An infinite parallel planes with emissivities e1 and e2, the interchange factor for radiation from surface 1 to surface 2 is given by

(e₁ + e₂)/ e₁ + e₂ - e₁e₂

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.

The evaporator changes the low pressure liquid refrigerant from the expansion valve into

high pressure liquid refrigerant

low pressure liquid and vapour refrigerant

low pressure vapour refrigerant

According to Stefan-Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

square of the absolute temperature

cube of the absolute temperature

fourth power of the absolute temperature

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

Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)

The relative coefficient of performance is equal to

Actual C.O.P. x Theoretical C.O.P.

(Theoretical C.O.P.)/ (Actual C.O.P.)

(Actual C.O.P.) /(Theoretical C.O.P.)

Actual C.O.P. x Theoretical C.O.P.

Film coefficient is defined as the ratio of

temperature drop through the films of fluids to the thickness of film of fluids

thermal conductivity to the equivalent thickness of the film of fluid

temperature drop through the films of fluids to the thickness of film of fluids

thickness of film of fluid to the thermal conductivity

thickness of film of fluid to the temperature drop through the films of fluids

In a vapour compression refrigeration system, a throttle valve is used in place of an expander because

it leads to significant cost reduction

it considerably reduces mass of the system

it improves the C.O.P., as the condenser is small

the positive work in isentropic expansion of liquid is very small

it leads to significant cost reduction

The reduced ambient air cooling system has

two cooling turbines and two heat exchangers

one cooling turbine and one heat exchanger

one cooling turbine and two heat exchangers

two cooling turbines and one heat exchanger

two cooling turbines and two heat exchangers

A perfect black body is one which

reflects all the heat radiations

absorbs heat radiations of all wave lengths falling on it

reflects all the heat radiations

387 + Mcqs in Heat Transfer Refrigeration and Air Conditioning Page 6 McqOptions

251.	When the discharge pressure is too high in a refrigeration system, high pressure control is installed to stop the compressor.
A.	Correct
B.	Incorrect
C.	Can't say
D.	None of these
Answer» B. Incorrect

Discussion

252.	The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called
A.	wet bulb temperature
B.	dry bulb temperature
C.	dew point temperature
D.	none of these
Answer» B. dry bulb temperature

Discussion

253.	A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be
A.	1 kW
B.	2 kW
C.	3 kW
D.	4 kW
Answer» E.

Discussion

254.	An infinite parallel planes with emissivities e1 and e2, the interchange factor for radiation from surface 1 to surface 2 is given by
A.	(e₁ + e₂)/ e₁ + e₂ - e₁e₂
B.	1/e₁ + 1/e₂
C.	e1 + e2
D.	e1e2
Answer» B. 1/e₁ + 1/e₂

Discussion

255.	Sulphur dioxide is extremely toxic and non-flammable.
A.	True
B.	False
C.	Can't say
D.	None of these
Answer» B. False

Discussion

256.	The wet bulb temperature at 100% relative humidity is __________ dry bulb temperature.
A.	same as
B.	lower than
C.	higher than
D.	None of these
Answer» B. lower than

Discussion

257.	Which of the following would lead to a reduction in thermal resistance?
A.	In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
B.	In convection, stirring of the fluid and cleaning the heating surface.
C.	In radiation, increasing the temperature and reducing the emissivity.
D.	all of the above
Answer» E.

Discussion

258.	The expression is used for calculating
A.	relative humidity
B.	humidity ratio
C.	degree of saturation
D.	pressure of water vapour
Answer» C. degree of saturation

Discussion

259.	The freezing point of sulphur dioxide is
A.	-56.6°C
B.	-75.2°C
C.	-77.7°C
D.	-135.8°C
Answer» C. -77.7°C

Discussion

260.	Free convection flow depends on
A.	density
B.	coefficient of viscosity
C.	gravitational force
D.	all of these
Answer» E.

Discussion

261.	The boiling point of R-12 is about - 30°C.
A.	True
B.	False
C.	Can't say
D.	None of these
Answer» B. False

Discussion

262.	In a pressure enthalpy chart, the space to the left of the saturated liquid line represents
A.	wet vapour region
B.	superheated vapour region
C.	sub-cooled liquid region
D.	none of these
Answer» D. none of these

Discussion

263.	The evaporator changes the low pressure liquid refrigerant from the expansion valve into
A.	high pressure liquid refrigerant
B.	low pressure liquid and vapour refrigerant
C.	low pressure vapour refrigerant
D.	none of these
Answer» D. none of these

Discussion

264.	The wave length corresponding to the maximum energy is inversely proportional to the absolute temperature. This statement is called Planck's law.
A.	Yes
B.	No
C.	Can't say
D.	None of these
Answer» C. Can't say

Discussion

265.	During dehumidification process, the relative humidity
A.	remains constant
B.	increases
C.	decreases
D.	None of these
Answer» D. None of these

Discussion

266.	A composite slab has two layers of different materials with thermal conductivities k1 and k2. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
A.	k1 k2
B.	k1 + k2
C.	(k₁ + k₂)/ k₁ k₂
D.	2 k₁ k₂/ (k₁ + k₂)
Answer» E.

