Frosting to the application and development of air source heat pump has been a certain limit, at home and abroad on the issue of a number of research work, summed up the following main aspects.
2.2. 1 frost formation mechanism research
Sun Yuqing et al.'s study of the complex heat and mass transfer problems (ie, the so-called Stefan problem) of the unsteady, phase transition, moving boundary, the introduction of nucleation theory, crystal dynamics theory and meteorology theory, A more accurate physical and mathematical model was established, and frost suppression was studied. Theoretical studies and experiments have shown that the surface of the heat exchanger is sprayed with a highly hydrophobic coating to reduce the surface energy and increase the contact angle between the water vapor and the water vapor, which is effective for suppressing frosting. In addition, in order to suppress the frost, the humidifier can heat the humidification of the heat treatment, conditions can increase the wind speed, so that the formation of ice or cold water droplets as soon as possible through the heat exchanger wall.
Zhao Lanping et al. Also reviewed the study of frosting mechanism and analyzed and discussed the problems of frost physical properties, frost layer growth, heat transfer and mass transfer during frosting process.It was pointed out that although frost mechanism Has made great progress, but in many ways need further study.
Cai Liang et al. Analyzed the crystal structure of the box observed in experiments.Then the frost layer growth model at different stages was proposed and simulated by computer. Based on the simulated frost crystal structure, the energy balance equation is listed for each node, and the thermal conductivity of the frost layer is obtained.
Na B. et al.'s study was based on a theoretical analysis of the frosting nucleation process on cold surfaces in January, suggesting that the air on the cold wall should reach a supersaturated state to form frost nuclei, and the supersaturation depends on the contact angle Related surface energy. The simplified equation of supersaturation on the surface of the calculated layer is established by boundary layer analysis, and the experimental results are compared with the experimental results. On the basis of this, a new supersaturation model for predicting frost deposition and growth rate is proposed. At the same time compared with others' experimental data, the results show that the supersaturation model is better than the saturated model.