Design And Visualization Experiment Research On CO₂ Supercritical Gas Cooler

With the rising consciousness of green energy-saving, CO₂ heat pump water heater has found favors with many people for its excellent properties. Theoretical analysis, simulation, design and experiments about CO₂ heat pump water heater system were studied in this research. A newly designed gas cooler with visualization device was designed and lots of experimental research and analysis were followed.Firstly, basic research of CO₂ transcritical circulating on which the CO₂ heat pump water heater depended were studied. It gave analysis of CO₂ supercritical thermal properties, supercritical heat transfer theory and the influence factors of supercritical heat transfer.The special thermal properties of CO₂ in supercritical cooling conditions and the influence of lubricating oil made it complicated to design a suitable gas cooler. Through compute simulation, selecting the appropriate heat transfer correlation, and considering the impact of oil influence on heat transfer, a new gas cooler was designed. A series of contrastive experiments showed that the new gas cooler had a enhanced performance, and the system efficiency reached 3.8 when the hot water reached 55℃. In the same pressure ratio or the evaporation temperature condition, new gas cooler heat transfer performance was be promoted. There was an optimum evaporation temperature in each system, and the optimal evaporation temperature of new gas cooler ranged from 1 to 3℃.At last the visualization equipment was designed, in which the CO₂ side used a high purity and high pressure resisting quartz glass as a mirror, and organic glass pipe in the water side. And by experimental observation using high resolution camera, CO₂/oil mixture flowing Pattern were recorded and analyzed. By observation or ordinary camera, it presented as fog. In fact, it was gas-liquid two-phase flow observed by high-speed photography. The CO₂/oil mixture show different states at different operating pressure and temperature, which provided a new basis for the study of the impact of oil on heat transfer.