and dehumidification, dry bulb temperature

  • remains constant
  • increases
  • decreases
Q.17

The emissivity for a black body is

  • 0
  • 0.5
  • 0.75
  • 1
Q.18

The conditioned air supplied to the room must have the capacity to take up

  • room sensible heat load only
  • room latent heat load only
  • both room sensible heat and latent heat loads
  • none of the above
Q.19

Fouling factor is used

  • in heat exchanger design as a safety factor
  • in case of Newtonian fluids
  • when a liquid exchanges heat with a gas
  • none of the above
Q.20

The coefficient of performance of electrolux refrigerator is the ratio of

  • heat supplied by the gas burner to the heat absorbed by the evaporator
  • heat absorbed by the evaporator to the heat supplied by the gas burner
  • heat supplied by the gas burner minus the heat absorbed by the evaporator to the heat supplied by the gas burner
  • heat absorbed by the evaporator minus the heat supplied by the gas burner to the heat absorbed by the evaporator
Q.21

The wet bulb temperature atrelative humidity is __________ dew point temperature.

  • same as
  • lower than
  • higher than
Q.22

For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference (tm) for parallel flow is __________ that for counter flow.

  • equal to
  • less than
  • greater than
Q.23

Sulphur dioxide is extremely toxic and non-flammable.

  • True
  • False
Q.24

Which of the following would lead to a reduction in thermal resistance?

  • In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
  • In convection, stirring of the fluid and cleaning the heating surface.
  • In radiation, increasing the temperature and reducing the emissivity.
  • all of the above
Q.25

Free convection flow depends on

  • density
  • coefficient of viscosity
  • gravitational force
  • all of these
Q.26

The process of removing moisture from the air, without change in its dry bulb temperature, is called dehumidification.

  • Correct
  • Incorrect
Q.27

The natural convection air cooled condensers are used in

  • domestic refrigerators
  • water coolers
  • room air conditioners
  • all of these
Q.28

The sulphur sticks, in case of leakage of ammonia refrigerant, gives white smoke.

  • True
  • False
Q.29

The use of heat exchangers is made in

  • radiators in automobile
  • condensers and boilers in steam plants
  • condensers and evaporators in refrigeration and air conditioning units
  • all of the above
Q.30

A vapour absorption refrigerator uses __________ as a refrigerant.

  • water
  • ammonia
  • freon
  • aqua-ammonia
0 h : 0 m : 1 s