Scholars@Duke
Chuan-Hua Chen

Chuan-Hua Chen

Associate Professor of Mechanical Engineering and Materials Science
Thomas Lord Department of Mechanical Engineering and Materials Science
chuanhua.chen@duke.edu
178 Hudson Hall, Box 90300, Durham, NC 27708-0300
178 Hudson Hall, Dept. Mechanical Engineering, Durham, NC 27708-0300

Selected Publications

Droplet actuation on superhydrophobic substrates via electric field gradients

Journal Article Applied Physics Letters · March 18, 2019 A superhydrophobic surface is non-sticking to aqueous droplets due to minimized solid-liquid contact, but the small contact area also poses challenges to droplet maneuvering. This letter reports a technique using electric field gradients to actuate aqueous ... Full text Cite

Hotspot Size Effect on Conductive Heat Spreading

Journal Article IEEE Transactions on Components, Packaging and Manufacturing Technology · September 1, 2017 Solid heat spreaders, particularly those made of copper or graphite, are often benchmark solutions for hotspot thermal management. In this paper, we present exact and approximate analytical solutions of steady-state hotspot cooling with a planar heat sprea ... Full text Cite

Asymmetric drop coalescence launches fungal ballistospores with directionality.

Journal Article Journal of the Royal Society, Interface · July 2017 Thousands of fungal species use surface energy to power the launch of their ballistospores. The surface energy is released when a spherical Buller's drop at the spore's hilar appendix merges with a flattened drop on the adaxial side of the spore. The launc ... Full text Cite

Hotspot cooling with jumping-drop vapor chambers

Journal Article Applied Physics Letters · April 3, 2017 Hotspot cooling is critical to the performance and reliability of electronic devices, but existing techniques are not very effective in managing mobile hotspots. We report a hotspot cooling technique based on a jumping-drop vapor chamber consisting of para ... Full text Cite

Capillary-inertial colloidal catapults upon drop coalescence.

Journal Article Applied physics letters · July 2016 Surface energy released upon drop coalescence is known to power the self-propelled jumping of liquid droplets on superhydrophobic solid surfaces, and the jumping droplets can additionally carry colloidal payloads toward self-cleaning. Here, we show that dr ... Full text Cite

Self-Propelled Droplet Removal from Hydrophobic Fiber-Based Coalescers.

Journal Article Physical review letters · August 2015 Fiber-based coalescers are widely used to accumulate droplets from aerosols and emulsions, where the accumulated droplets are typically removed by gravity or shear. This Letter reports self-propelled removal of drops from a hydrophobic fiber, where the sur ... Full text Cite

Self-propelled sweeping removal of dropwise condensate

Journal Article Applied Physics Letters · June 1, 2015 Dropwise condensation can be enhanced by superhydrophobic surfaces on which the condensate drops spontaneously jump upon coalescence. However, the self-propelled jumping in prior reports is mostly perpendicular to the substrate. Here, we propose a substrat ... Full text Cite

The minimum flow rate scaling of Taylor cone-jets issued from a nozzle

Journal Article Applied Physics Letters · January 13, 2014 A minimum flow rate is required to maintain steady Taylor cone-jets issued from an electrified nozzle. This letter reports that the well-known scaling law proportional to the charge relaxation time and independent of the nozzle diameter is only applicable ... Full text Cite

Electrohydrodynamic cone-jet bridges: Stability diagram and operating modes

Journal Article Journal of Electrostatics · January 1, 2014 An electrohydrodynamic cone-jet bridge is formed when two opposing Taylor cones are bridged by a liquid jet. We used high-speed video imaging to systematically investigate the operating regimes of the cone-jet bridge established between a nozzle and a liqu ... Full text Cite

Numerical simulations of self-propelled jumping upon drop coalescence on non-wetting surfaces

Journal Article Journal of Fluid Mechanics · January 1, 2014 Coalescing drops spontaneously jump out of plane on a variety of biological and synthetic superhydrophobic surfaces, with potential applications ranging from self-cleaning materials to self-sustained condensers. To investigate the mechanism of self-propell ... Full text Cite

Self-propelled jumping upon drop coalescence on leidenfrost surfaces

Journal Article Journal of Fluid Mechanics · January 1, 2014 Self-propelled jumping upon drop coalescence has been observed on a variety of textured superhydrophobic surfaces, where the jumping motion follows the capillary-inertial velocity scaling as long as the drop radius is above a threshold. In this paper, we r ... Full text Cite

Self-cleaning of superhydrophobic surfaces by self-propelled jumping condensate.

