Flow separation in flow past a solid object is caused by

The properties of mercury at $$300K$$ are : density $$ = 13529kg/{m^3},$$ $${C_P} = 0.1393$$ $$kJ/kgK,$$ dynimic viscosity $$ = 0.1523\,\, \times \,\,{10^{ - 2}}\,\,N - s/{m^2}$$ and thermal conductivity $$=8.540$$ $$W/m$$-$$K$$. The Prandtl number of the mercury at $$300K$$ is

A copper tube of $$20$$ $$mm$$ outer diameter, $$1$$ $$mm$$ thickness and $$20$$ $$m$$ long (Thermal conducti-vity$$ = 400$$ $$W/mK$$) is carrying saturated steam at $${150^ \circ }C$$ (Convective $$HTC\,\, = \,\,150\,\,W/{m^2}K$$). The tube is exposed to an ambient temperature of $${27^ \circ }C.$$ The convective $$HTC$$ of air is $$5\,W/{m^2}K.$$ Glass wool is used for insulation (Thermal conductivity $$ = 0.075\,\,W/mK$$). If the thickness of the insulation used is $$5$$ $$mm$$ higher than the critical thickness of insulation, calculate the rate of heat lost by the steam and the rate of steam condensation in $$kg/hr$$ (The enthalpy of condensation of steam $$ = 2230\,\,kJ/kg$$)

The value of Biot number is very small (less than $$0.1$$), when