Review of restraint frost method on cold surface

Many researchers have focused on the investigation into frost formation mechanism and tried to find various effective defrosting methods in recent years. Study on frost is divided into three stages: the frost formation process and mechanism, defrosting methods, and restraint frost methods. The three stages are carried out sequentially or in parallel. Compared to defrost, restraint frost is becoming more welcomed by peoples because of no energy or smaller consume. The affecting factors on frosting directly induce frost formation on cold surface, which leads to blockage, performance decrease, and even malfunction of the low temperature heat exchanger. This paper divides the factors into three categories: the characteristics (temperature, humidity and velocity) of the moist air, the features （temperature, structure and position, treatment）of the cold surfaces, the interaction between the air or the formed frost and the cold surface (electric field, ultrasonic wave, magnetic field, oscillation effects). One or several of the factors must be changed in order to restrain frost formation. Relative humidity is considered as that it has a larger effect on the frost formation, compared to the air temperature and air velocity. However, only a few researches pay attention to the restraint frost by controlling the characteristics of moist air. The structural parameters such as the fin spaces have the most important effect on the heat transfer performance of a heat exchanger under frosting conditions. Therefore, an optimization of the heat exchanger design should be considered for restraint frost. Hydrophobic surface is recognized as an effective way to improve the energy efficiency of a refrigeration system under frosting conditions. However, the research results are not as satisfactory as expected because of the difficult fabrication of scalable hydrophobic properties.