Assignment__11

Assignment__11 - Prob 11.5 PROBLEM 11.2 PROBLEM STATEMENT A...

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Prob 11.5 PROBLEM 11.2 PROBLEM STATEMENT: A refrigeration system using refrigerant R134a is to have a capacity of 2 tons. The cycle is the ideal vapor compression cycle. The evaporator exit pressure is 0.15 MPa, and the condenser inlet temperature is 60°C. Determine the compressor power requirement in kilowatts. DIAGRAM DEFINING SYSTEM AND PROCESS: P 3 4 1 2s P 1 = P 4 T 1 3 2s 4 P 2s = P 3 s GIVEN: R134a, ideal vapor compression cycle, T 2s = 60°C, P 1 = 150 kPa FIND: ASSUMPTIONS: SFSS, NKEPE GOVERNING RELATIONS: 1. Refrigeration capacity, 2. Ideal compressor power requirement, QUANTITATIVE SOLUTION:

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From the property tables for R134a. Hence, from the two governing relations, the compressor power requirement is DISCUSSION OF RESULTS: The unit “tons” defines the total rate of cooling, . This term had its origin in the days when ice was manufactured in large plants and distributed to homes for preserving food in ice-boxes. A ten-ton refrigeration plant could produce approximately 20,000 lbm of ice per day. PROBLEM 11.5 PROBLEM STATEMENT: A Carnot engine operating between two temperature reservoirs of 817°C and 25°C rejects 20 kJ/s. The engine drives the compressor of an ideal vapor compression refrigerator whose inlet and exit pressures are 0.17 and 1.1 MPa, respectively. Calculate the coefficient of performance and the refrigerator's capacity in tons if the refrigerant is R-134a. DIAGRAM DEFINING SYSTEM AND PROCESS: Prob 11.6 T H =1090 K T C =298 K s P 1 =P 4 T 1 3 2 4 P 2 =P 3
GIVEN: Refrigerant 134a in an ideal vapor compression refrigerator P 1 =0.17 MPa, P 2 =1.1 MPa Carnot heat engine, T C =25°C, T H =817°C, FIND: Coefficient of performance and refrigeration capacity, ASSUMPTIONS: 1. Ideal refrigeration cycle (no D P in evap. or condens., reversible compressor) 2. SFSS, NKEPE GOVERNING RELATIONS: 1. 2. Coefficient of performance, 3. Refrig capacity: QUANTITATIVE SOLUTION: First, determine the power output of the Carnot engine. From the definition of h HE ,

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To determine COP, evaluate states using Table 15s and 16s, By interpolation from Table 16s, Thus: DISCUSSION OF RESULTS: This problem illustrates how cooling capacity of a refrigeration system can be related back to the fundamental energy required to obtain that cooling. By assuming a best- case scenario for the initial energy converter (the Carnot engine), the minimum amount of primary fuel consumption, , could be estimated. PROBLEM 11.6 PROBLEM STATEMENT: A vapor compression refrigeration cycle using refrigerant R134a operates with a condenser temperature of 100°F and an evaporator temperature of 40°F. The compressor has an efficiency of 65 percent and there is no subcooling of the liquid leaving the condenser. Plot the cycle coefficient of performance versus the degree of superheating of the refrigerant R134a leaving the
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This note was uploaded on 09/01/2010 for the course ME 320 taught by Professor Dr.kinne during the Spring '07 term at University of Texas.

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Assignment__11 - Prob 11.5 PROBLEM 11.2 PROBLEM STATEMENT A...

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