Today we will talk about the surface temperature, wind speed, frosting and heat transfer of the fin evaporator.
The design of fin evaporator should not only consider its own heat exchange area, fin thickness and spacing, but also its use environment. Only by comprehensive consideration can a better performance heat exchanger be designed. When designing, first understand the following things about the surface temperature, wind speed, frosting and heat exchange of the fin evaporator to guide the general design direction.
1. When the temperature of the cold surface is constant, the higher the front wind speed, the greater the density of the frost layer. When the wind speed is constant, the lower the temperature of the cold surface, the greater the density of the frost layer.
2. Due to the blocking effect of the frost layer and the increase of the surface roughness of the air flow path due to frosting, the pressure drop of the air passing through the evaporator continues to increase, and as the air pressure drop increases, the air volume passing through the evaporator continues to decrease. Small, which is extremely detrimental to the heat exchange of the evaporator.
3. Under the condition of the same heat exchange area, the fewer the number of tube rows, the slower the evaporator frosting speed, which can prolong the heat pump defrosting cycle. Therefore, when designing the evaporator, under the condition of the same heat exchange area, fewer tube rows should be selected, but the reduction of the number of tube rows will affect the compactness of the evaporator
4. If the fin spacing is set to be relatively small, the evaporator will be severely frosted and affect the operation of the heat pump; if it is set to be larger, the heat exchange area needs to be increased to increase the volume of the evaporator.
5. The fin spacing has a significant effect on the heat transfer coefficient and depends on the critical Reynolds number Re, while the number of tube rows has almost no effect on the air pressure drop;
6. The influence of the fin spacing is controlled by the number of tube rows. The smaller the fin spacing, the greater the resistance coefficient, and the number of tube rows has little effect on the resistance coefficient;
7. The fewer the number of tube rows, the greater the heat transfer coefficient. The study of 7.152mm tube diameter shows that when Re<2000, the heat transfer coefficient of single-row tubes is greater than that of multi-row tubes.
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