Study On The Effect Of Medium-Gap-Medium Arrangement On Direct Evaporative Cooling Performance

Mechanical compression refrigeration equipment has high energy consumption,environmental pollution and other problems,so the development of green and efficient air conditioning system has important significance for the green and low-carbon transformation.Evaporative cooling technology has the advantages of energy saving,environmental protection and health,which uses water evaporation to reduce air temperature.Compared with traditional mechanical compression refrigeration equipment,it can save nearly 80%power consumption.Meanwhile,it uses water as the refrigerant with no pollution for the environment.The media arrangement has an effect on the performance of the direct evaporative cooling system.In this paper,a medium-gap-medium arrangement is proposed,and its cooling and resistance performance are studied by two research methods,i.e.,experimental test and numerical simulation.The paper also explores the feasibility of evaporative cooling using seawater to save freshwater resources.The research will provide reference for optimizing media arrangement and exploring the feasibility of evaporative cooling using seawater.Firstly,the model CELdek7060 medium is selected in the test.A low-speed wind tunnel was designed to experimentally study the heat and mass transfer performance and resistance performance for normal media(100 mm and 300 mm)and medium-gap-medium arrangement(100 mm medium+100 mm gap+100 mm medium).And the paper has developed the empirical correlations of heat and mass transfer performance and resistance performance for the media.Then,this paper experimentally studies the feasibility of three concentrations of seawater for evaporative cooling.Evaporative cooling using seawater and freshwater were compared that the heat and mass transfer performance and resistance performance,and the heat transfer coefficients of evaporative cooling using seawater with different concentrations were fitted.Finally,a three-dimensional numerical simulation model of medium-gap-medium arrangement was constructed.It is studied that the mechanism of heat and mass transfer between gas and liquid in the process of evaporative cooling,and obtained that the distribution rules of aerodynamic field,temperature field and humidity field.And it also obtained that the influence rules of different inlet air conditions parameters on evaporative cooling performance.The main conclusions of this paper are as following:(1)The experimental results show that the medium-gap-medium arrangement has better economic feasibility.Compared with 300 mm medium-gap-medium and 200 mm normal medium,the air side pressure drop of 300 mm medium-gap-medium is close to that of 200 mm normal medium,and the cooling effectiveness of 300 mm medium-gap-medium is better than that of 200 mm normal medium.The cooling effectiveness of 300 mm medium-gap-medium is 4.5%higher than that of 200 mm normal medium,and the air side pressure drop of 300 mm medium-gap-medium is close to that of 200 mm normal medium.The pressure drop of 300 mm medium-gap-medium is 2.3～33.1 Pa lower than that of normal medium at thickness of 300 mm,and its cooling effectiveness is 5.8%～5.4%lower than normal medium at 300 mm within air speeds of 0.5～3.0 m/s.(2)The cooling effectiveness of seawater is slightly lower than that of freshwater.The pressure drop values caused by seawater at different concentrations and freshwater are close at the same air speed and thickness medium.The cooling effectiveness of seawater is slightly lower than that of freshwater,and it decreases with the increase of seawater concentration.For 100 mm and 300 mm thick normal media,the cooling effectiveness values of seawater(1 times seawater concentration)are 2.8%～7%and 2.8%～4.9%lower than that of freshwater,respectively,within the air speeds of 0.5～3.0 m/s.(3)It can be obtained that the cooling ratio of each area in the medium-gap-medium arrangement,and the influence of different inlet air conditions on the evaporative cooling performance by numerical simulation.The heat and mass transfer between gas and liquid is mainly related to the temperature difference,humidity difference,gas-liquid contact time and area between the two phases.The temperature and humidity difference gradually decreases along the direction of air flow,and the gas-liquid contact time and area in the media section are larger than that in the gap section.The temperature drop of air through 100 mm medium,100 mm gap and 100 mm medium are 4.3℃,1.3℃ and 1.6℃,respectively,at the air speed of 1.5 m/s,inlet air dry bulb temperature of 27℃,inlet air wet bulb temperature of ℃.All media section accounted for 82.5%of the cooling,while gap section accounted for 17.5%of the cooling.The temperature,humidity and air speed of the inlet air all have influence on the evaporative cooling performance,and the air speed has the most influence.In conclusion,compared with 200 mm and 300 mm normal media,300 mm medium-gap-medium has better economic feasibility.The cooling effectiveness of seawater is slightly lower than that of freshwater when it is used in evaporative cooling,but the application of seawater in evaporative cooling has a significant benefit for evaporative cooling applied in coastal areas for saving freshwater.The research will provide reference for optimizing media arrangement and exploring the feasibility of evaporative cooling using seawater.