Performance evaluation of single tubular aluminium foam heat exchangers

Five samples of aluminium foam-wrapped tubular heat exchanger are being tested for heat transfer performance and pressure drop characteristics. The foam layer has thickness (or height) varied from 5 mm to 20 mm. The tests are carried out on each heat exchanger, installed horizontally in a cross-flow arrangement inside an open circuit wind tunnel, one at a time with air velocity varying between 0.5 and 5 m/s. Heat transfer rate from 75 °C hot liquid, circulating through the core tube, to external air is evaluated. These results, together with temperature differential between the ambient air and the foam surface, allow evaluation of the overall thermal resistance. Pressure drops across each sample are recorded. The performance of the foam heat exchangers is assessed by comparing their thermo-hydraulic results against those of a conventional finned tube with similar dimensions and tested under the same conditions. The results show that, within the designated air velocity range, the foam heat exchangers with thicker foam layer perform better than those with thinner foam layer. However, the heat transfer advantage does not increase linearly with foam thickness – signifying the existence of an optimum thickness when an increase in pressure drop at increased air velocity is taken into account. Finally, the correlations to predict the overall thermal resistance and pressure drop are presented.