Evaporation is the process to convert water into steam. Evaporation process occurs in steam boiler especially in water wall tubes area. One of evaporation process is bubbly flow. When temperature of water in water wall tubes is equal to saturation temperature of water, the little bubbles will arise especially near metal wall tubes. Saturation temperature of water will be reached faster in area near metal wall tubes because the heat is transferred first from metal wall tubes to water inside. Flow area of little bubbles can be called as Bubbly Flow.
|Figure 1: Bubbly Flow in Evaporation Process|
In the bubbly flow, bubbles of steam on one side can be small and round and on other side it could be great with a round and flat shape. In this condition the size of the bubbles is not always exactly same, but it is expected have uniform size.