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

Abstract

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.

Thermo-Hydraulics of Tube Banks With Porous Interconnectors Using Water as Cooling Fluid

“…This reduction can be attributed to the absence of the pressure drop penalty originally caused by the recirculation and vortices behind individual tubes in the inline configuration without the porous medium. A similar observation was made by Raju and Narasimhan (2007) in their numerical study of inline tube bank with porous interconnectors. In the present experimental study a maximum of 12 percent pressure drop reduction was observed for the range of flow considered.…”

“…1a is considered for numerical simulation, initially without contact resistance between tubes and porous interconnectors and later by introducing thermal contact resistance. A commercially available CFD software is used for the simulations The numerical procedure followed here is similar to that detailed in Raju and Narasimhan (2007).…”

“…The heat transfer rate of the tube with porous inserts whose diameters approach the diameter of the tube is about 1.6 to 5.5 times larger than the smooth tube cases in laminar, transitional and turbulent ranges of Reynolds numbers. Raju and Narasimhan (2007) have investigated forced convection of inline tube banks with porous inserts under laminar flow. They have reported uniform heat transfer enhancement for all configurations and less pressure drop for some configurations than the configurations without porous inserts.…”

“…Based on the literature survey it can be summarised that a proper selection of metal foam inserts is crucial for enhancement of heat transfer characteristics. The objectives of this work are to perform an experimental investigation on the use of tube-to-tube porous interconnectors to reduce pressure drop in the inline tube bank arrangement as suggested in Raju and Narasimhan (2007) and to study the heat transfer effects for the staggered tube bank arrangement. Figure 1(a) shows the schematic of the inline configuration considered for the forced convection heat transfer experiments.…”

Experimental study of mixed convection heat transfer in a vertical duct filled with metallic porous structures

“…They pointed out important reasons that negate a direct comparison between the numerical and experimental results. Raju and Narasimhan [10], using a numerical study, presented a novel approach of treating near compact heat exchangers (in-line tube to tube arrangement) as global porous media for estimating the global thermo-hydraulic characteristics. The authors presented correlations for nondimensional pressure drop and Nusselt number for characterizing the thermo-hydraulic performance of the chosen near compact heat exchanger configurations.…”