falling film vs wiped film evaporator

Falling film evaporator is a kind of high-efficiency evaporation equipment, which is collectively called wiped  evaporator with rising film evaporator and scraper type film evaporator.

The advantages of film evaporator are remarkable, and it is widely used in chemical, light industry and food processing industry to achieve the purpose of liquid concentration. The structure of falling film evaporator is actually not complicated, it can be simply understood as a set of cloth membrane device inside the vertical column tube heat exchanger, but it has another obvious difference with the ordinary heat exchanger, its shell process is fixed for the heating fluid, and the tube process is fixed for the evaporated material. The material in the tube process of the falling film evaporator is from the top of the tube into the heat exchanger tube, with its own gravity along the tube biscuit downward flow, before entering the heat exchanger tube, need to go through the cloth film device cloth film, so when entering the heat exchanger tube will be in the form of a thin film, in the material from top to bottom of the process of evaporation of water out, so as to achieve the purpose of material concentration, shell process if the steam condensing heating or heat conduction oil heating, if the use of steam is up into the next out If the shell process is heated by steam condensation or heat-conducting oil, if the steam is used, it should be bottom-up. It can be seen that the flow direction of the medium inside and outside the tube is not always counter-current. But this is not important, because the pressure inside the tube is basically unchanged, will not cause the fluid temperature change, the medium temperature change inside the tube is only due to the medium concentration change and cause the boiling point to rise (this is only slightly higher).

　　Analysis of the advantages of falling film evaporator.

　　(1)The short residence time of the material in the heat exchanger tube will not affect the chemical properties of heat-sensitive materials.

　　(2)The material in the heat exchanger tube is in the form of thin film and fast flow rate, and the evaporation heat exchange coefficient is large.

　　(3) the pressure drop is almost 0, the process tube material in atmospheric pressure environment, completely by its own gravity along the tube wall downward flow, can save energy; .

　　(4) because the tube process material by its own gravity along the inner wall of the tube downward flow, rather than using the pressure difference to promote, so you can choose a low temperature difference; .

　　(5)The material retention in the tube space is very small.

　　(6)The material in the tube process is heated and shows convective boiling, so the surface state of the heat exchanger tube almost does not affect the material boiling.

　　Analysis of disadvantages of falling film evaporator.

　　(1)The evaporation effect of the equipment is directly related to the distributor, and the design, manufacture and installation requirements for the distributor are very high.

　　(2) High equipment installation requirements, mainly for the verticality requirements, assuming that the length of the heat exchanger tube is 9m, the equipment verticality is required ≤ 6. 4mm.

　　(3) need to ensure that the inner wall of the equipment heat exchanger tube is completely wet but the thickness of the cloth film can not be too large, the need for very accurate design calculations of the material feed and heat exchanger tube length to meet such requirements.

　　(4) Because the design and manufacturing requirements are very high resulting in very high equipment procurement costs.

　　(5) For easy scaling or materials containing solids in suspension is not applicable.