Thermo-Hydraulic Trade-offs in Multi-Row Inline Tube Bundles: High-‎Fidelity CFD Validation for Waste Heat Recovery Systems

Abstract

A fair degree of thermal-hydraulic acumen on multi-row tube bundles is necessary for optimizing the Waste Heat Recovery System (WHRS), and an accompanying CFD study is performed on a 10-row inline bundle subjected to crossflow at a Reynolds number of 45,000 (based on maximum velocity). The authors segregate the degree to which aerodynamic “shadowing” has taken effect separately from turbulence buildup across the rows using a row-by-row heat flux equation complementing isolated turbulence building studies employing the SST k-ω model (with y+ < 1 wall treatment). They find a thermal “valley” at Row 2, where a 35% drop in local Nusselt number (from 178.4 to 115.6) occurs due to fluid stagnation in the wake. Turbulence buildup, however, is slow, yielding a 13-fold increase in Turbulence Kinetic Energy (TKE) (from 1.25 m²/s² to 17.20 m²/s²) row-wise. It is initiated at Row 4 (Nu = 158.3), with a periodicity set by Row 7 (Nu = 170.8), this thermal recovery finally approaches an idealised asymptotic state of “just” 172.0, row by row to the 10^th row. With respect to pressure drop, a fairly large form drag of 845.2 Pa for Row 1 falls drastically to 312.8 Pa at Row 2 (reflex action of the negative pressure array), and thereafter approaches the 380 Pa region, row on row from Row 3. The natural form of perturbation in turbulence levels in the latter rows (TKE can be as high as 35) tends eventually to delay the separation of the boundary layer from 82° (Row 1) to 98° (Row 5). A method of validating experimental dense tube arrays, purposed for recapturing a fraction of the energy now squandered to the atmosphere, is presented..