Journal Article Proceedings of the National Academy of Sciences of the United States of America · May 2013 The self-cleaning function of superhydrophobic surfaces is conventionally attributed to the removal of contaminating particles by impacting or rolling water droplets, which implies the action of external forces such as gravity. Here, we demonstrate a uniqu ... Full text Cite

Vapor chambers with jumping-drop liquid return from superhydrophobic condensers

Journal Article International Journal of Heat and Mass Transfer · March 15, 2013 In closed-loop phase-change systems, self-propelled jumping drops on a superhydrophobic condenser offer a new mechanism to return the working fluid to the evaporator, eliminating the requirement for either external forces or wick structures along the retur ... Full text Cite

Pulsating electrohydrodynamic cone-jets: From choked jet to oscillating cone

Journal Article Journal of Fluid Mechanics · December 25, 2011 Pulsating cone-jets occur in a variety of electrostatic spraying and printing systems. This paper reports an experimental study of the pulsation frequency to reconcile two models based on a choked jet and an oscillating cone, respectively. The two regimes ... Full text Cite

Planar jumping-drop thermal diodes

Journal Article Applied Physics Letters · December 5, 2011 Phase-change thermal diodes rectify heat transport much more effectively than solid-state ones, but are limited by either the gravitational orientation or one-dimensional configuration. Here, we report a planar phase-change diode scalable to large areas wi ... Full text Cite

Nonclogging Resistive Pulse Sensing with Electrohydrodynamic Cone-Jet Bridges

Journal Article Physical Review X · December 1, 2011 A new paradigm of resistive pulse sensing (Coulter counting) is developed using a liquid bridge in lieu of a solid pore as the sensing aperture, whereby the flexible liquid aperture circumvents the clogging issue of conventional Coulter counters. The elect ... Full text Cite

Thermocapillary actuation of binary drops on solid surfaces

Journal Article Applied Physics Letters · September 5, 2011 On hydrophobic solid surfaces, aqueous drops are typically not conducive to thermocapillary actuation. This letter reports thermal mobilization of water drops by encapsulating them with a long-chain alcohol. On a parylene-coated silicon substrate, a water- ... Full text Cite

Wetting and dewetting transitions on hierarchical superhydrophobic surfaces.

Journal Article Langmuir : the ACS journal of surfaces and colloids · June 2011 Many natural superhydrophobic structures have hierarchical two-tier roughness which is empirically known to promote robust superhydrophobicity. We report the wetting and dewetting properties of two-tier roughness as a function of the wettability of the wor ... Full text Cite

Electrohydrodynamic Stability

Conference · January 1, 2011 Stability of electrohydrodynamic flows is essential to a variety of applications ranging from electrokinetic assays to electro-spray ionization. In this series of lecture notes, a few basic concepts of electrohydrodynamic stability are illustrated using tw ... Full text Cite

Electrohydrodynamic coulter counting

Journal Article 14th International Conference on Miniaturized Systems for Chemistry and Life Sciences 2010, MicroTAS 2010 · December 1, 2010 A new paradigm of Coulter counting is developed using electrohydrodynamic liquid jets in lieu of solid state pores as the sensing aperture. The electrohydrodynamic jet was successfully used to detect micron-sized particles through resistive pulse sensing. ... Cite

Self-propelled jumping drops on superhydrophobic surfaces

Journal Article Physics of Fluids · September 30, 2010 Full text Open Access Cite

Beetle inspired electrospray vapor chamber

Journal Article Proceedings of the ASME Micro/Nanoscale Heat and Mass Transfer International Conference 2009, MNHMT2009 · July 12, 2010 We present the proof-of-concept for a biomimetic electrospray vapor chamber (BEVAC) which can potentially eliminate the wick structures and thermal interface materials Used in conventional vapor chambers, and enable direct Oooling of the backside of a micr ... Full text Cite

Development of an adaptive vapor chamber with thermoresponsive polymer coating

Journal Article Proceedings of the ASME Micro/Nanoscale Heat and Mass Transfer International Conference 2009, MNHMT2009 · July 12, 2010 We propose a novel concept for an adaptive vapor chamber using a thermoresponsive polymer coating to enhance heat transfer and reduce local thermal gradients. By coating the wick structures with stimulus-responsive polymer brushes with an upper critical so ... Full text Cite

Self-propelled dropwise condensate on superhydrophobic surfaces.

Journal Article Physical review letters · October 2009 In conventional dropwise condensation on a hydrophobic surface, the condensate drops must be removed by external forces for continuous operation. This Letter reports continuous dropwise condensation spontaneously occurring on a superhydrophobic surface wit ... Full text Cite

Restoring superhydrophobicity of lotus leaves with vibration-induced dewetting.

