Aerosol particles separation by means of a microfluidic thermophoretic device – AERATOR

The study of aerosols dynamics is crucial for the development of new technologies that can help reduce the impact of aerosols on human health and climate change. This project aims to design and fabricate a proof-of-concept microfluidic aerosol separator by means of the thermophoretic effect in gas flows (particle deflection in a temperature field). The separator that will be developed in this project will serve to collect and analyze particles ranging from 0.01 to 2.5 um. The consortium will be composed by three consolidated teams which are experts in experimental microfluidics (ICA), numerical methods for rarefied gases (IUSTI) and the development of a multi-instrumented microfluidic platform (sensor and micro heater for thermal management) (LAAS). An important first step of the project will be devoted to characterize experimentally the physical response of aerosol particles to a temperature gradient (thermophoresis) in confined gas flows. The particle deposition distance on the cold surface of a channel and separation efficiencies will be measured for different temperature gradient intensities and for various sizes and thermal conductivities of spherical model particles. In parallel, the consortium will develop numerical models of the phenomenon using different tools. The Navier-Stokes-Fourier equations, with adequate boundary conditions of velocity and thermal slips and temperature jump, hold only for large aerosol particles. However, the simulation of the thermophoresis phenomenon becomes a challenge when the particle size becomes comparable to the molecular mean free path of the carrier gas. At atmospheric conditions, the molecular mean free path of air is around 65 nm, so for particles whose size is comparable to this dimension, the continuum modeling becomes invalid (rarefied gas). The novelty of the proposed work consists in developing a multiscale approach: the simulations based on a continuum approach will provide the knowledge about the global pressure, temperature, velocity fields of the carrier gas as well as of the particle density distribution inside the channel. The simulation of an aerosol particle displacement submitted to the pressure and temperature gradient fields using the kinetic approach will allow to obtain the expressions of the thermophoretic forces as a function of different types of gas aerosol/particle surface interactions. The integration of these data in the macroscopic level model of the force balances will improve the existing numerical databases. The experimental results will allow to validate the numerical models. By using the created numerical and experimental databases a first design of a micro-thermophoretic-separator prototype will be fabricated by means of modern lithography techniques that allow on-chip sensors and thermal management integration. The microfabrication of the prototypes will take advantage of two manufacturing processes that have been developed and mastered by LAAS and that will be optimized to fulfill the challenging requirements of the project: (i) polysilicon diodes that can be used as high- performance temperature micro-sensors and micro-heaters, and (ii) lamination of dry-films to obtain wafer-scale, multi-level, photolithography aligned microfluidic features. This ambitious project will produce the first microfluidic thermophoretic aerosol separator prototype of the literature.