Enhanced Heat Transfer Analysis And Programming Design For Evaporative Condenser

Evaporative condenser is a heat exchanger which has a high efficiency. Its comprehensive performance is superior to other types of condensers. The research on the heat transfer mechanism of evaporative condenser and structural optimization can save energy and water, which is important to our economic development.This paper is mainly a theoretical analysis, method of numerical simulation and procedure development. The following aspects are described in this paper.(1) Through the analysis of the working process of evaporative condenser, we know that the process of heat from refrigerant inside tube to air outside tube in the evaporative condenser includes not only convective heat transfer but also convective mass transfer. Coupled heat and mass transfer,the working process of evaporative condenser is very complicated.(2) Through the analysis of thermal resistance of evaporative condenser,we can know that thermal resistance of water film inside tube and condensation resistance outside tube are the most easily to be changed in evaporative condenser. Controlling or reducing both resistances is a main method of heat transfer enhancement to evaporative condenser.The theoretical analysis shows that if the vertical tube is used, it not only reduces condensation resistance, but also can make the water film outside tube more uniform, which can reduce the water film resistance. Compared the water film distribution of vertical tube and horizontal tube by method of numerical simulation, we can get the same conclusion by theoretical analysis.(3) Establishing model of vertical tube evaporative condenser and using the numerical methods to analyze the situation of heat transfer and water film distribution under different wind speed and spray density conditions,we can get some conclusions: Under the same wind speed, the water film of water-air countercurrent will be thicker than that of water-air downstream. When water-air countercurrent, the thick of water film has little change with wind speed in 1-3m/s. Follows wind speed increases, the water film is obviously thicker and more unstable. When water-air downstream, the thick of water film has little change with wind speed in 1-7.5m/s. Follows wind speed increases, the water film will be ruptured.Regardless of countercurrent or downstream, the wind speed increases will lead to increased system pressure drop and enhanced heat transfer capability under the same spray density.Under the same wind speed, the increase of spray density will lead to the increase of water film resistance and the reduce of heat transfer capability. Compared to countercurrent, downstream has better performance.(4) Condensation resistance can be reduced by the grooves arranged in the inside tube. When the refrigerant is ammonia, condensation heat transfer performance of the groove tube designed and developed in this paper is increased by 90% or more than smooth tube. When the height of the vertical tube is lm, its condensation heat transfer coefficient is increased by 50% or more than horizontal tube under the same conditions.(5) A convenient computer program can be got through programming on the curves intersect method by Visual Basic,which makes the design calculation of evaporative condenser become simpler and faster.Based on the improvement of existing methods, improved temperature drop method will be given in this paper.