Thermocompression
The energy input is here given by the energy of a quantity of steam (motive steam), at a pressure higher than those of both the inlet and the outlet vapors. The quantity of compressed vapors is therefore higher that the inlet :
Where Qd is the steam quantity at ejector delivery, Qs at ejector suction and Qm is the motive steam quantity. For this reason, a thermocompression evaporator often features a vapor condenser, due to the possible excess of steam necessary for the compression if compared with the steam required to evaporate the solution. The quantity Qm of motive steam per unit suction quantity is a function of both the motive ratio of motive steam pressure vs. suction pressure and the compression ratio of delivery pressure vs. suction pressure. In principle, the higher the compression ratio and the lower the motive ratio the higher will be the specific motive steam consumption, i. e. the less efficient the energy balance.
Read more about this topic: Vapor-compression Evaporation