Efficiency of a Carnot engine is given as 80%. If the cycle direction be reversed, what will be the value of COP of reversed Carnot Cycle?
1.25
0.8
0.5
0.25
Correct Answer :
D. 0.25
Related Questions
In vapour compression cycle the condition off refrigerant is dry saturated vapour
After passing through the condenser
Before passing through the condenser
After passing through the expansion or throttle valve
Before entering the compressor
In vapour compression cycle, the condition of refrigerant is saturated liquid
After passing through the condenser
Before passing through the condenser
After passing through the expansion throttle valve
Before entering the expansion valve
In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about
1
1.25
2.15
5.12
Accumulators should have adequate volume to store refrigerant charge at least
10 %
25 %
50 %
75 %
The bank of tubes at the back of domestic refrigerator is
Condenser tubes
Evaporator tubes
Refrigerant cooling tubes
Capillary tubes
The horizontal and non-uniformly spaced lines on a psychrometric chart indicates
Dry bulb temperature
Wet bulb temperature
Dew point temperature
Specific humidity
Formation of frost on evaporator in refrigerator
Results in loss of heat due to poor heat transfer
Increases heat transfer rate
Is immaterial
Can be avoided by proper design
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)
0.622 Pv / (Pb - Pv)
μ/[1 - (1 - μ) (Ps/Pb)]
[Pv (Pb - Pd)]/ [Pd (Pb - Pv)]
None of these
In a vapour compression system, the condition of refrigerant before entering the expansion or throttle valve is
High pressure saturated liquid
Wet vapour
Very wet vapour
Dry vapour
Domestic refrigerator working on vapour compression cycle uses the following type of expansion device
Electrically operated throttling valve
Manually operated valve
Thermostatic valve
Capillary tube
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 (Electrolux) refrigerator, no compressor, pump or fan is required.
The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.
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
Which of the following cycles uses air as the refrigerant?
Ericson
Stirling
Carnot
Bell Coleman
In a refrigeration system, heat absorbed in comparison to heat rejected is
More
Less
Same
More for small capacity and less for high capacity
An important characteristic of absorption system of refrigeration is
Noisy operation
Quiet operation
Cooling below 0°C
Very little power consumption
The comfort conditions in air conditioning are at (where DBT = Dry bulb temperature, and RH = Relative humidity)
25°C DBT and 100% RH
20°C DBT and 80% RH
22°C DBT and 60% RH
25°C DBT and 40% RH
Rating of a domestic refrigerator is of the order of
0.1 ton
5 tons
10 tons
40 tons
For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then
Bigger cabinet should be used
Smaller cabinet should be used
Perfectly tight vapour seal should be used
Refrigerant with lower evaporation temperature should be used
Ammonia absorption refrigeration cycle requires
Very little work input
Maximum work input
Nearly same work input as for vapour compression cycle
Zero work input
In mechanical refrigeration system, the refrigerant has the maximum temperature
In evaporator
Before expansion valve
Between compressor and condenser
Between condenser and evaporator
The higher temperature in vapour compression cycle occurs at
Receiver
Expansion valve
Evaporator
Compressor discharge
During humidification process, dry bulb temperature
Remains constant
Increases
Decreases
None of these
A refrigeration system
Removes heat from a low temperature body and delivers it to a high temperature body
Removes heat from a high temperature body and delivers it to a low temperature body
Rejects energy to a low temperature body
None of the above
The conditioned air supplied to the room must have the capacity to take up
Room sensible heat load only
Room latent heat load only
Both room sensible heat and latent heat loads
None of the above
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 total pressure exerted by the mixture of air and water vapour is equal to the sum of pressures which each constituent would exert, if it occupied the same space by itself. This statement is called
Kinetic theory of gases
Newton's law of gases
Dalton's law of partial pressures
Avogadro's hypothesis
Absorption system normally uses the following refrigerant
Freon-11
Freon-22
CO2
Ammonia
An evaporator is also known as
Freezing coil
Cooling coil
Chilling coil
All of these
The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called
Sub-cooling or under-cooling
Super-cooling
Normal cooling
None of these
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)