A tube of diameter d = 0.30 m and surface temperature ϑR = 60 ◦C is placed in the ground (λ = 1.20W/K m) such that its axis lies 0.80 m below the surface. The air temperature is ϑA = 10 ◦C; the heat...

A tube of diameter d = 0.30 m and surface temperature ϑR = 60 ◦C is placed in the ground (λ = 1.20W/K m) such that its axis lies 0.80 m below the surface. The air temperature is ϑA = 10 ◦C; the heat transfer coefficient between the air and the earth’s surface is α = 8.5W/m2K. How large is the heat loss Q/L ˙ per length L of the tube?