A steam generator consists of a bank of stainless steel (k = 15 W/m ∙ K) tubes having the core configuration of figure and an inner diameter of 13.8 mm. The tubes are installed in a plenum whose square cross section is 0.6 m on a side, thereby providing a frontal area of 0.36 m². Combustion gases, whose properties may be approximated as those of atmospheric air, enter the plenum at 900 K and pass in cross flow over the tubes at 3 kg/s. If saturated water enters the tubes at a pressure of 2.455 bars and a flow rate of 0.5 kg/s, how many tube rows are required to provide saturated steam at the tube outlet? A convection coefficient of 10,000 W/m² ∙ K is associated with boiling in the tubes.