A steel pipe having internal diameter of 2 cm, outer diameter of 2.4 cm and thermal conductivity of steel of 54 W/mK carries hot water at 95°C. Heat transfer coefficient between the inner surface of steel pipe and the hot water is 600 W/m2K. An asbestos insulation with thermal conductivity of 0.2 W/mK and thickness 2 cm is put on the steel pipe. Heat is lost from the outer surface of the asbestos insulated pipe to the surrounding air at 30°C, heat transfer coefficient for the outer surface of the insulation being 8 W/m2K.
i) The rate of heat transfer per meter length of the pipe.
ii) Determine the temperatures at the inner, outer surfaces of the steel pipe and the outer surface of the insulation.
iii) What do you understand by the term “critical radius of insulation”? What is the value of critical radius in the above question? What is the rate of heat loss, if thickness of insulation were to correspond to critical radius? Comment on the results.