Design a tube bank that will increase the temperature of a 1

Design a tube bank that will increase the temperature of a 1200 CFM How of air from 35 degree F to 100 degree F. Assume a constant pressure of 1 atm. Each tube will have a diameter of 0.5 in and a length of 24 in The tube configuration must fit in an area of 18 in by 18 in. Assume reasonable uniform surface temperature for the outside of the tubes.

Solution

Given:

1200CFM = 2038.8132 M³/hr = 0.566337m³/s.

35 ^oF = 1.6670C: 100^oF = 37.78 ^oC

Each tube diameter = 0.5 in = 0.127m

Each tube length = 24 in = 0.6096m

The tube configuration must be fitted in 0.4572m x 0.4572m

Solution:

Specific heat of air = 1.005 KJ/kgK

mass flow rate of air in kg/sec = 0.566337*1.235 = 0.69942 kg/sec

where 1.235 is density of air.

Heat to be added in order to raise the temperature from 1.667 ^oC to 37.78^oC = 0.69942*1.005*(37.78-1.667) = 20.2811KJ/s.

Considering gap between two tubes = 19mm

Number of tubes which can be fitted in 1 row =0.4572/(0.127+0.019) = 3.1

So, 3 tubes can be fitted in 1 row.

As it is square cross section, therefore, there will be 3 rows.

So 3 tubes by 3 rows can be fitted in area of 18 in x 18 in.