Comparison of Experiments and Simulation of Joule Heating in ac Electrokinetic Chips

  • Williams S
  • Chamarthy P
  • Wereley S
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Abstract

ac electrokinetic manipulations of particles and fluids are important
techniques in the development of lab-on-a-chip technologies. Most of
these systems involve planar micro-electrode geometries, generating
high strength electric fields. When these fields are applied to a
dielectric medium, Joule heating occurs. Understanding electrothermal
heating and monitoring the temperature in these environments are
critical for temperature-sensitive investigations including biological
applications. Additionally, significant changes in fluid temperature
when subjected to an electric field will induce electrohydrodynamic
flows, potentially disrupting the intended microfluidic profile. This
work investigates heat generated from the interaction of ac electric
fields and water at various electrical conductivities (from 0.92 mS/m
to 390 mS/m). The electrode geometry is an indium tin oxide (ITO)
electrode strip 20 mu m wide and a grounded, planar ITO substrate
separated by a 50 mu m spacer with microfluidic features. Laser-induced
fluorescence is used to measure the experimental changes in
temperature. A normalization procedure that requires a single
temperature-sensitive dye, Rhodamine B (RhB), is used to reduce
uncertainty. The experimental electrothermal results are compared with
theory and computer simulations.

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Authors

  • Stuart J. Williams

  • Pramod Chamarthy

  • Steven T. Wereley

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