Water vapour is the gas formed when water passes from liquid to the gaseous state due to the input of heat.
When all the water molecules remain in a gaseous state, we speak of dry vapour. If this vapour is in a colder atmosphere, part of it condenses as small drops of water, and in this case we will have wet vapour.
Vapour Quality definition
Vapour quality is the mass fraction of vapour in the liquid-vapour mixture, such that dry vapour is equivalent to quality equal to 1, i.e. 100% vapour. Values between 0 and 1, on the other hand, indicate water content in the mixture, with value 0 being for saturated liquid.
When we think of vapour, we visualise a white cloud. This would be the case with wet vapour, as the tiny drops of water are visible and form the cloud. Dry vapour, on the other hand, is colourless and therefore invisible.
Vapour quality is very important in vapour production plants. The presence of condensate not only reduces heat exchange efficiency, but also produces noise and erosion in both pipes and equipment.
Working with vapour quality close to 1 is therefore ideal to ensure maximum efficiency and a long working life.