Heat Transfer Performance of Threaded Copper Tubes in Finned Heat Exchangers

Heat transfer performance is one of the crucial performance indicators of threaded inner tubes, and the tooth shape of threaded inner tubes has a significant impact on their heat transfer performance. Generally speaking, the larger the tooth shape of the threaded inner tube, the better its heat transfer performance. This is because the tooth shape of the threaded inner tube can increase the turbulence inside the pipeline, enhancing the heat transfer between the fluid and the inner wall of the pipeline, thereby improving the heat transfer efficiency.

Additionally, the shape and size of the tooth shape also affect the heat transfer performance. For example, triangular tooth shapes have better heat transfer performance compared to rectangular tooth shapes, and the depth and width of the tooth shape also affect the heat transfer performance. Generally, the deeper and wider the tooth shape, the higher the heat transfer performance. Therefore, when designing threaded inner tubes, factors such as the shape and size of the tooth shape need to be considered to achieve better heat transfer performance.

Threaded inner tubes are commonly used enhanced heat transfer elements, mainly enhancing heat transfer through the following aspects:

1. Increasing Heat Transfer Area:

The tooth shape of threaded inner tubes can increase the surface area inside the pipeline, thereby increasing the heat transfer area and improving heat transfer efficiency. Generally, threaded inner tubes can increase the surface area by 20% to 25% compared to smooth tubes of the same diameter.

2. Increasing Turbulence:

The tooth shape of threaded inner tubes can increase the turbulence inside the pipeline, creating a helical flow on the inner wall of the pipe. Helical flow increases the relative velocity between the fluid and the pipe wall, promoting more vigorous fluid motion, which can thin the thickness of the laminar sublayer. The centrifugal force generated by helical flow can throw droplets carried in the steam back to the wall, delaying the onset of wall dryout and enhancing heat transfer between the fluid and the inner wall of the pipeline.

3. Disruption of Thermal Boundary Layer:

The tooth shape of threaded inner tubes can disrupt the thermal boundary layer, with the main function of boundary layer separation being to agitate the boundary layer, encouraging more uniform mixing of fluid at that location, making it easier for the fluid to contact the inner wall of the pipeline, thus improving heat transfer efficiency.

4. Increasing Fluid Mixing:

The tooth shape of threaded inner tubes can increase fluid mixing, distributing the fluid more evenly within the pipeline, thereby improving heat transfer efficiency.

In conclusion, using threaded inner tube structures allows the fluid to be stirred when rotating, delaying the occurrence of the first type of heat transfer deterioration, which can prevent film boiling. When the second type of heat transfer deterioration is about to occur, it can throw droplets carried in the steam back to the wall, delaying the onset of dryout. Threaded inner tubes can increase the flow heat transfer coefficient inside the tube, increase the critical heat flux density, and delay the occurrence of heat transfer deterioration. Even if heat transfer deterioration occurs, it can improve the heat transfer characteristics and effectively reduce wall temperature.