Draft to be produced due to friction in square cross-section duct in mm of water.

Question

The following data related to a boiler using induced draught system :

Length of the duct carrying flue gas Mean size of the square dust Mean flue gas velocity in the duct Mean temperature of gases passing through duct Plenum pressure Number of 900 bends Number of 450 bends Number of draft in every 900 bend Draft available from chimney Fuel bed resistance for undefined stoker Fan efficiency Motor efficiency driving fan Characteristic gas constant for gases Friction factor, f, corresponding to round section duct

150 m 75 cm2 900 m/min 2270C 15 cm of water 4 4 cm of water 1.5 cm of water 10 cm of water 60% 92.5% 294 kJ/kg-K 0.006

 

Assuming that a 45⁰ bend equal one-half of 90⁰ bend and that the resistance offered by square duct is 20% greater than similar round duct, determine :

1. Draft to be produced due to friction in square cross-section duct in mm of water.
2. Draft due to velocity head of flue gases in mm of water.
3. Total draft for the boiler.
4. Draft to be produced by induced fan.

      v . Power required to drive fan.