Experimental Performance Investigation of New Low-GWP Refrigerants for Use in Two-Phase Evaporative Cooling of Electronics

With growing global warning concerns on the current breed of HFC refrigerants, a search for more environmentally-friendly fluids has already begun. Potential alternatives to replace R134a should have significantly lower global warming potential (GWP), operate at similar system pressures, and maintain all other advantages of R134a (non-flammability, dielectric properties, etc.). This study investigates four possible alternatives that have been identified by AHRI in its Low-GWP Alternative Refrigerants Evaluation Program. These refrigerants were R1234yf, R1234ze, N-13a (HDR-17), and N-13b (HDR-15). Each of these refrigerants was experimentally examined and compared to R134a in a two-phase pumped loop cooling system using a specifically designed test stand. This test stand included a liquid pump, an evaporator with a heating component, and an air-cooled condenser. For each test, refrigerant volume flow rate was varied to achieve the desired exit quality at a specified heat load while maintaining a constant amount of subcool. The heat loads were varied from 500 W to 1000 W while the exit quality ranged from 30% to 80%. R1234yf required substantial volume flow rate increases to achieve similar cooling effects as R134a; however, R1234ze, N-13a, and N-13b appear to be much more viable solutions, due to smaller increases in volume flow rate required. A number of variables were examined to determine the thermal performance of each refrigerant, including cold plate surface temperatures, cold plate inlet and outlet refrigerant temperatures, and heat transfer coefficients. At 30% exit quality and a heat load of 500 W, R1234yf, R1234ze, N-13a, and N-13b required 33.13%, 13.14%, 12.54%, and 9.35% higher volume flow rates, respectively, compared to R134a. At 80% exit quality and 1000 W heat load, these differences were 36.65%, 13.61%, 15.12%, and 8.67%, respectively. Increases in required flow rates also resulted in higher pump power consumptions and increased system pressure drops compared to R134a