Water Tube Boilers-An Overview

Water tubes boilers are boilers where the water flows in pipes above a furnace or a burner.  The hot gases in the burner warm the water.  Watertube boilers are used for high capacity applications.  They can built for very high pressure designs.

The water tubes are connected to a steam drum on top.  The steam rises to the steam drum from where it is collected.  High efficiency is possible with water tube boilers.  Since the water flows through the tubes, very good water chemistry needs to be maintained to prevent deposits and corrosion. 
Large heating surface can be obtained by adding more number of tubes.  The heat transfer is by convection.  The flow rate of the water in the tubes is higher and hence greater efficiency is possible. 
The water tube boiler can control its own pressure and is known as a self controlled boiler.  This is because if steam is extracted from the drum, the pressure inside falls.  This causes the water in the tubes to flow faster.  This results in more heat transfer and the original pressure is quickly attained.