bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptive Neuro-Fuzzy Modeling of the Thermal Conductivity of Alumina-Water Nanofluids
Authors: Mehrabi Mehdi , Sharifpur Mohsen , Meyer Josua P.
Published: July 2013

By using on Adaptive Neuro-Fuzzy Inference System (ANFIS) as well as experimental data, a model was established for the prediction of the thermal conductivity ratio of alumina (Al2O3)-water nanofluids. In the ANFIS the target parameter was the thermal conductivity ratio, and the nanoparticle volume concentration, temperature and Al2O3 nanoparticle size were considered as the input (design) parameters. In the development of the model, the empirical data was divided into train and test sections. The ANFIS network was instructed by eighty percent of the experimental data and the remaining data (twenty percent) were considered for benchmarking. The results which were obtained by the proposed Adaptive Neuro-Fuzzy Inference System (ANFIS) model were in good agreement with the experimental results.
Effect of Al2O3 Nanolubricant on a Turbo-BII R134a Pool Boiling Surface
Authors: Kedzierski M. A.
Published: July 2013

This paper quantifies the influence of Al2O3 nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a Turbo-BII-HP boiling surface. An Al2O3 nanolubricant (a lubricant containing dispersed nano-size particles) was made by suspending nominally 10 nm diameter Al2O3 particles in a synthetic polyolester to roughly a 1.0% volume fraction. The nanoparticles caused, on average, a 12% degradation in the boiling heat transfer relative to that for R134a/polyolester mixtures without nanoparticles for the three lubricant mass fractions that were tested. The degradation was nearly constant for heat fluxes between 20 kW/m2 and 120 kW/m2. It was speculated that the boiling heat transfer degradation was primarily due to a combination of (1) film boiling in the reentrant cavity rendering the nucleate boiling enhancement mechanism of the nanoparticles ineffective and (2) a reduction in bubble frequency due to the increased surface wetting as caused by the nanoparticles. In addition, these degradation factors might be mitigated with increased nanoparticle loading.
Applications of Nano Hot-Film Sensor for Micro/Nanoscale Thermal Measurement
Authors: Takahashi Koji , Hirotani Jun , Nishiyama Takashi , Ikuta Tatsuya , Takamatsu Hiroshi
Published: July 2013

Platinum hot-film sensors, whose typical size is 500nm wide × 10μm long × 40nm thick, are developed for investigating micro and nanoscale thermal events. This paper reports four kinds of applications with measurement principle, sensitivity analysis, and test results. Thermal conductivity of individual nanowire, represented by carbon nanotube, has been measured by bridging the specimen between the sensor and a heat sink. Here a new device is newly developed, which enables us to measure quantitatively both intrinsic thermal conductivity of the specimen and thermal contact resistance between the specimen and a target material. Focused beam-induced deposition is also measured by comparing the thermal conductance of deposited sensor and pristine one. Flow sensor is another application and we investigate the performance of carbon nanotube (CNT) fins deposited on the sensor by using dielectrophoresis technique to enhance the flow signal. The applicability of this sensor for measuring the thermal conductivity of fluid of very limited volume (femto-liter order) is also analytically studied.
Development of Boiling Type Cooling System Using Electrostatic and Electroconvection Force
Authors: Kano Ichiro , Higuchi Yuta , Chika Tadashi
Published: July 2013

The paper describes results from an experimental study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling at atmospheric pressure with polished smooth boiling surface. A micro scaled electrode with slits for bubbles to come out was designed in order to create non uniform high electric field strength and to produce electrohydrodynamics (EHD) convection with the application of dc voltage. The application of high electric field strongly enhanced the heat flux and the heat transfer coefficient. From observations of the behavior of bubbles over the electrode and the boiling surface condition, the instability between the liquid and the vapor increased the heat flux, the heat transfer coefficient and the CHF.
Towards High Energy Density, High Conductivity Thermal Energy Storage Composites
Authors: Shamberger Patrick J. , Forero Daniel E.
Published: July 2013

