Draught and Wright the types of Draught
Draught is defined as the difference between absolute gas pressure at any point in a gas flow passage and the ambient (same elevation) atmospheric pressure. Draught is plus if Patm < Pgas and it is minus Patm > Pgas. Draught is achieved by small pressure difference which causes the flow of air or gas to take place. It is measured in milimetre (mm) or water.
The purpose of draught is as follows:
i) To supply required amount of air to the furnace for the combustion of fuel
The amount of fuel that can be burnt per square root of grate area depends upon the quantity of air circulated through fuel bed.
ii) To remove the gaseous products of combustion.
Classification of DRAUGHT:
If only chimney is used to produce the draught, it is called natural draught.
If the draught is produced by steam jet or fan it is known as artificial draught
Steam jet Draught:
It employs steam to produce the draught
It employs fan or blowers to produce the draught.
The flue is drawn (sucked) through the system by a fan or steam jet
The air is forced into system by a blower or steam jet.
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