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An Experimental-Numerical Study Of Heat Transfer Enhancement In A Minichannel Using Asymmetric Pulsating Flows, Parth S. Kumavat, Sajad Alimohammad, Seamus M. O'Sullivan

Articles

The development of current and next-generation high-performance electronic devices has led to miniaturization in more densely packed spaces. The increasing power levels have resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Implementation of single-phase cooling systems using pulsating flow is viewed as a potential solution to the problems involving high energy density electronics. This work involves a combined experimental and numerical analysis of pulsating flows in a rectangular mini channel undergoing asymmetric sinusoidal flow pulsation formats. The mini channel design includes a heated bottom section approximated as a constant heat flux boundary …

Numerical Study Of The Time-Periodic Electroosmotic Flow Of Viscoelastic Fluid Through A Short Constriction Microchannel, Jianyu Ji, Shizhi Qian, Armani Marie Parker, Xiaoyu Zhang

Mechanical & Aerospace Engineering Faculty Publications

Electroosmotic flow (EOF) is of utmost significance due to its numerous practical uses in controlling flow at micro/nanoscales. In the present study, the time-periodic EOF of a viscoelastic fluid is statistically analyzed using a short 10:1 constriction microfluidic channel joining two reservoirs on either side. The flow is modeled using the Oldroyd-B (OB) model and the Poisson-Boltzmann model. The EOF of a highly concentrated polyacrylamide (PAA) aqueous solution is investigated under the combined effects of an alternating current (AC) electric field and a direct current (DC) electric field. Power-law degradation is visible in the energy spectra of the velocity fluctuations …

Long-Range Aceo Phenomena In Microfluidic Channel, Diganta Dutta, Keifer Smith, Xavier Palmer

Electrical & Computer Engineering Faculty Publications

Microfluidic devices are increasingly utilized in numerous industries, including that of medicine, for their abilities to pump and mix fluid at a microscale. Within these devices, microchannels paired with microelectrodes enable the mixing and transportation of ionized fluid. The ionization process charges the microchannel and manipulates the fluid with an electric field. Although complex in operation at the microscale, microchannels within microfluidic devices are easy to produce and economical. This paper uses simulations to convey helpful insights into the analysis of electrokinetic microfluidic device phenomena. The simulations in this paper use the Navier–Stokes and Poisson Nernst–Planck equations solved using COMSOL …

Directional Notches As Microstructures To Promote Nucleation And Heat Transfer In Pool Boiling, Callum Mclaughlin

Theses

Heat generation in electronic hardware has become a major limiting factor in achieving maximum efficiency in modern computer parts. Classically forced flow convection systems are used to remove this heat at high rates but can be costly to implement and can take up space that may be needed for other critical components. In response to this, systems that use fewer parts scale in compact spaces are needed. In these situations, pool boiling as a heat transfer mechanism can excel. Pool boiling removes heat through the evaporation of fluid. On a flat surface pool boiling is chaotic and this random nature …

Simulation Of Droplet Impacting A Square Solid Obstacle In Microchannel With Different Wettability By Using High Density Ratio Pseudopotential Multiplerelaxation- Time (Mrt) Lattice Boltzmann Method (Lbm), Wandong Zhao, Ying Zhang, Wenqiang Shang, Zhaotai Wang, Ben Xu, Shuisheng Jiang

Mechanical Engineering Faculty Publications and Presentations

In this paper, a pseudopotential high density ratio (DR) lattice Boltzmann Model was developed by incorporating multi-relaxation-time (MRT) collision matrix, large DR external force term, surface tension adjustment external force term and solid-liquid pseudopotential force. It was found that the improved model can precisely capture the two-phase interface at high DR. Besides, the effects of initial Reynolds number, Weber number, solid wall contact angle (CA), ratio of obstacle size to droplet diameter ( 1 χ ), ratio of channel width to droplet diameter ( 2 χ ) on the deformation and breakup of droplet when impacting on a square obstacle …

Effect Of Interfacial Curvature On Drag Reduction Of Superhydrophobic Microchannels, Chunxi Li, Zhang Shuo, Xuemin Ye

