The velocity distribution for water (20°C) near a wall is given by u = a(y/b)1/6, where a =10 m/s, b=2 mm, and y is the distance from the wall in mm. Determine the shear stress in the water at y 1= mm.

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]