The Theoretical Calculation And Optimal Design Of Direct Evaporative Colling Media

This paper took the direct evaporative cooling media as the main research object on the base of the general mathematical calculation model of evaporative cooling equipment presented by Halasz Boris. Based on the principle of conservation of energy and principle of conservation of mass, we took a considering of the influence of the system caused by the water quality change in the process of water evaporation or condensation when we built the model. We set up a mathematical calculation model of direct evaporative cooling (DEC) media by adopting micro element method that described in detail in the process of inner relation of air and water contact which were more tally with the actual situation. Based on this, we verified the accuracy of the calculation model, through further experimental data and related references data. A good agreement between the experiment and calculations with deviation less than±15% was demonstrated. The experiment result was coincident with that of the calculations. And it demonstrated the mathematic calculation model is reasonable and effective.We did further analysis of resistance by using the numerical simulation method. Using GAMBIT software to build three dimensional numerical mode of a media and combining with the corresponding discrete phase, we solved the model by using FLUENT software that based on the air and water flow stat of the media. Among them, we used water droplets to do simulate calculation of the liquid membrane in the packing. Those equations were solved with Euler method that supposed the air as continuous phase. And it were solved with Lagrange method that supposed the water droplets as dispersed phase. According to the calculated results, we got equations about resistance coefficient, Reynolds number, Liquid Webber number, and the dimensionless flow parameters by mathematical fitting method.Through analyzing the inner relationship of the structure parameters of media, got a approximate calculation formula to calculate the surface of media. At the same time, we defined a comprehensive performance as the judgment of the performance of media. Using the ratio of an unit refrigerating capacity and the work per unit time of resistance to reflect comprehensive performance of media. In the same conditions, changing the corrugated length and wave height, through using the formula of no dimensional mathematical model of thermodynamic to calculate the refrigerating capacity and using simulation software calculate the resistance of the air, also the comprehensive performance is calculated accordingly. The calculation results show that, within constraints, under the condition of wave height not change, the wave height 30mm of media has the largest comprehensive performance coefficient, with the value of 0.73;under the condition of corrugated length not change, wave height 6mm of media has the largest comprehensive performance coefficient, with the value of 1.47.