Question

Kerosene enters a 5 cm diameter tube at 35C with a velocity of 3 m/s. The tube is wrapped with a resistance heating element so that when it is energized a uniform heat flux is imposed on the tube. At the exit of the tube, the temperature of the kerosene is to be 45C. A constraint is placed on the process, such that the local kerosene temperature cannot exceed 80C; this is likely to occur at the wall of the tube outlet. Assume the following thermal properties for kerosene: density = 807 kg/m3 , cp = 2,093 J/kgC, k = 0.113 W/mC, u = 1.21 × 10-3 Ns/m2 . Consider the following:

i) Determine the required power rating (W) of the resistance heater.

ii) Calculate the necessary length (m) of the tube.

Answer 1