Water flows downhill through a 2.16-in.-diameter steel pipe. the slope of the hill is such that for each mile (5280 ft) of horizontal distance, the change in elevation is δz. determine the maximum value of δz if the flow is to remain laminar and the pressure all along the pipe is constant.

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]