EXERCISE 1 CHAPTER 11

QUESTION 1 1. An ideal vapor-compression refrigeration cycle that uses refrigerant-134a as its working fluid maintains a condenser at 1000 kPa and the evaporator at 4°C. Determine the amount of power required to service a 400 kW cooling load. this system’s COP.

1. An ideal vapor-compression refrigeration cycle that uses refrigerant-134a as its working fluid maintains a condenser at 1000 kPa and the evaporator at 4°C. Determine a) the amount of power required to service a 400 kW cooling load. b) this system’s COP.

the amount of power required to service a 400 kW cooling load. 1. An ideal vapor-compression refrigeration cycle that uses refrigerant-134a as its working fluid maintains a condenser at 1000 kPa and the evaporator at 4°C. Determine the amount of power required to service a 400 kW cooling load. (i) FIND THE PROPERTIES AT EACH STATE (1,2,3,4):

(ii) GIVEN ǬL =400kW=400kJ/s, FIND ṁ 1. An ideal vapor-compression refrigeration cycle that uses refrigerant-134a as its working fluid maintains a condenser at 1000 kPa and the evaporator at 4°C. Determine the amount of power required to service a 400 kW cooling load. (ii) GIVEN ǬL =400kW=400kJ/s, FIND ṁ (iii) FIND Ẇin

1. An ideal vapor-compression refrigeration cycle that uses refrigerant-134a as its working fluid maintains a condenser at 1000 kPa and the evaporator at 4°C. Determine b) this system’s COP.

QUESTION 2 2. A refrigerator uses refrigerant-134a as the working fluid and operates on an ideal vapour-compression refrigeration cycle between 0.12 and 0.7 MPa. The mass flow rate of the refrigerant is 0.05 kg/s. Show the cycle on T-s diagram with respect to saturation line. Determine the rate of heat removal from the refrigerated space and the power input to the compressor the rate of heat rejection to the environment, the coefficient of performance

2. A refrigerator uses refrigerant-134a as the working fluid and operates on an ideal vapour-compression refrigeration cycle between 0.12 and 0.7 MPa. The mass flow rate of the refrigerant is 0.05 kg/s. Show the cycle on T-s diagram with respect to saturation line. Determine (a) the rate of heat removal from the refrigerated space and the power input to the compressor (i) FIND THE PROPERTIES AT EACH STATE (1,2,3,4):

(a) the rate of heat removal from the refrigerated space and the power input to the compressor (ii) FIND ǬL & Ẇin

(b) the rate of heat rejection to the environment, (iii) FIND ǬH

(c) the coefficient of performance (iv) FIND COPR

QUESTION 3 3. A gas refrigeration system (as in Figure Q3.1) using air as the working fluid has a pressure ratio of 5. Air enters the compressor at 0°C. The high pressure air is cooled to 35°C by rejecting heat to the surroundings. The refrigerant leaves the turbine at -80°C and then it absorbs heat from the refrigerated space before entering the regenerator. The mass flow rate of air is 0.4 kg/s. The isentropic efficiencies of the compressor and the turbine are 80% and 85% respectively. Using constant specific heats at room temperature, Determine the effectiveness of the regenerator Determine the rate of heat removal from the refrigerated space. Determine the COP of the cycle Determine the refrigeration load and COP if this system operated on the simple gas refrigeration cycle. Use the same compressor inlet temperature as given, and the same compressor and turbine efficiencies. Figure 3.1

A gas refrigeration system (as in Figure Q3 A gas refrigeration system (as in Figure Q3.1) using air as the working fluid has a pressure ratio of 5. Air enters the compressor at 0°C. The high pressure air is cooled to 35°C by rejecting heat to the surroundings. The refrigerant leaves the turbine at -80°C and then it absorbs heat from the refrigerated space before entering the regenerator. The mass flow rate of air is 0.4 kg/s. The isentropic efficiencies of the compressor and the turbine are 80% and 85% respectively. Using constant specific heats at room temperature, T1 =273.2K i) Gather the information: ii) Find the properties of air at room temperature: T5 =193.2K T3 =308.2K FROM TABLE A-2

(iii) From isentropic relations; find T2s and T5s (iv) From compressor efficiency, find T2 472.5K 432.4K

(v) From turbine efficiency & isentropic relation, find T4 (iv) Write the energy balance for regenerator to find T6 SOLVING THE SIMULTANEOUS EQUATIONS TO FIND T4 472.5K 432.4K 281.3K 246.3K

Determine the effectiveness of the regenerator Determine the rate of heat removal from the refrigerated space, ǬL 472.5K 432.4K 281.3K 246.3K

(c) Determine the COP of the cycle 472.5K 432.4K 281.3K 246.3K

(d) Determine the refrigeration load and COP if this system operated on the simple gas refrigeration cycle. Use the same compressor inlet temperature as given, and the same compressor and turbine efficiencies. 472.5K 211.6K 194.6K

(d) Determine the refrigeration load and COP if this system operated on the simple gas refrigeration cycle. Use the same compressor inlet temperature as given, and the same compressor and turbine efficiencies. 472.5K 211.6K 194.6K