The Douglas DC-3 ( Fig. 6.84 ) has a maximum velocity of 229 mi/h at an altitude of 7500 ft. Each of its two engines provides a maximum of 1200 hp. Its weight is 25,000 lb, aspect ratio is 9.14, and wing area is 987 ft 2 . Assume that the propeller effi ciency is 0.8, and the Oswald effi ciency factor is 0.7. Calculate the zero-lift drag coeffi cient for the DC-3.

Athin walled concentric tube exchanger is used to cool engine oil from 160°c to 60°c with water that is available at 25°c acting as a coolant. the oil and water flow rates are each at 2 kg/s, and the diameter of the inner tube is 0.5 m and the corresponding value of the overall heat transfer coefficient is 250 w/m2. oc. how long must the heat exchanger be to accomplish the desired cooling? cpwater=4.187 kj/kg-candcpengine el=2.035 kj/kg·°c, oil . 120]