Intensification of transfer phenomena via ultrasound in continuous milli-reactors

Miniaturisation consists of carrying out operations in micrometric or millimetric devices that usually take place in centimetric or metric devices. The reason for this practice is to increase the surface/volume ratio in order to intensify the transfer phenomena (mass and thermal). This makes it possible to further increase the control of the operating conditions (pressure, temperature, etc.) and to improve the performance of the operation (yield, selectivity, etc.). However, the confinement of the operating environment generally implies a laminar flow in it, which can cause mixing problems while promoting fouling and plugging. Ultrasound can be used to solve these problems through the effects generated by the radiation force such as acoustic currents and acoustic cavitation. The objective of the thesis was to study a single-phase (liquid/liquid) and a two-phase (liquid/solid) mixture in a mini ultrasonic channel called MERCUS (Mini-Exchanger-Reactor Continuous UltraSound). For both systems, a spatio-temporal analysis of the mixture was carried out as a function of the ratio of electrical power to flow rate, viscosity and the time ratio of ultrasound application. The liquid/liquid mixing analysis is based on a colorimetric method relating the grey scale level to the concentration of solute E133 from monochrome (black and white) pictures of the mixing zone. The analysis of the liquid/solid mixture is based on a binarisation method using the contrast between water and polyamide particles to binarise monochrome pictures of the mixing zone. Ultrasonic waves have been shown to homogenise the two systems in less than two seconds (the mixing speed depends on the power and flow rate). An optimum electrical energy density to homogenise the two systems (without unnecessary energy losses) was detected at 260 J/ml for our ultrasonic channel when the viscosity of the medium was 1 mPa[dollar]times[dollar]s. Increasing the viscosity and reducing the ultrasonic application time ratio degraded the mixture. Finally, the results showed that regardless of the method of ultrasonic application (continuous or intermittent) the mixing quality of the system (single-phase or two-phase) depends mainly on the amount of energy per volume transmitted to the flowing fluid.