(413d) Microfluidic Approaches for Accessing Thermodynamic Properties of Fluid Systems

Thermodynamic experimental data under high pressure and high temperature conditions are valuable in the industry. Knowing if a fluid will be in a liquid state or a in a vapour phase, or if it will be monophasic or multiphasic is crucial in oil production or catalysis processes for example. Unfortunately, these data are quite poor in the literature for numerous complex fluid systems. Reaching a phase equilibrium in classical Pressure-Volume-Temperature cells takes time (at least 24h), therefore experimental campaigns are time-consuming, expensive and they may be subjected to problems when working with particular fluids (toxicity, dangerousness). Thanks to scale reduction, microfluidic systems allow thermodynamic equilibria to be reached within minutes or less. Moreover, only a few milliliters of fluids are required and the volumes involved significantly reduce the risks of working under high pressure/temperature conditions. The particular case of Silicon/Pyrex microfluidic devices provides the mechanical resistance to hold pressure of more than 100 bar. Besides, the high heat transfer coefficient value of silicon allows accessing a good control of the device temperature. In addition, Pyrex still provides an easy optical access and in-situ characterizations can be carried out (µPIV, fluorescence, Raman spectroscopy, UV-Vis).

Over the past years, several methods using microfluidic devices have been developed to determine thermodynamic properties such as phase equilibriums, viscosity and density. We present here a microfluidic approach to build phases diagrams and phase envelops of fluid mixtures based on the optical detection of the bubble/dew points. We will also present a way to simultaneously determine the viscosity and the density of a fluid mixture of known composition by measuring the pressure drop between the inlet and the outlet of a microfluidic chip. We will put forward results obtained using Silicon/Pyrex microfluidic systems of our own fabrication. These microsystems can hold a pressure up to 140 bar. These studies are a first step in the development of methodologies that can be extended to complex fluids for energy applications.