For obtaining high COP, the pressure range of compressor should be
High
Low
Optimum
Any value
Correct Answer :
B. Low
Related Questions
The reciprocating refrigerant compressors are very suitable for
Small displacements and low condensing pressures
Large displacements and high condensing pressures
Small displacements and high condensing pressures
Large displacements and low condensing pressures
The boiling point of ________ is 10.5°C.
Ammonia
R-12
Sulphur dioxide
Carbon dioxide
Pressure of water vapour is given by
0.622 Pv/ (Pb - Pv)
μ/[1 - (1 - μ) (Ps/Pb)]
[Pv (Pb - Pd)]/ [Pd (Pb - Pv)]
None of these
In case of sensible cooling of air, the coil efficiency is given by
B.P.F. - 1
1 - B.P.F.
1/ B.P.F.
1 + B.P.F.
The thermostatic expansion valve is used in __________ type of evaporators.
Flooded
DX coil
Dry
None of these
Vertical lines on pressure-enthalpy chart show constant
Pressure lines
Temperature lines
Total heat lines
Entropy lines
The wet bulb temperature during sensible cooling of air
Remains constant
Increases
Decreases
None of these
Chaperon equation is applicable for registration at
Saturation point of vapour
Saturation point of liquid
Sublimation temperature
Triple point
In a vapour compression refrigeration system, a throttle valve is used in place of an expander because
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
Moisture in Freon refrigeration system causes
Ineffective refrigeration
High power consumption
Freezing automatic regulating valve
Corrosion of whole system
Condensing temperature in a refrigerator is the temperature
Of cooling medium
Of freezing zone
Of evaporator
At which refrigerant gas becomes liquid
The air cooling system mostly used in transport type aircrafts is
Simple air cooling system
Simple evaporative air cooling system
Bootstrap air cooling system
All of these
The operating pressure for refrigerating units using R-12 as a refrigerant is
2 bar
8 bar
15 bar
30 bar
In a psychrometric process, the sensible heat added is 30 kJ/s and the latent heat added is 20 kJ/s. The sensible heat factor for the process will be
0.3
0.6
0.67
1.5
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
The process, generally used in summer air conditioning to cool and dehumidify the air, is called
Humidification
Dehumidification
Heating and humidification
Cooling and dehumidification
In vapour compression refrigeration system, refrigerant occurs as liquid between
Condenser and expansion valve
Compressor and evaporator
Expansion valve and evaporator
Compressor and condenser
In larger industrial and commercial reciprocating compression systems, refrigerant widely used is
Ammonia
Carbon dioxide
Sulphur dioxide
R-12
Which of the following refrigerant has the highest freezing point.
Ammonia
Carbon dioxide
Sulphur dioxide
R-12
In a psychrometric chart, specific humidity (moisture content) lines are
Vertical and uniformly spaced
Horizontal and uniformly spaced
Horizontal and non-uniformly spaced
Curved lines
Chaperon equation is a relation between
Temperature, pressure and enthalpy
Specific volume and enthalpy
Temperature and enthalpy
Temperature, pressure, specific volume and enthalpy
In a vapour compression cycle, the refrigerant immediately after expansion valve is
Liquid
Sub-cooled liquid
Saturated liquid
Wet vapour
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 condensing pressure due to the presence of non-condensable gases, as compared to that actually required for condensing temperatures without non-condensable gases,
Will be higher
Will be lower
Will remain unaffected
May be higher or lower depending upon the nature of noncondensable gases
Environmental protection agencies advice against the use of chlorofluorocarbon refrigerants since
These react with water vapour and cause acid rain
These react with plants and cause greenhouse effect
These react with oxygen and cause its depletion
These react with ozone layer
Air refrigerator works on
Reversed Carnot cycle
Bell Coleman cycle
Both (A) and (B)
None 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 (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 refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250 K. If the temperature at the end of constant pressure cooling is 300K and rise in the temperature of air in the refrigerator is 50 K, then the net work of compression will be (assume air as working substance with Cp = 1 kJ/kg)
25 kJ/kg
50 kJ/kg
100 kJ/kg
125 kJ/kg
One tonne of refrigeration (1TR) means that the heat removing capacity is
21 kJ/min
210 kJ/min
420 kJ/min
620 kJ/min
The fluids used in Electrolux refrigerator are
Water and hydrogen
Ammonia and hydrogen
Ammonia, water and hydrogen
None of these