A small, two-stage, vapor-compression refrigeration unit using R-134a produces 15.0 tons of refrigeration with an evaporator pressure of 100. kPa and a condenser pressure of 1200. kPa. The intermediate flash chamber operates at 400. kPa and the isentropic efficiencies of the compressors in each loop are both 89.0%. The following operating specifications have been developed for the stages (loops):
Stage (Loop) A
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Station 1A Compressor A inlet
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Station 2sA Compressor A outlet
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Station 3A Condenser A outlet
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Station 4hA Expansion valve A outlet
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P1A = 400.kPa
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P2sA = 1200.kPa
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X3A = 0.00
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H4hA = h3A
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S2sA = S1A
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P3A = 1200.kPa
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Stage (Loop) B
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Station 1B Compressor B inlet
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Station 2sB Compressor B outlet
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Station 3B Condenser B outlet
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Station 4hB Expansion valve B outlet
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X1B = 1.00
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P2sB = 400.kPa
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X3B = 0.00
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H4hB = h3B
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P1B = 100.0kPa
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S2sB = S1B
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P3B = 400.kPa
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For this design, determine
a. The mass flow rate of the refrigerant.
b. The system's coefficient of performance.
c. The total power required by the compressor.