Preliminary experimental investigation on a transcritical R744 condensing unit using the novel PWM ejector

In this work the preliminary experimental performance study on an innovative control technique for two-phase ejectors in transcritical R744 condensing units is presented. Currently two-phase ejectors cannot be properly capacity controlled without sacrificing ejector and system efficiency in these units. The novel capacity control methodology involves the pulse-width modulation (PWM) of the refrigerant flow through the ejector. At the compressor speed of 50 Hz, water temperatures at the gas cooler inlet between 30 °C and 40 °C and R744 evaporating temperature of roughly -5.5 °C, the collected data revealed that the discharge pressure can be appropriately controlled as well as increased by up to about 28 bar. Also, at the optimum operation conditions the unit with the PWM ejector presented enhancements in coefficient of performance (COP) by between 10.0% and 12.1% over the system using the passive ejector and by between 23.7% and 31.2% compared to the solution with flash gas by-pass valve. Finally, the proposed methodology presents low cost, simplicity, low vulnerability to clogging and much more significant potential than its today’s available competitors.