Abstract:
Jet impingement combined with phase change in the form of boiling has been proven to enhance heat transfer in thermal management applications. When added to surface enhancement, a further increase in heat transfer can be envisaged. Surface enhancement in the form of pin-fins are investigated numerically for a confined single jet of HFE 7100 impinging on a copper surface under boiling conditions. ANSYS Fluent with the Rensselaer Polytechnic Institute boiling model embedded in the Eulerian multiphase framework is utilised. After validating the resulting boiling curve against experiments with an in-line arrangement of pin-fins, a parametric study to investigate the effect of pin geometry, and pattern was performed. Key parameters included Reynolds numbers, pin-fin heights, pin-fin spacing and a star pattern. The objective of the parametric analysis was to limit the dry-out regions in the domain. Finding that local dry-out is decreased through decreasing flow obstruction and heat transfer is mainly linked to surface augmentation. Our results show that for the experimental configuration, 17 % of the pin-fin area experienced dry-out at the 23.2 W/cm2 input heat flux. Dry-out was practically eliminated for low pin-fins spaced far apart as expected. But, when keeping the surface augmentation factor constant in a star pattern, the dry-out area was reduced from 17 % to 1 % at the same input heat flux without a significant change in the wall superheat. In addition, the star pattern distribution allowed for a substantial increase in the critical heat flux compared to the in-line arrangement. It was also demonstrated that the pressure drop over the domain was independent of the surface enhancement as it was dominated by the jet stagnation pressure.
