In an industrial facility, air is to be preheated before entering a furnace by geothermal water at 120C flowing through the tubes of a tube

In an industrial facility, air is to be preheated before entering a furnace by geothermal water at 120ºC flowing through the tubes of a tube bank located in a duct. Air enters the duct at 20ºC 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 SL = ST =  5 cm. There are 6 rows in the flow direction with 10 tubes in each row.

Determine the rate of heat transfer per unit length of the tubes.

 

AIR V=4.5 m/s T- 120C T = 20C O o o O O o o O SL = S7 = 5 cm D=15 cm