Using the naphthalene sublimation technique, the radial distribution of the local convection mass transfer coefficient for uniform flow normal to a circular disk has been correlated by an expression of the form.

The stagnation point Sherwood number (Sh0) depends on the Reynolds (ReD = VD/v) and Schmidt (Se = v/DAB) numbers and data have been correlated by the following expression: Obtain an expression for the average Nusselt number (Nu D = hD/k) corresponding to heat transfer from an isothermal disk exposed to the foregoing flow conditions. If a = 1.2 and n = 5.5, what is the rate of heat transfer from a disk of diameter D = 20 mm and surface temperature Ts = 125°C to an airstream for which ReD = 5 X 104 and T∞ = 25°C? Typically, boundary layer development from a stagnation point yields a decaying convection coefficient with increasing distance from the stagnation point. Provide a plausible explanation for why the opposite trend is observed for the disk.

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h(r)D Shp DAB Sh. h(r= 0)D Sh, = 0.814RE Sc36 DAB Naphthalene coating