Experiments on vapour-liquid equilibrium of CO2-ionic liquid under flow conditions and influence on its refrigeration cycle

Abstract

CO2 is a potential alternative refrigerant because of its excellent thermodynamic properties and environmental friendliness, but its high operating pressure in the refrigeration cycle limits its wide application. To reduce the operational high pressure of the conventional CO2 compression refrigeration system, a novel CO2 compression-absorption refrigeration system with ionic liquid (IL) as absorbent was proposed. The IL [emim][Tf2N] was selected and combined with CO2 as a working pair. Experimental investigations on the dynamic vapour-liquid equilibrium of CO2-[emim][Tf2N] under flow conditions and the influence on its refrigeration cycle were conducted. The effects of solution pump frequency, CO2 inlet temperature and pressure, and system pressure ratio on the key parameters such as depressurization amplitude, absorption completion and desorber temperature were investigated. Within the working conditions of this study, the system operational high pressure could be reduced by 29% at most, and the absorption completion of CO2-IL mixture at the absorber outlet could reach about 70%. It was found that both CO2 inlet pressure and temperature had important effects on the key parameters, and a larger pressure ratio could obtain larger depressurization amplitude and absorption completion and lower desorption temperature. These provide a reference for further optimizing system design and improving system performance.