Experimental Research On CO₂ Sinple Tube Pool-Boiling Heat Transfer

As more and more international researches have concerned on natural working fluid CO₂ transcritical cycle, improvement of each refrigeration cycle's part performance and the promotion of its practicality all become the key problems of current concerning research. Through theoretical analysis in the thesis, combined with experimental research, CO₂ pool-boiling evaporator was studied.Through calculation and comparison boiling correlations outside-tube with those of in-tube, it is found that CO₂ pool-boiling heat transfer coefficient is much higher than in-tube heat transfer coefficient. The analysis results also supply the basic data for the comparison with experimental data.The thermo-physical properties of carbon dioxide in the subcritical region are analyzed and compared with those of the conventional refrigerants in this thesis. Dry-up phenomena of CO₂ in-tube boiling heat transfer is analyzed, the characteristics CO₂ nucleation growth mechanism are investigated. The concept of CO₂ pool-boiling evaporator is presented. All the above studies can help to understand the theoretical for designing CO₂ pool-boiling evaporator in high efficiency and practicality.A CO₂ single tube pool-boiling evaporator was designed and made by ourselves. The primary CO₂ heat pump system was improved. Through experiment research on CO₂ single tube pool-boiling heat transfer, the relationship of heat transfer coefficient variety with heat flux and pressure was found, and compared with the experimental correlations. The experiment data are closed to theretical results of Cooper correlation, average error is 9.85%. The behaviors of bubbles in the experiment of CO₂ pool-boiling were observed. Finally, an experimental correlation of CO₂ single tube pool-boiling and a diagram of evaporator heat transfer coefficient is summarized in this thesis. All the results will give helps for study and design of CO₂ pool-boiling evaporator from experiments and data.