Consider a flat plate with the surf-ace heat flux specified as ,, l2O W/m2 when 0 { x { 15 cm, 4,, : ll0 W/m2 when x ) 15 cm. Air at atmospheric pressure and 20"C flows over this plate at 3 m/s. Estimate the variation of wall temperature with the distance x fiom the leading edge in the laminar boundary layer region, and evaluate the wall temperature numerically at 30 cm.

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]