Fabrication And Investigation The Mechanism Of Condensation And Frosting On The Surface Of Micro-nanoporous Aluminum Fins

Energy consumption of air conditioning system is of great significance to building energy conservation.It is widely used in refrigeration dehumidification in summer and heating in winter.Energy saving of air conditioning system can not only reduce building energy consumption,but also meet the development requirements of low-carbon buildings The research results show that the heat transfer coefficient and dehumidification ability of the air conditioning fins with micro and nano structures on the surface can be effectively increased and the frost resistance of the fins can be improved in winter.In this paper,micro-nanoporous aluminum fins with different pore diameters were prepared by anodic oxidation method,their pore depth was 60±5 μm and the pore diameters were 30 nm(sample 2),90 nm(sample 3),200 nm(sample 4),300 nm(sample 5),and 400 nm(sample 6)respectively.Meanwhile,polished aluminum fin(sample 1)was used as experimental contrast fin.The contact Angle,specific surface area and fractal dimension of micro-nanoporous aluminum fins were measured and calculated.The morphology of condensation and frost formation were observed through the experimental test platform built The surface condensation and frosting properties were systematically analyzed by weighing method,and the influencing factors of surface condensation and frosting properties were studied.The mathematical calculation models of the change of the amount of condensation and frosting on the surface with time were established respectively.At the same time,the nucleation driving force and nucleation barrier mechanism of water molecules on the surface were studied,and the influencing factors of surface nucleation rate and nucleation density were analyzed.On this basis,the mechanism of condensation and frosting on the surface of micro-nanoporous was studied by combining the theoretical model and experimental results,and a simulation model of surface wetting was established.The test values and model values were compared and analyzed.The condensation results showed that the polished aluminum fin surface was bead shaped condensation and the micro-nanoporous aluminum fins surface were film shaped condensation.The time them taken for the surface of the micro-nanoporous aluminum fins to be completely covered by condensed water were much less than that of the polished aluminum fin.The average condensation rate of sample 4 was 97.3%higher than that of sample 1.According to the comparison of the average condensation rate of sample 4 and sample 1 at different surface temperatures,the average condensation rate corresponding to the surface temperature of sample 4 at 15 ℃ was greater than that corresponding to the surface temperature of sample 1 at 10℃,and it was approximately equal to the average condensation rate corresponding to the surface temperature of sample 1 at 5 ℃,from which it could be analyzed that the evaporator temperature can be increased by 5～10℃ with sample 4 as the heat transfer fin material on the air conditioning evaporator under the same dehumidification amount.The frosting results showed that the frosting resistance of micro-nanoporous aluminum fins were better than that of polished aluminum fin,among which sample 3 had the best frosting resistance and sample 1 had the worst frosting resistance,and the amount of frosting on the surface of sample 3 was reduced by up to 36.7%compared to sample 1.Samples 3 and 6 showed good anti-frosting performance in low temperature and high humidity environment,which made up for the disadvantage of super hydrophobic air conditioning aluminum fins losing anti-frosting performance in high humidity environment,and expanded the fin’s climate adaptability.Combined with Gibbs free energy,surface adsorption model and surface fractal theory,the mechanism of condensation and frost formation on the surface of micro-nanoporous was analyzed,and the influence parameters of condensation and frost formation on the surface of micro-nanoporous were studied.The surface condensation properties of micro-nanoporous were mainly affected by Gibbs free energy and surface adsorption mechanism.The calculation model of the average condensation rate and the composite mechanism parameters was established,the relative error between the model value and the experimental value was 10.6%.The frosting properties of micro-nanoporous surface were influenced by Gibbs free energy,surface adsorption and surface fractal dimension.The initial frost morphology model was established by theoretical analysis.Sample 3 was a hydrophilic fin with high surface adsorption and low surface fractal dimension.This special property made the surface generate sparse ice at the bottom first,which acts as an overhead heat insulation for the subsequent frost growth,so it still had good frost resistance performance under low temperature and high humidity environmentCFD simulation model of surface wettability was established by using sample contact Angle,the wetting phenomena on different surfaces were simulated.The simulation results showed that sample 1 was bead shaped condensation and sample 2 to sample 6 were film shaped condensation.The classical condensation model was revised by the air velocity influence factor and micro-nanoporous surface performance influence factor.The revise condensation model was established,and the average relative error of condensation test and revised model calculation was 7.26%.The average relative errors of sample 1 and sample 3 in testing and model calculation were 14.88%and 24.80%respectively for frosting experiment.After the micro-nanoporous surface performance influence factor revised,the average relative error between the testing and model calculation of sample 3 was reduced to 7.07%.