Nom de l'encadrant
Nicolas Grenier
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Numerical Simulation of Bubble Dilatation under Low Pressure
In the context of global warming, working fluids of air conditioners or heat pumps are harmful for climate and active research is ongoing to find replacement solutions. A potential candidate is to use water as working fluid. But to evaporate at ambient temperature at which air conditioners operate working pressure must be very low, around hundredth of atmospheric pressure.
Apart from mechanical design and processing issues at this subatmospheric pressure, these heat exchangers experience inefficiency due to lack of understanding of boiling phenomenon at low pressure where usual correlations at atmospheric pressure are no more valid. Experimental studies are scarce while numerical simulations are inexistent on the subject to help build new correlations.
Phase change is a complex phenomenon involving multi-physics and multi-parameters and is more complex at low pressure since hydrostatic pressure cannot be no more neglected compared to interface pressure. In these conditions a boiling bubble can grow up to 15 centimetres in height
and be subject to very heterogeneous conditions on its interface which affect bubble shape and growth. Many other parameters (pressure, temperature, etc.) could impact bubble along its lifetime and are difficult to control in experiments.
We propose to use numerical simulations to give some insights while simplifying the problem.
Firstly by considering hydrodynamical aspect of bubble growth, we could investigate in the dilatation of an isothermal gas inclusion at low pressure under a free-surface. First numerical results with in-house two-fluids compressible solver [1] show good qualitative reproducibility of
experimental results (with phase change, ignored in simulations).

The objective of this master internship is twofold: to pursue the validation of the solver in this low pressure regime and then to explore new flow regimes where background pressure intensity could play a role in bubble dynamics.
Validations will be conducted in coordination with LAFSET laboratory (CNAM Paris) where researchers already collected data on the low pressure exchanger experimental facility. New experimental parameters will be added to provide new data to extend the validity range of the numerical tool.
Then new regimes unreachable by experimental set-up will be explored by mean of simulations. It will help to understand which physics play key role in this complex flow and may benefit experiments by steering them into potentially optimal configurations.
This master internship is mainly oriented towards numerical simulations along with results analysis and comparison to experiments. According to candidate skills and motivation, extensions regarding numerical improvement of the solver (preconditioning, phase change modelling, ...) could beconsidered.
transferts et énergétique
Mots clés
  • Ecoulements diphasiques
  • Energétique
Date de début
5 mois

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