In flash (equilibrium) distillation, a definite fraction of liquid is vaporised in such a way that the evolved vapour & residual liquids are in equilibrium with each other
Distillation under vacuum is a substitute for steam distillation
In differential (simple) distillation, the vapour is removed as soon as it is formed without appreciable condensation
Flash distillation, differential distillation & steam distillation are all continuous distillation processes
Bubble cap trays though most expensive are the best in situations, where low vapour rates is to be handled and a positive liquid seal is essential at all flow rates
Murphree efficiency of all the three trays are nearly equal, however the peak efficiency is generally higher for seive and valve trays than the bubble cap
Valve trays have the highest turn down ratio (i.e. the ratio of the highest to the lowest vapour flow rates) and thus provides the maximum flexible operating range
Maintenance cost for valve and seive trays are comparatively more than bubble cap tray due to their relatively complicated construction features
EXAMIANS