Influence of pore density on thermal development in open-cell metal foam

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Experimental results for oscillatory water flow in 10-ppi metal foam at low-frequencies

This experimental study presents results and interpretation of oscillatory water flow in open-cell metal foam. The tested foam had 10 pores per inch and a porosity of 88%. At relatively low frequencies, three flow displacements were employed in the experiment. The influence of frequency and displacement on pressure loss and friction factor is discussed. A correlation of friction factor as a function of the kinetic Reynolds number was determined. Porous media parameters, permeability and drag coefficient, were also found for the same foam via steady-state flow experiments in the Darcy and Forchheimer regimes. The friction factor of oscillating flow was found to be higher than that of steady state. The findings of this study are considered important for oscillating heat transfer in metal foam

Heat transfer measurements for non-Darcy flow in 10-ppi metal foam

Metal foam is a class of porous media with very high porosity (around 90%) and a large surface area density. The foam internal structure is web-like of thin ligaments surrounding cells that are open to flow. This structure promotes thermal dispersion because it offers a lot of mixing of a flowing fluid. Break up and inception of the boundary layers are phenomena adding to the convective heat transfer. The thermal conductivity of the solid phase of metal foam is also high. Because of all these attributed, metal foam is an excellent heat exchanger technology. There is a need for more experimental data regarding heat transfer in metal form. In this paper, experimental heat transfer data for water flow in commercial open-cell aluminum foam cylinder heated at the wall by a constant heat flux (14,998 W/m2 and 26,347 W/m2), is presented. The foam had 10 pores per inch (ppi) and a porosity around 87%. The measurements included wall temperature along flow direction as well as average inlet and outlet temperatures of the water. Flow speeds were in the non-Darcy regimes: transitional and Forchheimer flow regimes. The behavior of the wall temperature clearly shows thermal development conditions. The experimental Nusselt number is presented as a function of axial distance in flow direction, and showed what seemed to be periodic thermal development. The experimental data can be used for validation of other analytical solutions. The results can also be used to verify numerical models and metal-foam heat exchangers used in air-conditioning for example

High-frequency oscillating water flow in highly-porous media: experimental results for 10-ppi metal foam

It is well known that oscillating flow can increase heat transfer over steady-state flow. Inserting porous media in the path of a flow also enhances convection heat transfer. Combining these two effects (oscillating flow and porous media) is supposed to substantially augment heat transfer. In order to understand the heat transfer in such arrangement, one must first understand the flow behavior. Oscillating water flow in open-cell metal foam having 10 pores per inch (ppi) has not been reported in the literature. In this paper, main characteristics of oscillating water flow in 10-ppi open-cell metal foam is reported. The foam had a porosity of 87%. Three flow displacements 74.3, 97.2 and 111.5 mm were applied at the relatively high flow frequencies of 0.46, 0.58 and 0.69 Hz. The effect of flow displacement and frequency on important parameter is presented and discussed. The appropriately defined friction factor correlated well with the kinetic Reynolds number. Steady-state experiments were also conducted for Darcy and Forchheimer water flow through the same metal foam, and the permeability and form/inertial drag coefficient were obtained. Comparisons of the friction factor for oscillating and steady flows is presented. The results of this study are very likely applicable to similar foam-like highly porous media, and is critical for interpreting oscillating heat transfer in metal foam