An insulation tube has inner radius 0.02 m and outer radius 0.04 m. Fluid flowing through the tube maintains the temperature on the inner wall at 600C. Heat is lost through each metre of tube length according to dT Fourier's law where: dr -1 9 2kr q= 680 W m - is the heat transfer rate per metre of length k = 0.2 W m- C is the thermal conductivity constant r is the radius from the centre of the tube T is the temperature in C. Calculate the external temperature of the tube.