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How Hubei Chemical Machinery Strengthens the Heat Transfer Performance of Fin Tube Heat Exchangers

Classification: Company Dynamics

Time2019-01-19

The thermal storage heat exchanger relies on a thermal storage medium composed of solid fillers to transfer heat, with hot and cold fluids alternately flowing through the channels made up of the thermal storage medium. When the hot fluid flows through, it stores heat in the thermal storage medium, causing its temperature to gradually rise. When the cold fluid flows through, the thermal storage medium releases heat, causing its temperature to gradually decrease, and this process repeats.

　　Heat exchangers can be classified into three types based on their working principles: wall-type, mixed-type, and thermal storage type.

　　In a wall-type heat exchanger, there is a solid wall between the hot fluid and the cold fluid, and the two fluids are separated by the solid wall, not in contact with each other. Heat transfer must occur through the wall.

　　Mixed-type heat exchangers rely on the direct contact of cold and hot fluids for heat exchange, and theoretically, the mixed medium should exit at the same temperature and pressure after heat exchange.

　　Thermal storage type heat exchangers transfer heat through a thermal storage medium made of solid fillers, with hot and cold fluids alternately flowing through channels formed by the thermal storage medium. When the hot fluid flows through, it stores heat in the thermal storage medium, gradually increasing its temperature, while when the cold fluid flows through, the thermal storage medium releases heat, gradually decreasing its temperature, and this process repeats.

　　Next, we will mainly discuss wall-type heat exchangers and perform thermodynamic comparative calculations based on experimental data.

　　Ways to improve the heat exchange performance of heat exchangers

　　The heat transfer equation is Q = KAΔt, and many researchers focus on improving the heat transfer coefficient K. For forced circulation air coolers, effective measures can be taken to reduce the thermal resistance on the air side or to control the liquid supply amount on the refrigerant side by using selective liquid supply methods, or using high-efficiency heat transfer tubes can significantly improve the heat transfer coefficient. Additionally, increasing the fluid flow rate can increase the heat transfer coefficient, but the flow resistance also increases accordingly, so there is a limit to enhancing the heat transfer coefficient K by increasing the fluid flow rate. Furthermore, enhancing heat transfer can be achieved by increasing the heat transfer area, but this should not be done by increasing the overall size of the equipment, but rather by considering the structure of the equipment itself.

　　Increasing the heat transfer area can generally be divided into two approaches: expanding the outer surface area of the tubes and expanding the inner surface area of the tubes.

　　Currently, the increase in the outer surface area of the tubes is mainly achieved by adding fins or extended surfaces, which expand the heat transfer area to reduce convective heat transfer resistance, thereby achieving enhanced heat transfer.

　　The effective heat transfer area per unit volume of the equipment can be increased through the following methods:

　　① Use extended surfaces for the transfer area, such as adding fins, ribs, or pins to the heat transfer surface on the side with a smaller convective heat transfer coefficient;

　　② Increase the existing heat transfer surface, such as treating the surface with hydrophobic coatings, porous coatings, or using double-wavy tubes;

　　③ In terms of enhancing the tubes in heat exchangers, the development of special-shaped tubes is mainly aimed at increasing the heat transfer area. Types of special-shaped tubes include spiral groove tubes, transverse groove tubes, scaling tubes, wave tubes, swirl tubes, rough surface tubes, and spiral flat tubes.

　　By improving and optimizing the structure of finned tube heat exchangers, and then comparing the heat transfer performance with that of the heat exchanger before improvement, the result shows that the heat transfer coefficient of the improved heat exchanger has been enhanced.

　　1. Adjust the spacing of the fins in the heat exchanger to create variable fin spacing.

　　When air flows through the evaporator, water vapor in the air continuously accumulates on the surface of the finned tubes, causing the relative humidity to decrease due to dehumidification. The amount of frost on the surface of the finned coil decreases along the airflow direction. If a variable fin spacing structure is adopted, it can maintain a higher heat transfer efficiency under frosting conditions and extend the defrosting time. When the evaporator adopts a variable fin spacing structure, it actually forms a staggered distribution of the fins. When air flows across the staggered fins, the staggered distribution allows the upstream fins to create a bypass effect on the downstream fins. Due to the bypass effect of the front fins, the heat transfer of the front half of the fins is enhanced, while the distribution of the rear fins narrows the flow path, increasing the flow rate, which also enhances the heat transfer of the rear half of the fins.

　　Due to this structural form being a staggered fin arrangement, when the fluid flows over the fins, the airflow is first disturbed by the upstream fins, thus enhancing the heat transfer on the fins of the first few rows of tubes. When the airflow passes through the last few rows of tubes, the flow cross-section rapidly narrows, increasing the flow rate, which further compresses the fluid and intensifies the disturbance. Therefore, the addition of a set of fins at the back also enhances the heat transfer.

Keyword： How Hubei Chemical Machinery Strengthens the Heat Transfer Performance of Fin Tube Heat Exchangers

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Xianghua Machinery Xianghua Machinery

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