Optimization of a household refrigerator considering alternative refrigerants

Michael George McKellar, Purdue University

Abstract

With the eventual ban of chlorinated refrigerants, alternative refrigerants are under consideration to supply the refrigeration needs of the industry. Introducing new refrigerants to existing refrigeration systems may decrease the thermal efficiency of the system. The goal of this research is to develop and present a method that aids in the design of new refrigeration systems considering the alternative refrigerants. Algebraic equations were developed to model a vapor compression refrigeration system. The refrigerator model was successfully combined with a multi-dimensional, non-linear, constrained, optimization search routine. Searches for optimal refrigeration system designs were performed by minimizing the sizes of the heat exchangers and the total power into refrigeration system. The sensitivity of the output from the refrigerator model to polytropic index and the compression efficiency was analyzed. As the polytropic index increases, the heat transfer to the compression process increases which in turn increases the work of compression. As the compression efficiency increases, the power into the refrigeration system decreases. The compression efficiency does not affect the work of compression. Based on the results from the combined refrigerator model and optimum search routine, the polytropic index has a greater effect on the optimal design of a refrigeration system than does the compression efficiency. Minimizing the size of the heat exchangers conflicts with minimizing the total power into the refrigeration system. Minimizing the sizes of the heat exchangers increases the pressure difference between the condenser and the evaporator, while minimizing the total power decreases the pressure difference. The irreversibilities and heat transfer within the compressor decrease as the total power into the refrigeration system is minimized. The refrigerants examined, R12, R134a, and R152a, converge to the same evaporation and condensation temperatures when the refrigerants are substituted into existing refrigeration systems. When minimizing the combined objective function of the total power and heat exchanger size, the optimal designs for the refrigerants examined have the same heat exchanger sizes and the same evaporation and condensation temperatures. The condensation and evaporation pressures and refrigerant mass flow rates are affected by the thermodynamic properties of the refrigerant.

Degree

Ph.D.

Advisors

Tree, Purdue University.

Subject Area

Mechanical engineering

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