Thermocompressors are widely used in a large number of industries that use steam as their heating medium or as a power generating utility. They are devices that use the energy of a high pressure fluid to move a low pressure fluid and enable it to be compressed to a higher pressure according to the principle of energy conversion. They work like a vacuum pump but without usage of any moving part and so they can save energy. The performance of a thermocompressor highly depends on its geometry and operating conditions. This paper first describes the flow behavior within a designed model of a thermocompressor using the computational fluid dynamics code, FLUENT. Since the flow is turbulent and supersonic, CFD is an efficient tool to reveal the phenomena and mixing process at different part of the thermocompressor which are not simply obtained through an experimental work. Then its performance is analyzed by choosing different operating conditions at the boundaries and also different area ratios which is one of the significant geometrical factors to describe the thermocompressor performance. Finally, the effect of various nozzle exit plane diameters which cause different Mach numbers at the nozzle exit is investigated on the thermocompressor performance. The results indicate that these variables can affect both the entrainment ratio and critical back pressure. This device uses water vapor as the working fluid and operates at 7.5 bar motive pressure, 63°C and 80°C for suction and discharge temperatures, respectively
