Experimental analysis of various expansion devices for subcritical CO2 condensing units.

The aim of this investigation is to experimentally compare the performance of three different expansion devices operating in subcritical CO2 condensing units. The first considered expansion device was the conventional high pressure expansion valve (baseline). The second evaluated expansion device was an<br/>ejector relying on the novel pulse-width modulation (PWM) technique to modulate the refrigerant flow effectively. Finally, the PWM approach was used for controlling the ejector motive nozzle while the refrigerant was not allowed to be drawn by the ejector suction nozzle. The results showed that the PWM motive nozzle offers similar effectiveness to a conventional high pressure valve in subcritical regime. Also, it was observed that the PWM ejector could control the high pressure effectively as well as increase the energy efficiency by up to 5.3 % compared to the baseline in transition regime. No need for the installation of the<br/>conventional high pressure valve was observed.