Wall Nusselt Number

This graph shows results from heat transfer experiments designed to find out how the wall heat transfer coefficient changes as the effects of the discrete nature of the packing become stronger as N decreases. The Nu_w results for spheres shown are not spread so widely as the k_r/k_f values, although a similar pattern emerges. For higher N, there is only a small effect of N, then a strong increase at N = 2.7, a decrease back to values consistent with the high-N results for N = 2.0, a strong decrease for N = 1.8, followed by a monotonic increase as N decreases from 1.8 to 1.14. The values of Nu_w are well-represented by straight lines, although prior work would suggest that Nu_w should be proportional to Re^0.6-0.75 as Re increases. This apparent linearity may be due to the relatively narrow range of Re achievable in the experimental apparatus of this study. The slopes of the lines fitted to the Nu_w data appear to decrease distinctly with decreasing N, and there also seems to be an effect on the intercept.