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This study reports on heat transfer characteristics on a curved surface subject to an inclined circular impinging jet whose impinging angle varies from a normal position 9 = 0 deg to 9 = 45 deg at a fixed jet Reynolds number of Rej = 20,000. Three curved surfaces having a diameter ratio (DIDfl of 5.0, 10.0, and infinity (i.e., a flat plate) were selected, each positioned systematically inside and outside the potential core of jet flow where Dt is the circular jet diameter. Present results clarify similar and dissimilar local heat transfer characteristics on a target surface due to the convexity. The role of the potential core is identified to cause the transitional response of the stagnation heat trans fer to the inclination of the circular jet. The inclination and convexity are demonstrated to thicken the boundary layer, reducing the local heat transfer (second peaks) as opposed to the enhanced local heat transfer on a flat plate resulting from the increased local Reynolds number.

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Impingement heat transfer in a circular block of an open-cell metal foam with high porosity (ε 0.94) is experimentally studied at two distinctive flow regimes, semiturbulent (Re j 1800 and 2800) and fully turbulent (Re j 7500 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.Nomenclature a = laminar length, m C = jet exit-to-foam tip distance, m D f = diameter of circular foam block, m D j = round jet diameter, m F = inertial coefficient H = distance between jet exit and substrate, m H f = height of circular foam block, m h = heat transfer coefficient, W∕m 2 K I = input direct current to heating element, A K = permeability, m 2 L = length of potential core of round jet, m L u = length of undisturbed region of round jet, m Nu avg = area average Nusselt number, hD j ∕k f p s = static pressure, Pa p t = stagnation pressure, Pa Re j = jet Reynolds number, ρV jc D j ∕μ (not V in but V jc ) T a = ambient temperature, K T e = jet exit fluid temperature, K T s = substrate temperature, K V = input direct current voltage to heating element, V V c = axial velocity component of round jet at r equal to zero, m∕s V jc = axial velocity component of round jet at r and z equal to zero, m∕s r, θ, z = cylindrical coordinate system ε = porosity μ f = dynamic viscosity of air, Pa · s ρ = density of air, kg∕m 3