Thermal energy storage (TES) materials absorb transient pulses of heat, allowing for rapid storage of low-quality thermal energy for later use, and effective temperature regulation as part of a thermal management system. This paper describes recent development of salt hydrate-based TES composites at the Air Force Research Laboratory. Salt hydrates are known to be susceptible to undercooling and chemical segregation, and their bulk thermal conductivities remain too low for rapid heat transfer. Here, we discuss recent progress towards solving these challenges in the composite system lithium nitrate trihydrate/graphitic foam. This system takes advantage of both the high volumetric thermal energy storage density of lithium nitrate trihydrate and the high thermal conductivity of graphitic foams. We demonstrate a new stable nucleation agent specific to lithium nitrate trihydrate which decreases undercooling by up to ∼70% relative to previously described nucleation agents. Furthermore, we demonstrate the compatibility of lithium nitrate trihydrate and graphitic foam with the addition of a commercial nonionic silicone polyether surfactant. Finally, we show that thermal conductivity across water-graphite interfaces is optimized by tuning the surfactant concentration. These advances demonstrate a promising route to synthesizing high energy density, high thermal conductivity TES composites.
Pool Boiling Heat Transfer of Borated (H3BO3) Water on a Nanoporous Surface
Authors: Amaya Miguel , Kwark Sang M. , Gurung Ajay , You Seung M.
Published: July 2013

With regard to potential application in pressurized water reactors (PWRs), a nanoporous heated surface was tested in pool boiling of an aqueous solution of boric acid (H3BO3), or borated water (1% volume concentration). The effect of different system pressures and different surface orientations on pool boiling heat transfer was studied. The nanoporous surface consisted of a coating of alumina nanoparticles applied on a 1 cm2 flat copper surface through nanofluid boiling. An uncoated surface in borated water was similarly tested, and due to boric acid deposition, the boiling heat transfer (BHT) degraded and the critical heat flux (CHF) enhanced relative to pure water. Also, the possibility of transient pool boiling behavior of borated water was investigated but none was detected. For all pressures and orientations, the nanoporous surface further enhanced the CHF of borated water to the CHF produced by the nanoporous surface in pure water. Over the nanoporous surface, the CHF of borated water was increasingly better with decreasing pressure, than that over the plain surface. However, BHT degraded slightly further. Boric acid deposition over the nanoporous surface was believed to be the source of this BHT degradation, but played no apparent role in the further CHF enhancement.
Experimental Study of a High Performance Aligned Graphite Thermal Interface Material
Authors: Zhao Y. , Strauss D. , Chen Y. C. , Liao T. , Chen C. L.
Published: July 2013

Thermal interface materials (TIMs) play a critical role in microelectronics packaging. In this paper, a novel aligned-graphite/solder TIM is described. Unlike traditional TIMs infiltrated with randomly-oriented high-conductivity fillers, the aligned-graphite/solder TIMs provide both extraordinarily high thermal conductivity along the heat transport direction, and controllable stiffness to conform to surfaces with different roughness and hardness, greatly improving the overall heat transfer performance. In addition, vertically connected solder layers can lock the graphite layers in place and reinforce the strength of the entire package.

Thermal performance of the graphite TIMs was determined experimentally based on the ASTM-D5470 method with comparison to two commercially available TIMs. The graphite TIMs also experienced a thermal cycling test and a high temperature stability test to establish its performance merit in practical applications.

Experiments showed that the overall thermal resistivity of a 150-to-200-μm-thick graphite TIM film was less than 0.035 °C/(W/cm2) when bonding two smooth copper surfaces together at a processing pressure of 30 psi, which corresponds to an approximately 2–3X improvement over a Ag-Sn solder alloy (Indalloy 121). Preliminary thermal cycling and high temperature stability tests showed that the thermal performance of the graphite TIM was very stable, and did not degrade during these tests. The tests also indicated that the presence of surface roughness of 10 μm on one of the copper surfaces reduced the overall thermal resistivity by approximately 30%. A numerical simulation verified this trend.
Design of Liquid-Metals Heating-Induced Temperature Gradient Focusing in Microfluidic Channels
Authors: Gao Meng , Gui Lin , Liu Jing
Published: July 2013

Temperature gradient focusing (TGF) is a highly efficient focusing technique for the concentration and separation of charged analytes in microfluidic channels. Design and control of an appropriate temperature gradient are very important for protein concentration and separation. In this study, we propose a new technique to generate the temperature gradient for the focusing purpose. This technique utilizes a microchannel filled with liquid-metals as a heater in the microfluidic chip. By applying electrical current, the liquid-metal microchannel generates Joule heat to form temperature gradient in the microfluidic chip. To optimize the temperature gradient, several typical designs were investigated. The results show the best design which provides the largest linear temperature gradient. The parametric studies present a clear guideline for designing aTGF microfluidic chip.
Broadband Absorption Enhancement in Thin Film Solar Cells Using Inverse Optimization of Light Trapping Mechanisms
Authors: Hajimirza Shima , Heltzel Alex , Howell John
Published: July 2013

