Thermal Characterization of Open Lattice Structures Used as Heat Exchanger Surfaces

Abstract

Numerical simulation is performed to evaluate flow field and thermal characteristics in heat exchange matrices. The heat exchanger geometry evaluated consists of an isotropic open lattice structure containing group-interconnected, millimeter-scale, thermally conductive ligaments. The Reynolds number range of interest is Re = 3-1000. The flow fields investigated in this paper are both laminar and turbulent. The laminar flow fields are solved using direct numerical simulation (DNS), while turbulent flow fields are solved by large-eddy simulation (LES). The mean velocity profiles and velocity fluctuations are compared to each other and to experimental data for a packed bed of spheres. Friction factor and Colburn j-factor are calculated from the simulated flow fields and averaged in time. They are compared to the algebraic correlations reported in the literature for a packed bed of spheres and to experimental data for a screen laminate.

Thermal/Fluid Characteristics of Elliptic Cross Section Filament Box Lattice Matrices as Heat Exchanger Surfaces

“…Following Gullbrand et al [8], a single unit cell, shown in Fig. 9, was used to perform the numerical simulations.…”

“…They have shown that metal fraction, dimensionless specific surface area and dimensionless effective thermal conductivity can range as: 0≤ 1-ε ≤ 0.94, 0.93 ≤ βD ≤ π and 0 ≤ Ke ≤ π/4. Gullbrand et al [8] considered laminar and turbulent convection in circular cross section filament box lattices. Their work shows that steady laminar flow persists up to at least a Reynolds number of 100, with transition to unsteady flow at a Reynolds number of 300.…”

“…Numerical simulations are performed to evaluate flow and thermal characteristics. To study the effect of adding ellipticity to the filaments, friction factors and Stanton numbers are compared to the circular cross section filament case [8]. Since transition from laminar to turbulent flow is expected to occur in the range of mesh Reynolds number.…”

Comparison of LES and RANS Simulations of Turbulent Convection in a Structured Porous Media

“…The friction factor value increases with increasing level of turbulent kinetic energy. KWM predicts the smallest value of turbulent kinetic energy in the domain and seems to behave more similar to an unsteady flow than to a turbulent flow [4]. The Pearson Product Moment correlation is calculated for the relation between friction factor and volume-averaged turbulent kinetic energy.…”

“…Gullbrand and coworkers [4] have recently reported on single-phase convection in mm-scale box lattices. They found that steady laminar flow persists up to a Reynolds number of 100, with transition to an unsteady flow at a Reynolds number of 300.…”