Heat transfer characteristics of a micro-scale impinging slot jet

In the present study, heat transfer characteristics of a micro-scale slot jet impinging on a heated flat plate are experimentally investigated. The effects of Reynolds numbers ( Re = 150–5000) and nozzle-to-plate spacings ( Z/d h = 0.5–10) on the Nusselt number are considered. Based on the experimental results, correlations on the stagnant and average Nusselt numbers for the micro-scale impinging slot jet are developed as a function of Reynolds number and nozzle-to-plate spacing. At Reynolds numbers ( Re < 2500), different from the existing results, the present study shows that the heat transfer characteristics of the micro-scale impinging slot jet are similar to those of the macro-scale impinging slot jet. However, at Reynolds numbers ( Re ⩾ 2500), the present study shows that the heat transfer characteristics of the micro-scale impinging slot jet are different from those of the macro-scale impinging slot jet. Firstly, a maximum local Nusselt number occurs at a shifted peak of about x/d h = 1.75 under the condition of large nozzle-to-plate spacing ( Z/d h > 1), rather than at the stagnation point. Secondly, the effect of the nozzle-to-plate spacing on the Nusselt number is significant. The exponent on Reynolds number is the function of nozzle-to-plate spacing Nu ∝ Re f ( Z / d h ) , rather than a constant value.