4-18. Consider an infinitely long rod whose cross section is a sector of a circle of radius R (Fig. 4-58). One side surface of the rod is subjected to the heat flux g"(r) while the other is insulated. The peripheral surface transfers heat to the ambient at temperature T with the heat transfer coefficient h. Find the particular form of q"(r) for which the problem admits a product solution. h. T. FIG. 4-58