Abstract
This study numerically investigates the thermal performance of non-isothermal finned horizontal tube under natural convection. The parameters considered include fin diameter, fin spacing, fin material and tube diameter, with fin thickness fixed at 0.5 mm. The effect of the temperature uniformity is found to affect the total heat output of the finned tube. The computational results show that when the fin temperature is relatively uniform (aluminum fins), the total heat output becomes greater for a smaller tube diameter; on the contrary, when the fin temperature is non-uniform (stainless-steel fins), the total heat output becomes greater for a larger tube diameter. The uniformity of fin temperature, and tube diameter as well, would affect the optimum fin spacing. Consequently, applying the empirical optimum-spacing formula available in the literature leads to notable discrepancies for the cases with non-isothermal fins or large tube diameters. Under natural convection, the distributions of temperature and heat transfer coefficient on the fins deviate from being axisymmetric due to the buoyancy flow. For stainless-steel fins, the non-uniformities of fin temperature and heat transfer coefficient are far more serious than for aluminum fins. On the non-uniform fins, the region above the tube could be distributed with negative local heat transfer coefficients. In calculating the fin efficiencies of highly non-uniform fins, the axisymmetric theoretical methods in the literature may yield significant errors. The present results indicate that both temperature uniformity and tube diameter are highly influential to the thermal performance of finned horizontal tube.