In this paper, global optimization techniques are used to design broadband solar absorption enhancement in thin film amorphous silicon (a-Si) solar cells, using periodic nanostructures on the top and bottom surfaces of the cell. Considering a combination of silver rectangular gratings and indium tin oxide (ITO) coatings on both surfaces of the a-Si, numerical optimization techniques such as Simulated Annealing and a local constrained Quasi-Newton algorithm are used to optimize the surface texture patterns. Numerical results indicate that, unlike the case of metallic gratings on the front surface, a periodic silver grating structure on the back surface results in a modification of the absorption spectrum largely independent of the effect of anti-reflection ITO coatings on the front of the cell. Furthermore, additional improvement can be obtained by using a thin rear surface ITO layers. Therefore, using a combination of metallic gratings and ITO coatings on both sides, a wideband absorption spectrum enhancement is achievable. Simulations predict integrated enhancement factors as high as 2.0 (100% improvement) for the case of metallic grating on the back surface and ITO layers on the front, and as high as 2.2 (120% improvement) when a combination of grating and ITO coatings on both sides is used. Such noteworthy improvements are made possible by efficient multi-parameter optimization supplanting an intractable exhaustive search.
Experimental Investigation of an Open Loop Pulsating Heat Pipe Using Ferrofluid
Authors: Mohammadi Maziar , Taslimifar Mehdi , Saidi Mohammad Hassan , Shafii Mohammad Behshad , Afshin Hossein , Kazemzadeh Hannani Siamak
Published: July 2013

The present work investigates the thermal performance of a five turn Open Loop Pulsating Heat Pipe (OLPHP). The effects of working fluid namely water and ferrofluid, heat input, ferrofluid concentration, charging ratio, and orientation will be considered. Experimental results show that using ferrofluids can enhance the thermal performance in comparison with the case of distilled water. In addition, applying a magnetic field on the OLPHP charged with ferrofluid reduces its thermal resistance. Variation of the ferrofluid concentration results in different thermal performance of the OLPHP. Best charging ratio for the distilled water and ferrofluid without magnetic field is 60% in most of the cases, while in the case of ferrofluid in the presence of magnetic field at low heat inputs, 20% and at high heat inputs 60% of charging ratios have lowest thermal resistance.
Comparison of Spectral Energy Density Methods for Predicting Phonon Properties
Authors: Larkin Jason M. , Massicotte Alexandre D. , Turney Joseph E. , McGaughey Alan J. H. , Amon Cristina H.
Published: July 2013

To predict the thermal conductivity of a dielectric or insulating material requires the phonon frequencies and lifetimes. Techniques for predicting these quantities have been proposed based in molecular dynamics simulation and lattice dynamics calculations. Here, two expressions for the phonon spectral energy density are described and applied to two test systems: Lennard-Jones argon and Stillinger-Weber silicon. One spectral energy density expression is derived from lattice dynamics theory, while the other uses only the atomic velocities from molecular dynamics simulation. We find that while the spectral energy density using only atomic velocities can predict the phonon frequencies, it is not generally able to predict the lifetimes due to terms omitted in the derivation.
Temperature Dependent Thermal Properties in LEDs for Solid State Lighting
Authors: Su Zonghui , Malen Jonathan A. , Huang Li , Davis Robert F.
Published: July 2013

Over 20% of electricity in US is used by lighting. Solid state lighting (SSL) efficiency can surpass that of incandescent and fluorescent lighting techniques. Nonetheless SSL efficiency is greatly reduced at high temperatures that result from inadequate heat dissipation. SSL requires blue and green light emitting diodes (LEDs) made from Gallium Nitride (GaN) and Indium Gallium Nitride (InGaN) to eventually generate white light. Conduction within the LED is a major thermal resistance for heat dissipation, and motivates study of thermal properties of LED materials, including GaN and InGaN. Bulk thermal properties are poor estimates of thin film properties due to increased boundary and defect scattering of phonons in the films. By examining real nitride based LED architectures with the 3-omega technique, thin film thermal conductivities of nucleation, buffer, contact, and active regions were measured from 100–400K. We find that the AlN nucleation layer is a bottleneck to heat transfer, having a thermal conductivity (κ) two orders of magnitude less than bulk crystalline AlN. Further, the temperature dependent behavior is characteristic of an amorphous solid. TEM images of the AlN layer show a very high dislocation density (4×1010 cm−2). We hypothesize that scattering from these dislocations as well as the film boundaries, causes the observed behavior.
Study on Condensation of Biomass Pyrolysis Gas by Spray Bio-Droplets
Authors: Cheng Wen-long , Xie Kun , Shi Wen-jing
Published: July 2013

Bio-oil, produced from biomass feedstock like rice hull, straw, wood flour and other biomass wastes by fast pyrolysis where the biomass feedstock is heated and pyrolized with a rapid rate and the pyrolysis gases produced are condensed rapidly, is an interesting potential alternative fuel oil.

