Numerical Simulation And Optimization Of The Counter Flow Dew Point Evaporative Cooler

In recent years,the vigorous development of the construction industry has brought huge energy consumption and resources and environmental loads while meeting people’s basic housing needs.In order to reduce building energy consumption and reduce pollutant emissions,the HVAC industry,which is a large building energy consumer,should try to increase the efficiency of the use of related equipment while satisfying people’s production and living comfort.Dew point evaporative cooling technology has attracted the attention of many scholars due to its green environmental protection,economical and energy saving characteristics,and is gradually becoming a potential substitute for mechanical compression refrigeration.If the cooling efficiency of the existing dew-point evaporative cooler can be improved through structural optimization,not only can the use cost be saved,but also the energy consumption of the air conditioning system can be greatly reduced.In practical applications,the primary air inlet of a counter flow dew-point evaporative cooler is usually located on the side of the channel,and the fluid distribution in the channel is not uniform.This uneven fluid distribution makes the heat exchange space in the cooler not fully utilized,thereby reducing the cooling efficiency of the cooler.Aiming at this problem,based on the theoretical analysis of the heat and moisture transfer process of the counter-flow dew-point evaporative cooler,a two-dimensional mathematical model describing the heat and moisture transfer process inside the cooler was established,and the model was solved by the existing simulation software.The structural parameters of the counter-current dew-point evaporative cooler with side air inlet,namely the inlet length,channel width,channel length,and the ratio of the channel length to the inlet length,were explored to influence the air distribution uniformity and cooling performance.The results show that when the channel width of the cooler is 0.3m and the channel length is 1.2m,the cooling efficiency increases first and then decreases with the increase of the inlet length.Under different inlet length conditions,the channel width has different effects on the outlet temperature.When the inlet length is less than 0.15 m,the outlet temperature increases with the increase of the channel width;when the inlet length is greater than 0.15 m,the outlet temperature decreases first and then increases as the channel width increases.Increasing the channel length and the ratio of the channel length to the inlet length can improve the cooling efficiency.For a cooler with a channel width of 0.3m,the ratio of the channel length to the inlet length is recommended to be controlled between 3 and 5.Next,in order to improve the uneven distribution of fluid in the cooler,we optimized the structure of the cooler and proposed a counter flow dew-point evaporative cooler with a built-in grille.Cooling efficiency under different inlet air temperature and humidity,inlet air speed and secondary air and primary air volume conditions.The results show that different grille types have different effects on the cooling effect.The addition of a single layer grille does not improve the uniformity of fluid flow,and the corresponding cooling efficiency is not significantly improved.The single-layer sparse grille concentrates the primary air to the one side of the channel,increasing the flow non-uniformity,which worsens the heat transfer.After adding a double-layer grille,the fluid distribution is the most uniform and the cooling efficiency is the highest.Compared with the counter flow dew-point evaporative cooler without grille,under the conditions of different inlet air temperature(25℃～45℃)and moisture content(6.9g/kg～14.5g/kg),double layers grille can reduce the outlet air temperature by 1.33℃ to 4.22℃ and increase the wet bulb efficiency by 9.74% to 37.9%.When the inlet air speed is 1.5m/s～8.5m/s,the addition of double-layer grille increases the wet bulb efficiency by 17.32% and the dew point efficiency by 12.32% on average.When the air volume ratio is 0.4 to 0.6,the addition of a double-layer grille increases the wet bulb efficiency by an average of 20.6% and the dew point efficiency by an average of 13.78%.