A long tube carrying hot fluid is surrounded by a thick, plastic pipe, both sides of which are metalized. External diameter of internal tube equals to 40mm, emissivity of the surface equals to ε1 = 0.6. Dimensions of the plastic tube are: = 60mm, dout = 70mm; emissivities: = 0.2, out = 0.4. Thermal conductivity of plastic = 0.15 W/m*K. The region between internal and external tubes is evacuated. The outer surface of external tube is exposed to a large room whose walls are at 22° and experiences convection with air at 27° and a convection heat transfer coefficient equals to 15 W/m²*K. What is the temperature of the internal tube (carrying hot fluid) if the temperature of external surface of the plastic tube equals to 60°?
