We are looking for a post-doc to join our research team and perform experiment on heterogeneous cavitation to explore the origin of cavitation nuclei.

The apparition of macroscopic bubbles inside a liquid either by boiling when temperature increases, from cavitation when pressure decreases or in supersaturated solution (large quantity of dissolved gas) originates from nano/microscopic bubbles, named nuclei. These nuclei are trapped in surface defects or stabilized by floating impurities. The nucleation, in this case, is called heterogeneous in opposition to the homogeneous nucleation occurring without pre-existing nuclei which required tremendous excitation, e.g. -140 MPa for the cavitation [1]. Although the nuclei are usually assumed to be formed during liquid immersion, we recently show that they can also spontaneously appear [2]. The aim of the overall project is to unravel the mechanism responsible for this generation of nuclei.

To probe the invisible nuclei (nano/microbubbles), the experiment consists in focusing acoustic waves on a well-controlled surface defect to vary the pressure. If a nucleus is hidden inside the defect, it will become unstable and grow to a visible size, i.e. acoustic cavitation, allowing its detection through optical means. Furthermore, the nucleus initial size can be assessed by measuring the critical pressure at which cavitation occurs thanks to the crevice model of heterogenous cavitation [3]. The nuclei reformation dynamic can then be monitored by repeating the experiment several times.
 
The post-doc will take part in the improvement of the experimental setup and protocol. Once the setup calibrated, different parameters such as defect shape or dissolved gas content will be tested to explore their influence on the nuclei generation. The results will be analyzed to identify possible nucleation mechanisms.

We are looking for a candidate with strong interest in experiments and coding (Python or Matlab) to control the setup. A fluid mechanics background, especially in diffusion and capillarity, is needed to interpret the results. Knowledge in acoustics is advisable but not mandatory.

During this postdoc funded by the ANR (CANURE), the candidate will acquire expertise in acoustics, cavitation, capillarity, wetting and dissolved gas transport. Moreover, the postdoc will gain strong experimental skills through the elaboration of the complex setup.

 

References:

[1] F. Caupin & E. Herbert, Cavitation in water : a review, C. R. Physique, 2006, 7, 1000-1017

[2] A. Bussonnière, Q. C. Liu & P. A. Tsai, Cavitation nuclei regeneration in water-particle suspension, Phys. Rev. Lett., 2020, 124, 034501

[3] A. A. Atchley & A. Prosperetti, The crevice model of bubble nucleation. JASA, 1989, 86(3), 1065-1084

Cavitation bubbles appearing during few milliseconds on a surface after an acoustic pulse.

CONTACTS

Adrien Bussonnière, MSC, adrien.bussonniere@u-paris.fr

Valentin Leroy, MSC, valentin.leroy@u-paris.fr