Consider the air cooling system and conditions of Problem 8.31, but with a prescribed pipe length of L = 15 m.

(a) What is the air outlet temperature, Tm.o? What is the fan power requirement?

(b) The convection coefficient associated with airflow in the pipe may be increased twofold by inserting a coiled spring along the length of the pipe to disrupt flow conditions near the inner surface. If such a heat transfer enhancement scheme is adopted what is the attendant value of Tm.o? Use of the insert would not come without a corresponding increase in the fan power requirement. What is the power requirement if the friction factor is increased by 50%?

(c) After extended exposure to the water a thin coating of organic matter forms on the outer surface of the pipe, and its thermal resistance (for a unit area of the outer surface) is Rt,o = 0.050 m2 ∙ K/W. What is the corresponding value of Tm.o without the insert of part (b)?