Pick out the correct equation.
The unit of heat transfer co-efficient is
The value of Stefan-Boltazman constant in SI unit is
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The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h_{0} = heat transfer coefficient at the outer surface)
A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are k_{A} and k_{B} and the specific heat capacities are C_{PA} and C_{PB} for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when