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ASCOMP’s CFD-based services are provided to empower Med-Tech and Microfluidics sectors, with applications of relevance to medical diagnostics and drug delivery segments for the first, and to heat management in electronics and high-power density systems for the second. Flow control in Med-Tech systems (pressure, Marangoni, electro-wetting, acoustics) is central to future technological advances, like biological reactors, microreactors, biochannel arrays, or lab-on-a-chip devices. TransAT has proven to be highly effective in predicting this class of flows thanks to its predictive capabilities of falling films, spreading and de-wetting of liquids on substrates, chemical reaction of binary mixtures, micro-bubbles and droplet motion, phase change or transition. Our simulations virtually inform about tiny flow details, which are otherwise impossible to detect by measurement technologies. As is testified by the selected examples below, TransAT allows accurate prediction of a wide range of microfluidics flows.

Microchannel flows

Two-phase flow microchannel heat sinks are today used to cool electronic systems with high power density, because latent heat during the phase-change process can be leveraged to capture and transfer high heat fluxes. But the implementation of two-phase microchannels is challenging due to the instability of the vapor-liquid interfaces (bubbles and slugs), leading to local dry-out and thus poor cooling efficiency. In two-phase microfluidic flows, surface tension forces are dominant relative to other forces, and the Knudsen number is large, reducing the length scale characteristic of the problem. Thus, capturing these flows at these reduced length scales require the use of advanced multiphase flow techniques combined with appropriate microscale physics models, in particular wetting.

Heat management using enhanced-surfaces materials

A hot spot appearing on an electronics circuit can generate heat that either hampers the performance of the heat-releasing structure itself or damage the neighboring components. Enhanced surfaces materials (e.g. thermal spreaders) are employed for efficient heat channeling. Another possible strategy for dissipating the heat is to use anisotropic thermal conductive thin layers to guide the heat to the sink. A conventional heat conductor is normally roughly isotropic. The idea is inspired by new highly efficient mode of thermal conduction discovered recently, namely heat transport by magnetic excitations in quasi one-D insulating materials. The magnetic conduction is highly anisotropic, and has mostly been studied in novel transition metal oxides with 1-D spin structures. In TransAT, heat flow on such materials could be modelled, including in two-phase flow conditions as shown below.

Flow control in Bio-chips

The control of the flow (drops carrying reagents) in miniaturized bio-chips is a hot theme in the med-tech sector. The concept, where a tiny fluid microprocessor performs complex tasks relevant to chemistry or biology, has been a subject of academic interest, and there are encouraging signs that industrial lab-on-a-chip applications are growing, exemplified by microfluidic devices for DNA sequencing. The control can be achieved by various ways: wetting by fixing an ultra-thin film (right example), by Marangoni forces or imposing a temperature gradient (left example), or via imposing an external magneto-electrical or acoustic field to move the droplets The cases above illustrate the predictive capacity of TransAT in treating these subjects.

Drop on demand in microfluidic chips

The techniques of in-chip drop on demand consists in dispensing picoliter to nanoliter drops on demand directly in the channels of a polymer microfluidic chip, at frequencies up to 2.5 kHz and with precise volume control. Several features of the in-chip drop on demand technique have direct relevance to lab-on-a-chip applications discussed previously. Individual microdrops can be dispensed from the chamber to the channeling system in various modes: the T-junction is probably the most popular dispensing prototypes today, where a cross-flow through square channels is used to produce bubble. The efficiency of micro-dispensers is measured in terms of frequency and size of the droplets, which directly depend on the way capillary forces are modelled. The successful examples shown below were obtained by TransAT.

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