In a boot-strap air evaporative cooling system, the evaporator is provided

between the combustion chamber and the first heat exchanger

between the first heat exchanger and the secondary compressor

between the secondary compressor and the second heat exchanger

between the second heat exchanger and the cooling turbine

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

A good refrigerant should have

high operating pressures and low freezing point

high latent heat of vaporisation and low freezing point

high operating pressures and low freezing point

high specific volume and high latent heat of vaporisation

low C.O.P. and low freezing point

The critical pressure of a liquid is the pressure

above which a liquid will explode

above which a liquid will remain a liquid

above which a liquid will explode

above which a liquid will always convert into a vapour

below which a liquid will always be in vapour form

Thermal diffusivity of a substance is

directly proportional to the thermal conductivity

inversely proportional to density of substance

inversely proportional to specific heat

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.

If a gas is to be liquified, its temperature must be

increased to a value above its critical temperature

reduced to a value below its critical temperature

The thermostatic expansion valve operates on the changes in the

degree of superheat at exit from the evaporator

The refrigerant supplied to a compressor must be

dry saturated liquid refrigerant

a mixture of liquid and vapour refrigerant

265 + Mcqs in Heat Transfer, Refrigeration and Air Conditioning Page 4 McqOptions

151.	The radiation emitted by a black body is known as
A.	black radiation
B.	full radiation
C.	total radiation
D.	all of these
Answer» E.

Discussion

152.	The natural convection air cooled condensers are used in
A.	domestic refrigerators
B.	water coolers
C.	room air conditioners
D.	all of these
Answer» B. water coolers

Discussion

153.	The process, generally used in winter air-conditioning to warm and humidity the air, is called
A.	humidification.
B.	dehumidification
C.	heating and humidification
D.	cooling and dehumidification
Answer» D. cooling and dehumidification

Discussion

154.	At 100% relative humidity, wet bulb temperature, dry bulb temperature, dew point temperature and saturation temperature are equal.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

155.	Bell-Coleman cycle is a
A.	reversed Carnot cycle
B.	reversed Otto cycle
C.	reversed Joule cycle
D.	reversed Rankine cycle
Answer» D. reversed Rankine cycle

Discussion

156.	According to Prevost's theory of exchanges, every body irrespective of its temperature continuously emit heat radiations to the surrounding bodies and at the same time receives heat radiations from the surrounding bodies.
A.	True
B.	False
Answer» B. False

Discussion

157.	In a boot-strap air evaporative cooling system, the evaporator is provided
A.	between the combustion chamber and the first heat exchanger
B.	between the first heat exchanger and the secondary compressor
C.	between the secondary compressor and the second heat exchanger
D.	between the second heat exchanger and the cooling turbine
Answer» E.

Discussion

158.	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

159.	A good refrigerant should have
A.	high latent heat of vaporisation and low freezing point
B.	high operating pressures and low freezing point
C.	high specific volume and high latent heat of vaporisation
D.	low C.O.P. and low freezing point
Answer» B. high operating pressures and low freezing point

Discussion

160.	The thermal diffusivity for gases is generally __________ those for liquids.
A.	equal to
B.	less than
C.	greater than
Answer» D.

Discussion

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

Discussion

162.	The critical pressure of a liquid is the pressure
A.	above which a liquid will remain a liquid
B.	above which a liquid will explode
C.	above which a liquid will always convert into a vapour
D.	below which a liquid will always be in vapour form
Answer» B. above which a liquid will explode

Discussion

163.	Thermal diffusivity of a substance is
A.	directly proportional to the thermal conductivity
B.	inversely proportional to density of substance
C.	inversely proportional to specific heat
D.	all of the above
Answer» E.

