The Performance Research Of Evaporative Cooling Heat Exchanger

The heat and mass transfer of evaporative cooling heat exchanger process is complicated. Many researchers studied how to enhance the performance of heat and mass transfer of the equipment, through analyzing the influence of different factor, and adopting the experiment combined with numerical model and the simulation software for analysis. At present, there is no accurate computational formula for the design of evaporative heat exchanger, empirical correlations is mostly adopted in actual application. In this paper, evaporative cooling heat exchanger is studied through the combination of experiment and theory.According to the basic theory of heat transfer and thermodynamics, the model is simplified, and a mathematic model of the evaporative cooling heat exchanger is established.The changing circumstance of temperature and enthalpy value of the internal of the equipment, import and export and periphery of the coil is analyzed. Some existing heat and mass transfer coefficient correlations are given.This paper mainly studies the influence of spray water density, face velocity on the surface of the coil and air parameters on the heat and mass transfer performance of the equipment. The test platform of a small size evaporative cooling heat exchanger was set up for the experimental research, and the enthalpy different laboratory is used to control temperature and humidity. Experimental conclusions are as the followings:(1)For the determination of the structure of the equipment,the spray density has lager effect on the overall heat transfer performance and litter effect mass transfer. The best circulating water spray density of the equipment is 0.0314kg·m-2·s-1, and the overall heat transfer performance of the equipment can achieve maximum.(2)The total heat transfer coefficient and mass transfer coefficient increase with the increase of wind speed. In experimental range, when wind speed is 3.04m/s, the total heat transfer coefficient curve appeared inflection point. The wind speed is continued to increase, but the increase of the total heat transfer coefficient is not obvious. From the total heat transfer coefficient and mass transfer coefficients overall analysis, the best wind speed scope of the equipment is 3.04 m/s ~ 3.22 m/s.(3)When the wet bulb temperature is reduced, the total heat transfer is increased, the heat and mass transfer coefficient of the equipment is slightly increased. When the wet bulb temperature is rised to 28℃ from 22℃, the total heat transfer is reduced to 9804 W from 14876 W, the total heat transfer coefficient is reduced to 576 W·m-2·k-1 from 599 W·m-2·k-1. When the import relative humidity is reduced, the heat and mass transfer process of the equipment will be promoted, so is the heat and mass transfer coefficient. When the relative humidity improved to 85% from 55%, the heat transfer coefficient of the equipment reduced by 7.8%.(4)Through the analysis of the experiment and theory, the water film heat transfer coefficient is between relational calculation values at domestic and abroad. The water spray, coil diameter, spray water temperature and air mass flow will affect the heat transfer coefficient of water film. The mass transfer coefficient is higher than relational calculation values The mass transfer coefficient is determined by the quality of the air flow rate, and combined with comparative analysis based on the experimental data, we fit the mass transfer coefficient correlations.In the actual experiment, there are difficulties in the measurement of the experimental data and observation of the experimental phenomenon, two-dimensional, steady and incompressible model are established.The FLUENT modules of the ANSYS software are applied, to simulate the air flow, distribution of temperature and pressure changes with the change of spray water and the head-on air volume within the equipment. When the face velocity of the coil surface is 3.0 m/s, the spray water flow rate is 0.036kg·m-2·s-1, the performance of the heat exchanger is better, When the equipment running constant, the temperature of the air outlet is lower than the inlet temperature which conforms to the experimental data.By adopting the method combined the theory with the experiment, the best spray density and face velocity and the influence of air parameters on the heat and mass transfer of the evaporative cooling heat exchanger are obtained. The main influencing factors of heat and mass transfer parameters of water film surface are got. It can provide reference for evaporative heat exchanger design and research in the future.