Three-layer pipe aluminum tube fin evaporator is widely used in refrigeration and air-conditioning systems. Its frost characteristics and corresponding defrosting strategies under different working conditions have a significant impact on system performance.
First, under low temperature and high humidity conditions, when the evaporator surface temperature is lower than the air dew point temperature, water vapor in the air will quickly condense and frost will form on the surface of the fins and aluminum tubes. At this time, the frost will form quickly, and the frost layer will gradually thicken and become more evenly distributed. Since the thermal conductivity of frost is much lower than that of metal, the heat exchange efficiency of the evaporator will drop sharply and the air resistance will increase.
For example, in cold and humid winter, the evaporator of the outdoor unit of the air conditioner is prone to this situation. As the frost layer accumulates, the cooling capacity is greatly reduced and energy consumption increases.
Secondly, under medium temperature and low humidity conditions, the frosting process is relatively slow. Frost often forms first in local low-temperature areas of the evaporator, such as near the refrigerant inlet or corners with low air flow velocity. The frost layer shows uneven growth and may form local accumulation of frost patches.
Under this working condition, although the impact of frost on heat exchange is not as rapid and severe as that under low temperature and high humidity conditions, long-term operation will still degrade system performance. For example, in some areas where the temperature difference between day and night is large and the humidity is not high in spring and autumn, the frost on the evaporator cannot be ignored.
For rapid frost formation under low temperature and high humidity conditions, a commonly used defrosting strategy is hot gas bypass defrost. By introducing the high-temperature hot gas discharged from the compressor into the evaporator, the frost layer is melted. This method of defrosting is fast, but it will cause certain fluctuations in indoor temperature, and the defrosting process consumes a lot of energy. Electric heating defrost can also be used, using electric heating wires to generate heat to defrost. The advantage is that it is simple to control, but it consumes a lot of energy and the heating is uneven.
Under medium temperature and low humidity conditions, a scheduled defrost strategy can be adopted, and a fixed defrost time interval can be set based on experience. However, this method may start defrosting before the frost layer reaches a level that seriously affects performance, resulting in a waste of energy; or the defrosting may not be timely when working conditions change.
Finally, to optimize the defrost strategy, sensor technology can be incorporated. For example, a temperature sensor and a humidity sensor are installed on the surface of the evaporator to monitor working conditions parameters in real time, and accurately determine the defrosting timing based on the frost layer thickness prediction model. At the same time, new defrosting technologies are developed, such as ultrasonic defrosting, which uses ultrasonic vibration to loosen and fall off the frost layer, reducing interference to system operation, improving defrosting efficiency and energy saving, and adapting to three-layer pipe aluminum tube under different working conditions. Solve the frost problem of fin evaporator and improve the operational stability and energy efficiency of the entire refrigeration or air conditioning system.
