Numerical simulation on the forced convection heat transfer of porous medium for turbine engine heat exchanger applications

The porous medium shows tremendous potential application as heat exchangers in turbine engines. However the forced convection heat transfer performance in porous medium at high velocities ( > 20 m/s) is difficult to obtain from experiments. In this work, the open-Kelvin model, alternatively termed as sphere-subtraction and pillar models, have been generated to investigate the heat transfer characteristics of porous media with high porosity within a velocity range of 4-90 m/s, by employing the computational fluid dynamics (CFD) method. The results indicated that the pressure drop, heat transfer coefficient, and volumetric heat transfer coefficient increases along with the CPI (cells per inch) and decreases with increasing porosity. The pressure drop has been more sensitive to porosity than CPI. At high velocities, the effect of CPI and porosity on the convection heat transfer performance is more obvious. The transverse area of the throat and skeleton size are the two key structure parameters affecting the pressure drop. Under high velocities, the pressure drop has a quadratic increase owing to the velocity increase, whereas the volumetric heat transfer coefficient has a logarithmic increase, which causes the overall heat transfer performances (j/f) to decrease rapidly to a lower level. The changes in the porosity and CPI are not sufficient to improve the j/f at high velocities, and hence, the optimization of the pore structure is the key factor. The pillar model, which can be considered as an optimization model of sphere-subtraction model, has an increase rate of 121% in the j/f at a velocity of 90 m/s.