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11-59 Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.4 MPa and 160 kPa with refrigerant-134a as the working fluid. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counterflow heat exchanger where the pressure in the upper and lower cycles are 0.4 and 0.5 MPa, respectively. In both cycles, the refrigerant is a saturated liquid at the condenser exit and a saturated vapor at the compressor inlet, and the isentropic effi- ciency of the compressor is 80 percent. If the mass flow rate of the refrigerant through the lower cycle is 0.25 kg/s, determine (a) the mass flow rate of the refrigerant through the upper cycle, (b) the rate of heat removal from the refrigerated space. and (c) the COP of this refrigerator. Answers: (a) 0.384 kg/s (b) 42.0 kW, (c) 2.12

11-59 Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.4 MPa and 160 kPa with refrigerant-134a as the working fluid. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counterflow heat exchanger where the pressure in the upper and lower cycles are 0.4 and 0.5 MPa, respectively. In both cycles, the refrigerant is a saturated liquid at the condenser exit and a saturated vapor at the compressor inlet, and the isentropic effi- ciency of the compressor is 80 percent. If the mass flow rate of the refrigerant through the lower cycle is 0.25 kg/s, determine (a) the mass flow rate of the refrigerant through the upper cycle, (b) the rate of heat removal from the refrigerated space. and (c) the COP of this refrigerator. Answers: (a) 0.384 kg/s (b) 42.0 kW, (c) 2.12

Elements Of Electromagnetics
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
Problem 1.1MA
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Determine

Exergy destroyed in the heat exchanger

Exergy of condenser

Exergy of evaporator

Exergy destroyed of entire system

11-59 Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.4 MPa and 160 kPa with refrigerant-134a as the working fluid. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counterflow heat exchanger where the pressure in the upper and lower cycles are 0.4 and 0.5 MPa, respectively. In both cycles, the refrigerant is a saturated liquid at the condenser exit and a saturated vapor at the compressor inlet, and the isentropic effi- ciency of the compressor is 80 percent. If the mass flow rate of the refrigerant through the lower cycle is 0.25 kg/s, determine (a) the mass flow rate of the refrigerant through the upper cycle, (b) the rate of heat removal from the refrigerated space. and (c) the COP of this refrigerator. Answers: (a) 0.384 kg/s (b) 42.0 kW, (c) 2.12
Transcribed Image Text:11-59 Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.4 MPa and 160 kPa with refrigerant-134a as the working fluid. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counterflow heat exchanger where the pressure in the upper and lower cycles are 0.4 and 0.5 MPa, respectively. In both cycles, the refrigerant is a saturated liquid at the condenser exit and a saturated vapor at the compressor inlet, and the isentropic effi- ciency of the compressor is 80 percent. If the mass flow rate of the refrigerant through the lower cycle is 0.25 kg/s, determine (a) the mass flow rate of the refrigerant through the upper cycle, (b) the rate of heat removal from the refrigerated space. and (c) the COP of this refrigerator. Answers: (a) 0.384 kg/s (b) 42.0 kW, (c) 2.12
Sort [1] [2] [3] [4] [5] [6] [7] [8] P₁ [kPa] 160 500 500 160 400 1400 1400 t₁ [K] -15.6 21.1 15.71 -15.6 8.91 56.71 52.4 8.91 In X₁ no 1 0 1 0 h₁ [kJ/kg] 241.1 270.4 73.33 73.33 255.6 288 127.2 127.2 nin hs [kJ/kg] 264.5 281.5 S₁ [kJ/kg*K] 0.9419 0.9419 0.2802 0.2905 0.9269 0.9269 0.4532 0.472 11.10 "Tamna Unit Settings: SI C kPa kJ mass deg COP = 2.122 na=0.8 QT = 49.26 [kW] ma = 0.3839 [kg/s] nb = 0.8 Win = 19.77 [kW] mb = 0.25 [kg/s] QL = 41.95 [kW] Click on this line to see the array variables in the Arrays Table window 7 potential unit problems were detected. Compilation time = 125 ms COP = 16 Check Units Calculation time = 16 ms ma = 114181 Ikast mb = 11 25 1kg/s
Transcribed Image Text:Sort [1] [2] [3] [4] [5] [6] [7] [8] P₁ [kPa] 160 500 500 160 400 1400 1400 t₁ [K] -15.6 21.1 15.71 -15.6 8.91 56.71 52.4 8.91 In X₁ no 1 0 1 0 h₁ [kJ/kg] 241.1 270.4 73.33 73.33 255.6 288 127.2 127.2 nin hs [kJ/kg] 264.5 281.5 S₁ [kJ/kg*K] 0.9419 0.9419 0.2802 0.2905 0.9269 0.9269 0.4532 0.472 11.10 "Tamna Unit Settings: SI C kPa kJ mass deg COP = 2.122 na=0.8 QT = 49.26 [kW] ma = 0.3839 [kg/s] nb = 0.8 Win = 19.77 [kW] mb = 0.25 [kg/s] QL = 41.95 [kW] Click on this line to see the array variables in the Arrays Table window 7 potential unit problems were detected. Compilation time = 125 ms COP = 16 Check Units Calculation time = 16 ms ma = 114181 Ikast mb = 11 25 1kg/s
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