Theoretical And Experimental Research On Key Technology Of Refrigeration And Heat Pump Systems Based On Refrigerant Decrease And Substitute

As the international community pays more and more attention to the ozone layer depletion and global warming, refrigerant decrease and substitute is becoming a focus in research of the refrigeration and heat pump industry. This thesis mainly brings out two methods of substituting refrigerant: the decreasing & technology and permanent substitutes. We have also made some theoretical and experimental study on the key technology of these two methods.According to a large number of statistics, we have found that adopting the falling film evaporation in large and medium-sized heat pump systems reduces refrigerant charge by 30% compared with the widely used flooded evaporation. So the falling film evaporation has good prospects of application. Based on this, we established a heat transfer model and did simulation calculation on the flooded evaporation and falling film evaporation. And the results show that the heat transfer coefficient of the flooded evaporation and falling film evaporation increases with the rising heat flux and evaporation pressure. However, for the dry falling film evaporation, film Renault number is an important factor. As the film Renault number increases, there will be a critical value for the dry-out phenomena, and the heat transfer coefficient increases before reaching the critical value and then it will stay unchanged thereafter. We built up a test-bed for the horizontal single tube flooded and falling film evaporation. Through heat transfer experimental research on the two types of heat transfer, the results show that the theoretical analysis is rational and we also find that the heat transfer coefficient of falling film evaporation is 6.3% higher than the flooded type under the same conditions. In addition, this thesis gives a new correlation of heat transfer that is within a 13% deviation from the numerous data and is relatively accurate.In order to directly observe the heat transfer mechanism of the two heat transfer models, we made the visual test-bed. Through observing and analyzing the flooded boiling phenomena, we find that bubbles of the nucleus of boiling on the heating surface can be stable and unstable; the lasting time from the bubble occurring to the bubble departing the wall is about 4ms-5ms; the bubble diameter while departing is between 1.4-1.8mm; flooded boiling generates larger bubbles than the falling film boiling and the bubbles need more time to depart the surface; the convection and boiling interruption phenomena in falling film boiling is more evident, but the dry-out tends to occur when the heat flux is large.In the permanent substitute scheme, this thesis adopted the two–stage CO₂ cycle and came up with the designing and manufacturing of the key parts of the two-stage CO₂ rolling piston compressor. Analysis of the two-stage cycle shows that the efficiency of the two-stage cycle is 12-25% higher than the single stage cycle. This thesis made dynamic analysis and finite-element analysis on the two-stage compressor and the results show that when the compressor starts to exhaust, every part suffers the largest intensity of bearing and the distortion of low-pressure compressor is worse than the high-pressure, especially the eccentric part of the low pressure, which offers references for the optimization design. The simulation on the temperature of two-stage compressor indicates that the exhaust temperature is not high because of the intermediate cooling of the two-stage compression and the temperature of the compressor body is lower than 60℃.In order to test the CO₂ two-stage rolling piston compressor, we designed the test-bed for the compressor and did tests for the low pressure stage, high pressure stage and two-stage compressor. The test results show that the compressor operates smoothly and the efficiency of the low pressure stage and high pressure stage is 35% and 45⁷5% respectively. Further more, we brought out the implement plan to increase the efficiency.