The selection of defoamer should comply with the following points:

1. Insoluble or difficult to dissolve in foaming fluid

To break the foam, the defoamer should be concentrated on the foam film. When it breaks the foam, it should be concentrated instantly, and it should also be kept in this state when suppressing the foam. Therefore the defoamer should be supersaturated in the foaming solution, and only insoluble can it easily reach a supersaturated state. Only when it is insoluble or difficult to dissolve, it is easy to aggregate at the gas-liquid interface, easy to concentrate on the bubble film, and play a role at lower concentrations. For defoamer used in water systems, the molecules of the active ingredients must be strongly hydrophobic and weakly hydrophilic, with an HLB value in the range of 1.5-3 for the best effect.

2. The surface tension is lower than that of the foaming liquid

Only when the intermolecular force of the defoamer is small and the surface tension is lower than that of the foaming solution, can the defoamer particles immerse and expand on the foam film. It is worth noting that the surface tension of the foaming solution is not the surface tension of the solution, but the surface tension of the auxiliary foaming solution.

3. Has affinity with the foaming fluid

 To make the defoamer diffuse faster, the active ingredient of the defoamer must have affinity with the foaming fluid.If the active ingredient of the defoamer is too close to the foaming liquid, it will dissolve; if it is too sparse, it will be difficult to disperse. Only when the closeness is appropriate can the effect be good.

4. No chemical reaction with foaming fluid

Defoamer reacts with foaming fluid. On one hand,the defoamer will lose its effect, on the other hand, it may produce harmful substances to affect the growth of microorganisms.

5. Small volatility, long action time

The first step is to determine the system in which the defoamer needs to be used，a water-based system or an oily system. As the fermentation industry,it is necessary to use oily defoamers, such as polyether modified silicon or polyether.Water - based paint industry will use water - based defoamers, such as silicone defoamers.Selecting defoamers, comparing the amount added,the reference price, will can obtain the most suitable and economical defoamer products.