Study of the influence of operating parameters on the intensification of heat transfer in the presence of ultrasound
My thesis work was carried out within the Energy team at the LEGI, under the direction of Nicolas Gondrexon and co-supervised by Sébastien Ferrouillat.
Abstract:
This thesis focus on the use of ultrasound as a method to enhance heat transfer in forced convection. The objective of this thesis is to better understand the physical mechanisms involved, and thus optimise the operating parameters for industrial purposes.
To reach this aim, a test section, consisting of a flow channel and a heating plate, was used. This test section allows to integrate one or two ultrasonic emitters. The study of ultrasound influence is here based on an analysis of convective heat transfer and hydrodynamics. In addition, the study is carried out with two different ultrasonic frequencies, 25 kHz and 2 MHz.
At first, the effects produced by the combination of several ultrasonic fields of different frequencies were studied. The results showed that the combination of ultrasonic fields can improve the cavitational activity, which induce turbulence within the flow. When this turbulence is generated close of the heating wall, the enhancement of the heat transfer produced by the ultrasound is greater than in the case of a single ultrasound field. Then, the influence of ultrasound on heat transfer, depending on the flow regime is investigated.
The increase of the Reynolds number results in an attenuation of the hydrodynamic effects produced by the ultrasound, however the effects on heat transfer differ according to the ultrasound frequency. The overall results of this study demonstrated a link between the heat transfer enhancement induced by ultrasound and the initial thickness of the thermal boundary layer in silent conditions. Finally, an energy analysis showed the interest of using ultrasound to enhance heat transfer for industrial applications.
Membres du jury :
Olivier Louisnard, Maitre assistant, IMT Mines-Albi, Rapporteur
Marc Miscevic, Maitre de conférences, Université Toulouse 3, Rapporteur
Viviane Renaudin, Professeure, Université de Lorraine, Examinatrice
Henda Djeridi, Professeure, Grenoble INP, Examinatrice
Nicolas Gondrexon, Professeur, Université Grenoble Alpes, Directeur de thèse
Sébastien Ferrouillat, Maitre de conférences, Université Grenoble Alpes, Co-encadrant de thèse
Odin Bulliard-Sauret, Maitre de conférences, Université Grenoble Alpes, Invité
Laure Vignal, Ingénieure de recherche, Université Grenoble Alpes, Invitée