Thermal optimization of circular tubes and heat pipes with axial internal fins

Abstract

In the present work, two kinds of heat transfer devices, which are commonly used in engineering applications, are dealt with: one is an internally finned tube and the other is a heat pipe with axial internal fins. The new analytical solutions for velocity and temperature profiles in the internally finned tube are presented. It is found that two simplifying assumptions employed in the previous study may lead to significant errors in predicting the temperature distributions of the internally finned tube, as the number of fins increases or the thermal conductivity ratio, the porosity, or the dimensionless fin height decreases. In order to optimize the thermal performance of the internally finned tube, the total thermal resistance is minimized for a pumping power. It is shown that there exists an optimum value for the total thermal resistance with respect to the fin height as well as the number of fins and the porosity. Finally, the effects of the pumping power and the tube diameter on the thermal performance of the internally finned tube are examined. A mathematical model for precisely predicting the thermal performance of a heat pipe with axial internal fins is developed. The effects of the liquid-vapor interfacial shear stress, the contact angle, and the amount of liquid charge are included in the present model. In particular, the axial variations of the wall temperature and the evaporation and condensation rates are considered by solving the one-dimensional conduction equation at the wall and the augmented Young-Laplace equation, respectively. The results obtained from the proposed model are in close agreement with several existing experimental data for the wall temperatures and the maximum heat transport rate. From the validated model, it is found that the assumptions employed in most previous studies may lead to significant errors for predicting the thermal performance of the heat pipe by comparing among the results obtained from the proposed and the simplifi...