Cooling rate of the biomass pyrolysis gas is an important factor effecting the production of bio-oil. In order to speed up the cooling rate, the high temperature biomass pyrolysis gas is cooled and condensed by spray droplets of produced bio-oil with low temperature in this paper. It was assumed that the chemical reactions among the components of pyrolysis gas can be ignored, a theoretical model based on the classic film model and the Maxwell-Stefan equation was presented to simulate the heat and mass transfer characteristics of the spray condensation of biomass pyrolysis gas. The effects of the initial pyrolysis gas temperatures, the initial bio-oil droplets temperatures and diameters, and the flow ration of the gas and the liquid droplets on the heat and mass transfer between the gas and the liquid droplets were analyzed by the model.
Assessment of Fourier-Based Thermal Models Used in Frequency-Domain Thermoreflectance Data Analysis
Authors: Sellan D. P. , Mishra V. , Malen J. A. , McGaughey A. J. H. , Amon C. H.
Published: July 2013

We assess a Fourier-based thermal model used in frequency-domain thermoreflectance data analysis. The Boltzmann transport equation (BTE) is first used to simulate sub-continuum phonon transport in a semi-infinite solid. We then compare the BTE-predicted temperature profiles to those predicted by an analytical solution of the Fourier-based conduction equation. The two models agree well when ωτ < 1, where ω is the surface-temperature modulation-frequency and τ is the bulk phonon relaxation time, but diverge when ωτ > 1.
A Study of Small Molecule Absorption in Polydimethylsiloxane
Authors: Brewer Bryson , Gao Yandong , Li Deyu
Published: July 2013

While polydimethylsiloxane (PDMS) has proven to be a popular material in the construction of microfluidic devices, the polymer network structure of PDMS makes it permeable to some molecules. This feature can be problematic for applications where thin PDMS walls are used to separate two different molecular streams or cell populations. Therefore, a better understanding of factors affecting small molecule absorption in PDMS is important for better design and operation of microfluidic devices.

We report on studies of various factors in the absorption of fluorescent dyes in PDMS. Results show significant effects of thermal aging of PDMS on the absorption of the hydrophobic molecule Nile Red. In addition, the short-term hydrophobic recovery of the PDMS devices after being plasma bonded to a glass slide was investigated. Furthermore, we have tested the effects of aspiration and flushing, which show that the wetting property (hydrophilic or hydrophobic) of the flushing solvents can significantly affect the absorption of the Nile Red dye. Finally, parallel tests of PDMS absorption of fluorescein isothiocyanate (FITC) were conducted with no absorption observed.
A Simple Approach to Probe the Extracellular Signaling Pathways Using Ligand Traps
Authors: Gao Yandong , Brantley-Sieders Dana , Majumdar Devi , Chen Jin , Webb Donna , Li Deyu
Published: July 2013

Cells communicate with one another through a huge variety of extracellular soluble signaling molecules. A common method in biology to investigate the signaling pathways is to inactivate the gene coding the interested ligand or receptor from cells using modern DNA technology, known as gene knockout. Even though very effective, however, gene knockout is a time-consuming and cost-prohibitive process and requires huge amount of efforts to conduct. Here we present a simple method to probe the extracellular signaling pathways through engineering a semi-permeable barrier between two cell populations. In this approach, ligand traps, receptor-coated nano/micro-particles, are embedded inside the nanoporous barrier. Because the receptors have the ability to selectively bind to certain ligand(s) with high affinity, the associated ligands can be ‘trapped’ inside the barrier when they try to perfuse from one cell population to the other. As a result, the targeted soluble ligands can be effectively blocked from the molecular exchange between the two cell populations. We have demonstrated the feasibility of this novel approach using fluorescent proteins. An analytical model has also been developed to guide the design of the ligand-trap-embedded barrier.
Microfluidics for Controlled Production of Thin Films and Particles
Authors: Baah David , Tigner Julaunica , Britton Bernard , Floyd-Smith Tamara
Published: July 2013

