Ahorizontal pipe 15 cm in diameter and 4 m long is buried in the earth at a depth of 20 cm. the pipe-wall temperature is 75 degree c and the earth surface temperature is 5 degree c. assuming that the thermal conductivity of the earth is 0.8w/m. degree c. calculate the heat lost by the pipe. what is the heat lost if the pipe was buried at a depth of 180 cm?

Explanation:

The given data for case (1) is as follows.

  h = 20 cm = 0.2 m

Assuming that a rectangular slab is placed above the pipe and we will calculate the heat transfer as follows.

              Q =

  where,    A = area

                  L = length

                  k = thermal conductivity = 0.8 W/m

              = change in temperature.

Therefore, putting the given values into the above formula as follows.

            Q =

                =

                = 168 W

For case (2), h = 180 cm = 1.8 m

Therefore, heat lost will be calculated as follows.

                       Q =

                           =

                           = 18.67 W

Thus, we can conclude that 18.67 W heat lost if the pipe was buried at a depth of 180 cm.