Abstract
A detailed computational study was performed for the case of a wall-bounded pin-fin-array in a staggered arrangement, representative of industrial configurations designed to enhance heat transfer. In order to evaluate the level of turbulence modelling necessary to accurately reproduce the flow physics at three (3) different Reynolds numbers (3,000, 10,000 and 30,000), four models were selected: two eddy-viscosity URANS models (k-ω-SST and ϕ-model), an Elliptic Blending Reynolds-stress model (EB-RSM) and Large Eddy Simulation (LES). Global comparisons for the pressure loss coefficients and average Nusselt numbers were performed with available experimental data which are relevant for industrial applications. Further detailed comparisons of the velocity fields, turbulence quantities and local Nusselt numbers revealed that the correct prediction of the characteristics of the flow is closely related to the ability of the turbulence model to reproduce the large-scale unsteadiness in the wake of the pins, which is at the origin of the intense mixing of momentum and heat. Eddy-viscosity-based turbulence models have difficulties to develop such an unsteadiness, in particular around the first few rows of pins, which leads to a severe underestimation of the Nusselt number. In contrast, LES and EB-RSM are able to predict the unsteady motion of the flow and heat transfer in a satisfactory manner.
Highlights
Heat transfer augmentation has been an open question since the invention of the first Stirling engine in the early nineteenth century
The pressure loss coefficient is based on the total pressure drop from the inlet to the outlet of the domain and is defined as f = P /(2ρVB2GN ), where N is the number of rows
It is well known that, in the case of wakes (a) of infinite cylinders [14] or wall-mounted obstacles [15], the RANS models cannot accurately predict the recirculation region, and that Unsteady Reynolds-Averaged Navier-Stokes (URANS) can drastically improve the prediction by resolving a significant part of the large-scale unsteadiness, which is a major contributor to the mixing of momentum
Summary
Heat transfer augmentation has been an open question since the invention of the first Stirling engine in the early nineteenth century. In thermal-hydraulics systems one of the main objectives is the effective heat transfer with minimum pressure drop across the working system. In addition to the complex underlying flow physics, this case is close to several industrial configurations found in internal cooling of gas-turbine blades, electronic devices and nuclear thermal-hydraulics. The use of pin-fin-arrays has proved to be an effective technique in achieving enhanced rates of heat transfer in the past. Some of the earlier experimental studies done by [1,2,3,4] and more recently by [5,6,7,8,9] report a number of flow characteristics including the heat transfer and pressure loss coefficients through various configurations of pin-fin-arrays
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