Admission (Economizer) Port Optimization of a Voorhees Modified Reciprocating CO2 Compressor

Abstract

Admission (the use of an economizer) is a well-known method to reduce the expansion losses of a refrigeration system. The alternative refrigerant carbon dioxide (CO2) has a relatively large isentropic exponent. Therefore, refrigeration systems using CO2 as a refrigerant have a high potential for raising efficiency by admission. Reciprocating piston compressors are favored for CO2 refrigeration applications due to the compression chamber's small sealing length and resulting low internal leakage rate. This paper presents a methodology to investigate the influence of the admission (economizer) port design of a reciprocating compressor on the admission process. The port's geometry—especially its cross-sectional area—has a large impact on the system efficiency at operation conditions and therefore needs to be optimized. For this purpose, an optimization process has been established. It is based on indicator diagram analysis. To exemplify, the measurements of three admission ports were compared at constant suction pressure (1.2 MPa relates to an evaporation temperature of −35°C) and varying admission pressures (1.4–2.6 MPa). Based on the results, the optimal port diameter for the targeted operation condition is obtained by interpolation.