Intensification of heat and mass transfer by ultrasound: application to heat exchangers and membrane separation processes.

This paper aims to illustrate the interest of ultrasound technology as an efficient technique for both heat and mass transfer intensification. It is demonstrated that the use of ultrasound results in an increase of heat exchanger performances and in a possible fouling monitoring in heat exchangers. Mass transfer intensification was observed in the case of cross-flow ultrafiltration. It is shown that the enhancement of the membrane separation process strongly depends on the physico-chemical properties of the filtered suspensions.

Improvement of heat transfer by means of ultrasound: Application to a double-tube heat exchanger.

A new kind of ultrasonically-assisted heat exchanger has been designed, built and studied. It can be seen as a vibrating heat exchanger. A comprehensive description of the overall experimental set-up is provided, i.e. of the test rig and the acquisition system. Data acquisition and processing are explained step-by-step with a detailed example of graph obtained and how, from these experimental data, energy balance is calculated on the heat exchanger. It is demonstrated that ultrasound can be used efficiently as a heat transfer enhancement technique, even in such complex systems as heat exchangers.

Enhancement of the knowledge on the ultrasonic reactor behaviour by an interdisciplinary approach.

Our work is a step to a better understanding of high frequency ultrasonic reactors behaviour. Using finite elements calculations, it was demonstrated that localization of chemical and physical effects can be well correlated with mechanical behaviour of ultrasound emitter. This complementary approach enables us to propose a full interpretation of the sonochemical reactor behaviour. A major reason of scientific interest on ultrasound is the well-known enhancement of chemical or physical phenomena. This is so important that "Enhancement" is probably the most used word in the title of related publications. To fully understand experimental results, present work demonstrates that ultrasound needs also to significantly enhance a very difficult knowledge transfer operation that might be named interdisciplinary co-working. Hence, ultrasound is now used and studied in many different fields of science such as acoustic, chemistry, medical imaging, disease treatment (lithotripsy), non-destructive testing. Each one has his own vocabulary, approach, and method to describe the phenomenon. In this work four different methodologies were involved to study of the same effect but using a chemical, chemical engineering, physical and mechanical approach respectively. All these viewpoints were then brought together in order to explain new original results.

Velocity study in an ultrasonic reactor.

In order to determine the parameters required to describe and to optimize sonochemical reactors, we have investigated the water flow inside such a reactor. With this aim, the experimental velocity field has been measured by tomography laser. The influence of certain parameters such as the electric power, the water height and the fluid viscosity has been evaluated. At the same time, the water movement has been studied theoretically using Nyborg's model. We have tried to improve this model by considering a three-dimensional velocity.

Degradation of pentachlorophenol aqueous solutions using a continuous flow ultrasonic reactor: experimental performance and modelling.

The degradation of aqueous solutions of pentachlorophenol (PCP) in a three-stage sonochemical reactor operating in the continuous flow mode has been investigated. The experimental reactor may be considered as a series of three high-frequency ultrasonic units. The influence of several parameters such as ultrasonic power, reactor volume and volumetric feed flow rate on the reactor performance is reported. Application of classical basic chemical engineering principles leads to a model that enables us to predict the PCP concentration within the reactor. In steady state, experimental conversion rates are shown to be in good agreement with model predictions.

Experimental study of the hydrodynamic behaviour of a high frequency ultrasonic reactor.

In relation to design and modeling of sonochemical reactors, the hydrodynamic behaviour of a high-frequency ultrasonic reactor has been investigated. Residence time distribution (RTD) measurements have been performed by means of a tracer method. The influence of ultrasound on the response to an inlet pulse was evidenced. It was shown that the reactor behaves like a completely stirred tank reactor (CSTR) as soon as ultrasonic irradiation operates. Preliminary observations on acoustic streaming occurring within the reactor will also be presented.