Due to the solution of the membrane molecular distillation systems flow in single type evaporator, convection heat transfer coefficient is greatly improved, thus can make the solution in the heating chamber through one cycle is no longer meet the requirements of concentration, thus has more advantages than circular evaporator. Solution not cycle benefits are:
(1) short residence time of solution in the evaporator, and especially suitable for heat-sensitive materials evaporate.
(2) the concentration of the solution, not like circular always close to complete liquid concentration, thus the evaporator of effective temperature difference is bigger. Its main drawback is that: the load fluctuation is quite sensitive, when the design or operation is not difficult to film at the time, at this point, the convection heat transfer coefficient will be markedly reduced.
Scraper evaporator evaporator shell with heating steam jacket, which is equipped with rotating blade scraper. Scraper is fixed and rotor type two kinds, the former and the inner wall of the shell of the gap of 0.5 ~ 1.5 mm, the thin film distillation clearance between the wall and the latter with the revolutions of the rotor. Upper material liquid by the evaporator along the tangent direction to join (also add to the scraper coaxial thrown tray). Due to gravity, centrifugal and rotary scraper scraping effect, the solution of thin film formed on the inner wall of the apparatus for backspin, evaporation and concentration, and in this process is complete liquid discharge at the bottom. The evaporator is a one-way type using a powered film evaporator, its outstanding advantage is adapted to the material is very strong, and short residence time, usually a few seconds or a few seconds, so it can be adapted to the high viscosity, such as extract, honey, etc.) and crystallization, scaling, heat-sensitive materials. But its complex structure, large power winterization filtration consumption, heat transfer surface per square metre about 1.5 ~ 3 kw. In addition, its capacity is small and high manufacturing installation requirements.