Discussion

164.	The emissivity for a black body is
A.	0
B.	0.5
C.	0.75
D.	1
Answer» E.

Discussion

165.	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

166.	The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number), where is equal to
A.	-1/3
B.	-2/3
C.	1
D.	-1
Answer» B. -2/3

Discussion

167.	For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference () for parallel flow is __________ that for counter flow.
A.	equal to
B.	less than
C.	greater than
Answer» B. less than

Discussion

168.	A vapour absorption refrigerator uses __________ as a refrigerant.
A.	water
B.	ammonia
C.	freon
D.	aqua-ammonia
Answer» E.

Discussion

169.	Thermal conductivity of air increases with rise in temperature.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

170.	The material of pipe lines for a system using ammonia as a refrigerant should be copper.
A.	Yes
B.	No
Answer» C.

Discussion

171.	The C.O.P. of a Carnot refrigerator in winter will be __________ as compared to C.O.P. in summer.
A.	same
B.	lower
C.	higher
Answer» D.

Discussion

172.	If a gas is to be liquified, its temperature must be
A.	increased to a value above its critical temperature
B.	reduced to a value below its critical temperature
C.	equal to critical temperature
D.	none of the above
Answer» D. none of the above

Discussion

173.	The thermostatic expansion valve is used in __________ type of evaporators.
A.	flooded
B.	DX coil
C.	dry
Answer» D.

Discussion

174.	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
Answer» C.

Discussion

175.	The curved lines on a psychrometric chart indicates
A.	dry bulb temperature
B.	wet bulb temperature
C.	dew point temperature
D.	relative humidity
Answer» E.

Discussion

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

Discussion

177.	A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be
A.	lack of cooling water
B.	water temperature being high
C.	dirty condenser surface
D.	all of these
Answer» E.

Discussion

178.	The counter-current flow heat exchanger can transfer __________ heat than parallel flow heat exchanger.
A.	less
B.	more
Answer» C.

Discussion

179.	The freon group of refrigerants are
A.	halo-carbon refrigerants
B.	azeotrope refrigerants
C.	inorganic refrigerants
D.	hydro-carbon refrigerants
Answer» B. azeotrope refrigerants

Discussion

180.	The thermostatic expansion valve operates on the changes in the
A.	degree of superheat at exit from the evaporator
B.	temperature of the evaporator
C.	pressure in the evaporator
D.	none of the above
Answer» B. temperature of the evaporator

Discussion

181.	In a vapour compression system, the condition of refrigerant before entering the expansion or throttle valve is
A.	high pressure saturated liquid
B.	wet vapour
C.	very wet vapour
D.	dry vapour
Answer» B. wet vapour

Discussion

182.	The freezing point of R-12 is
A.	-86.6°C
B.	-95.2°C
C.	-107.7°C
D.	-135.8°C
Answer» E.

Discussion

183.	The refrigerant supplied to a compressor must be
A.	superheated vapour refrigerant
B.	dry saturated liquid refrigerant
C.	a mixture of liquid and vapour refrigerant
D.	none of these
Answer» B. dry saturated liquid refrigerant

Discussion

184.	One tonne of refrigeration (1TR) means that the heat removing capacity is
A.	21 kJ/min
B.	210 kJ/min
C.	420 kJ/min
D.	620 kJ/min
Answer» C. 420 kJ/min

Discussion

185.	A boot-strap air cooling system has
A.	one heat exchanger
B.	two heat exchangers
C.	three heat exchangers
D.	four heat exchangers
Answer» C. three heat exchangers

Discussion

186.	The boiling point of __________ is -10.5°C.
A.	ammonia
B.	R-12
C.	sulphur dioxide
D.	carbon dioxide
Answer» D. carbon dioxide

Discussion

187.	The operating pressure for refrigerating units using R-12 as a refrigerant is
A.	2 bar
B.	8 bar
C.	15 bar
D.	30 bar
Answer» C. 15 bar

Discussion

188.	The specific humidity during heating and humidification process.
A.	remains constant
B.	increases
C.	decreases
Answer» C. decreases

Discussion

189.	For a white body, absorptivity (α ) = 0, reflectivity (ρ) = 1 and transmittivity (τ) = 0.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

