b) A transformer dissipates 80 kW to cooling oil entering at 30C and leaving at 70C. The oil is divided equally between 25 parallel tubes in a heat exchanger. Calculate the convection heat transfer coefficient of the oil in the heat exchanger tubes. Inner tube diameter = 6 mm. Oil properties: For laminar flow: P = 800 kg/m = 1.98 kJ/kgK = K = 0.073 kg/ms 135x 106 kW/mK Nud = For turbulent flow; Nud = 0.125(Red Pr) 1/3 0.023(Red)0.8 (Pr) 0.4 (18 marks)