Heat and Mass Transfer
A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

1/h₁ + 1/h₂ + 1/h₃
h₁ + h₂ + h₃
None of these
(h₁.h₂.h₃)1/3

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Heat and Mass Transfer
Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

k.
(dT/dx)
k.
(dx/dT)
k. (dx/dT)
k. (dT/dx)

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