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Research Papers: Flows in Complex Systems

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

[+] Author and Article Information
Stuart J. Williams

Department of Mechanical Engineering, University of Louisville, Louisville, KY 40292stuart.williams@louisville.edu

Pramod Chamarthy

General Electric, Niskayuna, NY 12309pramodchamarthy@yahoo.com

Steven T. Wereley

Mechanical Engineering, Purdue University, West Lafayette, IN 47907wereley@purdue.edu

J. Fluids Eng 132(2), 021103 (Feb 04, 2010) (7 pages) doi:10.1115/1.4000740 History: Received May 27, 2009; Revised October 22, 2009; Published February 04, 2010; Online February 04, 2010

## 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 $20 μm$ wide and a grounded, planar ITO substrate separated by a $50 μm$ 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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## Figures

Figure 1

LIF thermometry experimental setup

Figure 2

ac electrokinetic chip for N-LIFT experiments

Figure 3

Schematic of the electrical and thermal problem space and boundary conditions for the numerical model

Figure 4

Normalized fluorescence intensity for RhB

Figure 5

A portion of the numerical simulation showing the increase in temperature due to Joule heating for a fluid sample with conductivity σ=200 mS/m and applied voltage V=20 Vpp

Figure 6

(a) N-LIFT results showing the temperature increase in the medium (σ=200 mS/m) above the electrode strip at 25 Vpp. (b) Averaged temperature values across the strip.

Figure 7

Obtained maximum change in temperature values versus voltage squared obtained from N-LIFT experiments (data points) and numerical simulations (lines)

Figure 8

Obtained maximum change in temperature values versus conductivity obtained from N-LIFT experimental measurements (data points) and numerical simulations (lines)

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