New Types of Low Global Warming, Energy Efficient Refrigeration Architectures Using a Trans-Critical Rotary Pressure Exchanger

CO₂ refrigeration has been a strong candidate for ultra-low global warming refrigeration. However efficiency of a transcritical CO₂ refrigeration cycle suffers in hotter ambient due to the excessive amount of flash gas produced that needs to be re-compressed back to high gas cooler pressure. Exergetic analysis of such a cycle indicates that a large amount of exergy is destroyed through entropy production during the throttling across a Joule-Thompson valve. To solve this problem, this paper presents new CO₂ refrigeration architectures using a novel rotary Trans-Critical Pressure Exchanger (TCPX) to achieve high cycle efficiencies. TCPX reduces compression work required by the cycle using a direct fluid-to-fluid pressure exchange between high-pressure supercritical CO₂ and low-pressure gaseous CO₂, that takes place within its rotary ducts, thus allowing for an efficient pressure recovery. A TCPX placed between the gas cooler and receiver/evaporator serves simultaneously as a compressor and as an isentropic expansion device all within a single rotary device. It utilizes acoustic compression waves generated in a multi-ducted high-speed rotor to compress the low-pressure CO₂ without requiring external mechanical energy input and simultaneously expands high-pressure supercritical CO₂ to produce a two-phase, cold fluid stream ready for heat absorption. Various refrigeration architectures integrated with this TCPX are designed and the energy savings provided by TCPX are evaluated.