Experimental investigation of the pressure-drop characteristics of open-cell metal foam with air-gaps under non-Darcy flow regimes

Multi-layer metal foam with discrete air gaps between neighbored layers can have wide engineering applications, and its pressure drop characteristic is the crucial performance that needs to be predicted precisely. Experimental studies were carried out to investigate the influences of the air gaps and their layouts on the pressure drop characteristics of the multi-layer open-cell metal foam within a wide flow velocity range to develop efficient models for pressure drop predictions. The accumulated metal foam thickness and air gap distance were kept unchanged in the tests, and four sets of test sections with different air gap layouts were tested. The varying airflow speed across the metal foam was realized by adjusting the inlet pressure level of the test section to reveal the relations of the pressure drop versus the mass flow rate. Results indicate that in the multi-layer and multi-gap configurations, the Forchheimer model in the transition regime and bilinear model in the turbulent regime is still applicable for predicting the pressure drop; however, the insertion of air gaps between the metal foam slices leads to an increased pressure drop coefficient. Meanwhile, the first air gap leads to a higher pressure drop compared to the subsequent air gaps and shifts the flow regime transition point towards an even more minor flow rate operating point, while the subsequent air gaps present almost the same influences on the metal foam pressure drop characteristics and transition point. With the experimental study, two models for predicting the pressure drop characteristics of open-cell metal foam with and without air gaps in the transition and turbulent flow regimes with a broadened range are presented.