Numerical Study on Thermal and Fluid Dynamic Behavior of a Compact Heat Exchanger Partially Filled with Metal Foam

Abstract

Received: 18 February 2019 Accepted: 4 May 2019 Designers of heat exchangers are regularly searching for new methods that enhance the heat transfer efficiency. A possible substitute of the conventional fins is the use of open-cell metal foams. Low density, good rigidity, high thermal conductivity and huge value of surface/volume ratio represent the best characteristics of porous media. For these features, metal foams are used in several applications such as heat exchangers, fuel cells, heat sinks and solar thermal plants. The need to create new systems in reduced volumes led to the adoption of the aluminum foams for their great specific area surface that allows to have compact heat exchanger characterized by a high thermal performance. A numerical investigation has been accomplished to analyze the thermal and fluid dynamic behavior of a tubular heat exchanger partially filled with aluminum foam. The Darcy – Brinkman Forchheimer flow model and the thermal non-equilibrium model (LTNE) for the energy are applied to carry out two-dimensional simulations on the metal foam heat exchanger. The foam has a porosity and (number) pores per inch respectively equal to 0.935 and 20. The heat exchanger is analyzed for different air flow rates and a fixed surface tube temperature. The results are given as average and local heat transfer coefficient evaluated on the external surface of the tubes. Furthermore, the local air temperature profiles in the smaller cross section, between two consecutive tubes are given. Finally, the Energy Performance Ratio (EPR) is evaluated in order to demonstrate the thickness of metal foam that improve the system performances.