Explain about the Vacuum Evaporators?

It is common to construct various vacuumised vessels in series that is why the product moves from one vacuum chamber to the next and thus becomes progressively more concentrated in stages. With such type of an arrangement the successive stages are maintained at increasingly higher degrees of vacuum, and the hot water vapour generated by the first stage is utilized to heat the second stage, the vapour from the second stage heats the third stage and so on. In this manner maximum use of heat energy is made. Such system is known as a multiple effect vacuum evaporator. It is a widely utilized system for concentrated tomato paste.