A pipe of 60 mm dia. carries oil at 230°C, with heat transfer coefficient of 250 W/ m 2 .K. The pipe is insulated with a material (k = 0.06 W/m.K). On the outer surface of insulation, a plastic...

A pipe of 60 mm dia. carries oil at 230°C, with heat transfer coefficient of 250 W/ m².K. The pipe is insulated with a material (k = 0.06 W/m.K). On the outer surface of insulation, a plastic coating (k = 1.6 W/m.K) 1 mm thick is applied. Calculate the radial thickness of insulation, which will reduce the outside temperature of coating to 50°C, when the ambient air temperature is 20°C with convective and radiative heat transfer coefficients of 6 and 8 W/m².K, respectively. Calculate the percentage reduction in the heat loss with this thickness of insulation.