A homemade heat exchanger consists of a copper plate, 0.5 m square, with twenty 1.5 cm I.D. copper tubes soldered to it. The ten tubes on top are evenly spaced across the top and parallel with two sides. The ten on the bottom are also evenly spaced, but they run at 90? to the top tubes. The exchanger is used to cool methanol flowing at 0.48 m/s in the tubes from an initial temperature of 73?C, using water flowing at 0.91 m/s and entering at 7?C. What is the temperature of the methanol when it is mixed in a header on the outlet side? Make a judgement of the heat exchanger.