Dimethyl ether(DME)can be used as refrigerant because it has a property to liquefy easily at roomtemperature,0.53MPa. In this report, using DME as a refrigerant is numerically evaluated by a comparisoncoefficient of performance(COP)at standard refrigeration cycle and single or double stage compressionrefrigeration cycle at-30℃ between a DME refrigerant and conventional refrigerants. The results showedthat the DME refrigerant is superior as compared with conventional refrigerant in term of COP at standardrefrigeration cycle.
In the investigation of natural convection, many empirical equations have been proposed. However, almost all of them are for rarefied gas regions or over atmospheric pressure. The purpose of this study is to propose an empirical equation of natural convection heat transfer which considers the pressure dependency caused by pressure change. The pressure is given between the vacuum region and more than atmospheric pressure. In this study, the temperature field formed under the cooled disk is analyzed by an experimental measurement using laser holographic interferometry. The test section is set in a vacuum chamber, and the pressure ratio between the test field and atmospheric pressure is set as 0.1 to 2.0. The medium gas chosen here is dry air, argon, CO2, helium, and neon in order to expand the range of experimental conditions. The temperature difference between the cooled disk and the medium gas is adjusted from 30 K to 50 K every 10 K. As a result, the average Nusselt number near the cooled surface is expressed as a function of Rayleigh number in the range of 56 1× 10 < < 6 × 10 Ra .