Journal of System Simulation

Abstract: The two-dimensional fluid flow in superhydrophobic microchannels with transverse grooves was numerically simulated with Fluent to investigate the impact of the liquid-gas interface curvature on the effective slip behavior in the laminar regime. The effects of shear-free fraction, normalized periodic cell length and Reynolds number on the normalized slip length and pressure drop reduction are also examined. The results show that as protrusion angle increases, the normalized slip length and pressure drop reduction exhibit with single-hump variations. When θ=θ_opt, increments in the normalized slip length and pressure drop reduction tend to be greater as shear-free …

Enhance Flow Boiling In Microchannels By Regulating Two-Phase Transport Patterns, Wenming Li

Theses and Dissertations

Flow boiling in microchannels is one of the most promising cooling techniques for microelectronics. Using latent heat by vaporization can significantly improve heat dissipation of high power density electronic devices. Most of the failure of electronic devices is induced by the occurrence of critical heat flux (CHF), which defines the maximum operating conditions. However, the vigorous rapid generation of vapor through phase change leads to chaotic two-phase flows in microchannels, resulting in flowinstability in terms of severe flow, temperature and pressure drop fluctuations. Particularly, the very well-known bubble confinement exacerbates the two-phase flow instabilities and greatly deteriorates heat transfer performance …

Enhanced Flow Boiling Heat Transfer In Radial Microchannel And Offset Strip Fin Geometries, Alyssa Recinella

Theses

Devices used for various electronic purposes are increasing in power consumption and performance. Due to this growth, the amount of heat dissipated over a small surface area has proportionally continued to increase. Despite previous efforts involving single phase natural and forced convection, these methods are no longer effective in high heat removal. Research in two-phase liquid cooling has become more prominent. Boiling has the potential to yield large critical heat flux values, high heat transfer coefficients and lower pressure drops. Many different surface enhancements and working fluids have been tested to increase efficiency and minimize heat losses.

Flow boiling in …

Repair Severed Nerve Connections Through A Multi-Branch Microchannel Scaffold To Control The Direction Of The Regenerated Nerve, Luis Enrique Castanuela Ramon

Theses and Dissertations

Damage to the peripheral nervous system may result in functional abnormalities due to disrupted nerve connections. Existing methods of repairing severed nerve connections in the peripheral nervous system have limitations and disadvantages such as a limited availability of donor nerves and a lack of control of the direction of nerve regeneration within nerve conduits. A handcrafted multi-branch microchannel scaffold improves upon the current methods of nerve repair by incorporating microchannels, which guide and accommodate the nerve regeneration to distal ends, allowing for the treatment of nerve injuries involving multiple branches with fewer surgeries. This scaffold is also made more accessible …

Flow Boiling Heat Transfer Over Open Microchannels With Tapered Manifold, Ankit Kalani

Theses

Boiling can provide several orders of magnitude higher performance than a traditional air cooled system in electronics cooling application. It can dissipate large quantities of heat while maintaining a low surface temperature to fluid difference. Flow boiling with microchannels has shown a great potential with its high surface area to volume ratio and latent heat removal. However, flow instabilities and early critical heat flux (CHF) have prevented its successful implementation. A novel flow boiling design based on a mechanistic approach is taken to overcome the above mentioned disadvantages while presenting a very low pressure drop. The design uses open microchannels …

Assessing Defrosting Performance On Hydrophilic, Hydrophobic, And Micro-Patterned Heat Transfer Surfaces, Nickolas C. Schmiesing, Andrew D. Sommers

International Refrigeration and Air Conditioning Conference

In this work, differences in drainage rates and defrosting effectiveness were explored for surfaces of differing wettability. Both patterned and non-patterned surfaces were explored. To date, six surfaces have been examined— an uncoated, untreated aluminum plate (Sample 1), an identical plate treated with a hydrophilic coating (Sample 2), a plate containing evenly-spaced micro-channels with no surface coating (Sample 3), a plate containing evenly-spaced micro-channels with a hydrophobic coating (Sample 4), and a surface containing a microstructural roughness gradient both with and without a hydrophobic surface coating (Samples 5 and 6). Cyclical tests containing frosting periods and defrosting periods were conducted …

Characterization Of Thermoplastic Fusion Bonding Of Microchannels Using Pressure Assisted Boiling Point Control System, Kavya Dathathreya

LSU Master's Theses

An innovative method of thermoplastic fusion bonding using a pressure assisted boiling point control (PABP) system was characterized to determine the optimum parameters for bonding polymethyl methacrylate (PMMA) components containing microchannels and thin, 250 µm cover sheets. The PABP system enables precise control of the temperature boundary condition and the applied pressure by immersing the components being bonded in boiling water and varying the vapor pressure. Test structure geometries containing microchannels of two depths and four different aspect ratios were designed: 1:10 (Depth: 10µm, Width: 100 µm and Depth: 5µm, Width: 50 µm), 1:50 (Depth: 10µm, Width: 500µm and Depth: …

