Why there's a buzz in the world about pmp? Please help me guys it's HW​

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]

The sum of the normal stresses does not change as the stress state rotates through an angle. a)-trune b)- false

Asolid steel sphere (k=63.9 w m-1 k-1 , ? =7832 kg m-3 , c=0.523 kj kg-1 k-1 ), 100 mm in diameter is initially at a uniform temperature of 500o c and is suddenly quenched in a large oil bath for which t? = 100o c and h = 3200 w m-2 k-1. estimate the time required for the sphere to cool to 200o c and to 110o c