3. Conclusion

Closed-loop methods can be divided into three subgroups: static-synthetic methods, static-analytical methods and quasi-static methods. A key advantage of these methods is that the system under study can be brought into equilibrium for as long as required. Closed-loop methods lead to relatively simple devices, both in terms of design and operation. Homogeneity of equilibria in cells can be achieved in several ways:

• oscillating cell movements or internal agitation with magnetic rods for static methods;

• mechanical or thermal by circulation of one or more phases with quasi-static methods.

Synthetic methods have a major advantage. Most of them allow visual observation of the phenomena under study. What's more, the cells are technologically extremely simple, since no sampling...