Heatline visualization of forced convection laminar boundary layers

This paper reports in closed form the similarity heatfunctions H for laminar boundary layer flow on a flat wall. Plots of the constant-H lines (‘heatlines’) show that the path of convection from a hot free stream to a cold wall is unlike the path of convection from a hot wall to a cold fluid. The true path of convection in laminar boundary layer flow is visualized in charts drawn for both heat transfer modes (cold wall, hot wall), several Prandtl numbers (0.02, 0.72, 7) and isothermal walls and constant-flux walls. The paper stresses the heat transfer features that are brought into view for the first time by the heatline patterns. As a supplementary contribution, the paper reports the exact similarity solution for the wall with uniform flux in the Pr→ 0 limit, and proposes a closed-form local Nusselt number correlation that covers the entire Pr range.