Probing fluid flow using the force measurement capability of optical trapping
Date
2013
Authors
Eom, N.
Sedev, R.
Wedding, B.
Connor, J.
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Conference paper
Citation
2013 Chemeca proceedings - Challenging Tomorrow, 2013, pp.208-213
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Chemeca 2013: Australasian Conference on Chemical Engineering (29 Sep 2013 : Brisbane, Australia)
Abstract
Interest in microfluidics has rapidly expanded over the past decade particularly for use as miniature chemical reactors. Microfluidic channels are now complex as they combine several functions on a single chip. Fluid flow details are extremely important but few methods are suitable to probe fluid flow because of the confined geometry. We use optical trapping of a small dielectric particle to probe the fluid flow. A highly focused laser beam attracts particles suspended in a liquid to its focal point. Thus particles can be trapped and positioned in 3D. By measuring the displacement of the trapped particle from its equilibrium position one can estimate the external force causing the displacement. The trap stiffness (spring constant) of the optical trap is very low making it an extremely sensitive force measuring device. Rather than using the optical trap to position and release a particle for independent velocimetry measurement, we map the fluid flow by directly measuring the hydrodynamic force acting on a trapped particle. The flow rate of a dilute aqueous electrolyte flowing through a plastic microchannel (w h l = 5 mm 0.4 mm 50 mm) was mapped successfully by monitoring the force acting on a small (1 mum dia.) silica particle. The fluid velocity profile obtained experimentally was in very good agreement with the theoretical prediction. Our flow mapping approach is relatively easy and reliable and can be used in any low-opacity dilute as well as concentrated suspensions flowing in microchannels of various geometries.
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Copyright 2013 Engineers Australia