Water at a flow of m = .215 kg/s is cooled from 82 degrees C to 42 degrees C by passing it though a thin-walled tube of diameter D=6 cm and maintaining a coolant at T=15 degrees C in cross flow over the tube.
(a) What is the required tube length if the coolant is air and its velocity is V=25m/s.
(b) What is the tube lenght if the coolant is water and V=7m/s.