An air duct heater consists of an inline tube bank array of

An air duct heater consists of an in-line tube bank array of electrical heating elements (tubes) as shown. There are 3 rows of tubes and 4 elements per row. Air with an upstream velocity of 12 m/s moves in cross flow over the elements which have a diameter of 12 mm, length of 250 mm, and are maintained at a surface temperature of 350deg C.

Evaluate air properties at the inlet temperature, except when a correlation specifically requires properties at the tube surface temperature.

a) Find the maximum air velocity in the tube bank.

b) Find the maximum Reynolds number based on tube diameter in the tube bank.

c) Find the average heat transfer coefficient for the bank. Use an appropriate Nusselt number equation.

d) Find the outlet air temperature from the tube bank.

Solution

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