190.	The process of removing moisture from the air, without change in its dry bulb temperature, is called dehumidification.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

191.	When the discharge pressure is too high in a refrigeration system, high pressure control is installed to stop the compressor.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

192.	A grey body is one whose absorptivity does not vary with temperature and wave length of the incident ray.
A.	True
B.	False
Answer» B. False

Discussion

193.	The wet bulb temperature during sensible cooling of air
A.	remains constant
B.	increases
C.	decreases
Answer» D.

Discussion

194.	In absorption vapour systems, the refrigerant widely used is R-12.
A.	Correct
B.	Incorrect
Answer» C.

Discussion

195.	Hydrogen is used in electrolux refrigeration system so as to __________ the rate of evaporation of the liquid ammonia passing through the evaporator.
A.	equalise
B.	reduce
C.	increase
Answer» D.

Discussion

196.	The final relative humidity of the air during cooling and dehumidification is generally __________ than that of entering air.
A.	lower
B.	higher
Answer» C.

Discussion

197.	The emissivity of a polished silver body is __________ as compared to black body.
A.	same
B.	low
C.	very low
D.	high
Answer» D. high

Discussion

198.	In a pressure enthalpy chart, the space between the saturated liquid line and saturated vapour line, represents sub-cooled liquid region.
A.	True
B.	False
Answer» C.

Discussion

199.	R-11 has the highest critical point temperature.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

200.	A composite slab has two layers of different materials with thermal conductivities and . If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
A.
B.	+
Answer» E.

Discussion

Explore topic-wise MCQs in Mechanical Engineering.

The radiation emitted by a black body is known as

The natural convection air cooled condensers are used in

The process, generally used in winter air-conditioning to warm and humidity the air, is called

At 100% relative humidity, wet bulb temperature, dry bulb temperature, dew point temperature and saturation temperature are equal.

Bell-Coleman cycle is a

According to Prevost's theory of exchanges, every body irrespective of its temperature continuously emit heat radiations to the surrounding bodies and at the same time receives heat radiations from the surrounding bodies.

In a boot-strap air evaporative cooling system, the evaporator is provided

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

A good refrigerant should have

The thermal diffusivity for gases is generally __________ those for liquids.

Free convection flow depends on

The critical pressure of a liquid is the pressure

Thermal diffusivity of a substance is

The emissivity for a black body is

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

The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number), where is equal to

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

A vapour absorption refrigerator uses __________ as a refrigerant.

Thermal conductivity of air increases with rise in temperature.

The material of pipe lines for a system using ammonia as a refrigerant should be copper.

The C.O.P. of a Carnot refrigerator in winter will be __________ as compared to C.O.P. in summer.

If a gas is to be liquified, its temperature must be

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

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

The curved lines on a psychrometric chart indicates

During humidification process, __________ increases.

A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be

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

The freon group of refrigerants are

The thermostatic expansion valve operates on the changes in the

In a vapour compression system, the condition of refrigerant before entering the expansion or throttle valve is

The freezing point of R-12 is

The refrigerant supplied to a compressor must be

One tonne of refrigeration (1TR) means that the heat removing capacity is

A boot-strap air cooling system has

The boiling point of __________ is -10.5°C.

The operating pressure for refrigerating units using R-12 as a refrigerant is

The specific humidity during heating and humidification process.

For a white body, absorptivity (α ) = 0, reflectivity (ρ) = 1 and transmittivity (τ) = 0.

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

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

A grey body is one whose absorptivity does not vary with temperature and wave length of the incident ray.

The wet bulb temperature during sensible cooling of air

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

Hydrogen is used in electrolux refrigeration system so as to __________ the rate of evaporation of the liquid ammonia passing through the evaporator.

The final relative humidity of the air during cooling and dehumidification is generally __________ than that of entering air.

The emissivity of a polished silver body is __________ as compared to black body.

In a pressure enthalpy chart, the space between the saturated liquid line and saturated vapour line, represents sub-cooled liquid region.

R-11 has the highest critical point temperature.

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