Explanation Write the relation between the specific enthalpies at the inlet and exit of throttling. h i = h e (I) Here, specific enthalpy of the refrigerant at the inlet of throttling is h i and specific enthalpy of the refrigerant at the exit of throttling is h e . Write the formula to calculate the coefficient of performance ( COP ) for the heat pump. COP = q L w in COP = h 2 − h 4 h 2 − h 1 (II) Here, heat removed is q L , the work input to the system is w in , specific enthalpy at the inlet of compressor is h 1 , specific enthalpy at the exit of compressor is h 2 , specific enthalpy at the inlet of throttling is h 3 , and the specific enthalpy at the exit of throttling is h 4 . Conclusion: From the Table A-12 of “Saturated refrigerant R-134a: Pressure”, obtain the specific enthalpy of saturated vapor ( h 1 ) at compressor inlet pressure of 0.32 MPa as h 1 = h g = 251.93 kJ / kg s 1 = s g = 0.93026 kJ / kg ⋅ K From the Table A-13 of “Superheated refrigerant R-134a”, obtain the specific enthalpy at the corresponding pressure ( P 2 ) of 1.2 MPa and specific entropy ( s 2 ) of 0.93026 kJ / kg ⋅ K by interpolation. Write the formula of extrapolation method of two variables. y 2 = ( x 2 − x 1 ) ( y 3 − y 1 ) ( x 3 − x 1 ) + y 1 (III) Here, the variables denoted by x and y are specific entropy and specific enthalpy. Show temperature and enthalpy values from the Table A-13E. Entropy ( s 2 ) , in kJ / kg ⋅ K Enthalpy ( h 2 ) , in kJ / kg 0

8th Edition

ISBN: 9780073398174

Author: Yunus A. Cengel Dr., Michael A. Boles

Publisher: McGraw-Hill Education

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Chapter 11.10, Problem 134FEP

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The coefficient of performance of the heat pump.

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Chapter 11.10, Problem 133FEP

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Thermodynamics: An Engineering Approach

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