A hot gas at 300°C flows through a long metal pipe 100mm outer diameter and 3mm thick. From the standpoint of safety and energy conservation, mineral wool insulation of thermal conductivity 0.052W/m K is wrapped around it so that the exposed surface of the insulation is at a temperature of 50°C. Calculate the thickness of insulation required to achieve this temperature if inner heat transfer coefficient 29W/m2K and outer heat transfer coefficient is 12W/m2K and the surrounding air temperature is 25°C. Also calculate the corresponding heat loss rate per unit length.

Asbestos insulation of thermal conductivity 0.2W/m K is put on a steel pipe of 16mm inner diameter and 20mm outer diameter. Hot water at 90°C flows through the pipe and the heat transfer coefficient is 500 W/m2 K. Heat is lost from the outer surface by natural convection to surrounding air at 30°C and the heat transfer coefficient is 10 W/m2 K. Calculate the heat loss rate per meter length of the pipe for no insulation and insulation thicknesses of 5, 10, 20, 30, 40 and 50mm. Plot the results and explain the variation obtained.