Consider the in-line tube bank of Problem 7.90 (D = 10 mm, L = 1 m, and ST = SL = 15 mm), with condensing steam used to heat atmospheric air entering the tube bank at Ti = 25°C and V = 5 m/s. In this case, however, the desired outlet temperature, not the number of tube rows, is known. What is the minimum value of NL needed to achieve an outlet temperature of To > 75°C? What is the corresponding pressure drop across the tube bank?