The use of elliptical flat tubes in heat exchangers is mainly due to the following reasons:
1. Advantages of heat transfer performance
Large heat transfer area: Under the same cross-sectional area, the heat transfer periphery of an elliptical flat tube is longer than that of a circular tube, providing a larger heat transfer area and allowing for more complete heat transfer. For example, in a tube fin heat exchanger, elliptical flat tubes can increase the contact area with the fins and improve the overall heat transfer efficiency.
Enhanced fluid disturbance: The flow cross-sectional area of an elliptical flat tube is relatively small compared to a circular tube. When the flow rate remains constant, the flow velocity of the fluid inside the tube increases, the disturbance is strengthened, and the convective heat transfer inside the tube is enhanced. For the fluid outside the tube, the elliptical flat tube is approximately streamlined, and the resistance is small when the fluid is swept outward. It can increase the flow velocity and enhance external heat transfer while allowing the same flow resistance.
Uniform temperature distribution: Through CFD computational fluid dynamics simulation, it is known that the velocity and temperature distribution around the elliptical flat tube are more uniform, which is conducive to full heat transfer of the tube and can effectively reduce local overheating or undercooling phenomena in the heat exchanger, improving the stability and efficiency of heat transfer.
2. Good fluid mechanics properties
Reduce flow resistance: Elliptical flat tubes can reduce air side resistance. When the long axis direction of the elliptical tube is consistent with the direction of fluid flow, the separation point moves backward relative to the circular tube, and the flow loss caused by the Karman vortex street in the separation zone is greatly reduced. In a heat exchanger with the same air volume and windward area, the actual net flow channel of the elliptical flat tube has a relatively lower windward wind speed, which can effectively reduce the turbulence on the leeward side and further reduce the windward resistance.
Reducing vibration risk: Taking the spiral twisted elliptical flat tube as an example, the shell side fluid flows in a spiral forward form, avoiding the pressure drop caused by the constantly changing direction of fluid flow in traditional baffle heat exchangers and reducing the vibration of heat transfer tubes caused by lateral flushing heat transfer.
3. Structural design and space utilization advantages
More compact arrangement: Elliptical flat tubes can be arranged more compactly, allowing for the placement of more heat exchange tubes in the same space, making the heat exchanger structure more compact and increasing the heat transfer per unit volume, effectively reducing the overall volume and footprint of the heat exchanger. In some space limited places such as ships, small-scale chemical plants, etc., it has great advantages.
Self supporting structure: When assembling a spiral twisted elliptical flat tube into a heat exchanger, it can rely on the point contact of the outer spiral line for self support, without the need for additional tube bundle supports, saving materials and costs, and avoiding flow dead zones and scaling problems caused by supports.
4. High comprehensive economic benefits
Reduce operating costs: The elliptical flat tube heat exchanger has low wind side resistance, and during operation, the energy consumption of power equipment such as fans is low, which can reduce long-term operating costs. At the same time, its higher heat transfer efficiency can reduce the energy consumption required to achieve the same amount of heat transfer.
Reduce maintenance costs: Due to the structural characteristics of the elliptical flat tube, there is no dead zone in the shell side, and it has good anti scaling performance, which can reduce the frequency and cost of cleaning and maintenance of the heat exchanger. Moreover, it has high strength, and the base pipe is not easily frozen and cracked in winter, with a long service life, which also reduces the cost of equipment replacement and maintenance.
