| In the current situation of high-grade energy becoming more and more valuable,heat pump has been widely used in building heating and ventilation,energy,alternative collective boiler and other aspects in recent years for its advantages,such as lower pollution,energy saving and high efficiency,and convenient use.With the development of intelligent control system of heat pump equipment,the efficiency of condenser and evaporator becomes the breakthrough of heat pump energy efficiency.In the past,the research of finned tube heat exchanger was mostly flat fin,but it was restricted by the air thermal conductivity in the compact space.At the same time,for the research of casing heat exchanger equipment,the high efficiency of phase change heat transfer makes it a new research and development trend.In this paper,four kinds of slotted structures are proposed,and experiments and hydrodynamics calculations are carried out.For the spiral corrugated tube condenser,a reinforced redistributor structure is proposed.The main research and conclusions of this paper are as follows::(1)The heat transfer and resistance characteristics of finned tube heat exchanger under different inlet wind speeds were studied experimentally.The enhanced finned tube model with different slotted shapes and sizes were established,and the influence of structural parameters such as fin spacing in finned tube evaporator was studied.For the flat fin and the enhanced fin with slotted structure,the change of convective heat transfer coefficient and unit pressure drop on the air side in a certain range of Reynolds number was studied.The influence of slotted enhanced structure on the surface flow field of finned tube was compared.The dimensionless correlation between Nusselt number Nu and friction factor f is obtained according to the heat transfer and resistance characteristics of 60 different types of finned tube structures.(2)The experimental study of eight-start spiral bellows with different outer diameter was carried out under different flow rate and condensation temperature.The heat transfer coefficient of the inner side of the tube in the spiral corrugated tube condensation heat exchanger was studied and the correlation formula of Nusselt number Nu in the tube side was fitted.The influence of the structure and operation parameters such as the superheat of refrigerant inlet,the flow rate in the shell side,and the pipe diameter on the condensation heat transfer and resistance characteristics were studied by extrapolation.Through the total heat transfer coefficient,the change of condensation resistance at different Reynolds numbers on both sides were obtained.(3)According to the three-dimensional distribution of liquid phase refrigerant,the reinforced structure model of the redistributor was established.The heat transfer and resistance characteristics of the shell side of the condenser under different pipe diameter and redistributive spacing are obtained by fluent and other processing software.The local Nusselt number Nu of the strengthened tube was analyzed by Tecplot and other post-processing platforms to study the micro effect of the strengthened structure on the three-dimensional flow field.Based on the field synergy principle,the temperature field and velocity field gradient of the fin evaporator before and after strengthening were analyzed,and the field synergy angle distribution near the slot was studied by three-dimensional structure integral contour maps.According to the performance evaluation criteria PEC of heat exchanger,the economy of spiral bellows and slotted finned tubes with different structure parameters was analyzed. |
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