Abstract: A liquid heater or plate evaporator for partially evaporating liquid from a solution within the heater to increase its concentration, including evaporator and heater plates arranged in an alternating sequence in tandem and having heating or liquid channels between adjoining plates, the plates having registering apertures for heating medium, the solution to be evaporated, condensate therefrom and for a product mixture comprising concentrated solution and vapor each evaporator plate aperture having a distributor and guides to uniformly distribute the solution across the evaporator plate and to discharge it through discharge apertures located in a lower part on either side of the plate.