falling film evaporator design
Evaporation is the use of heating, so that the solution in the volatile solvent in the boiling state, part of the vaporization and remove it, falling film evaporator is suitable for heat-sensitive solutions, commonly used in the food industry, with the falling film evaporator design optimization, in higher concentrations of salt water can also be used, Kang Jing Hui small and everyone together to understand the principle of falling film evaporator design.
The material liquid of falling film evaporator is added from the top of the evaporator, and under the action of gravity, it forms a film-like descent along the wall of the tube, and evaporates and thickens in the process, and gets the concentrated liquid at its bottom. Falling film evaporator into film mechanism is different from rising film evaporator, therefore, falling film evaporator can evaporate higher concentration, concentration and heat-sensitive materials. However, because the liquid film is not easily distributed evenly in the tube, the heat transfer coefficient is smaller than that of the rising film evaporator, and it is still not applicable to the materials that are easy to crystallize or easy to scale.
The solution becomes membrane flow in the one-way type evaporator, so the convection heat transfer coefficient is greatly improved, which makes the solution can reach the required concentration in the heating chamber once through no more circulation, so it has greater advantages than the circulating type evaporator.
The advantages brought by the solution not circulating are: 1, the solution's residence time in the evaporator is very short, thus it is especially suitable for the evaporation of heat-sensitive materials; 2, the concentration of the whole solution, unlike the circulating type, is always close to the concentration of the finished liquid, thus the effective temperature difference of this evaporator is larger.
In the design of falling film evaporator, there are six issues to be considered, namely, the basic size of equipment, pressure drop, minimum flow rate, heat transfer coefficient, liquid flood and liquid distribution.
1, the basic size of the falling film evaporator: the principle of tube diameter selection is to use a small tube diameter for operation above atmospheric pressure; vacuum operation uses a large tube diameter, the higher the vacuum, the larger the selected tube diameter.
2, the pressure drop of the falling film evaporator: the pressure drop of the falling film evaporator is generally not large, to choose to calculate the appropriate value.
3, in the design of the falling film evaporator to control the operating flow in the minimum flow, in order to avoid the scaling of the falling film evaporator tube wall phenomenon.
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