title: Long-range electrothermal fluid motion in microfluidic systems.
abstract: AC electrothermal flow (ACEF) is the fluid motion created as a result of Joule heating induced temperature gradients. ACEF is capable of performing major microfluidic operations, such as pumping, mixing, concentration, separation and assay enhancement, and is effective in biological samples with a wide range of electrical conductivity. Here, we report long-range fluid motion induced by ACEF, which creates centimeter-scale vortices. The long-range fluid motion displays a strong voltage dependence and is suppressed in microchannels with a characteristic length below ~300 μm. An extended computational model of ACEF, which considers the effects of the density gradient and temperature-dependent parameters, is developed and compared experimentally by particle image velocimetry. The model captures the essence of ACEF in a wide range of channel dimensions and operating conditions. The combined experimental and computational study reveals the essential roles of buoyancy, temperature rise, and associated changes in material properties in the formation of the long-range fluid motion. Our results provide critical information for the design and modeling of ACEF based microfluidic systems toward various bioanalytical applications.
authors.affiliation: Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, Arizona, 85721, USA; Departments of Biomedical Engineering, The Pennsylvania State University, University Park, PA 16802 USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, Arizona, 85721, USA.
authors.forename: Qinlong
authors.initials: Q
authors.lastname: Ren
authors.affiliation: Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, Arizona, 85721, USA.
authors.forename: Tingting
authors.initials: T
authors.lastname: Liu
authors.affiliation: Departments of Biomedical Engineering, The Pennsylvania State University, University Park, PA 16802 USA; College of Medicine, The University of Arizona, Tucson, 85724, USA.
authors.forename: Siu Ling
authors.initials: SL
authors.lastname: Leung
authors.affiliation: GeneFluidics Inc., Irwindale, California, 91010, USA.
authors.forename: Vincent
authors.initials: V
authors.lastname: Gau
authors.affiliation: Department of Urology, Stanford University, Stanford, California, 94305, USA.
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Liao
authors.affiliation: Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, Arizona, 85721, USA.
authors.forename: Cho Lik
authors.initials: CL
authors.lastname: Chan
authors.affiliation: Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, Arizona, 85721, USA; Departments of Biomedical Engineering, The Pennsylvania State University, University Park, PA 16802 USA; Departments of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802 USA; Department of Surgery, Milton S. Hershey Medical Center, The Pennsylvania State University, Hershey, PA 17033 USA.
authors.forename: Pak Kin
authors.initials: PK
authors.lastname: Wong
keywords: AC electrothermal flow; buoyancy; computational fluid dynamics; electrokinetics; microfluidics