Discussion

267.	The pressure at the outlet of a refrigerant compressor is called
A.	suction pressure
B.	discharge pressure
C.	critical pressure
D.	back pressure
Answer» C. critical pressure

Discussion

268.	According to Stefan-Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the
A.	absolute temperature
B.	square of the absolute temperature
C.	cube of the absolute temperature
D.	fourth power of the absolute temperature
Answer» E.

Discussion

269.	Dew point temperature is the temperature of air recorded by a thermometer, when the moisture present in it begins to condense.
A.	Correct
B.	Incorrect
C.	Can't say
D.	None of these
Answer» B. Incorrect

Discussion

270.	In absorption vapour systems, the refrigerant widely used is R-12.
A.	Correct
B.	Incorrect
C.	Can't say
D.	None of these
Answer» C. Can't say

Discussion

271.	If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called
A.	absorptive power
B.	emissive power
C.	emissivity
D.	none of these
Answer» C. emissivity

Discussion

272.	In figure shown, E is a heat engine with efficiency of 0.4 and R is a refrigerator. It is given that Q2 + Q4 = 3Q1. The C.O.P. of the refrigerator is
A.	2.5
B.	3.0
C.	4.0
D.	5.0
Answer» E.

Discussion

273.	Relative humidity is given by (where pv = Partial pressure of water vapour, pb = Barometric pressure, ps = Pressure of saturated air, pd = Pressure at dry bulb temperature, pw = Saturation pressure corresponding to wet bulb temperature, and μ = Degree of saturation)
A.	0.622 Pv / (Pb - Pv)
B.	μ/[1 - (1 - μ) (Ps/Pb)]
C.	[Pv (Pb - Pd)]/ [Pd (Pb - Pv)]
D.	none of these
Answer» C. [Pv (Pb - Pd)]/ [Pd (Pb - Pv)]

Discussion

274.	The capillary tube, as an expansion device, is used in
A.	domestic refrigerators
B.	water coolers
C.	room air conditioners
D.	all of these
Answer» E.

Discussion

275.	Sulphur dioxide has the lowest boiling point.
A.	Yes
B.	No
C.	Can't say
D.	None of these
Answer» C. Can't say

Discussion

276.	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
Answer» C. Pb = pa x pv

Discussion

277.	The heat transfer by conduction through a thick sphere is given by
A.	Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)
B.	Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)
C.	Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)
D.	Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)
Answer» C. Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

Discussion

278.	The relative coefficient of performance is equal to
A.	(Theoretical C.O.P.)/ (Actual C.O.P.)
B.	(Actual C.O.P.) /(Theoretical C.O.P.)
C.	Actual C.O.P. x Theoretical C.O.P.
D.	none of these
Answer» C. Actual C.O.P. x Theoretical C.O.P.

Discussion

279.	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.	k. A. (dT/dx)
B.	k. A. (dx/dT)
C.	k. (dT/dx)
D.	k. (dx/dT)
Answer» B. k. A. (dx/dT)

Discussion

280.	Emissivity of a body will be equal to its absorptivity at all temperatures.
A.	Yes
B.	No
C.	Can't say
D.	None of these
Answer» C. Can't say

Discussion

281.	In aqua-ammonia absorption refrigeration system, incomplete rectification leads to accumulation of water in
A.	condenser
B.	evaporator
C.	absorber
D.	none of these
Answer» B. evaporator

Discussion

282.	The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
A.	Wien's law
B.	Stefan's law
C.	Kirchhoff's law
D.	Planck's law
Answer» D. Planck's law

Discussion

283.	The counter-current flow heat exchanger can transfer __________ heat than parallel flow heat exchanger.
A.	less
B.	more
C.	Can't say
D.	None of these
Answer» C. Can't say

Discussion

284.	During humidification process, __________ increases.
A.	wet bulb temperature
B.	relative humidity
C.	dry bulb temperature
D.	specific humidity
Answer» C. dry bulb temperature

Discussion

285.	Film coefficient is defined as the ratio of
A.	thermal conductivity to the equivalent thickness of the film of fluid
B.	temperature drop through the films of fluids to the thickness of film of fluids
C.	thickness of film of fluid to the thermal conductivity
D.	thickness of film of fluid to the temperature drop through the films of fluids
Answer» B. temperature drop through the films of fluids to the thickness of film of fluids

Discussion

286.	The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called
A.	First law of thermodynamics
B.	Newton's law of cooling
C.	Newton's law of heating
D.	Stefan's law
Answer» C. Newton's law of heating

Discussion

287.	A condenser of refrigeration system rejects heat at the rate of 120 kW, while its compressor consumes a power of 30 kW. The coefficient of performance of the system will be
A.	1/4
B.	1/3
C.	3
D.	4
Answer» E.

