Interferograms

Interferometric data for the smaller copper block of height 10 mm and a protrusion of 5 mm is presented first. Figure 4.36 shows thinned fringes in the proximity of the heater at temperatures of and . Since the fluid below the lower surface is nearly stationary, fringes in this region have not been shown. The images have been recorded with varying magnifications to maintain clarity. The outermost fringe can be treated as the edge of the boundary- layer thickness can, however, be used for analysis. For an assumed quadratic temperature as well as constant heat flux boundary conditions is

An examination of figure 4.36 shows the following trends. With temperature increasing from the thermal boundary-layer thickness decreases. Further increase in temperature to does not lead to any significant reduction in the boundary-layer thickness. At the boundary-layer thickness is nonzero at the leading edge of the heated block. For the other two temperatures, is small at this location.

A drop in the value of boundary layer thickness indicates an increase in the local Nusselt number. Hence the Nusselt number on the vertical face increase as one goes from . This increase is only marginal between and , the fringe density, and hence,  heat flux over the upper horizontal face, continually increases as one move from . This is also a source of increasing the average Nusselt number with clip temperature.