Exhaust gases at 1 atm and 300°C are used to preheat water in an industrial facility by passing them over a bank of tubes through which water is flowing at a rate of 6 kg/s. The mean tube wall temperature is 80°C. Exhaust gases approach the tube bank in normal direction at 4.5 m/s. The outer diameter of the tubes is 2.1 cm, and the tubes are arranged in-line with longitudinal and transverse pitches of S_L = S_T = 8 cm. There are 16 rows in the flow direction with eight tubes in each row. Using the properties of air for exhaust gases, determine

(a) The rate of heat transfer per unit length of tubes,

(b) And pressure drop across the tube bank,

(c) The temperature rise of water flowing through the tubes per unit length of tubes. Evaluate the air properties at an assumed mean temperature of 250°C and 1 atm. Is this a good assumption?