The window-mounted air conditioner (AC) supplies 15 m/min of air at 15°C, 1 bar to a room. Air returns from the room to the evaporator of the unit at 25°C. The air conditioner operates at steady state on a vapor-compression refrigeration cycle with Refrigerant 134a entering the compressor at 400 kPa, 10°C. Saturated liquid refrigerant at 900 kPa leaves the condenser. The compressor has an isentropic efficiency of 70%, and refrigerant exits the compressor at 9 bar. Determine the following. Assume air flow is at 100 kPa. Enthalpy of R134a at the compressor inlet (kJ/kg)? O A. 167.25 O B. 201.55 O C. 135.27 O D. 256.59 O E. 122.52

The window-mounted air conditioner (AC) supplies 15 m/min of air at 15°C, 1 bar to a room. Air returns from the room to the evaporator of the unit at 25°C. The air conditioner operates at steady state on a vapor-compression refrigeration cycle with Refrigerant 134a entering the compressor at 400 kPa, 10°C. Saturated liquid refrigerant at 900 kPa leaves the condenser. The compressor has an isentropic efficiency of 70%, and refrigerant exits the compressor at 9 bar. Determine the following. Assume air flow is at 100 kPa. Enthalpy of R134a at the compressor inlet (kJ/kg)? O A. 167.25 O B. 201.55 O C. 135.27 O D. 256.59 O E. 122.52

Refrigeration and Air Conditioning Technology (MindTap Course List)

8th Edition

ISBN:9781305578296

Author:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Publisher:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Chapter28: Special Refrigeration Applications

Section: Chapter Questions

Problem 15RQ: Why is two-stage compression popular for extra-low-temperature refrigeration systems?

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Data for steady-state operation of a vapor-compression refrigeration cycle with Refrigerant 134a as theworking fluid are given in the table below. State 1 is at the compressor inlet. The cooling capacity (i.e therate at which heat is removed from the cooled space) is 4.6 tons. 1 ton of refrigeration is equivalent to211 kJ/min. Ignoring heat transfer between the compressor and its surroundings, sketch the ?-? diagramof the cycle and determinea) the mass flow rate of the refrigerant, in kg/min.b) the isentropic compressor efficiency.c) the coefficient of performance.State ? (bar) ? (°C) ℎ (kJ/kg) ? (kJ/kg-K)
2. In an ammonia vapor compression refrigeration cycle, 5 kg/min of refrigerant are circulated. The evaporating temperature of the cycle is designed at -18°C, and the refrigeration engineer decided to consider to superheat the ammonia as it leaves the evaporator by 5°C; the compressor discharge is at 12 bars, 125°C. The ammonia leaves the condenser as saturated liquid. Assume no pressure drop happens as the refrigerant flows in the system. Sketch the Ph and Ts diagram and find, a. Volume flow rate, m3/sec b. Capacity, tons c. Work, hp d. The compressor efficiency. Use the table below to get the necessary value of properties.
1.) An actual 35 TR refrigerating system operates using R22 refrigerant. Refrigerant enters the evaporator at 264.29 kPa and leaves saturated vapour at 244.83 kPa. Refrigerant enters the compressor at – 10°C. Refrigerant leaves the compressor at condensing pressure of 1400 kPa and 70°C and leaves the condenser at 30°C. Compression process is polytropic with n = 1.23. Draw the p-h diagram of the cycle (labeling the pressures and temperatures in each condition). (b) Define and determine the necessary enthalpies and determine the following: (c) IHP and (d) heat rejected during compression, kW
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Q2/ A vapor-compression refrigeration system operates on the cycle. The refrigerant is tetrafluoroethane. For Evaporation T = 0°C; condensation T = 26°C; n(compressor) = 0.79; refrigeration rate = 600 kJ-s—1., determine the circulation rate of the refrigerant, the heat-transfer rate in the condenser, the power requirement, the coefficient of performance of the cycle
A vapor-compression refrigeration cycle with Refrigerant 134a as the working fluid operates with an evapo-rator temperature of 50◦F and a condenser pressure of 180 lbf/in2Saturated vapor enters the compressor. Refrigerantenters the condenser at 140◦F and exits as saturated liquid. The cycle has a refrigeration capacity of 5 tons (a) the refrigerant mass flow rate, in lb/min. b) the compressor isentropic efficiency. (c) the compressor power, in horsepower. (d) the coefficient of performance.
5. A refrigeration system using R-12 as refrigerant consists of throe evaporators of capacities 20 TR at – 5°C, 30 TR at 0°C and 10 TR at 5°C. The vapours leaving the three evaporators are dry and saturated. The system is provided with individual compressors and multiple expansion valves. The condenser temperature is 40°C and the liquid refrigerant leaving the condenser is saturatoed. Assuming isentropic compression in each compressor, find (a) the mass of refrigerant flowing through cach evaporator, (b) the power required to drive the system, and (c) the C.O.P. of the system. [Ans. 27.4 kg/min, 42.25 kg/min: 34.12 kg/min; 38.4 kW; 5.56]
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