A hemispherical furnace of $$1$$ $$m$$ radius has the inner surface (emissivity, $$\varepsilon = 1$$) of its roof maintained at $$800K,$$ while its floor $$\left( {\varepsilon = 0.5} \right)$$ is kept at $$600K$$. Stefan-Boltzmannn constant is $$\,5.668 \times {10^{ - 8}}$$ $$W/{m^2}.{K^4}.$$ The net radiative heat transfer (in $$kW$$) from the roof to the floor is __________.

Two large diffuse gray parallel plates, separated by a small distance, have surface temperatures of $$400$$ $$K$$ and $$300$$ $$K.$$ If the emissivities of the surfaces are $$0.8$$ and the Stefan-Boltzmann constant is $$5.67 \times {10^{ - 8}}$$ $$W/{m^2}{K^4},$$ the net radiation heat exchange rate in $$kW/{m^2}$$ between the two plates is

Consider two infinitely long thin concentric tubes of circular cross section as shown in the figure. If $${D_1}$$ and $${D_2}$$ are the diameters of the inner and outer tubes respectively, then the view factor $${F_{22}}$$ is given by

Radiative heat transfer is intended between the inner surfaces of two very largen isothermal parallel metal plates. While the upper plate (designated as plate $$1$$) is a black surface and is the warmer one being maintained at $${727^ \circ }C,$$ the lower plate (plate $$2$$) is a diffuse and gray surface with an emissivity of $$0.7$$ and is kept at $${27^ \circ }C.$$ Assume that the surfaces are sufficiently large to form a two-surface enclosure and steady state conditions to exist. Stefan Boltzmann constant is given as
$$5.67 \times {10^{ - 8}}\,W/{m^2}{K^4}$$

The irradiation (in $$kW/{m^2}$$) for the upper plate is