Experimental techniques for monitoring sedimentation in optically opaque suspensions

A review of established and developing techniques for monitoring solid flux, and in some cases particle size, is presented for sedimenting multi-phase systems that are opaque and therefore unsuited to interrogation using conventional optical methods. The techniques are classified according to the physical principle employed for the measurement, relative cost of the equipment, precision, versatility, ease of operation, state of development and their ability to function in non-invasive or invasive modes. Requirements and limitations of these techniques are discussed with respect to their application to colloidal dispersions, emulsions and to mixed colloidal/non-colloidal suspensions.
Practical examples of phase-flux determinations are given for devices involving (i) ultrasonics, (ii) capacitance, (iii) inductance and (iv) direct measurement by physical interruption and sampling of a sedimentation process.