Experimental Investigation And Theoretical Analysis Of Blockage In CO₂ Safety Valves And Their Downstream Pipes

As an environment-friendly working fluid, carbon dioxide (CO₂) has gained increased interest in refrigeration applications. Safety valves are required to protect these systems from overpressures, where the fluid upstream the safety valve is supercritical fluid or vapor-liquid two-phase mixture under the pressure of 3¹6 MPa. Since the triple point pressure of CO₂ lies between the atmospheric pressure and the system working pressure, solid CO₂ might be formed and further freeze and/or block the releasing path. The freezing and blockage of the CO₂ safety valve is one of the key problems to be solved in order to marketing the CO₂ refrigeration system. This paper has done some exploratory research on it.In order to verify the possibilities of blockage during releasing, an experimental observation was made by applying meanders and sudden expansion pipe as worst releasing flow condition, and the the possibilities and danger of the blockage in the downstream pipe was studied.An experimental setup was built to study the freezing and blockage characteristics during the throttling release of two-phase CO₂ under the room temperature. Needle valves were used to substitute safety valves and study the effect of valve opening and upstream vapor quality on the freezing and blockage characteristics. Transparent double glass tubes were used to simulate...