1
GATE ME 1991
Subjective
+5
-0
An object has the shape of cubical box of side $$10cm,$$ with no top cover. The box is placed inside a room whose dimensions are much larger than those of the box. All the five surfaces of box are at a temp of $${500^ \circ }C$$ and have an emissivity of $$0.6.$$ The walls of the room are at $${25^ \circ }C$$ and have an emissivity of $$0.4.$$ All these surfaces can be assumed to be diffuse-gray. Find the net radiative heat loss from the inner surface of the box to the walls of the room.
Stephen Boltzmann constant $$5.67 \times {10^{ - 8}}\,\,W/{m^2}{K^4}$$. View factor between two parallel square plates placed directly opposite to each other is $$0.2$$
2
GATE ME 1989
Subjective
+5
-0
Two black plates, each one meter square, are placed parallel to each other in such a way that the radiation shape factor for the system is $$0.4.$$ If the plates are maintained at $${800^ \circ }C$$ and $${400^ \circ }C$$ respectively, determine the net radiant heat transfer between the plates. Also calculate the net heat exchange if the plates were infinite in size. Stephen Boltzmann constant $$= 5.67 \times {10^{ - 8}}\,\,W/{m^2}{K^4}$$
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