The index which correlates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as
Mean radiant temperature
Effective temperature
Dew point temperature
None of these
Correct Answer :
B. Effective temperature
Related Questions
The bypass factor (B. P. F.) in case of sensible heating of air is (Where td₁ = Dry bulb temperature of air entering the heating coil, td₂ = Dry bulb temperature of air leaving the heating coil, and td₃ = Dry bulb temperature of heating coil)
(td₂ - td₃)/(td₃ - td₁)
(td₃ - td₂)/(td₃ - td₁)
(td₃ - td₁)/(td₂ - td₃)
(td₃ - td₁)/(td₃ - td₂)
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
1/e₁ + 1/e₂
e₁ + e₂
e₁e₂
The thermostatic expansion valve operates on the changes in the
Degree of superheat at exit from the evaporator
Temperature of the evaporator
Pressure in the evaporator
None of the above
A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be
1.33
2.33
3.33
4.33
The superheating in a refrigeration cycle
Does not alter C.O.P.
Increases C.O.P.
Decreases C.O.P.
None of these
In mechanical refrigeration system, the refrigerant has the maximum temperature
In evaporator
Before expansion valve
Between compressor and condenser
Between condenser and evaporator
The C.O.P. of a refrigeration cycle with lowering of condenser temperature, keeping the evaporator temperature constant, will
Increase
Decrease
May increase or decrease depending on the type of refrigerant used
Remain unaffected
During a refrigeration cycle, heat is rejected by the refrigerant in a
Compressor
Condenser
Evaporator
Expansion valve
The relative humidity is defined as
The mass of water vapour present in 1 m3 of dry air
The mass of water vapour present in 1 kg of dry air
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.
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
Superheating in a refrigeration cycle
Increases C.O.P
Decreases C.O.P
C.O.P remains unaltered
Other factors decide C.O.P
Which of the following statement is correct?
The constant enthalpy lines are also constant wet bulb temperature lines.
The wet bulb and dry bulb temperature are equal at saturation condition.
The wet bulb temperature is a measure of enthalpy of moist air.
All of the above
The specific humidity during humidification process
Remains constant
Increases
Decreases
None of these
Moisture in Freon refrigeration system causes
Ineffective refrigeration
High power consumption
Freezing automatic regulating valve
Corrosion of whole system
The lowest thermal diffusivity is of
Iron
Lead
Aluminium
Rubber
In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by
Liquid pump
Generator
Absorber and generator
Absorber, generator and liquid pump
In a spray washing system, if the temperature of water is higher than the dry bulb temperature of entering air, then the air is
Heated and dehumidified
Heated and humidified
Cooled and humidified
Cooled and dehumidified
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
None of these
The unit of thermal diffusivity is
m/hK
m/h
m²/h
m²/hK
During dehumidification process, the relative humidity
Remains constant
Increases
Decreases
None of these
Moisture should be removed from refrigerants to avoid
Freezing at the expansion valve
Restriction to refrigerant flow
Corrosion of steel plates
All of these
The refrigerant used in small tonnage commercial machines (hermetically sealed units) is
Ammonia
Carbon dioxide
Sulphur dioxide
R-12
The difference between dry bulb temperature and wet bulb temperature, is called
Dry bulb depression
Wet bulb depression
Dew point depression
Degree of saturation
Most thermostatic expansion valves are set for a superheat of
5°C
10°C
15°C
20°C
The boiling point of carbon dioxide is
-20.5°C
-50°C
-63.3°C
-78.3°C
The horizontal and non-uniformly spaced lines on a psychrometric chart indicates
Dry bulb temperature
Wet bulb temperature
Dew point temperature
Specific humidity
A good refrigerant should have
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
Hydrogen is used in Electrolux refrigeration system so as to _________ the rate of evaporation of the liquid ammonia passing through the evaporator.
Equalise
Reduce
Increase
None of these
In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature
Which lies between the dry bulb and wet bulb temperatures of the incoming stream
Which lies between the wet bulb and dew point temperatures of the incoming stream
Which is lower than the dew point temperature of the incoming stream
Of adiabatic saturation of incoming stream
In order to collect liquid refrigerant and to prevent it from going to a ________, a device known as accumulator is used at the suction of compressor.
Compressor
Condenser
Expansion valve
Evaporator
The ratio of heat extracted in the refrigerator to the work-done on the refrigerant is called
Coefficient of performance of refrigeration
Coefficient of performance of heat pump
Relative coefficient of performance
Refrigerating efficiency