The Study Of The Influence Of The Inclination Angle Of The Micro Heat Exchanger On Its Surface Frost Characteristics

With the continuous development of heat pump technology and refrigeration technology,frost phenomenon generally exists on the surface of the cold end heat exchanger,which seriously affects the heat exchange efficiency,increases the energy consumption of the system,and even affects the normal operation of the system,which violates our country.Strategic goals for energy saving,emission reduction and sustainable development.At present,research scholars have done a lot of work on the frosting characteristics of the hydrophilic and hydrophobic surface materials,the dynamics of the condensation process,the influence of the electromagnetic field on the frosting process,the numerical simulation calculation of the frost layer,and the optimization of the energy saving and defrosting of the system.The dynamic process of condensation and frost formation and the characteristics of condensation and frost formation under different gravitational potential fields caused by angles are relatively inadequate.This paper analyzes the theoretical basis and experimental research on the condition of operating temperature 20℃,relative humidity 70%,inlet wind speed 2.3m/s humid air flowing parallel to the surface temperature of-10℃ micro heat exchanger The frosting process.The condensation dynamics behavior of the upper surface of the micro heat exchanger under different gravitational potential fields caused by the change of tilt angle(θ=0°,15°,30°,60°),the average droplet size distribution,critical condensation particles Diameter,number of droplets distributed.The theoretical calculation of the droplet height deformation due to the gravity component of the droplet,and a method to determine the amount of droplet displacement at different tilt angles is given.For the whole process of frosting,the experimental data such as the temperature difference between inlet and outlet,relative humidity,moisture content of inlet and outlet,air temperature above the experimental surface,etc.were used to indirectly analyze the condensation amount,frost amount and exchange rate of the micro-heat exchanger with different gravity potential fields.Influence of thermal performance.Finally,the temperature distribution and velocity distribution of wet air during the freezing process of droplets were numerically simulated by COMSOL,and the gravity source term of the N-S equation was modified.The internal flow of droplets under different gravitational potential fields was given,compared and explained.Experimental phenomena.The research results are as follows:1.When T_f=20℃,T_w=-10℃,RH=70%,the inclination angle of the micro heat exchanger θ=0°,15°,30°,60°,the different gravity potential fields have a significant effect on the condensation and frost process,with the increase of the inclination angle The condensation time is shortened,and the average particle size of the condensed droplets at the same time gradually decreases.The experiment found that the cold surface above the heat exchanger placed horizontally had the fastest condensation rate and the longest condensation time.The critical condensation particle size was 0.037mm,and the critical average particle size was 0.057mm.At,the average kinetic energy of a single droplet reaches the maximum,and the phenomenon of droplets sliding and merging during condensation is obvious.In the process of frost formation,as the inclination angle increases,the critical nucleation particle size decreases,the crystallization rate increases,and the frost layer collapse and remelting phenomena are obvious.2.The experimentally measured inlet and outlet temperature and relative humidity data show that the greater the horizontal inclination of the heat exchanger,the better the heat exchange effect after frost formation,and the lower the temperature of the air flowing through the heat exchanger The rank of heat exchange amount corresponding to the tilt angle of the whole process of frost is 0°>60°>30°>15°.During the growth period of the frost layer,it is recommended that the heat exchanger maintain a 30 0 placement angle to reduce the collapse and remelting of the frost branches to cause the frost layer structure to condense,forming a dense structure of the frost layer and increasing the convection heat resistance.Affect the heat exchange efficiency of the heat exchanger.3.Judging from the changes in the moisture content calculated in the experiment,during the condensation stage,as the inclination of the heat exchanger is increased,the condensing capacity continues to decrease,and the condensing capacity is ranked as 0°>15°>60°>30°.At=30° and 60°,the amount of condensation at different times is not much different.It is recommended that the heat exchanger be placed at an inclination angle of 60。,which is more conducive to heat exchange.After 210s of frost layer growth,the frost formation is ranked as 0°>60°>30°>15°.Based on the above conclusions,the heat exchange efficiency is higher when the heat exchanger is placed at an angle of θ=60°,and the frost layer structure is more conducive to heat exchange and defrosting.4.Numerical simulation found that the influence of the freezing process of droplets on the air flow is mainly reflected in the temperature distribution above the droplets.The latent heat of phase change caused a local temperature rise and a temperature gradient.The air on both sides of the droplet is in direct contact with the cold surface.The thermal resistance is small,the flow rate is slow,the heat transfer is more sufficient,and the temperature boundary layer is more obvious.Therefore,the size and number of droplets in the condensation process determine the non-wetting of the cold surface.The surface area,the size of the wetted area is 0°>15°>60°>30°.