A Microchannel With Repeated Sharp Corners For Single Stream Particle Focusing, Liang-Liang Fan, Xu-Kun He, Liang Zhao, Yu Han, Jiang Zhe

Dr. Jiang Zhe

A new microfluidic device for fast and high throughput microparticle focusing is reported. The particle focusing is based on the combination of inertial lift force effect and centrifugal force effect generated in a microchannel with a series of repeated sharp corners on one side of the channel wall. The inertial lift force effect induces two focused particles streams in the microchannel, and the centrifugal force generated at the sharp corner structures tends to drive the particles laterally away from the corner. With the use of a series of the repeated, sharp corner structures, a single and highly focused particle stream …

A Microfluidic Mixer Utilizing Electrokinetic Relay Switching And Asymmetric Flow Geometries, Yiou Wang, Jiang Zhe, Prashanta Dutta, Benjamin Chung

Dr. Jiang Zhe

No abstract provided.

Enhancement Of Pool Boiling Heat Transfer Using A Combination Of Open Microchannels And Microporous Surfaces, Chinmay Patil

Theses

The continuous development of high performance chips and growing miniaturization trend in the electronics and microelectronics industry requires efficient systems removing large amount of heat over a small footprint. It has been experimentally proven that pool boiling has the ability to remove large heat fluxes by maintaining a small value of wall superheat. This heat transfer performance can be further augmented with the use of enhanced surfaces. The present research is focused on developing microporous surface coatings on the plain and microchannel surfaces to further enhance pool boiling heat transfer.

In this work, a two-step electrodeposition technique involving application of …

Two-Phase Flow And Heat Transfer Of A Non-Azeotropic Mixture Inside A Single Microchannel, Davide Del Col, Marco Azzolin, Stefano Bortolin

International Refrigeration and Air Conditioning Conference

In the recent years much attention has been paid to the use of fluorinated propene isomers for the substitution of high-GWP refrigerants. However, the HFOs (hydrofluoroolefins) cannot cover all the air-conditioning, heat pump, and refrigeration applications. In a recent study, it was found that the coefficient of performance (COP) and the capacity of heat pump cycles using HFO-1234ze(E) are significantly lower than those of R410A (Koyama et al., 2010). The main causes are the small latent heat and vapor density of R1234ze(E). To improve the COP and capacity, in the latest literature it was attempted to blend R1234ze(E) into another …

Electrohydrodynamic Manipulation Of Liquid Droplet Emulsions In A Microfluidic Channel, Jonathan Wehking

Electronic Theses and Dissertations

This work specifically aims to provide a fundamental framework, with some experimental validation, for understanding droplet emulsion dynamics in a microfluidic channel with an applied electric field. Electrification of fluids can result in several different modes of electrohydrodynamics (EHD). Several studies to date have provided theoretical, experimental, and numerical results for stationary droplet deformations and some flowing droplet configurations, but none have reported a method by which droplets of different diameters can be separated, binned and routed through the use of electric fields. It is therefore the goal of this work to fill that void and report a comprehensive understanding …

Osteogenic Potential Of Poly(Ethylene Glycol)–Poly(Dimethylsiloxane) Hybrid Hydrogels, Dany Munoz Pinto, Andrea Jimenez-Vergara, Yaping Hou, Heather Hayenga, Alejandra Rivas, Melissa Grunlan, Mariah Hahn

Dany J. Munoz Pinto

Growth factors have been shown to be potent mediators of osteogenesis. However, their use in tissue-engineered scaffolds not only can be costly but also can induce undesired responses in surrounding tissues. Thus, the ability to specifically induce osteogenic differentiation in the absence of exogenous growth factors through manipulation of scaffold material properties would be desirable for bone regeneration. Previous research indicates that addition of inorganic or hydrophobic components to organic, hydrophilic scaffolds can enhance multipotent stem cell (MSC) osteogenesis. However, the combined impact of scaffold inorganic content and hydrophobicity on MSC behavior has not been systematically explored, particularly in three-dimensional …

