Numerical Simulation And Applications Of Direct Evaporative Cooling System

With the development of human society, people's standard of living improves unceasingly, and the air conditionings become a necessity for people's living. But with the popularity of air-conditioning, human society faces new challenges. While the air conditionings give us comfortable life and working conditions, it also consumes massive energy. The refrigerating medium used for the traditional machinery refrigeration leaking into the atmosphere, will destroy the ozone layer, and accelerate the formation of green house effect; The outbreak of SARS in 2003, also aroused people's concern to the safety of air-conditioning systems. Direct evaporating cooling air-conditioning acquires energy from water evaporation. Comparing with mechanical refrigeration, it does not need work done during compression. Using water as refrigerating medium, it doesn't pollute the environment. Direct evaporative cooling is an air-conditioning mode taking advantage of energy-saving, environmental protection and health, and got the favor of HVAC.This paper researches the direct evaporative cooling air-conditioning , using of heat and mass transfer theories, hydrodynamics, aerodynamics, and other related theories, adopting analogue experiment means and the computer simulation technology. The structure of direct evaporative cool air-conditioning, mechanism of heat and mass transfer, and the major factors impact of direct evaporative cooler performance are synthetically studied in this paper.(1)With the theoretical analysis and calculation of direct evaporative cooling air-conditioning of heat and mass transfer, the relationship between cooling efficiency and its influencing factors are studied.(2) Analyzing characteristic property of direct evaporative cooling, according to heat and mass transfer theory, hydromechanics, aerodynamics, and other relevance theories, structure mathematic model of direct evaporative cooling air-conditioning is established, Selecting and using CFD commercial software FLUENT, the direct evaporative cooling process is simulated. With numerical simulation and experiment research, different conditions are made by changing filler thickness, air velocity and the states of air inlet. Filler thickness and air velocity can directly affect the evaporative cooling work performance. Temperature drop and cooling efficiency will increase as the filler thickness (air velocity reducing) increasing. Dry-bulb temperature, wet-bulb temperature and relative humidity have little impact in the direct evaporative cooling efficiency, but temperature drop and psychometric difference will increase as the dry-bulb and wet bulb temperature difference increasing.(3)In order to broaden the application of direct evaporative cooling, this paper analyses the application of direct evaporative cooling in fresh air pretreatment and multi-stage evaporative cooling. This paper constructs liquid desiccant evaporative cooling systems, introduces liquor desiccant and regeneration process, propose several models of desiccant evaporative cooling systems. The results show: fresh air desiccated before mixed with return air should save more energy than reverse procedure. Using return air indoor as renewable air, which not only strengthen the pre-cooling of air, recycling the energy of return air, but also improve the efficiency of regeneration, and lower energy consumption.