What is the difference between finned and conventional tube heat exchangers?

A finned tube heat exchanger is composed of many tubes with fins arranged in a sequence. Metal fins are installed on the inside or outside of the metal tube, and their shapes include spiral, star, ring, and so on. Finned tube heat exchangers are primarily used for heating or cooling gases, with the air coolers used in oil refinery operations being a common example of such heat exchangers. This type of heat exchanger can significantly improve the efficiency of heat transfer in gases, while reducing the size of the heat exchanger and the amount of metal material used. But its manufacturing process is complex and costly. It is required that the fluid flowing on one side of the fins be clean, as cleaning them is difficult. Search on the forum; there’s a lot of relevant information available.

The main purpose of adding fins to a heat exchanger is to enhance heat transfer; fins are generally used on the side with a lower heat transfer coefficient. Enhance heat transfer by increasing the heat exchange area. For example, heat transfer is better in air and water; the heat transfer coefficient on the air side is around 100, while that on the water side can reach 3000–4000 or even higher. At this point, adding fins on the air side facilitates heat exchange, allows the size of the equipment to be reduced, and special fin structures can also help save water. The overall heat transfer coefficient of the heat exchanger in question is lower than that of the side with a weaker heat transfer capacity; therefore, enhancing heat transfer on the side with poorer performance can improve the overall efficiency of the heat exchanger.

What was said upstairs is quite correct. Finned heat exchangers are generally used in situations where there is a large difference in the heat transfer coefficients on the two sides, such as in gas-liquid, gas-high-pressure gas, and oil coolers. Fins can be divided into internal fins and external fins, and their purpose is to enhance heat transfer on the side with the lower heat transfer coefficient. The fin ratio can range from around 2 for threaded tubes to around 23 for fins with many fins. If the difference in heat transfer coefficients between the inside and outside isn’t significant, then the use of fins provides no benefit; in such cases, ordinary smooth tubes are sufficient. Another point is that when using a finned heat exchanger, the temperature generally should not exceed 280 degrees, and the operating pressure on the outer fins should not be too high.

The heat transfer coefficient of finned-tube heat exchangers is low, while that of conventional tube heat exchangers is higher. However, finned tubes have a larger effective surface area, which is n times that of the bare tubes, where n is the fin ratio.

Thank you all! We are using external finned heat exchangers; the heat transfer medium inside the tubes is boiler water at 205°C, while the medium on the outside side is high-temperature combustion gas at 375°C.

For information on external fins, one can refer to the book \"Air Coolers\" published by Harbin Institute of Technology. Take a look at this connection – it contains information related to fins: http://bbs.hcbbs.com/viewthread.php?tid=375000&highlight=%BF%D5%C6%F8%C0%E4%C8%B4%C6%F7%2B%D7%CA%C1%CF. The download link for this book is: http://bbs.hcbbs.com/viewthread.php?tid=4858&highlight=%BF%D5%C6%F8%C0%E4%C8%B4%C6%F7

Both finned-tube and conventional tube heat exchangers are widely used. Conventional tube heat exchangers are employed when the heat transfer coefficients of the fluids on both sides are not very different; our factory has used hundreds of such units, such as ammonia coolers and reboilers； Finned tube heat exchangers are used when there is a large difference in the heat transfer coefficients of the fluids on both sides. By adding fins to the side with the lower heat transfer coefficient, the surface area for heat exchange can be increased, and fluid turbulence can be promoted to reduce the heat transfer resistance. This effectively raises the heat transfer coefficient, thereby increasing the amount of heat transferred. As in the air-refrigerant type heat exchangers used in our factory, the refrigerant inside the tubes boils for heat exchange, while air outside the tubes facilitates forced convection for heat exchange; in this case, the heat transfer coefficients inside and outside the tubes differ significantly, by a factor of around 50. At this point, adding fins outside the tube can effectively enhance heat transfer by air.