Boiling is a process widely used in industrial and scientific applications to promote heat transfer because of high heat transfer coefficients associated to the phase change. It can be mentioned, for instance, the use of heat pipe to cool down compact electronic equipment and the heat exchangers in nuclear power reactors. Safety and design guidelines of such equipment rely on the fundamental understanding of heat transfer and fluid mechanics phenomena that occur in the near-wall region where the bubbles grow. For instance, it is well known that the dewetting dynamics (promoted by dry-spots formation) on the heated wall is a key parameter to understand the boiling crisis.  

Another near-wall feature at nucleate boiling is the formation of thin liquid films that can occur during the growth of vapor bubbles on the wall. This liquid layer with thickness up to a few microns (thus named ''microlayer'') is formed between the wall and the liquid-vapor interface of the bubble. The microlayer is a desired feature in boiling-based equipment. It acts as a heat transfer bridge, allowing a heat flux in the order of MW/m2 to be transferred from the wall to the liquid-vapor interface, promoting an efficient cooling of the wall. This results in the microlayer evaporation and its contribution to the overall bubble growth can be  up to 50%. The mechanism of microlayer formation, dry-spot dynamics and the related near-wall heat transfer phenomena are therefore an active research topic within the boiling community.         

Experiments performed in order to measure near-wall parameters, such as microlayer thickness and the dry spot size, are vital to validate novel physical models developed at CEA, in particular at STMF the ones implemented in the numerical simulations with TrioCFD. At STMF, a novel experimental installation has been developed in the framework of a PhD thesis to study the near-wall phenomena in boiling. The experimental setup uses advanced high-speed and high-resolution optical diagnostics (white light interferometry, infrared thermography and shadowgraphy) to measure microlayer thickness, wall temperature distribution and macroscopic bubble shape. The installation is, therefore, able to fully characterize the near-wall phenomena and provide data for the validation of numerical simulations.    
 
The postdoctoral researcher will benefit from this experimental installation to perform experiments in a variety of conditions of input power and subcooling, for instance, to study the physical phenomena related to the microlayer dynamics, heat transfer and dry-spot at bubble growth in nucleate boiling. The submission of one or two scientific papers within the postdoctoral period is expected.

The candidate holds a PhD in fluid mechanics/heat transfer. Experience in performing experiments with optical diagostics in boiling heat transfer is required.