Date of Award

Fall 1992

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

S. K. Chaturvedi

Committee Member

A. S. Roberts

Committee Member

S. N. Tiwari

Call Number for Print

Special Collections; LD4331.E56E75

Abstract

In this study, thermal performance of heat pump cycles is analyzed by employing several equations of state. The analysis presented here is particularly useful for applications where refrigerant properties need to be calculated from a thermodynamic equation of state. Such a situation, for example, would arise during a long-term numerical simulation of a solar-assisted heat pump system. In these cases, the direct use of thermodynamic property tables of refrigerants would not be possible in a computational procedure. The approach of using equations of state to predict thermodynamic properties is also useful for applications where new refrigerants or blends of refrigerants are to be used for various refrigeration and heat pump applications. In these cases, lack of refrigerant property data makes this approach attractive for thermal performance analysis of heat pump cycles.

Five different approaches, employing Redlich-Kwong (R-K), Peng-Robinson (P-R), and Carnahan-Staling-Desantis (CSD) equations of state, were used to predict the thermodynamic properties of refrigerant R-22 and R-152a, chosen here for illustration. In the unmodified R-K and P-R approaches, respective equations of state were used to predict vapor pressure, fugacity, enthalpy, and entropy of refrigerants. To improve the accuracy of predictive capabilities of these equations, the procedure was modified to include an empirical vapor pressure equation. In the modified approach, the R-K and P-R equations of state were used in conjunction with the Reidel vapor pressure equation to predict properties such as enthalpy and entropy. This modified procedure resulted in reasonably accurate prediction of refrigerant properties of R- 22 for both liquid and vapor states. The modified procedure using the Peng-Robinson equation of state with Reidel equation for vapor pressure yielded best results while the unmodified Redlich-Kwong equation of state yielded results that deviated significantly from data.

Comparison of results for these five methods and the R-22 property data from the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Handbook was conducted. It is noted that the modified Peng- Robinson and Carnahan-Staling-Desantis equation of states both predict. results that are in best accord with ASHRAE data for R-22. However, for R-152a the modified P-R approach was able to predict refrigerant property values with less error than the CSD method. A computer code, employing different equations of state, was developed to analyze numerically the thermal performance of a basic heat pump cycle.

Results obtained from various equations of state were compared with a cycle analysis using ASHRAE data for R-22. Finally, the computational technique developed in this study was applied to a solar-assisted heat pump cycle to study the effect of compressor capacity modulation on the transient system thermal performance.

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DOI

10.25777/x1a6-hn67

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