For the circular tube of equal length and diameter shown in fig below, the view factor $${F_{13}}$$ is $$0.17.$$ The view factor $${F_{12}}$$ in this case will be.

Water (Prandtl number $$=6$$ ) flows over a flat plate which is heated over the entire length. Which one of the following relationship between the hydrodynamic boundary layer thickness $$\left( \delta \right)$$ and thermal boundary layer thickness $$\left( {{\delta _t}} \right)$$ is true

Lumped heat transfer analysis of a solid object suddenly exposed to a fluid medium at a different temp is valid when.

A composite wall, having unit length normal to the plane of paper, is insulated at the top and bottom as shown in the figure. It is comprised of four different materials $$A, B, C$$ and $$D.$$
Dimensions are $$$\eqalign{ & {H_A} = {H_D} = 3cm, \cr & {H_B} = {H_C} = 1.5cm, \cr & {L_1} = {L_3} = 0.05m,\,\,\,\,\,\,\,\,\,\,{L_2} = 0.1m \cr} $$$

Thermal conductivity of the materials are $$$\eqalign{ & {K_A} = {K_D} = 50\,\,\,W/mK, \cr & {K_B} = 10\,\,W/mK,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{K_C} = 1\,\,W/mK \cr} $$$
The fluid temps and $$HTC$$(see fig) are $$$\eqalign{ & {T_1} = {200^ \circ }C,\,\,\,\,{h_1} = 50\,\,W/{m^2}K, \cr & T{}_2 = {25^ \circ }C,\,\,\,\,{h_2} = 10\,\,W/{m^2}K, \cr} $$$

Assuming one dimensional heat transfer condition. Determine the rate of heat transfer through the wall.