Date of Award

Spring 1-1-2013

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Mathison, Margaret

Second Advisor

Bowman, Anthony

Third Advisor

Farrar, Scott

Abstract

Low temperature (LT, -35 °C to -50 °C) and ultra low temperature (ULT, -50 °C to -100 °C) refrigeration is required in the life sciences industry for the production and storage of biological systems. The minimum practical storage temperature of a simple, single-stage refrigeration system is -30 °C, and this is incapable of meeting the requirements of biotechnology applications. Current LT and ULT refrigeration systems utilize cascade systems, which are combinations of single-stage refrigeration systems operating at successively lower temperatures. Because they use multiple compressors, cascade systems have higher capital and operating costs than simple single-stage vapor compression refrigeration systems. Equipment operating costs of LT and ULT refrigeration contribute significantly to the operating costs of biotechnology companies and therefore motivate the development of lower cost, higher performance refrigeration systems.

One approach to achieving greater efficiency is the development of single compressor systems that utilize a refrigerant mixture and a condensing separator. After compression, the refrigerants are separated and follow refrigeration cycles similar in working temperature and pressure to cascade systems to achieve the desired temperature and heat load capacity. The refrigerant mixture streams are combined at the suction side of the compressor and compressed again to complete the cycle. This concept has the benefit of using a single compressor to reach low temperatures rather than the multiple compressors used in cascade systems.

This work addresses the modeling, analysis and testing of a single compressor mixed refrigerant system (MRS) for low temperature applications. A model will be developed using first and second law principles of thermodynamics to calculate the refrigeration capacity, power consumption, coefficient of performance (COP), and second law efficiency. The model results will be validated through comparison with experimental results for a prototype system under steady-state conditions. Also, the model results will be explored to determine the impact of mixture composition on the system performance. Performance and benefits of the MRS will be compared to a similar cascade refrigeration system operating under similar conditions. The experimental performance of the prototype MRS will be used to make recommendations to advance the development of more efficient low temperature storage refrigeration systems.

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