Tailored materials with nano to micron dimensions are becoming increasingly important for niche applications in optics, personnel protection and biomedicine. Microfluidics is a robust platform for producing these tailored materials because of the spatial control that can be realized in microfluidic systems due to laminar flow profiles and small dimensions. For this work, a pre-polymer solution, consisting of water, polyethylene glycol diacrylate (PEGDA) and a photo-initiator, flows through a microfluidic channel. For the general scheme, the pre-polymer is exposed to UV light in the microfluidic channel to crosslink the polymer. Depending on the application, the model pre-polymer, PEGDA, may need to be substituted with a different photo-polymerizable pre-polymer to address issues such as chemical compatibility and moisture stability prior to commercialization. Nonetheless, proof-of-concept is demonstrated using PEGDA with results that are transferrable to other photo-polymerizable pre-polymers.

For this work, two distinct applications will be presented. In one application, the pre-polymer has a graded profile of nanoparticles. The nanoparticles modify the refractive index of the heterogeneous material and allow light to be directed through the material according to Snell’s Law. When the pre-polymer solution is polymerized, a thin film with a controlled refractive index profile is produced with potential for waveguiding applications. In a second application, the light is masked during UV exposure to produce particles instead of thin films. The particles can be of any two-dimensional extruded shape. If the pre-polymer solution is loaded with ceramic nanoparticles and sintered, ceramic particles that retain the shape of the original composite particle are produced. To date, numerous particle cross sections of polymeric particles and limited ceramic particles have been demonstrated with applications in liquid body armor, abrasives and drug delivery.
Measurement of Coherent Thermal Emission From Subwavelength Grating Structures by the Excitation of Magnetic Polaritons
Authors: Wang L. P. , Zhang Z. M.
Published: July 2013

Tailoring radiative properties such as spectral control of thermal emission is beneficial in many applications such as space cooling and energy harvesting. The effect of magnetic polaritons (MPs) on spectral modulation has been analyzed previously and shown to exhibit omnidirectional behaviors when magnetic polaritons are excited in metallic grating structures with a dielectric spacer on a metallic film. The present work provides an experimental demonstration of coherent thermal emission from such a microstructure in the infrared region at both room and elevated temperatures. Samples with different patterns are fabricated to study the geometric effect on the MPs. The emittance at elevated temperatures is directly measured using a home-built emissometer, while the room-temperature emittance is indirectly obtained from the reflectance measurements. The rigorous coupled-wave analysis and the LC model are employed to elucidate the mechanisms, by incorporating the Drude model with a temperature-dependent scattering rate.
Thermal Conductivity Enhancement of Room Temperature Ionic Liquids (RTILs) With Various Magnetic Nanoparticles
Authors: Nikapitiya N. Y. Jagath B. , Moon Hyejin
Published: July 2013

This paper reports an experimental study of thermal conductivity of room temperature ionic liquids (RTILs) based magnetic nanofluids. Various magnetic nanoparticles of metal oxides with high thermal conductivity, such as CuO, Al2O3, Fe3O4 and Carbon Nano Tubes (CNTs), were used to prepare magnetic nanofluids, while RTIL, trihexyl (tetradecyl) posphonium dicyanamide was used as the base fluid. Two major parameters that affect to the thermal conductivity enhancement of fluids were investigated. The effect of particle concentration and external magnetic fields were tested. It was observed that the magnetic nanofluids thermal conductivities increase with increment of particle concentration and external magnetic field parallel to the temperature gradient. Besides, it was observed that under higher magnetic fields, thermal conductivity enhancement tends to approach a saturation state. Surfactant was used to disperse magnetic nanoparticles within the RTILs. The transient hot wire method was used for this investigation.
Spectral and Directional Control of Thermal Radiation With Periodic Structured Materials
Authors: Wang Weijie , Fu Ceji , Tan Wenchang
Published: July 2013

Spectral and directional control of thermal emission holds substantial importance in different kinds of applications, where heat transfer is predominantly by thermal radiation. Several configurations have previously been proposed, like using gratings, photonic crystals, and resonant cavities. In the present work, we theoretically investigate the influence of periodic microstructures such as micro-scale gratings and photonic crystals on the thermal radiative properties of a structure constituted with these periodic microstructures. The enhanced thermal emission is found to be due to different excitation modes and the coupling between them. In order to offer insight into the mechanisms, we calculate and visualize the electromagnetic field profile at specified emission peaks. Furthermore, the emissivity pattern is calculated as a function of the emission angle and the angular frequency. The results reveal detailed spectral and directional dependence, and omnidirectional feature of thermal emission from the proposed structure. We show that it is possible to flexibly control the emission behavior by adjusting the structure dimensional parameters properly.
Thermomechanical Behavior of GaN Nanowires During Tensile Loading and Unloading
Authors: Jung Kwangsub , Cho Maenghyo , Zhou Min
Published: July 2013

