Research On Pool Boiling Heat Transfer Of Carbon Dioxide Single Tube Electricity Heating

For the deterioration of ozone depletion and greenhouse effect, natural working fluidcarbon dioxide is attracting much more attention. Increasing the heat exchange efficiency ofthe evaporator is one of the ways to improve the efficiency of carbon dioxide refrigerationsystem. Dry-out phenomenon is easy to occur when carbon dioxide liquid is boiling in tube,but this is not exist in boiling heat transfer outside tube, carbon dioxide has a less surfacetension, it is easy to boil at the same evaporation pressure, and has a higher pool boilingheat transfer coefficient. Pooling boiling heat transfer of carbon dioxide is studied in thispaper.(1) The thermo-physical properties change of carbon dioxide in critical region areanalyzed in the paper, and comparisons of carbon dioxide thermo-physical properties areconducted with natural refrigerant ammonia and propane in subcritical region, obtainingthat it is of better transportability and fluidity of carbon dioxide.(2) Common correlations of pool boiling heat transfer are summarized, influencingfactors of pool boiling heat transfer are analyzed, and a simplified correlation of carbondioxide heat transfer is attained. And it is compared with other heat transfer correlations,resulting in a good agreement. The methods, using to enhance pool boiling heat transfer, aresummarized in the paper.(3) The experimental section is designed, adopting single tube and electricity heating.The experimental device of carbon dioxide electricity heating pool boiling heat transfer arePut up. The experimental study of carbon dioxide single tube electricity heating poolboiling evaporator is conducted, obtaining the relationships between pool boiling heattransfer coefficient, evaporating pressure and heat flux at status of a horizontal plain tube.The pool boiling heat transfer correlations are fitted with experimental data at fourevaporating pressure. Finally the experimental data is compared with pool boiling heattransfer fitted correlation. The maximum deviation is within13.5%.(4) Visualization research of carbon dioxide pool boiling heat transfer is conduct, thebehaviors of bubbles in the experiment of carbon dioxide pool boiling were observed.Through analyzing the visual photos shows that the bubble detachment rate increases withthe increasing of heat flux.