The effects of thermal boundary conditions on the heat transfer characteristics of laminar flow in milli-scale confined impinging slot jets

Abstract

This study experimentally investigated the effects of thermal boundary conditions on the laminar heat transfer characteristics of milli-scale, confined slot jets with flat, convex, and concave surfaces. We explored two thermal boundary conditions at the impinging surface: uniform heat flux and uniform wall temperature. The Reynolds number (Re) ranges from 120 to 600, the dimensionless nozzle-to-surface distance (H/B) from 2 to 10, and the dimensionless curved surface diameter-to-nozzle width (D/B) is 90. The results show that near the stagnation region, local Nusselt numbers for all three surfaces increase at each x/B location as H/B changes from 10 to 2 regardless of thermal boundary condition. In the wall jet region, However, in the wall jet region the uniform heat flux condition produces higher Nusselt numbers than the uniform wall temperature. As a result, local Nusselt numbers for both thermal boundary conditions show cross-over regions at x/B=1-5 where the dependence of local Nusselt number on H/B changes, depending upon the x/B location. These behaviors illustrate the sensitivity of Nusselt numbers for laminar boundary layer and laminar slot jet flows to thermal boundary condition. Empirical correlations for both stagnation and local Nusselt numbers with a concave surface are in an agreement with the experimental results to within ±15%.