Role of Laminar Length of Round Jet Impinging on Metal Foams

Impingement heat transfer in a circular block of an open-cell metal foam with high porosity is experimentally studied at two distinctive flow regimes, semiturbulent ( and 2800) and fully turbulent ( and 15,000) regimes. The influence of jet structures and their variation with jet exit-to-foam spacing (impinging distance) on overall heat transfer are characterized. The laminar length appears in the semiturbulent jet but disappears in the fully turbulent jet. Its role is found to longitudinally translate the onset axial location of entrainment, which coincides with the potential core of the round jet. When the metal foam is positioned inside the laminar length, the overall heat transfer becomes insensitive to the impinging distance. A wider divergence of the semiturbulent jet and a faster decay of the axial momentum than the fully turbulent jet occur once entrainment takes place.