Porous Medium Interconnector Effects on the Thermohydraulics of Near-Compact Heat Exchangers Treated as Porous Media

A novel approach of treating near-compact heat exchangers (NCHX) (surface to volume ratio, $α=100-300m2∕m3$ with hydraulic diameter $DM∼6mm$⁠) as a “global” porous media, whose thermohydraulic performance is being influenced by the presence of “local” tube-to-tube porous medium interconnectors, connecting the in-line arrangement of tubes $(D=2mm)$ having square pitch of $XT=XL=2.25$⁠, is investigated in this study using numerical methods. The thermohydraulics of the global porous media (NCHX) are characterized by studying the effect of transverse thickness $(δ)$ and permeability (represented by $Dai$⁠) of the local metal foam type porous medium interconnectors on the global heat transfer coefficient (Nu) and nondimensional pressure drop $(ξ)$⁠. The fluid transport in the porous medium interconnectors is governed by the Brinkman–Darcy flow model while the volume averaged energy equation is used to model energy transport, with the tube walls kept at constant temperature and exchanging heat with the cooling fluid having $Pr=0.7$ under laminar flow $(10<Re<100)$⁠. For the chosen NCHX configuration, $ξ$ and Nu increases for an increase in Re and also with an increase in the thickness $(δ)$ of the interconnecting porous medium. However, as the local Darcy number $(Dai)$ of the interconnecting porous medium increases, the $ξ$ decreases but the Nu increases. Treating the heat exchanger as a global porous media this result translates to an increase in the $ξ$ and Nu as the global permeability (represented by $Dag$⁠) decreases, where the decrease in $Dag$ is because of either an increase in $δ$ or a decrease in $Dai$⁠. Separate correlations predicting $ξ$ and Nu as a function of Re and $Dag$ (which in turn is correlated to $δ$ and $Dai$⁠) have been developed for the chosen NCHX configuration, both of which predict the numerical data with $±20%$ accuracy.