An infinitely long furnace of $$0.5m \times 0.4m$$ cross-section is shown in the figure below. Consider all surfaces of the furnace to be black. The top and bottom walls are maintained at temperature $${T_1} = {T_3} = {927^ \circ }C,$$
while the side walls are at temperature $${T_2} = {T_4} = {527^ \circ }C.$$
The view factor, $${F_{1 - 2}}$$ is $$0.26.$$ The net radiation heat loss or gain on side $$1$$ is_________ $$W/m.$$ Stefan-Boltzman constant $$ = \,5.67 \times {10^{ - 8}}$$ $$W/{m^2}$$-$${K^4}$$

A fluid (Prandtl number, $$Pr=1$$) at $$500$$ $$K$$ flows over a flat plate of $$1.5$$ $$m$$ length, maintained at $$300$$ $$K.$$ The velocity of the fluid is $$10\,\,m/s.$$ Assuming kinematic viscosity, $$v = 30 \times {10^{ - 6}}\,\,{m^2}/s,$$ the thermal boundary layer thickness (in $$mm$$) at $$0.5$$ $$m$$ from the leading edge is _________.

The annual demand for an item is $$10,000$$ units. The unit cost is Rs. $$100$$ and inventory carrying charges are $$14.4\% $$ of the unit cost per annum. The cost of one procurement is Rs. $$2000.$$ The time between two consecutive orders to meet the above demand is _______ month(s).

Maximize $$\,\,\,\,Z = 15{x_1} + 20{x_2}$$
Subject to
$$\eqalign{ & 12{x_1} + 4{x_2} \ge 36 \cr & 12{x_1} - 6{x_2} \le 24 \cr & \,\,\,\,\,\,\,\,\,{x_1},\,\,{x_2} \ge 0 \cr} $$

The above linear programming problem has