Heat Transfer Refrigeration and Air Conditioning

Q1: Nusselt number (NN) is given by

A

B

C

D

Q2: The wet bulb temperature lines, on the psychrometric chart, are curved lines.

A True

B False

Q3: The by-pass factor for a cooling coil

A increases with increase in velocity of air passing through it

B decreases with increase in velocity of air passing through it

C remains unchanged with increase in velocity of air passing through it

D may increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering

Q4: The highest thermal diffusivity is of

A iron

B lead

C concrete

D wood

Q5: The coefficient of performance of Heat Pump is always __________ one.

A equal to

B less than

C greater than

Q6: The condition of refrigerant after leaving the compressor and before entering the condenser is superheated vapour.

A Yes

B No

Q7: The formation of frost on cooling coils in a refrigerator

A increases heat transfer

B improves C.O.P. of the system

C increases power consumption

D reduces power consumption

Q8: The heat transfer by radiation __________ a medium.

A requires

B does not require

Q9: Degree of saturation or percentage humidity is

A the mass of water vapour present in 1 m3 of dry air

B the mass of water vapour present in 1 kg of dry air

C the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.

D the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

Q10: Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

A

B

C

D

Q11: The sensible heat factor during cooling and dehumidification process is given by (where h1 = Enthalpy of air entering the cooling coil, h2 = Enthalpy of air leaving the cooling coil, and hA = Enthalpy of air at the end of dehumidification process)

A

B

C

D

Q12: Defrosting of a refrigerator may be done by stopping the compressor for a short period.

A Correct

B Incorrect

Q13: Which of the following represents a heat pump?

A

B

C

D

Q14: During sensible cooling of air __________ decreases.

A wet bulb temperature

B relative humidity

C dry bulb temperature

D specific humidity

Q15: The relative humidity decreases as air gets wet.

A True

B False

Q16: An electrolux refrigerator is called a __________ absorption system.

A single fluid

B two fluids

C three fluids

Q17: The temperature of ammonia after compression in a vapour compression system is

A 20 to 50° C

B 50 to 70° C

C 70 to 110° C

D none of these

Q18: The relative humidity is defined as

A the mass of water vapour present in 1 m3 of dry air

B the mass of water vapour present in 1 kg of dry air

C the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.

D the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

Q19: The heat transfer by conduction through a thick sphere is same as through a thick cylinder.

A True

B False

Q20: The amount of radiation mainly depends upon the

A nature of the body

B temperature of the body

C type of surface of the body

D all of these

Q21: Thermal conductivity of water __________ with rise in temperature.

A remains same

B decreases

C increases

D may increase or decrease depending upon temperature

Q22: The C.O.P. of an absorption type refrigerator is given by (where T1 = Temperature at which the working substance receives heat, T2 = Temperature of cooling water, and T3 = Evaporator temperature)

A

B

C

D

Q23: The optimum effective temperature for human comfort is

A higher in winter than in summer

B lower in winter than in summer

C same in winter and summer

D not dependent on season

Q24: The heat transfer takes place according to

A Zeroth law of thermodynamics

B First law of thermodynamics

C Second law of thermodynamics

D Kirchhoff's law

Q25: A water cooled condenser operates at a __________ condensing temperature than an air-cooled condenser.

A higher

B lower

Q26: The subcooling in a refrigeration cycle

A does not alter C.O.P.

B increases C.O.P.

C decreases C.O.P.

D none of these

Q27: The critical radius is the insulation radius at which the resistance to heat flow is

A maximum

B minimum

C zero

D none of these

Q28: Which of the following statement is wrong?

A The heat transfer in liquid and gases takes place according to convection.

B The amount of heat flow through a body is dependent upon the material of the body.

C The thermal conductivity of solid metals increases with rise in temperature.

D Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.

Q29: In case of solids, the heat transfer takes place according to radiation.

A Correct

B Incorrect

Q30: The humidity ratio or specific humidity is the mass of water vapour present in

A 1 m3 of wet air

B 1 m3 of dry air

C 1 kg of wet air

D 1 kg of dry air

Q31: In a refrigerating machine, heat rejected is __________ heat absorbed.

A equal to

B less than

C greater than

Q32: The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

A equal to one

B greater than one

C less than one

D equal to Nusselt number

Q33: A perfect black body is one which

A is black in colour

B absorbs heat radiations of all wave lengths falling on it

C reflects all the heat radiations

D transmits the heat radiations

Q34: The wet bulb temperature during sensible heating of air

A remains constant

B increases

C decreases

Q35: As relative humidity decreases, the dew point temperature will be __________ wet bulb temperature.

A same as

B lower than

C higher man

Q36: A refrigeration system

A removes heat from a low temperature body and delivers it to a high temperature body

B removes heat from a high temperature body and delivers it to a low temperature body

C rejects energy to a low temperature body

D none of the above

Q37: 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.

A equal to

B directly proportional to

C inversely proportional to

Q38: For ammonia refrigerating systems, the tubes of a shell and tube condenser are made of

A copper

B aluminium

C steel

D brass

Q39: According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

A Pb = pa - pv

B Pb = pa + pv

C Pb = pa x pv

D Pb = pa/pv

Q40: During adiabatic saturation process on unsaturated air __________ remains constant.

A relative humidity

B dew point temperature

C dry bulb temperature

D wet bulb temperature

Q41: Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)

A

B

C

D

Q42: During a refrigeration cycle, heat is rejected by the refrigerant in a

A compressor

B condenser

C evaporator

D expansion valve

Q43: The heat transfer by conduction through a thick sphere is given by

A

B

C

D

Q44: In aqua-ammonia and Lithium-bromide water absorption refrigeration systems, the refrigerants are respectively

A water and water

B water and lithium bromide

C ammonia and lithium bromide

D ammonia and water

Q45: While designing the refrigeration system of an aircraft, the prime consideration is that the

A system has high C.O.P.

B power per TR is low

C mass of refrigerant circulated in the system is low

D mass of the refrigeration equipment is low

Q46: In a psychrometric process, the sensible heat added is 30 kJ/s and the latent heat added is 20 kJ/s. The sensible heat factor for the process will be

A 0.3

B 0.6

C 0.67

D 1.5

Q47: The difference between dry bulb temperature and wet bulb temperature, is called

A dry bulb depression

B wet bulb depression

C dew point depression

D degree of saturation

Q48: Thermal diffusivity is a

A function of temperature

B physical property of a substance

C dimensionless parameter

D all of these

Q49: In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

A Reynold's number

B Grashoff's number

C Reynold's number, Grashoff's number

D Prandtl number, Grashoff's number

Q50: The process of heat transfer from a hot body to a cold body, in a straight line, without affecting the intervening medium, is called radiation.

A True

B False


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