Performance Of A Compact Absorption Heat Pump Containing Microchannel Absorber Components, Ward E. Tegrotenhuis, Dustin D. Caldwell, Paul H. Humble, Dale A. King, Shankar Krishnan

International Refrigeration and Air Conditioning Conference

Novel microchannel absorbers have been scaled-up and incorporated into a 5-kW-scale ammonia-water absorption heat pump. The planar microchannel absorbers operate with thin wick structures to enhance mass transfer in the absorption channels which are interleaved with microchannel heat exchange layers. The resulting rapid heat and mass transfer facilitates significant size reduction in the absorber and consequently the overall heat pump system. Based on the 5-kW-scale system design, up to 50% size reduction relative to current commercial equipment is projected. The microwick absorber technology is described and measured performance data are provided for proofof- concept single-channel devices up to multi-channel devices …

Experimental Study Of Pool Boiling Heat Transfer Enhancement Over Microchanneled Surfaces, Dwight Cooke

Theses

Pool boiling is of interest in heat transfer applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is still not comparable to the cooling ability provided by enhanced microchannels operating under single-phase conditions. This investigation focuses on the bubble dynamics and heat transfer on plain and structured microchanneled surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism through the use of a high speed camera. …

Advanced Thermal Models For Improved Design Of Counter Flow Microchannel Heat Exchangers, Bobby Mathew

Doctoral Dissertations

Theoretical models of counter flow microchannel heat exchangers subjected to scaling and secondary effects are developed in this dissertation. The scaling effects studied include axial heat conduction and viscous dissipation, while the secondary effects considered in this dissertation is that of external heat transfer via heat flux and temperature. The theoretical models developed are one-dimensional and consist primarily of ordinary governing equations that describe the axial variation of hot and cold fluid. For the case of axial heat conduction, the axial variation of wall temperature is also modeled. The models are dependent on various factors, such as Reynolds number, Prandtl …

Local Heat Transfer Distribution And Effect Of Instabilities During Flow Boiling In A Silicon Microchannel Heat Sink, Tailian Chen, S V. Garimella

CTRC Research Publications

Flow boiling of the perfluorinated dielectric fluid FC-77 in a silicon microchannel heat sink is investigated. The heat sink contains 60 parallel microchannels each of 100 lm width and 389 lm depth. Twenty-five evenly distributed temperature sensors in the substrate yield local heat transfer coefficients.
The pressure drop across the channels is also measured. Experiments are conducted at five flow rates through the heat sink in the range of 20–80 ml/min with the inlet subcooling held at 26 K in all the tests. At each flow rate, the uniform heat input to the substrate is increased in steps so that …

Design And Fabrication Of Structured Roughnesses In Microchannels With Integrated Mems Pressure Sensors, Tushara Pasupuleti

Theses

As the demand for cooling is increased for high-density powered electronic devices, researchers have proposed solutions to improve the efficiency of the microchannel liquid cooling system to meet these requirements. Introducing roughness in the microchannels is one of the approaches to enhance the heat transfer. The fluid flow behavior needs experimental investigation before exploring the heat transfer efficiency. A test structure consisting MEMS pressure sensors were fabricated along the length of the microchannel. Smooth microchannels and rough microchannels with structured roughness were fabricated. A fabrication process flow has been developed to fabricate the microchannel and the pressure sensor on the …

Experimental Investigation Of Flow And Heat Transfer Characteristics Of R -134a In Microchannels, Abdullahel Bari

Doctoral Dissertations

The purpose of this study was to investigate the flow and heat transfer characteristics of liquid refrigerant R-134a in rectangular microchannels. The research concentrated mostly upon single-phase experiments with limited investigation of boiling phenomenon in microchannels. Tests were performed using rectangular microchannels with hydraulic diameters ranging from 112 μm to 210 μm and aspect ratios varying approximately from 1.0 to 1.5. The Reynolds number in the experiments ranged from 1,200 to 13,000 although most data were collected in the transition and turbulent flow regimes.

