8.25 Engine oil is heated by flowing through a circular tube of diameter D 50 mm and length L 25 m and whose surface is maintained at 150 C. (a) If the flow rate and inlet temperature of the oil are 0.5 kg/s and 20 C, what is the outlet temperature Tm, o? What is the total heat transfer rate q for the tube? (b) For flow rates in the range 0.5 , compute and plot the variations of Tm, o and q with . For what flow rate(s) are q and Tm, o maximized? Explain your results.