Investigations of heat transfer, entropy generation and pressure build up for upward flow in a vertical channel equipped with a fin array

Abstract

The optimal thermal systems design criteria by maximizing the amount of heat transfer per pressure losses is a very important topic. In this work, flow and convection and radiation heat transfer characteristics are studied numerically for a flow in a vertical channel equipped with transverse fin array. The influences of fin height on heat transfer characteristics and fluid flow is investigated. Large number of fins is used (40 fins) in order to reach the fully developed conditions after few fins from the entrance. Based on the calculated data of temperature and velocity, the local entropy generation is calculated through the whole channel by solving the entropy generation equation. The results are validated against the available data in the literature and both results are in a good agreement. Optimizations for flow conditions and channel geometry are performed in order to obtain maximum heat transfer per pumping power losses. The results showed that the highest values of total heat transfer per pumping power losses are obtained at fin height to the gap width values of 0.1 and 0.3. The effect of heat transfer by radiation on entropy generation is examined and, the effect of the ratio, Gr/Re2, on the pressure field is also investigated. It was found that a positive pressure gradient appears downstream in the channel when the value of Gr/Re2 exceeds a certain limit. For Gr/Re2 values between 0 and 9, the pressure gradient is negative; however, when the value Gr/Re2 exceeds 9, the pressure starts to build up through the channel axis.