Repeat Prob. 8–127 assuming that a 0.25-mm-thick layer of mineral deposit (k = 3 W/m · K) formed on the inner surface of the pipe.

Data from problem 127

A house built on a riverside is to be cooled in summer by utilizing the cool water of the river, which flows at an average temperature of 15°C. A 15-m-long section of a circular duct of 20-cm diameter passes through the water. Air enters the underwater section of the duct at 25°C at a velocity of 3 m/s. Assuming the surface of the duct to be at the temperature
of the water, determine the outlet temperature of air as it leaves the underwater portion of the duct. Also, for an
overall fan efficiency of 55 percent, determine the fan power input needed to overcome the flow resistance in this section of the duct.

Transcribed Image Text:

Air 25°C, 3 m/s Air River, 15°C 15°C