The evaporator is a very important part of the four major pieces of refrigeration. The low-temperature condensed "liquid" body passes through the evaporator to exchange heat with the outside air, and "gas" absorbs heat to achieve the effect of refrigeration.
Evaporation is a unit operation that uses a heating method to heat a solution containing a nonvolatile solute to a boiling state, to vaporize and remove a portion of the solvent, and thereby increase the concentration of the solute in the solvent. There are several occasions in which evaporation is applied in industrial production:
1. Concentrate the dilute solution to make the product directly or reprocess the concentrated solution (such as cooling and crystallization) to make solid products, such as the concentration of electrolytic caustic soda solution, the concentration of sugar aqueous solution and the concentration of various fruit juices, etc.
2. Concentrate the solution and recover the solvent at the same time, such as concentrated debenzene of organophosphorus pesticide benzene solution, evaporation of alcohol extract in Chinese medicine production
3． In order to obtain pure solvents, such as desalination.
In short, in the chemical industry, food industry, pharmaceutical and other industries, evaporation operations are widely used.
1. Divided by evaporation:
Natural evaporation: That is, the solution evaporates at a temperature lower than the boiling point, such as sea salt. In this case, because the solvent only vaporizes on the surface of the solution, the solvent evaporation rate is low.
Boiling evaporation: The solution is heated to the boiling point and allowed to evaporate in the boiling state. This is basically the case for industrial evaporation operations.
2. Divided by heating method:
Direct heat source heating is an evaporation process in which fuel and air are mixed, and the high-temperature flame and smoke generated by combustion are sprayed directly into the evaporated solution through a nozzle to heat the solution and vaporize the solvent.
The indirect heat source heats the walls of the container to the evaporated solution. That is, the heat transfer process in the partition heat exchanger.
3． Divided by operating pressure:
Can be divided into atmospheric, pressurized and reduced (vacuum) evaporation operations. Obviously, for heat-sensitive materials, such as antibiotic solutions, fruit juice, etc., should be carried out under reduced pressure. For high-viscosity materials, pressurized high-temperature heat sources (such as heat transfer oil, molten salt, etc.) should be used for evaporation.
4． Divided by effect:
Can be divided into single-effect and multi-effect evaporation. If the secondary steam directly condensed by evaporation is no longer used, it is called single-effect evaporation. If the secondary steam is used as the next effect heating steam, and multiple evaporators are connected in series, this evaporation process is multi-effect evaporation.