Heat And Mass Transfer Performance Of Heat-source Tower Based On Packing Optimization

Sensible heat occupies the major part of total heat during winter and the heat transfer capability of heat-source tower in winter is much less than that in summer.To ensure the stable operation of heat pump system in winter,heat-source tower should be designed according to the winter conditions.Due to the problem of limited space,the volume of tower is too large which is designed on the basis of conventional cooling tower packings.According to the principle of heat and mass transfer,the specific surface area of heat-source tower should be increased to ensure larger gas-liquid contact area which leads to smaller volume of heat-source tower.It is necessary to consider how to effectively wet the surface of the packing and make use of the heat transfer area in the heat-source tower.In this article,heat-source tower is optimized from three different aspects including packing size optimization,packing surface wettability and use of large specific area packings.The results of this study provide a new idea for the optimal design of heat source tower and theoretical and experimental basis for the development of packings in heat source tower.To make full use of heat transfer area in heat-source tower,the size of packings needs to be optimized.Based on the analysis of the mechanism of heat and mass transfer in heat-source tower,the mathematical models of heat and mass transfer in heat-source tower under different working conditions are constructed.The mathematical models are used for the analysis of heat and mass transfer process between air of four different states and solution in heat-source tower.The influence of height and width of the packing on heat and mass transfer performance of the heat-source tower is studied by means of numerical simulation.It is necessary that the width of the packings should be reduced and the height of those should be increased for the design of heat-source tower.To wet the packing surface more effectively under the existing solution mass flux,the packing surface wettability needs to be improved.On the basis of the analysis of the wetting behavior of the ideal surface and rough surface,the mechanism of the falling film on the vertical plate and the influence of the pore structure on the liquid film flow are studied theoretically.The effective processing methods to improve the wettability of packing surface are proposed.The experimental device for the wettability of the packing surface is constructed.Wetted area of liquid film on unit packing surface area,film forming rate,is used as evaluation index.The hysteresis characteristics of dynamic liquid film formation are studied.And,the effects of different materials,roughness and pore structure on the film formation of the packing surface are analyzed.It is the fact that pore structure can improve the wettability of the packing surface and enhance the seepage effect of the liquid film on both sides of the packing.To reduce the volume of heat-source tower,a plastics porous corrugated plate packing which has large specific surface area and is punched with holes on its surface is proposed.It can increase the heat transfer area and improve the wettability of the packing surface.The experimental system of heat-source tower is built.And the effects of air and solution inlet parameters on the heat and mass transfer performance and flowing property of herringbone corrugated packing and porous corrugated packing are compared.The experimental correlations of heat and mass transfer coefficient in two kinds of heat-source towers are fitted.According to the study of the heat and mass transfer and flow performance of two kinds of packings,comprehensive performance is evaluated which leads to the conclusion that porous corrugated packing is more suitable for heat-source tower.The volume and pressure drop of porous corrugated packing heat-source tower is lower than those of the herringbone corrugated packing heat-source tower under the same condition.The results of this study provide a new idea for the optimal design of heat source tower and theoretical and experimental basis for the development of packings in heat source tower.