广东美的制冷设备有限公司

Small-diameter heat exchangers for air conditioning can reduce cost and refrigerant charge,which is of great significance for realizing energy savings and emission reduction.In this study,the plate fins of a 5 mm single-row air-conditioning condenser are optimized to replace a 7 mm single-row air-conditioning condenser.The optimization variables are tube spacing,fin width,and fin spacing,and the objectives are to maximize heat transfer and minimize air-side pressure drop and cost.The Taguchi method was selected for the experimental design and single-objective optimization,and the grey relational analysis and comprehensive performance index method were used for multi-objective optimization.The final optimum tube spacing,fin width,and fin spacing were 16.0 mm,16 mm,and 1.4 mm,respectively.The heat transfer was the same as that of the 7 mm tube condenser.The pressure drop was reduced by 35％,and the cost was reduced by 26％,validating the effective replacement of the 7 mm condenser.

The two-phase distribution uniformity of a refrigerant is an important factor affecting the heat exchanger performance.To address the poor uniformity of the liquid phase in the vertical header of the microchannel heat exchanger,a design scheme of a two-stage distribution header is proposed.The gas and liquid flow ratios of each branch under different dryness and total mass flow rates are compared by two-phase refrigerant distribution testing.The top branch of the empty header does not have a sufficient amount of liquid,while the bottom has excess liquid.The relative standard deviation(RSD)of the liquid phase for each branch is larger than 95％.The multiflow header uses the bottom inlet cavity to distribute the liquid,and then the liquid flows upward in the multiflow channel and enters the annular cavity through the side outlet hole.The liquid RSD of each branch is larger than 60％.When the core flow-regulated cavity and top distribution cavity are added into the multiflow header,the distribution performance is satisfactory,with RSDs of liquid and gas phases below 5％and 15％,respectively.

Electronic expansion valves(EEVs)in air conditioner systems may induce serious flow noise when the refrigerant flows into them with unstable two-phase flow patterns.The addition of a flow pattern regulator in the flow path of an EEV is expected to stabilize the refrigerant flow pattern,thereby reducing flow noise.Therefore,determining the influence of flow pattern regulators on the flow noise of EEVs is essential for optimizing their structural parameters.In this study,a method for flow pattern simulation was verified through experiments.Then,the influence of the structural parameters of the flow pattern regulator,including the hole interval,thickness,and hole diameter,on the flow noise of the EEV under the typical unstable slug flow pattern was determined.Finally,the structure of the flow pattern regulator was optimized by reasonably combining the parameters to minimize the flow noise of the EEV.The results showed that the flow noise increased as the hole interval increased,whereas it initially decreased and subsequently increased as the thickness or hole diameter increased.The hole diameter is the most important factor affecting flow pattern regulation,and flow noise can be significantly reduced by appropriately designing the hole diameter.Under the working conditions of this study,noise was reduced by 6.88 dB.

In order to improve the power density of the air conditioner, it is necessary to increase the operating frequency of the switching tube to reduce the volume of the passive device. Based on the working principle of Power Factor Correction（PFC）, the root cause of power device heating after HIGH frequency PFC is analyzed. By improving the control method and selecting more matched power devices, the power dissipation was reduced, which was verified by using an air conditioner with 7.2 kW of refrigeration capacity as the load of PFC for experiments. Compared with the existed technical solutions, the IGBT temperature of the PFC circuit can be reduced by more than 15℃ after using the control method and the design scheme, and the temperature of the fast recovery diode can be reduced by more than 10℃.

In this paper, the boiling heat transfer characteristics of the new R32 alternative refrigerant with low pollution, high energy efficiency, poor flammability and low toxicity are investigated under low-temperature conditions in horizontally orientated tubes. The flow boiling system is established and applied to study the R32 flow boiling heat transfer and pressure drop in small-diameter tubes with 3 mm and 4 mm diameters in horizontal orientation. The impact of mass flow rate, heat flux, saturated temperature and vapor quality on the R32 two-phase thermohydraulic performance is experimentally considered. The heat transfer jeopardization by the dry-out mechanism is also observed. The result shows that the heat transfer coefficient of the 3mm tube can be improved by 8%～12% compared to that of the 4mm tube while the critical heat flux is independent of tube diameter at a high flow rate. Meanwhile, compared with heat transfer characteristics, R32 saturation temperature is more sensitive to the two-phase flow resistance, the resistance loss increases by about 23% when the saturation temperature is reduced from 13 ℃ to 11 ℃. Finally, the corrected Fang’s correlation is applied to precisely predict the two-phase heat transfer coefficient of R32 in which over 88.56% of data can be controlled within the error of ±10%.