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Introduction to Low Finned Tubes

Low finned tubes are specialized components engineered to enhance heat exchange efficiency. They feature external fins crafted with precise height, distance, and thickness on the smooth tube’s surface, significantly increasing the surface area. These tubes are predominantly utilized in air-conditioning condensers and evaporators, with notable applications as condensers.

Working Principle of Low Finned Tubes

The effectiveness of low finned tubes lies in their expanded heat transfer area, achieved through their external fins with a finning coefficient between 2 to 3. This design allows the same metal materials to cover a larger surface area compared to smooth tubes, optimally enhancing the heat transfer coefficient. The fins disrupt the heat transfer surface flow layer, increasing surface turbulence and doubling the heat transfer effect.

Key factors influencing the enhanced heat transfer of low finned tubes include fin height, thickness, spacing, and material thermal conductivity. The fin spacing is tailored to the liquid’s surface tension and the shear force acting on the liquid film during flow. Moreover, the convection heat transfer on the smooth side and heat conduction at the base wall of the fin contributes to overall heat transfer efficiency.

Advantages and Applications

Low finned tubes excel in fouling resistance, as operational temperature changes cause expansion and contraction, preventing dirt formation—a common issue with smooth tubes. Their cleaning process is as straightforward as that of smooth tubes. Manufactured from ordinary smooth tubes through simple rolling, they maintain mechanical strength and corrosion resistance, ensuring long-term, reliable heat exchanger operations.

The structural parameters of these tubes include inner and outer diameters, wall thickness, and fin dimensions. Low finned tubes are ideal when the internal heat supply coefficient significantly exceeds the external. Typical applications encompass oil heat exchangers and condensation and boiling processes outside the tube, where surface tension enhances heat transfer efficiency.

Performance Considerations

1. Heat Transfer Optimization: The primary structural parameters determining heat transfer effectiveness are, in order: fin pitch, fin height, and fin thickness. Optimal fin pitch lies between 1-2 mm; exceeding this can diminish performance. Heat transfer benefits from increased fin pitch within this range, increased fin height, but reduced fin thickness.
2. Pressure Drop Impact: The pressure drop outside the tube is primarily influenced by fin height, increasing geometrically with height. Fin pitch also significantly affects pressure drop, while fin thickness has minimal impact.
3. Fluid Flow Dynamics: Increasing fluid flow rates both inside and outside intensifies heat exchange and pressure drop, with a notable difference when external flow rates increase, leading to a greater rise in pressure drop compared to heat exchange.