Refrigeration & Air Conditioning - Mechanical Engineering MCQ

Under saturated ambient air conditions:
[DBT = Dry bulb temperature,
WBT = Web bulb temperature]

Common data question 5 & 6

A refrigerator operates on an ideal vapor - compression refrigration cycle between 0.14 MPa and 0.8 MPa. The mass flow rate of the refrigerant is 0.05 kg/s. Take h_g (at 0.14 MPa) = 239.16 kJ/kg, S_g (at 0.14 MPa) = 0.94456 kJ/kgK, h_f (at 0.8 MPa) = 95.47 kJ/kg and h (at compressor exit) = 275.39 kJ/kg 

Q. The rate of heat removal from refrigerated space and the heat rejected to the atmosphere respectively are

Common data question 5 & 6

A refrigerator operates on an ideal vapor - compression refrigration cycle between 0.14 MPa and 0.8 MPa. The mass flow rate of the  refrigerant is 0.05 kg/s. Take h_g (at 0.14 MPa) = 239.16 kJ/kg, S_g (at 0.14 MPa) = 0.94456 kJ/kgK, h_f (at  0.8 MPa) = 95.47 kJ/kg and h (at compressor exit) = 275.39 kJ/kg 

Q. The COP of the refrigerator is

Horizontal lines moving towards the saturation curve on the psychrometric chart represents

Common Data Question 8 & 9

In a Carnot vapor refrigeration cycle refrigerant R - 134a is used as the working fluid. The refrigerant enters the condenser as saturated vapor at 28⁰C and leaves as saturated liquid. The evaporator operates at a temperature of -100C. The thermodynamic properties for the refrigerant are given below.

Q. The net work for the cycle is given by

Common Data Question 8 & 9
In a Carnot vapor refrigeration cycle refrigerant R - 134a is used as the working fluid. The refrigerant enters the condenser as saturated vapor at 28⁰C and leaves as  saturated liquid. The evaporator  operates at a temperature of -100C. The thermodynamic properties for the refrigerant are given below.

Q. The coefficient of performance of the cycle is

The dry-bulb, wet bulb and dew point temperatures are identical at

A room is filled with saturated moist air at 25⁰C and a total pressure of 100 kPa. The saturated pressure at 25⁰C is 3.1698 kPa. If the mass of dry air in the room is 100 kg, what is the mass of water vapour?

Common data for 12 & 13

A commercial refrigerator is used to keep the refrigerated space at -30⁰C by rejecting its waste heat to cooling water. This cooling water enters the condenser at 18⁰C (h_w = 75.47 kJ/kg) with a rate of 0.25 kg/s and leaves at 26⁰C (h_w = 108.94 kJ/kg). The refrigerant enters the condenser at 1.2 MPa, 65⁰C (h = 295.16 kJ/kg) and leaves at 42⁰C (h = 111.23 kJ/kg). The inlet state of the compressor is 60 kPa, -34⁰C (h = 230.03 kJ/kg) and the compressor is estimated to gain a net heat of 450W from the surroundings: 

Q. The refrigeration load will be

Common data for 12 & 13

A commercial refrigerator is used to keep the refrigerated space at -30⁰C by rejecting its waste heat to cooling water. This cooling water enters the condenser at 18⁰C (h_w = 75.47 kJ/kg) with a rate of 0.25 kg/s and leaves at 26⁰C (h_w = 108.94 kJ/kg). The refrigerant enters the condenser at 1.2 MPa, 65⁰C (h = 295.16 kJ/kg) and leaves at 42⁰C (h = 111.23 kJ/kg). The inlet state of the compressor is 60 kPa, -34⁰C (h = 230.03 kJ/kg) and the compressor is estimated to gain a net heat of 450W from the surroundings:

Q. The theoretical maximum refrigeration load for the same power input to the compressor is

A heat pump operates between the temperature of 32⁰C and -10⁰C. The rates of heat addition and heat rejection are 650W and 1000 W respectively. The COP for the heat pump is ____

(Important - Enter only the numerical value in the answer)
 

In a VARs heating in generator is done at 200⁰C, refrigeration in evaporator at -5⁰C and cooling in condenser at 27⁰C. The maximum COP of the system is

In an ideal VCRS, the enthalpy of the refrigerant before and after the evaporator are 90 kJ/kg and 200 kJ/kg. The circulation rate of refrigerant for each tonn of refrigerant is_____kg/min.

(Important - Enter only the numerical value in the answer)

The chemical formula for the refrigerant R-22 is given by

The efficiency of Carnot engine is given as 0.80. If the cycle direction is reversed, the COP of the Carnot
refrigerator is_____

(Important - Enter only the numerical value in the answer)

Organic material of 1800 kg is to be stored in refrigerator storage. The material is supplied at 27⁰C and is to be cooled to -30⁰C for preserving it. The cooling takes place in 12 hours. The specific heat of material is 2 kJ/kgK above freezing point and 0.6 kJ/kg-K below freezing point, which is -3⁰C. The latent heat of freezing is 230  kJ/kg. If the actual COP is half of the ideal COP, the power required to drive the plant is ____ kW.

(Important - Enter only the numerical value in the answer)

Moist air exists at a pressure of 1.01 bar. The partial pressure and saturation pressure of water vapour are 0.01 bar and 0.02 bar respectively. The relative humidity and humidity ratio of the moist air, respectively are