EV Series Copper Tube Finned Evaporator for Freezer

Circulating evaporator
This type of evaporator, solution in the evaporator for circulation flow. Because of the different reasons of causing the circulation, it can be divided into two categories of natural circulation and forced circulation.
1. Central circulation tube evaporator this kind of evaporator is also called as standard evaporator. Its heating chamber consists of vertical tube bundle, in the middle of which there is a central circulating tube with large diameter, and the rest of the heating tubes with smaller diameter are called boiling tubes. As the central circulation tube is larger, its unit volume of solution occupies the heat transfer surface, than the boiling tube unit solution occupies to be small, that is, the central circulation tube and other heating tubes in the degree of solution heating is different, so that the boiling tube of the vapor-liquid mixture density than the central circulation tube in the solution density is small, coupled with the rising steam upward suction, will make the evaporator in the solution to form by the central circulation tube down by the boiling tube Tube rising circular flow. This cycle, mainly caused by the density difference of the solution, so it is called the natural cycle. This effect is conducive to the heat transfer effect of the evaporator to improve.

In order to make the solution have good circulation, the cross-section area of the central circulation tube is generally 40-100% of the total cross-section area of the other heating tubes; the height of the heating tube is generally 1-2m; the diameter of the heating tube is between 25 and 75mm. This kind of evaporator is widely used due to the advantages of compact structure, convenient manufacture, better heat transfer and reliable operation. However, due to the structural limitations, the circulation speed is not large. Coupled with the solution in the heating chamber constantly circulating, so that its concentration is always close to the concentration of the completion of the liquid, and thus the boiling point of the solution is high, the effective temperature difference is reduced. This is the common disadvantage of circulating evaporator. In addition, the cleaning and maintenance of the equipment is not convenient enough, so this kind of evaporator is difficult to fully meet the requirements of production.

2. Hangs the basket type evaporator in order to overcome the circulating type evaporator in the evaporation liquid easy to crystallize, easy to scale and not easy to clean and so on the shortcoming, carries on the standard type evaporator structure to be more reasonable to improve, this is hangs the basket type evaporator. Heating room 4 like a basket, hanging in the lower part of the evaporator shell, and replace the central circulation tube with the ring-shaped aperture between the outer wall of the heating room and the inner wall of the evaporator. The solution rises along the center of the heating tube and then flows downwardly through the ring gap between the outer wall of the basket-type heating chamber and the inner wall of the evaporator to form a circulation. Because the ring gap area is about 100 to 150% of the total cross-sectional area of the heating tube, the solution circulation speed is bigger than the standard evaporator, and it can reach to 1.5 m/s. In addition, the heating chamber of this kind of evaporator can be taken out from the top for overhauling or replacing, and the heat loss is also smaller. Its main disadvantage is the structure is complex, unit heat transfer area of metal consumption is more.

3. Levin type evaporator above natural circulation evaporator, its circulation speed is not big enough, generally in 1.5m/s below. In order to make the evaporator more suitable for evaporation viscosity, easy to crystallize or scale serious solution, and improve the solution circulation speed to extend the operation cycle and reduce the cleaning times.

Its structure is characterized by the addition of a boiling chamber on the heating chamber. The solution in the heating chamber is subjected to the action of the static pressure added to the boiling chamber liquid column and does not boil in the heating tube, until it rises to the boiling chamber when the pressure is lowered to start boiling, and thus the boiling vaporization of the solution is moved from the heating chamber to the boiling chamber without a heat transfer surface, thus avoiding the formation of crystals or fouling in the heating tube. In addition, this kind of evaporator's circulating tube's cross-sectional area is about 2~3 times of the total cross-sectional area of the heating tube, the solution circulates the speed to be able to reach 2.5 to 3 m/s above, so the total heat transfer coefficient is also larger. This evaporator's main disadvantage is liquid column static pressure head effect caused by temperature difference loss (meaning see 6.3.1) is larger, in order to maintain a certain effective temperature difference requires heating steam to have higher pressure. In addition, the equipment is large, consumes much material, and requires a tall plant, etc. In addition to the above natural circulation evaporator, in the evaporation of viscosity, easy to crystallize and scale material, also use forced circulation evaporator. In this kind of evaporator, the circulation of the solution mainly relies on the external power, uses the pump to force it to flow along a certain direction and produce the circulation. The size of the circulating speed can be controlled by the pump flow regulation, generally in 2.5m/s or more. The heat transfer coefficient of forced circulation evaporator is also larger than that of general natural circulation. But its obvious disadvantage is the energy consumption is big, each square meter heating area needs about 0.4 ~ 0.8kW.

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