Paper 2174, Page 1 International Refrigeration and Air Conditioning Conference at Purdue, July 14-17, 2008 CONDENSING EJECTOR FOR SECOND STEP COMPRESSION IN REFRIGERATION CYCLES Mark J. BERGANDER 1 , PhD, P.E., Prof. David P. SCHMIDT 2 , David A. HEBERT 2 , Dr. Jerzy WOJCIECHOWSKI 3 , Mateusz SZKLARZ 3 , 1 Magnetic Development, Inc. Madison, CT, USA, Ph.: 203-421-3562, E-mail: mark@mdienergy.com 2 University of Massachusetts Amherst, MA, USA, Ph.: 413-545-1393, E-mail: Schmidt@ecs.umass.edu 3 AGH University of Science & Technology Cracow, Poland, Ph. 48-12-617-3078, E-mail: jwojcie@agh.edu.pl ABSTRACT This paper describes a novel approach to the Rankine vapor compression cycle for cooling and refrigeration. The specific innovation is the application of a two-phase device known as a “condensing ejector” (CE) for a second step of compression. The innovation has the potential of increasing the efficiency of the standard single-stage vapor compression cycle through a reduction of mechanical compression at the expense of harnessing kinetic energy of gas in the ejector device. In addition it will reduce the greenhouse gas emission by providing the same amount of cooling with less electric energy consumption. This is the continuation of the developmental work performed under the funding from the NSF and US Dept. of Energy. 1. INTRODUCTION The main objective of this project was to explore the possibility of using a condensing ejector as a second step compression in a vapor compression cycle (reversed Rankine cycle) for refrigeration and air-conditioning applications. The entire research consisted of synergistic theoretical analysis, numerical simulation and laboratory experiments. The main research activities were to: 1) develop the methodology for the design of a condensing ejector using refrigerants as working mediums, 2) confirm the theoretical model by practical experiments on the laboratory stand. The results indicated the potential for using a two-phase condensing ejector in refrigeration cycles. Our approach of using the ejector in refrigeration cycle significantly differs from prior attempts: 1) The ejector is placed after the compressor discharge to increase the final cycle pressure, while all to-date designs used ejectors for increasing the compressor suction pressure. 2) In all previous ejectors, the outlet pressure was intermediate between the pressures of motive and suction streams. Our design produces the outlet pressure higher than both inlet pressures. This is achieved by the creation of a “condensation shock”, when the vapor phase is quickly condensed onto the liquid stream, producing rapid transformation from two-phase into single-phase flow with a resulting rise in pressure. 2. THEORETICAL ANALYSIS AND NUMERICAL SIMULATION OF THE CE 2.1 Principle of the Condensing Ejector The condensing ejector is a two-phase jet device in which a sub-cooled refrigerant in a liquid state is mixed with its vapor phase, producing a liquid stream with a pressure that is higher than the pressure of either of the two inlet streams. In our new cycle, the compressor compresses the vapor to approximately 2/3 of the final pressure and additional compression is provided in an ejector, reducing the amount of mechanical energy required by a compressor and improving the efficiency theoretically by up to 35%. The theory of the condensing ejector has been known since 1970’s but all previous work was conducted on open systems. Specifically, the theory was described by Levy and Brown (1972), Van Wijngaarden (1972) and Fisenko (1986). This research is believed to be the first attempt to use such device in a refrigeration system, where inlet and outlet parameters must fall within constraints of a closed thermodynamic cycle.