Structural phase transformations from wurtzite to a graphite-like phase and from wurzite to a tetragonal phase in ZnO and GaN nanowires under tensile loading cause significant changes in thermal conductivity. Molecular dynamics simulations are carried out to investigate the effect of deformation and the phase transformations on the thermal conductivity of [0001]-oriented GaN nanowires. The calculation of conductivity at each state of the nanowires is based on the equilibrium Green-Kubo approach with quantum correction. Under tensile loading, initially wurtzite-structured wires transform into a tetragonal structure, causing the thermal conductivity to decrease as the strain increases. Unloading of the transformed wires is associated with a reverse transformation from the tetragonal structure to the wurtzite structure. Opposite to what is observed during the forward transformation during loading, the thermal conductivity increases as the strain decreases in the unloading process. However, during the reverse transformation, the nanowires consist of both tetragonal regions and wurtzite-structured regions. Such intermediate states are not observed during the loading process. Phonon scattering at the interfaces between the wurtzite and tetragonal regions during unloading causes the thermal conductivity of the nanowires to be lower compared with that during loading.
Thermal Characterization of Discrete Device Layers in AlxGa1−xN Based Ultraviolet Light Emitting Diodes
Authors: Natarajan Shweta , Watkins Bobby G. , Adivarahan Vinod , Khan Asif , Graham Samuel
Published: July 2013

The temperature rise in LEDs is an important parameter that must be determined for both thermal management and device lifetime/reliability assessment. Commonly used indirect methods of measuring the device temperature either estimate the multiple quantum well (MQW) temperature based on measuring temperature dependent device characteristics (e.g., forward voltage and electroluminescence methods), or they measure the average temperature across the device structure using optical methods such as infrared (IR) thermography and thermoreflectance. However, none give true insight into the vertical distribution of temperature in these structures. In this study, Raman spectroscopy is applied for the first time to operating UV LEDs to give the temperature rise in discrete layers within the LED device structure, going from the growth substrate to layers adjacent to theMQWs. Comparisons are made with IR themography to contrast with this depth sensitive measurement technique. It was observed that the peak temperatures in the device were much higher than the temperatures indicated by IR while the averaged temperatures through the structure compared favorably. Additional comparisons to electroluminescence measurements were also made which compared favorably with the peak temperatures found by Raman Spectroscopy.
Effect of Hydrogen Passivation on the Thermal Conductivity of Nanoporous Crystalline Silicon: A Molecular Dynamics Study
Authors: Fang Jin , Pilon Laurent
Published: July 2013

Effect of hydrogen passivation on thermal conductivity of nanoporous crystalline silicon was investigated using equilibrium molecular dynamics (MD) simulations from 500 to 1000 K. The porosity varied from 8% to 38% while the pore diameter ranged from 1.74 to 2.93 nm. Hydrogen passivation of the pore surface was found to reduce thermal conductivity by about 20% at 500 K due to enhanced phonon scattering by the passivated atoms at the nanopore surface. The effect of passivation diminished with increasing temperature. In fact, the phonon density of states at high temperatures was similar for both passivated and unpassivated silicon atoms. Finally, the thermal conductivity k was found to be linearly proportional to (1–1.5fv)/(Ai/4) where fv is the porosity and Ai is the pore interfacial area concentration. This scaling law was previously established for un-passivated silicon using non-equilibrium MD simulations.
Temperature Dependent Thermal Conductivity of Pure Silica MEL and MFI Zeolite Thin Films
Authors: Fang Jin , Huang Yi , Pilon Laurent , Lew Christopher M. , Yan Yushan
Published: July 2013

