Experimental investigation on enhanced thermal performance of staggered tube bundles wrapped with metallic foam

Tube bundles wrapped with metallic foam can be used in air-breathing engine as the compact heat exchanger due to its low density and high specific surface area. The enhanced thermal performance of metallic foam is crucial to design of staggered tube bundles with metallic foam fins. Previous studies have shown the effects of foam-structure on entire metallic foam, and discussed the influence of tube-bundle structure on the tube bundles qualitatively. However, the thermal and flow mechanisms on coupling of metallic foam and pure fluid which could expound enhanced heat transfer process of metallic foam fins are not yet fully explored. To address this, an experimental study was conducted to investigate the effects of structure parameters of metallic foam on thermal and flow characteristics in 2 mm outer-diameter staggered tube bundles wrapped with 2 mm thickness of metallic foam. This article reveals variation trend of heat transfer rate with change of key parameters: porosity and pore density. The results indicate that: 1, with increase of porosity, Nusselt number increases because of stronger penetrating ability, and heat convection dominates the heat transfer. 2, for variation of pore density, Nusselt number of high PPI samples is lower for thermal-insulation effect at low Reynold number. However, Nusselt number of high PPI samples is higher for greater amount of penetrating air at high Reynold number. 3, a new friction factor correlation of tube bundles is proposed to describe the pressure drop by dimensionless tube pitches, Reynolds number and Darcy number with maximum ±20% deviation. 4, a new Nusselt number correlation of tube bundles is given to reflect the heat transfer mechanism by Darcy number.