Figure 4 presents the results of the

data analysis procedure of schlieren images for evaluation of the temperature field and the Nusselt number distribution. Figure 4(a) shows the hue variation with respect to the non-dimensional height at cavity widths of The hue variation is large near the walls representing the lower wall region and for the top wall region). Hue is nearly constant in the central region i.e. for the range y/H = 0.2 to 0.8. Figure 4(b) shows the temperature gradient variation obtained using the calibration curve and Equation 3. The integration of the temperature gradient of Figure 4(b) along with the known wall temperatures leads to the temperature distribution shown in Figure 4(c). The temperature profiles show a steep variation in the near wall region and almost a zero slope at the centre of the cavity. The temperature gradient in the near wall region from Figure 4(c) is used in Equation 7 leading to the spanwise Nusselt number distribution in Figure 4(d). The central region of the lower wall shows a nearly constant Nusselt number, which decreases towards the corners of the cavity. This reduction in the Nusselt number is related to a zero heat flux at the side walls arising from the insulated boundary condition.

Figure 4: The steps involved during the quantitative analysis of color schlieren; (a) change in hue, (b) temperature gradient, (c) non-dimensional temperature and (d) Nusselt number. The non-dimensional temperature from the present experiment is compared with previous work in (e)