Analysis of transport phenomena on cooling a flat surface using swirl jet impingement with crossflow

Abstract

Enhancing airside convective heat transfer is a challenging problem due to the poor thermal properties of air and the high thermal resistance of the thermal boundary layer. This study presents an innovative method to improve the convective heat transfer of cross airflow over a flat plate using a Swirl jet to suppress the boundary layer thus reducing the thermal resistance. A three-dimensional numerical analysis was performed to study the transport phenomena that occur when a swirl air jet is issued perpendicular to a crossflow of air flowing over a hot flat plate. The finite element method with SST k-ω turbulence model was employed for this numerical study after validation with experimental data from the literature. A parametric study was performed by varying Reynolds number of the jet, Rej(2500−10000), dimensionless jet to plate spacings, Z/D(1−2), swirl number, SW(0.3−0.9), and blockage ratios, BR(0.4−0.6). The thermal performance was assessed by the average heat transfer coefficient, h‾j, in addition to the ratio of heat transfer coefficient between the proposed setup involving crossflow with jet to the reference case of crossflow without jet, h‾j/h‾woj, thus, a correlation is obtained for the average heat transfer coefficient. The friction factor, f, and the pumping power were used to evaluate hydraulic performance. The performance evaluation coefficient, PEC, was chosen to identify the best possible thermal and hydraulic performance. Results show that for all the cases under study, there is a clear enhancement of the heat transfer coefficient when employing a combination of swirl jet with crossflow over a flat plate compared to the case of crossflow without jet. The maximum value of PEC was 1.8 occurring at Reynolds number, Rej, of 10000, swirl number of 0.9, blockage ratio of 0.6, and jet-to-plate spacing of 2D.