Theoretical And Experimental Study On Dew Point Indirect Evaporative Cooler Of Polymer-porous Ceramic Composite

The application of evaporative cooling air conditioning in hot and dry areas has attracted more and more attention because of its high energy efficiency.Evaporative cooling air conditioning products at this stage are generally faced with the following technical obstacles: 1.Lower cooling efficiency;2.Lower temperature drop range;3.Larger equipment volume;4.Dependence on the surrounding environment.These technical obstacles have greatly restricted the promotion and application of evaporative cooling air conditioners.Due to the dew point indirect evaporative cooling technology due to its high cooling efficiency,compact core structure,a larger temperature drop range more and more become the main direction of evaporative cooling air conditioning at home and abroad.In this paper,based on the new hydrophilic materials and new cooler structure,a polymer-porous ceramic composite dew point indirect evaporative cooler is proposed.The dew point indirect evaporative cooler of the composite membrane was systematically studied from the aspects of the mathematical model of heat and mass transfer by dew point indirect evaporative cooling,material hydrophilicity experiment,cooler performance experiment and cooler simulation.(1)From the perspective of heat and mass transfer in thermodynamics,the mathematical models of heat and mass transfer of indirect evaporative coolers are established.(2)In the aspect of material hydrophilicity,we carried out experimental research on the wicking ability,diffusion wetting ability,moisture absorption and releasing wet ability of textile fabrics,non-woven fabrics,polymer fiber materials and kraft paper materials.At the same time,the surface microstructure image of the material was generated using field emission scanning electron microscopy.The experimental results show that the hydrophilicity of the polymer material is extremely superior.In the moisture absorption and desorption test,the moisture absorption and desorption ability is the best among the four materials tested.Moisture absorption process up to 6.05% of its own weight of water,moisture release process can reduce the material’s own weight of 6.21% of the water.By scanning electron microscopy,it is also clear that the voids in the polymer material are the largest.It is foreseeable that due to the superiority of the performance of these fabric materials,there is great potential for improving the efficiency of the dew point indirect evaporative cooling system.(3)Aiming at the newly developed countercurrent dew point indirect evaporative cooler,the dew point cooler was simulated by simulating standard drying,standard high humidity,Urumqi,Jiuquan,Xi’an and other five different environmental conditions in the enthalpy difference laboratory Performance test analysis.Experimental data show that the wet bulb efficiency of the countercurrent cooler reaches 105.6% under standard dry conditions(dry-bulb temperature of 38℃,wet-bulb temperature of 23℃)and air flow ratio of secondary air / primary air = 1.1.Dew point efficiency of 76%,the highest cooling capacity of 2.83 kW,dry bulb temperature drop of up to 15.2 ℃.The cooling performance of the dew point cooler has greatly improved the wet bulb efficiency of 60%~80% of the traditional indirect evaporative cooler.(4)Aiming at the technical principle,structure,heat and mass transfer characteristics of three different dew point coolers of compound type,cross type and countercurrent type,a comparative analysis is made.At the same time,three different dew-point coolers were used to experimentally study their wet-bulb efficiency,dew-point efficiency,temperature drop range,cooling capacity and so on in laboratory simulation conditions or practical applications.In terms of structural parameters,the concept of "flow / volume ratio" of dew point heat exchanger core is proposed.The "flow / volume ratio" of the three dew point heat exchanger cores with composite,cross and counter flow are 2.025,2.143 and 2.058,Basically the same.Performance test results show that the wet bulb efficiency of these three dew point coolers can exceed 100% in terms of cooling efficiency.In dry climate conditions,the combined dew point cooler wet bulb efficiency reaches 110% and the dew point efficiency reaches about 75%.For the crossover dew-point cooler,under the standard dry conditions(dry bulb temperature 38℃,wet bulb temperature 23℃),the wet bulb efficiency reached about 100%,and the dew point efficiency reached about 70%.The counterflow dew point cooler has the wet bulb efficiency of 105.6% and the dew point efficiency of about 76% in the same standard dry conditions(dry bulb temperature 38℃,wet bulb temperature 23℃).In dry conditions,the dew point efficiencies of all three dew point coolers can reach over 70%.In terms of temperature drop range,the cross-type dew point cooler temperature drop out of rheumatic ball temperature between 3 ℃ ~ 5.5 ℃,under standard drying conditions,out of the wind average dry-bulb temperature drop of about 15 ℃.Countercurrent dew point cooler out of the wet ball temperature drop between 4 ℃ ~ 5.5 ℃,the same conditions in the standard drying conditions,out of the average dry bulb temperature drop at 15.2 ℃.Are much higher than the composite dew point cooler.(5)The modeling software SolidWorks2014,for the counter-current dew point indirect evaporative cooling heat exchanger core for three-dimensional modeling.The flow simulation in SolidWorks was used to simulate the heat exchange in the counter-current dew point cooler.