Development of a heat transport model for open-cell metal foams with high cell densities

- Open-cell metal foams promising catalyst supports due to high thermal conductivity.
- Heat conduction efficiency was not far from the often-used Lemlich value of 1/3.
- Heat transfer resistance at the wall increases with increasing foam cell diameter.
- Structured tubular reactor wall heat transfer coefficient independent of flow rate.
- Shorter reactors: process intensification, smaller pressure drop: cost efficiencies.

If made of highly conductive materials, open-cell metal foams are particularly interesting as enhanced catalyst supports for fast exo/endo-thermic reactions due to their excellent heat transfer properties. We have extended previous investigations by running heat transfer experiments on open-cell metal foams with very high porosity (0.93 < ε < 0.98) and cell densities (60 and 110 PPI). The foam metal (FeCrAl alloy, NiCrAl alloy, copper, and cobalt), the temperature (300 °C-500 °C), the gas flow rate, and the flowing gas (N2 and He) were varied. Heat transfer data were collected during steady-state heating runs by measuring temperatures at 22 axial positions and 3 radial positions in the cylindrically shaped foams. A classical 2D heat transfer model was developed based on various correlations available in the literature to describe the heat transport phenomena. Altogether, 20 parameters were optimized in this model: thermal conduction efficiencies and effective wall gap sizes for each of the 8 foams, 2 effective wall heat transfer parameters in the upstream zone for the two gases used, 1 parameter in the radiative contribution, and 1 parameter in the dispersive contribution. The optimized model obtained by global regression shows a very satisfactory fit of the data for all the foams at all the test conditions. Thermal conduction through the solid connected structure was found to play a major role in the effective radial conductivity, with a heat conduction efficiency mostly quite close to the often-used Lemlich value of 1/3. Static gas conduction through an effective gap at the foam-wall interface was identified as the dominant resistance in the wall heat transfer.