The rate of heat flow through a body is 
. The term x/kA is known as
-
thermal coefficient -
thermal resistance -
thermal conductivity -
none of these
In larger industrial and commercial reciprocating compression systems, refrigerent widely used is
-
ammonia -
carbon dioxide -
sulphur dioxide -
R-12
A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
-
the better insulation must be put inside -
the better insulation must be put outside -
one could place either insulation on either side -
one should take into account the steam temperature before deciding as to which insulation is put where
A human body feels comfortable when the heat produced by the metabolism of human body is equal to the
-
heat dissipated to the surroundings -
heat stored in the human body -
sum of (a) and (b) -
difference of (a) and (b)
The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as
-
conduction -
free convection -
forced convection -
radiation
In aircraft, air refrigeration Cycle is used because of
-
low weight per tonne of refrigeration -
high heat transfer rate -
low temperature at high altitudes -
higher coefficient of performance
The overall coefficient of heat transfer is used in problems of
-
conduction -
convection -
radiation -
conduction and convection
The pressure at the inlet of a refrigerant compressor is called
-
suction pressure -
discharge pressure -
critical pressure -
back pressure
In a parallel flow heat exchanger, the rate of flow of heat and the rate of decrease of temperature are maximum.
-
Yes -
No
During sensible cooling,
-
relative humidity remains constant -
wet bulb temperature increases -
specific humidity increases -
partial pressure of vapour remains constant
The thermostatic expansion valve is also called
-
constant pressure valve -
constant temperature valve -
constant superheat valve -
none of these
The material of pipe lines for a system using freon as a refrigerant should be
-
brass -
copper -
steel -
aluminium
The boiling point of R-is about - 30°C.
-
True -
False
The process, generally used in summer air conditioning to cool and dehumidify the air, is called
-
humidification -
dehumidification -
heating and humidification -
cooling and dehumidification
When the air is passed through an insulated chamber having sprays of water maintained at a temperature higher than the dew point temperature of entering air but lower than its dry bulb temperature, then the air is said to be
-
cooled and humidified -
cooled and dehumidified -
heated and humidified -
heated and dehumidified
The wave length of the radiation emitted depends only on the temperature and is independent of the material of the body.
-
True -
False
The temperature of air recorded by a thermometer, when the moisture present in it begins to condense, is called wet bulb temperature.
-
Yes -
No
The leakage in a refrigeration system using ammonia is detected by
-
halide torch -
sulphur sticks -
soap and water -
all of these
Which of the following statement is wrong?
-
The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures. -
In vapour compression cycle, the useful part of the heat transfer is at the condenser. -
In ammonia-hydrogen (electolux) refrigerator, no compressor, pump or fan is required. -
The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.
The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called
-
conduction -
convection -
radiation
The specific humidity during cooling and dehumidification
-
remains constant -
increases -
decreases
In a pressure enthalpy chart, the space to the left of the saturated liquid line represents
-
wet vapour region -
superheated vapour region -
sub-cooled liquid region -
none of these
The lowest temperature during the cycle in a vapour compression system occurs after
-
compression -
expansion -
condensation -
evaporation
The specific humidity during cooling and dehumidification
-
remains constant -
increases -
decreases
The specific humidity during heating and humidification process.
-
remains constant -
increases -
decreases
The unit of thermal diffusivity is
-
m/hK -
m/h -
m2/h -
m2/hK
The cooling system used for supersonic aircrafts and rockets is
-
simple air cooling system -
boot-strap air cooling system -
reduced ambient air cooling system -
regenerative air cooling system
When the discharge pressure is too high in a refrigeration system, high pressure control is installed to stop the compressor.
-
Correct -
Incorrect
Which of the following statement is correct?
-
In vapour absorption refrigerator, the compression of refrigerent is avoided. -
Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser. -
In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke. -
all of the above
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.
-
True -
False