Experimental research on the two-phase flow nozzle performance of the ejector for carbon dioxide

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.

Natural refrigerant such as carbon dioxide which is a safe refrigerant without toxicity and flammability attracts attention from a viewpoint of environmental load-reducing. However, the energy loss at the expansion valve in carbon dioxide refrigerant cycle is three times larger than that of the usual cycle using refrigerant R-134a. The two-phase ejector is one of those devices which improve Coefficient Of Performance (COP) by using the expansion energy of the refrigerant. The object of the present paper is to elucidate the twophase flow nozzle performance of carbon dioxide from the experiment using the precise measurement of the pressure along the nozzle. It is found by the present experiment that the maximum energy conversion efficiency of two-phase flow nozzle for carbon dioxide is about the order of 95%. The experimental results show that there is some suitable length in divergent section of two-phase flow nozzle. In the shortest nozzle, the pressure decreases from the saturation are measured at the nozzle throat because of requirements for large superheat of liquid refrigerants. Those experimental results will be utilized for the design of the two-phase flow ejector using carbon dioxide as a refrigerant.