An r-134a refrigerator operates a simple vapor compression cycle (SVCC). The evaporator operates at -10 °C, while the condenser operates at 1 MPa. R-134a flows around the system at 10 g/s. a. Graph the cycle in a P-h diagram and calculate the temperature at the exit of the compressor, assuming it is 100% isentropically efficient. b. Calculate the power required by the compressor (in W) and the cooling effect of the refrigerator (in kW) c. Compute for the COP of the system. What is its percent difference from the reversible efficiency?

An r-134a refrigerator operates a simple vapor compression cycle (SVCC). The evaporator operates at -10 °C, while the condenser operates at 1 MPa. R-134a flows around the system at 10 g/s. a. Graph the cycle in a P-h diagram and calculate the temperature at the exit of the compressor, assuming it is 100% isentropically efficient. b. Calculate the power required by the compressor (in W) and the cooling effect of the refrigerator (in kW) c. Compute for the COP of the system. What is its percent difference from the reversible efficiency?

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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Q2: A simple R134a vapor compression system operates between 40°C condensing temperature and-10°C evaporating temperature. The system compressor has a piston displacement of 3 m'/min and volumetric efficiency of 75%. The temperature of vapor leaving the compressor is 60°C. The liquid refrigerant is subcooled by 10°C before entering to the expansion device. Calculate: a. Refrigerant mass flow rate. b. Refrigeration capacity. c. Indicated power. d. The COP.
A reversible refrigerator operates using a Carnot refrigeration cycle. It operates usingr-134a between 140 and 400 kPa. The refrigerant exits the compressor (and enters the condenser) assaturated vapor. It also leaves the condenser as saturated liquid.a. Sketch the P-v and T-s diagram of this cycle. Define the coordinate properties of each state oneach graph.b. Evaluate the specific heat and specific work properties of each (in kJ/kg). Indicate the sense.c. Evaluate the coefficient of performance using the specific heats and works from the previousitem. Did it match with the COPR obtained if you used the operating temperatures? Solve for states first. Then, show the solution to each of the above required in order.
2. A freezer of 20 TR capacity has evaporator and condenser temperatures of 30°C and 25°C respectively. The refrigerant R-12 is sub-cooled by 4°C before it enters the expansion valve and is superheated by 5°C before leaving the evaporator. The compression is isentropic and the valve throttling and clearance are to be neglected. If a six-cylinder, single acting compressor with stroke equal to bore running at 1000 r.p.m. is used, determine: A- C.O.P. of the refrigerating system, B- Mass of refrigerant to be circulated per min, C- Theoretical piston displacement per minute and D- Theoretical bore and stroke of the compressor.
A refrigerator operating using vapor-compression cycle uses R-134a as a working fluid. The condenser temperature is 65oC and the evaporator temperature is -15oC. The compressor operates at 80% efficiency. Suppose that we replace the expansion valve in the vapor-compression cycle with a turbine that operates at 80% efficiency. Determine the coefficient of performance of the refrigeration cycle. Provide the new state properties (i.e. H, P, T and S) for this changes and use CATT for any values needed
SUBJECT: THERMODYNAMIC COURSE: II ASSI.LACTURE: NATIQ ABBAS Example 2:- Refrigerant-134a enters the compressor of a refrigerator as superheated vapor at 0.14 MPa and -10°C at a rate of 0.05 kg/s and leaves at 0.8 MPa and 50°C. The refrigerant is cooled in the condenser to 26°C and 0.72 MPa and is throttled to 0.15 MPa. Disregarding any heat trans fer and pressure drops in the connecting lines between the components; determine (a) the rate of heat removal from the refrigerated space and the power input to the compressor, and (b) the coefficient of performance of the refrigerator. Solution: - P 0.14 MPa T=-10 C dut 246.36 kJ/kg OF P 0.8 MPa h2 = 286.69 kJ/kg P 0.72 MPa T= 26 C h3 = 87.83 kJ/kg h3 = h = 87.83 KJ/kg h4 = h3 (throttling) h4 87.83 kJ/kg 0.8 MPa 0.72 MPa/ 26 C 0.15 MPa 0.14 MPa -10°C SUBJECT: THERMODYNAMIC COURSE: II ASSI.LACTURE: NATIQ ABBAS SAMARRA RING
SUBJECT: THERMODYNAMIC COURSE: II ASSI.LACTURE: NATIQ ABBAS Example 2:- Refrigerant-134a enters the compressor of a refrigerator as superheated vapor at 0.14 MPa and -10°C at a rate of 0.05 kg/s and leaves at 0.8 MPa and 50°C. The refrigerant is cooled in the condenser to 26°C and 0.72 MPa and is throttled to 0.15 MPa. Disregarding any heat trans fer and pressure drops in the connecting lines between the components; determine (a) the rate of heat removal from the refrigerated space and the power input to the compressor, and (b) the coefficient of performance of the refrigerator. Solution: - P 0.14 MPa T=-10 C 212 h 246.36 kJ/kg da OF SAMARRA P 0.8 MPa VER h2 = 286.69 kJ/kg O P 0.72 MPa T= 26 C hg = 87.83 kJ/kg h3 =h = 87.83 KJ/kg h4 = h3 (throttling) h4 87.83 kJ/kg 0.8 MPa 50°C 0.72 MPa/ 26 C 0.15 MPa 0.14 MPa -10°C SUBIECT: THERMODYNAMIC COURSE: II ASSI.LACTURE: NATIQ ABBAS RING
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1. A refrigeration system operates on an ideal vapor compression using R-12 with an evaporator temperature of -30°C and condenser exit temperature of 49 30 °C and requires 74.6 kW motor to drive the compressor. What is the capacity of the refrigerator in tons of refrigeration? Enthalpy at condenser entrance = 382 kJ/kg, exit = 248.15 kJ/kg, at evaporator entrance 248.15 KJ/kg, exit = 338.14 kJ/kg.
1.A vapor-compression refrigeration system, using R-134a, is being used to keep a food storage room under desired cold temperature. At steady state conditions, the evaporator temperature is 0°C, and the condenser temperature is 48°C. The cooling load on the refrigeration system is 8 tons of refrigeration. Calculate the refrigerant flow rate, the compressor power if the compressor efficiency is 78%, and C.O.P.