Factors affecting heat transfer on the refrigerant side

Factors affecting heat transfer on the refrigerant side

1.Flow direction and velocity of steam

In the condenser, when the refrigerant vapor contacts the low-temperature wall surface, it exotherms and condenses into a liquid film, and flows downward under the action of gravity. The liquid film also has heat conduction resistance, and its thickening will increase the heat resistance on the refrigerant side and reduce the heat transfer system. Therefore, when the refrigerant vapor and the condensed liquid film move in the same direction, the separation of the liquid film and the heat transfer wall is faster, and the heat transfer system increases. When the refrigerant vapor and the condensate film move in the opposite direction, the decrease or increase of the heat transfer coefficient will depend on the flow rate of the refrigerant vapor. When the flow rate is small, the liquid film flows slowly, the liquid film becomes thicker, and the heat transfer coefficient decreases; when the flow rate is large, the liquid film will be carried by the refrigerant vapor to flow upwards and even be blown away, and the heat transfer coefficient increases.

　　2, the roughness of the heat transfer wall

　　The roughness of the heat transfer wall has a great influence on the thickness of the condensate film. When the wall surface is very rough, the resistance of the liquid film to flow will increase, so that the flow is slow, the liquid film becomes thicker, and the heat transfer coefficient decreases. According to experiments, when the heat transfer wall is severely rough, the heat transfer coefficient can be reduced by 20%-30%. Therefore, the heat transfer wall should be kept smooth and clean.

　　3, the refrigerant vapor contains air or other non-condensable gas

In the refrigeration system, there will always be some air and non-condensable gases decomposed by refrigerant and lubricating oil at high temperature. After these non-condensable gases enter the condenser, they will adhere to the vicinity of the condensate film, making the refrigerant The partial pressure of the vapor is reduced, thereby affecting the condensation and heat release of the refrigerant vapor, and the heat transfer coefficient is significantly reduced. Therefore, measures must be taken to prevent air from penetrating into the refrigeration system and to discharge the non-condensable gas in the system in time.

　　4, the refrigerant vapor contains lubricating oil

　　When the refrigerant vapor contains lubricating oil, the lubricating oil will also form an oil film on the heat transfer surface, which increases the thermal resistance and reduces the heat transfer coefficient. The influence of the oil in the refrigerant vapor on the heat of condensation depends on the degree of solubility of the lubricating oil in the refrigerant. For freon refrigeration systems, when the oil concentration is less than 6% to 7%, it is not necessary to consider its effect on heat transfer, but when it exceeds this limit, the heat transfer coefficient will decrease. Therefore, efficient oil separation equipment should be installed in the refrigeration equipment to reduce the oil content in the refrigerant.

　　 5. The structure of the condenser

　　The structure of the condenser is different, and the heat transfer on the refrigerant vapor side is also different. But no matter what kind of condenser, if you want to improve the heat transfer coefficient, you must ensure that the condensed liquid on the heat transfer surface is quickly removed, and the heat transfer surface is smooth and clean.