Discussion

288.	The wet bulb depression indicates __________ humidity of the air.
A.	absolute
B.	relative
C.	specific
D.	None of these
Answer» C. specific

Discussion

289.	The thermostatic expansion valve is used in __________ type of evaporators.
A.	flooded
B.	DX coil
C.	dry
D.	None of these
Answer» D. None of these

Discussion

290.	In a vapour compression refrigeration system, a throttle valve is used in place of an expander because
A.	it considerably reduces mass of the system
B.	it improves the C.O.P., as the condenser is small
C.	the positive work in isentropic expansion of liquid is very small
D.	it leads to significant cost reduction
Answer» D. it leads to significant cost reduction

Discussion

291.	The thermal diffusivity for solids is generally less than those for liquids and gases.
A.	True
B.	False
C.	Can't say
D.	None of these
Answer» C. Can't say

Discussion

292.	During heating and dehumidification process, dry bulb temperature
A.	remains constant
B.	increases
C.	decreases
D.	None of these
Answer» C. decreases

Discussion

293.	The reduced ambient air cooling system has
A.	one cooling turbine and one heat exchanger
B.	one cooling turbine and two heat exchangers
C.	two cooling turbines and one heat exchanger
D.	two cooling turbines and two heat exchangers
Answer» D. two cooling turbines and two heat exchangers

Discussion

294.	In a spray washing system, if the temperature of water is higher than the dry bulb temperature of entering air, then the air is
A.	heated and dehumidified
B.	heated and humidified
C.	cooled and humidified
D.	cooled and dehumidified
Answer» C. cooled and humidified

Discussion

295.	The wet bulb temperature at 100% relative humidity is __________ dew point temperature.
A.	same as
B.	lower than
C.	higher than
D.	None of these
Answer» B. lower than

Discussion

296.	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
Answer» D. none of these

Discussion

297.	The wet bulb temperature during sensible heating of air
A.	remains constant
B.	increases
C.	decreases
D.	None of these
Answer» C. decreases

Discussion

298.	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
Answer» C. reflects all the heat radiations

Discussion

299.	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
Answer» E.

Discussion

300.	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.	RN = hl/k
B.	RN = μ cp/k
C.	RN = ρ V l /μ
D.	RN = V²/t.cp
Answer» D. RN = V²/t.cp

Discussion

Explore topic-wise MCQs in Automobile Engineering.

When the discharge pressure is too high in a refrigeration system, high pressure control is installed to stop the compressor.

The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be

An infinite parallel planes with emissivities e1 and e2, the interchange factor for radiation from surface 1 to surface 2 is given by

Sulphur dioxide is extremely toxic and non-flammable.

The wet bulb temperature at 100% relative humidity is __________ dry bulb temperature.

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

The expression is used for calculating

The freezing point of sulphur dioxide is

Free convection flow depends on

The boiling point of R-12 is about - 30°C.

In a pressure enthalpy chart, the space to the left of the saturated liquid line represents

The evaporator changes the low pressure liquid refrigerant from the expansion valve into

The wave length corresponding to the maximum energy is inversely proportional to the absolute temperature. This statement is called Planck's law.

During dehumidification process, the relative humidity

A composite slab has two layers of different materials with thermal conductivities k1 and k2. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be

The pressure at the outlet of a refrigerant compressor is called

According to Stefan-Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Dew point temperature is the temperature of air recorded by a thermometer, when the moisture present in it begins to condense.

In absorption vapour systems, the refrigerant widely used is R-12.

If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called

In figure shown, E is a heat engine with efficiency of 0.4 and R is a refrigerator. It is given that Q2 + Q4 = 3Q1. The C.O.P. of the refrigerator is

Relative humidity is given by (where pv = Partial pressure of water vapour, pb = Barometric pressure, ps = Pressure of saturated air, pd = Pressure at dry bulb temperature, pw = Saturation pressure corresponding to wet bulb temperature, and μ = Degree of saturation)

The capillary tube, as an expansion device, is used in

Sulphur dioxide has the lowest boiling point.

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)

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

The relative coefficient of performance is equal to

Emissivity of a body will be equal to its absorptivity at all temperatures.

In aqua-ammonia absorption refrigeration system, incomplete rectification leads to accumulation of water in

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as

The counter-current flow heat exchanger can transfer __________ heat than parallel flow heat exchanger.

During humidification process, __________ increases.

Film coefficient is defined as the ratio of

The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

A condenser of refrigeration system rejects heat at the rate of 120 kW, while its compressor consumes a power of 30 kW. The coefficient of performance of the system will be

The wet bulb depression indicates __________ humidity of the air.

The thermostatic expansion valve is used in __________ type of evaporators.

In a vapour compression refrigeration system, a throttle valve is used in place of an expander because

The thermal diffusivity for solids is generally less than those for liquids and gases.

During heating and dehumidification process, dry bulb temperature

The reduced ambient air cooling system has

In a spray washing system, if the temperature of water is higher than the dry bulb temperature of entering air, then the air is

The wet bulb temperature at 100% relative humidity is __________ dew point temperature.

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

The wet bulb temperature during sensible heating of air

A perfect black body is one which

The amount of radiation mainly depends upon the

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)