Problem 3 (4 points) Use NTU Method

The oil in an engine is cooled by air in a cross-flow heat exchanger where both fluids are unmixed.Atmospheric air enters at 30°C and 0.53 kg/s. Oil at 0.026 kg/s enters at 75°C and flows through a tube of 10-mm diameter. Assuming fully developed flow and constant wall heat flux, estimate the oil-side heat transfer coefficient. If the overall convection coefficient is 53 W/m² K and the total heat transfer area is 1 m², determine the effectiveness. What is the exit temperature of the oil?

**Given: Properties for:Table A-5, Engine oil (guessing Tho~ 45°C, Th= (45+75)°C/2 = 333 K): Ch = 2047 J/kg. K,µμ = 7.45 × 10-2 N. s/m², k = 0.140 W/m. K;

Table A-4, Air (guessing Tc,o~ 40°C, Tc = (30+40)°C/2 = 308 K, 1 atm): cc = 1007 J/kg. K