This paper reports the temperature dependent cross-plane thermal conductivity of pure silica zeolite (PSZ) MEL and MFI thin films between 30 and 315 K. PSZ MFI thin films were made by in situ crystallization. They were b-oriented, fully crystalline and had a 33% porosity. PSZ MEL thin films were prepared by spin coating a suspension of MEL nanoparticles in 1-butanol solution onto silicon substrates followed by calcination and vapor-phase silylation with trimethylchlorosilane. The MEL films consisted of MEL nanoparticles embedded in a non-uniform and highly porous silica matrix. They featured porosity, relative crystallinity, and MEL nanoparticles size ranging from 40% to 59%, 23% to 47% and 55 to 80 nm, respectively. The cross-plane thermal conductivity of these PSZ thin films was measured using the 3ω method. Although the PSZ MFI thin film was fully crystalline and had smaller porosity than the MEL films, it was found to have thermal conductivity only slightly larger than that of MEL thin films for all temperatures. This was due to the fact that the MFI thin film had large microporosity and micropore surface area. This, in turn, greatly enhanced phonon-pore scattering and reduced thermal conductivity. In addition, for PSZ MEL films, the effect of increases in the relative crystallinity and nanoparticle size on the thermal conductivity was compensated by the simultaneous increase in porosity. Finally, all measured thermal conductivity was linearly proportional to Tn with n varying from 2 to 2.6 for temperature T < 60 K. This can be attributed to the fact that the PSZ thin films featured crystalline nanostructures which were highly disordered due to the large surface area of pores and nanocrystals.
Effect of Curvature on Near-Field Radiative Transfer: The Modified Proximity Approximation
Authors: Sasihithlu Karthik , Narayanaswamy Arvind
Published: July 2013

Near-field radiative transfer between two spheres can be computed using Rytov’s theory of fluctuational electrodynamics in which the strength of electromagnetic sources is related to temperature through the fluctuation-dissipation theorem, and the resultant energy transfer is described using an expansion of the dyadic Green’s function of the vector Helmholtz equation in a series of vector spherical waves. We show that when electromagnetic surface waves are active at a frequency the number of vector spherical waves required for convergence is proportional to Rmax/d when d/Rmax → 0, where Rmax is the radius of the larger sphere, and d is the smallest gap between the two spheres. Using this criterion, we show that the surface polariton mediated near–field thermal radiative conductance between two spheres of equal radii R scales as R/d as d/R → 0. We also propose a modified form of the proximity approximation to predict near–field radiative transfer between curved objects from simulations of radiative transfer between parallel surfaces.
Debris Detection in Hydraulic Oil Using a Microfluidic Inductive Pulse Device
Authors: Zhang Hongpeng , Huang Wen , Jin Junwei , Guo Li , Li Dongqing
Published: July 2013

Metal wear debris is an important component of oil particle contamination and is also an essential information carrier in hydraulic oil. Based on inductive Coulter counting principle, a microfluidic device to detect wear debris in oil is presented. The proposed device has the advantage that in theory the distance between wear particle in oil and an embedded coil is 0, which can greatly improve the sensitivity of detection. The relationship between coil parameters and inductive change of a coil is analyzed through the related experimental statistics. The result indicates it can distinguish effectively ferrous and nonferrous metal particles in oil, and the size of 19 μm iron particles and 40 μm copper particles can be detected.
Thermal Conductivity of Single-Crystal Silicon Microbridges Measured by Electrical Resistance Thermometry and Time-Domain Thermoreflectance
Authors: English Timothy S. , Phinney Leslie M. , Hopkins Patrick E. , Serrano Justin R.
Published: July 2013

Accurate thermal conductivity values are essential to the modeling, design, and thermal management of microelectromechanical systems (MEMS) and devices. However, the experimental technique best suited to measure thermal conductivity, as well as thermal conductivity itself, varies with the device materials, fabrication conditions, geometry, and operating conditions. In this study, the thermal conductivity of boron doped single-crystal silicon-on-insulator (SOI) microbridges is measured over the temperature range from 77 to 350 K. The microbridges are 4.6 mm long, 125 μm tall, and two widths, 50 or 85 μm. Measurements on the 85 μm wide microbridges are made using both steady-state electrical resistance thermometry and optical time-domain thermoreflectance. A thermal conductivity of ∼ 77 W/mK is measured for both microbridge widths at room temperature, where both experimental techniques agree. However, a discrepancy at lower temperatures is attributed to differences in the interaction volumes and in turn, material properties, probed by each technique. This finding is qualitatively explained through Boltzmann transport equation modeling under the relaxation time approximation.
Heat Transfer Performance of a Phase Change Microcapsule Fluid
Authors: Kalinowski Paul , Lawler John , Yang Bao , Cao Fangyu
Published: July 2013

