Chapter 11, Problem 11.25P

An automobile radiator may be viewed as a cross-flowheat exchanger with both fluids unmixed. Water,which has a flowrate of $0.05\text{ kg/s}$ , enters the radiatorat 400 K and is to leave at 330 K. The water is cooledby air that enters at 0.75 kg/s and 300 K.
(a) If the overall heat transfer coefficient is $200{\text{ W/m}}^2\cdot \text{K}$ ,what is the required heat transfer surface area?
(b) A manufacturing engineer claims ridges can bestamped on the finned surface of the exchanger,which could greatly increase the overall heattransfer coefficient. With all other conditionsremaining the same and the heat transfer surfacearea determined from part (a), generate a plot ofthe air and water outlet temperatures as a function of Ufor $200\le U\le 400{\text{ W/m}}^2\cdot \text{K}$ . What benefitsresult from increasing the overall convection coefficient for this application?