As discussed in Section 5.2, the lumped capacitance approximation may be applied if \(B_{i}<0.1\), and, when implemented in a conservative fashion for a long cylinder, the characteristic length is the cylinder radius. After its extrusion, a long glass rod of diameter \(D=15 \mathrm{~mm}\) is suspended horizontally in a room and cooled from its initial temperature by natural convection and radiation. At what rod temperatures may the lumped capacitance approximation be applied? The temperature of the quiescent air is the same as that of the surroundings, \(T_{\infty}=T_{\text {sur }}=27^{\circ} \mathrm{C}\), and the glass emissivity is \(\varepsilon=0.94\).