An infinitely long furnace of $$0.5m \times 0.4m$$ cross-section is shown in the figure below. Consider all surfaces of the furnace to be black. The top and bottom walls are maintained at temperature $${T_1} = {T_3} = {927^ \circ }C,$$
while the side walls are at temperature $${T_2} = {T_4} = {527^ \circ }C.$$
The view factor, $${F_{1 - 2}}$$ is $$0.26.$$ The net radiation heat loss or gain on side $$1$$ is_________ $$W/m.$$ Stefan-Boltzman constant $$ = \,5.67 \times {10^{ - 8}}$$ $$W/{m^2}$$-$${K^4}$$

A solid sphere $$1$$ of radius $$'r'$$ is placed inside a hollow, closed hemispherical surface $$2$$ of radius $$'4r'.$$ The shape factor $${F_{2 - 1}}$$ is ...

The total emissive power of a surface is $$500$$ $$W/{m^2}$$ at a temperature $${T_1}$$ and $$1200$$ $$W/{m^2}$$ at a temperature $${T_2}$$, where the temperatures are in Kelvin. Assuming the emissivity of the surface to be constant, the ratio of the temperatures $${{{T_1}} \over {{T_2}}}$$ is

Two infinite parallel plates are placed at a certain distance apart. An infinite radiation shield is inserted between the plates without touching any of them to reduce heat exchange between the plates. Assume that the emissivities of plates and radiation shield are equal. The ratio of the net heat exchange between the plates with and without the shield is