A liquid (NOT WATER) is passed through a tube with a square cross section of 0.01m x 0.01m at a Reynolds number of 2,000. The liquid has a Prandtl number of 1, a thermal conductivity of 0.2 W/mK, and a heat capacity of 4,000 J/kg*K. Simultaneously, air is blown at a speed of 20 m/s and a temperature of 25°C over the outside of the tube such that the flow is perpendicular to one of the square sides. The liquid enters the tube at 200°C and exits at 50°C. Presume the tube wall is extremely thin. a. For what length of tube can the developing entrance length be ignored and the internal flow approximated as fully developed throughout ?
b. If the tube is 20m long, what is the heat transfer between the two fluids ?
c. If the tube is 20m long, what is the mass flow rate of the liquid through the tube ?
Air: k = 0.03 W/mK, p = 1 kg/m?, v = 2e-5 méls, u = 2e-5 Pas,
a =2.9e-5 m²/s, B= 30-3K-!, Pr = 0.7, Cp = 1,000 J/kgK,