in an industrial facility air is to be preheated before entering a furnace by geothermmal water at 120 flowing through the tubes of tube bank located in a duct. air enters the duct at 20 and 1 atm with a mean velocity of 4.5 m/s and flows over the tubes in normal direction.the outer diameter of the tubes is 1.5 cm, and the tubes are arranged in-line with longitudinal and transverse pitches of s=s=5 cm. there are 6 rows in he flow direction with 10 tubes in each row, as shown in figure 7-18 determine the rate of heat transfer per unit length of the tubes ,and the pressure drop across the tube bank.