Performance improvement of counter-flowing double-pipe heat exchanger partially filled with a metal foam and rotating coaxially

Abstract

In order to enhance the amount of heat transported in a double-pipe heat exchanger, a compound enhancement is proposed herein incorporating both active and passive methods. The first one is through introducing secondary flows in the vicinity of the conducting surface using metal foam guiding vanes, which are fixed obliquely and rotating coaxially to trap fluid particles while rotation and then force them to flow over the conducting surface. The other is via covering the conducting surface between the two pipes with a metal foam layer to improve the heat conductance across it. This proposal is examined numerically by studying the three-dimensional, steady, incompressible, and laminar convective fluid flow in a counter-flow double-pipe heat exchanger partially filled with high porosity metal foam and rotating in a coaxial-mode. In regards to the influence of rotation, both the centrifugal buoyancy and Coriolis forces are considered in the current study. The generalised model is used to mathematically simulate the momentum equations in the porous regions employing the Boussinesq approximation for the density variation. Moreover, thermal dispersion has been taken into account with considering that fluid and solid phases are in a local thermal non-equilibrium. Computations are performed for a range of design parameters influencing the performance achieved such as the operating conditions and the configuration of the guiding vanes utilised. The results are presented by means of the heat exchanger effectiveness, pressure drop, and the overall system performance. The current proposal has proved its potential to enhance the heat transported considerably with saving significant amount of the pumping power required compared to the corresponding heat exchangers, which are fully filled with metal foam. Also, the data obtained reveal an obvious impact of the design parameters inspected on both the heat exchanged and the pressure loss; and hence, the overall performance obtained. Although the heat exchanger effectiveness can be improved considerably by manipulating the design factors, care must be taken to avoid unjustified expenses resulted from potential augmentation in pressure drop.