Heat and Mass Transfer
The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

Inversely proportional to
None of these
Directly proportional to
Equal to

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Heat and Mass Transfer
In counter flow heat exchangers

Both the fluids at exit are in their hottest state
Both the fluids at inlet are in their hottest state
One fluid is in hottest state and other in coldest state at inlet
Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

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Heat and Mass Transfer
The heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)

Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)
Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)
Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)
Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]

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