INVESTIGATIONS ON OPEN-CELL METAL FOAM–FITTED TUBES FOR HEAT TRANSFER ENHANCEMENT – A DISCUSSION ON ENHANCEMENT MECHANISMS

Abstract

Metal foams are drawing increasing attention due to their high surface area-to-volume ratio, high thermal conductivity, and low density. Heat exchanger manufacturers are constantly looking for innovative methods toward building highly efficient and compact heat exchangers. To enhance heat transfer, the effective thermal conductivity, fitment of foam on pipe, influence of working fluids, and effect of the bonding method are major areas of investigation. This paper aims to present a review of various investigations conducted on open-cell metal foam for enhancing heat transfer. The pore size distribution of metal foam directly influences the effective thermal conductivity. Recent progress toward bimodal pore size distribution has been reviewed and discussed. There exists a tradeoff between enhancing heat transfer and the corresponding pressure drop. Different configurations of fitting metal foam on pipes, such as fully filled, partially filled, and tubes wrapped with metal foam, are critically reviewed, and their performance is compared. The working fluid and its conditions used with metal foam has tremendous potential toward enhancing heat transfer. The influence of nonrefrigerants, refrigerants, and nanofluids has been presented in this regard. Different bonding methods and their influence on thermal resistance are also reviewed. To date, there is hardly any literature that addresses the performance of metal foam–fitted tubes in condensers and evaporators for vapor compression refrigeration systems. Metal foam-fitted tubes have shown promising results in terms of heat transfer enhancement. The outcome of this review provides insights into further research on the use of metal foam–fitted tubes for refrigeration applications.