Journal Article Physical review letters · October 2009 A lotus leaf retains water repellency after repeated condensation in nature but becomes sticky to water drops after condensation on a fixed cold plate. Our experiments show that mechanical vibration can be used to overcome the energy barrier for transition ... Full text Cite

Evaporation and condensation on two-tier superhydrophobic surfaces

Journal Article 2008 Proceedings of the ASME Micro/Nanoscale Heat Transfer International Conference, MNHT 2008 · August 20, 2008 Superhydrophobic surfaces exhibit large contact angle and small hysteresis which promote liquid transport and enhance heat transfer. Here, liquid-vapor phase change behavior is reported on superhydrophobic surfaces with short carbon nanotubes deposited on ... Full text Cite

Dropwise condensation on superhydrophobic surfaces with two-tier roughness

Journal Article Applied Physics Letters · May 21, 2007 Dropwise condensation can enhance heat transfer by an order of magnitude compared to film condensation. Superhydrophobicity appears ideal to promote continued dropwise condensation which requires rapid removal of condensate drops; however, such promotion h ... Full text Cite

Scaling laws for pulsed electrohydrodynamic drop formation

Journal Article Applied Physics Letters · September 29, 2006 A pulsed electrohydrodynamic jet can produce on-demand drops much smaller than the delivery nozzle. This letter describes an experimentally validated model for electrically pulsed jets. Viscous drag in a thin nozzle limits the flow rate and leads to intrin ... Full text Cite

Electrohydrodynamic "drop-and-place" particle deployment

Journal Article Applied Physics Letters · April 10, 2006 The "drop-and-place" paradigm aims at delivering and positioning liquid drops using a pulsed electrohydrodynamic jet. On-demand drops much smaller than the diameter of the delivery nozzle may also contain particles. We report proof-of-concept experiments o ... Full text Cite

Convective and absolute electrokinetic instability with conductivity gradients

Journal Article Journal of Fluid Mechanics · February 10, 2005 Electrokinetic flow instabilities occur under high electric fields in the presence of electrical conductivity gradients. Such instabilities are a key factor limiting the robust performance of complex electrokinetic bio-analytical systems, but can also be e ... Full text Cite

Computational study of band-crossing reactions

Journal Article Journal of Microelectromechanical Systems · April 1, 2004 A numerical study of band-crossing reactions is conducted using a quasi-one-dimensional (1-D) computational model that accounts for species bulk advection, electromigration velocities, diffusion, and chemical reaction. The model is used to simulate chemica ... Full text Cite

Instability of electrokinetic microchannel flows with conductivity gradients

Journal Article Physics of Fluids · January 1, 2004 Electrokinetic flow is leveraged in a variety of applications, and is a key enabler of on-chip electrophoresis systems. An important sub-class of electrokinetic devices aim to pump and control electrolyte working liquids with spatial gradients in conductiv ... Full text Cite

Electrokinetic microflow instability with conductivity gradients

Journal Article American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED · January 1, 2003 We have experimentally identified and quantified an electrokinetic flow instability that occurs in DC-electric-field driven microfluidic channels with significant conductivity gradients. We have, for the first time, developed a physical model for this inst ... Full text Cite

A planar electroosmotic micropump

Journal Article Journal of Microelectromechanical Systems · December 1, 2002 Electroosmotic (EO) micropumps use field-induced ion drag to drive liquids and achieve high pressures in a compact design with no moving parts. An analytical model applicable to planar, etched-structure micropumps has been developed. This model consists of ... Full text Cite

Electroosmotic flow pumps with polymer frits

Journal Article Sensors and Actuators, B: Chemical · February 28, 2002 Electroosmotic flow (EOF) pumps with flow rates on the order of 1ml/min have been designed and fabricated. These pumps use EOF to propel liquid solutions in a compact system with no moving parts. The pumping chamber is filled with densely packed non-porous ... Full text Cite

Electrokinetic flow instability in high concentration gradient microflows

Journal Article ASME International Mechanical Engineering Congress and Exposition, Proceedings · January 1, 2002 This paper documents the scalar imaging of an electrokinetic flow instability that is directly relevant to microfluidic systems that aim to handle and analyze heterogeneous sample streams. The instability occurs in simple T-junctions where two streams of d ... Full text Cite

Fabrication and characterization of electroosmotic micropumps

Journal Article Sensors and Actuators, B: Chemical · October 15, 2001 Electroosmotic flow (EOF) micropumps which use electroosmosis to transport liquids have been fabricated and used to achieve pressures in excess of 20 atm and flow rates of 3.6 μl/min for 2 kV applied potentials. These pumps use deionized water as working f ... Full text Cite

Development of a planar electrokinetic micropump

Conference ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) · January 1, 2000 Electrokinetic (EK) micropumps use electroosmotic flow to produce high pressures in a compact design with no moving parts. An EK micropump has been fabricated on a 50 x 75 x 1.2 mm soda-lime glass substrate using standard microlithography and chemical wet ... Full text Cite

Fabrication and characterization of electrokinetic micro pumps

Journal Article Thermomechanical Phenomena in Electronic Systems -Proceedings of the Intersociety Conference · January 1, 2000 Electrokinetic (EK) micropumps have been fabricated and demonstrated in which electroosmotic flow is used to transport fluids. Deionized water and pure acetonitrile have been used as working fluids to achieve low current density pumping conditions. These E ... Cite