The experimental data for friction factor measurement had a similar trend as predicted by macroscale theory …

Photo-Cross-Linked Pdmsstar-Peg Hydrogels: Synthesis, Characterization, And Potential Application For Tissue Engineering Scaffolds, Yaping Hou, Cody Schoener, Katherine Regan, Dany Munoz Pinto, Mariah Hahn, Melissa Grunlan

Dany J. Munoz Pinto

Inorganic−organic hydrogels with tunable chemical and physical properties were prepared from methacrylated star polydimethylsiloxane (PDMSstar-MA) and diacrylated poly(ethylene glycol) (PEG-DA) for use as tissue engineering scaffolds. A total of 18 compositionally unique hydrogels were prepared by photo-cross-linking, varying weight ratios of PEG-DA and PDMSstar-MA of different molecular weights (Mn): PEG-DA (Mn = 3.4k and 6k g/mol) and PDMSstar-MA (Mn = 1.8k, 5k, and 7k g/mol). Introduction of PDMSstar-MA caused formation of discrete PDMS-enriched microparticles dispersed within the PEG matrix. The swelling ratio, mechanical properties in tension and compression, nonspecific protein adhesion, controlled introduction of bioactivity, and cytotoxicity of hydrogels were …

Pressure-Driven Transport Of Particles Through A Converging-Diverging Microchannel, Ye Ai, Sang W. Joo, Yingtao Jiang, Xiangchun Xuan, Shizhi Qian

Mechanical Engineering Faculty Research

Pressure-driven transport of particles through a symmetric converging-diverging microchannel is studied by solving a coupled nonlinear system, which is composed of the Navier–Stokes and continuity equations using the arbitrary Lagrangian–Eulerian finite-element technique. The predicted particle translation is in good agreement with existing experimental observations. The effects of pressure gradient, particle size, channel geometry, and a particle’s initial location on the particle transport are investigated. The pressure gradient has no effect on the ratio of the translational velocity of particles through a converging-diverging channel to that in the upstream straight channel. Particles are generally accelerated in the converging region and then …

Laminar And Turbulent Flow Of A Liquid Through Channels With Superhydrophobic Walls Exhibiting Alternating Ribs And Cavities, Brady L. Woolford

Theses and Dissertations

There is significant interest in reducing the frictional resistance that occurs along a surface in contact with a liquid. A novel approach to reducing the frictional resistance across a liquid-solid interface is the use of superhydrophobic surfaces. superhydrophobic surfaces are created in this work by the use of micro-fabrication techniques where systematic roughness is fabricated on a substrate surface which is subsequently treated with a hydrophobic coating. This work reports an experimental study of superhydrophobic surfaces used to reduce drag in both laminar and turbulent channel flows. In the laminar flow regime reductions in frictional resistance greater than 55% were …

Mathematical Modeling Of Polymer Exchange Membrane Fuel Cells, Colleen Spiegel

USF Tampa Graduate Theses and Dissertations

Fuel cells are predicted to be the power delivery devices of the future. They have many advantages such as the wide fuel selection, high energy density, high efficiency and an inherent safety which explains the immense interest in this power source. The need for advanced designs has been limited by the lack of understanding of the transport processes inside the fuel cell stack. The reactant gases undergo many processes in a fuel cell that cannot be observed. Some of these processes include convective and diffusional mass transport through various types of materials, phase change and chemical reaction. In order to …

Pressure Losses Experienced By Liquid Flow Through Pdms Microchannels With Abrupt Area Changes, Jonathan Wehking

Electronic Theses and Dissertations

Given the surmounting disagreement amongst researchers in the area of liquid flow behavior at the microscale for the past thirty years, this work presents a fundamental approach to analyzing the pressure losses experienced by the laminar flow of water (Re = 7 to Re = 130) through both rectangular straight duct microchannels (of widths ranging from 50 to 130 micrometers), and microchannels with sudden expansions and contractions (with area ratios ranging from 0.4 to 1.0) all with a constant depth of 104 micrometers. The simplified Bernoulli equations for uniform, steady, incompressible, internal duct flow were used to compare flow through …

Magnetohydrodynamics In Microchannels And Adhesion Properties Of Nanoporous Alumina Films, Hussameddine Kabbani

UNLV Retrospective Theses & Dissertations

In the first part of this dissertation, RedOx-based magnetohydrodynamic (MHD) flows in three-dimensional (3D) microfluidic channels are investigated theoretically with a coupled mathematical model consisting of the Nernst-Planck equations for the concentrations of ionic species, the local electroneutrality condition of the electric potential, and the Navier-Stokes equations for the flow field. The induced currents and flow rates in 3D planar channels are compared with the experimental data obtained from the literature and those obtained from the previous two-dimensional mathematical model. Then a new approximate closed form solution for the velocity profile of steady incompressible MHD flows in a rectangular micro-channel …