Polyalphaolefins (PAOs) are widely implemented for electronics cooling. However, they have a low thermal conductivity. Adding nanoparticles to a PAO can significantly improve the thermal properties of the coolant. In this paper, the thermal performance of phase change materials (PCM) fluids with reduced supercooling in the phase transition was studied in a microchannel heat sink, and compared with that of the pure PAO. A test loop was designed and fabricated to test the synthesized PCM fluids. The PCM fluid with uncoated PCM particles has a 36% higher heat transfer coefficient than the pure PAO. The heat transfer coefficient of a silver coated PCM coated was also higher than of the pure PAO but lower than of the uncoated PCM. The thermal resistance of the uncoated PCM fluid was about 20% lower that of the PAO fluid at the same pumping power, despite the PCM fluid’s higher viscosity. Pumping tests run for several hours showed no effect on particle accumulation or settling within the heat transfer loop.
An Analytical Solution of the Generalized Phase-Lagging Equation for Ultra-Fast Heat Transfer in One-Dimensional Semi-Infinite Domain
Authors: Kulish Vladimir , Poletkin Kirill V.
Published: July 2013

The paper presents an integral solution of the generalized one-dimensional phase-lagging heat equation with the convective term. The solution of the problem has been achieved by the use of a novel technique that involves generalized derivatives (in particular, derivatives of non-integer orders). Confluent hyper-geometric functions, known as Whittaker’s functions, appear in the course of the solution procedure, upon applying the Laplace transform to the original transport equation. The analytical solution of the problem is written in the integral form and provides a relationship between the local values of the temperature and heat flux. The solution is valid everywhere within the domain, including the domain boundary.
Physics Based Simulation of Large Size Particle Transport in Biomedical Applications
Authors: Chen Zhijian , Przekwas Andrzej , Athavale Mahesh
Published: July 2013

In biomedical microdevices and medical applications there is a need to analyze fluid transport of solid structures with sizes comparable to channel dimensions. Examples include manipulation of biological cells in microfluidic devices or transport of thrombin particles in blood vessels. Computational modeling of such macroparticles is very difficult when the particle size is bigger than the size of the computational control volume (mesh element). In performing such simulations, conventional Lagrangian model of micro particles is not suitable since this approach doesn’t account particle’s volume blockage of the supporting Eulerian computational mesh. Other approaches such as deforming mesh or volume of fluid are either impractical of computationally very intensive or limited to structured meshes. We have developed a ‘macroparticle’ methodology where the large particle is represented as a large cluster of smaller particles (marker particles) that is “embedded” on a background computational grid. The macroparticle is then represented by blocking the cells in the background mesh that are overlapped by individual micro-particles. The discrete surface of the macroparticle is represented by partially or fully blocked cells of the background computational mesh. The translation /rotation/deformation motion of the macroparticle is calculated using a 6-DOF model with fluid pressure and shear forces acting on the particle surface used as forces and moments in calculating macroparticle position, velocity, acceleration and rotation. The size of the background grid determines the accuracy of the particle shape definition and the flow solution. The relevant physics and chemical conservation laws for each macroparticle are solved in a coupled, iterative method with the equation systems governing the background fluid domain.

This methodology has been successfully used for simulations of macroparticle-laden fluids in micro channels in biochips. As an application of this novel method, we have applied this technology to simulate a moving clot in blood flow and process of clot mechanical dissolution (thrombolysis).
Enhancement of Cryosurgery Using Biodegradable MgO Nanoparticles
Authors: He Zhi Zhu , Di De Rui , Liu Jing
Published: July 2013

Presently an unavoidable defect in nano-cryosurgery is involved with the toxicity and biocompatibility of the foreign particles. Attempting to overcome the shortcomings mentioned above, based on our previous work, MgO nanoparticles have been used as a biodegradable and nontoxic agent in enhancing the nano-cryosurgery output. In this paper we present a three dimensional numerical study to investigate the significant thermal effects of MgO nanoparticles on the iceball evolution during cryosurgery of target tissue. Both of theoretical analysis and numerical simulation confirm that the excellent thermo-physical properties of MgO nanoparticles may be a quite important factor during iceball growth. This work may enhance current understanding of the factors for determining the effects of cryosurgery.
Onset of Benard-Marangoni Instability on a Flat Meniscus in a Microchannel
Authors: Pan Zhenhai , Wang Hao
Published: July 2013

Attention Marangoni instability in a microchannel is of interest in various heat transfer and microfluidic applications. In this work, a numerical study is conducted on a flat meniscus in a square adiabatic microchannel. The evaporative heat flux is uniform, and thus the initial meniscus temperature is uniform. However, the simulations showed that a temperature gradient perpendicular to the meniscus can also lead to an instability that starts a strong Marangoni flow, which should be a type of the Benard-Marangoni instability that was originally observed on a thin liquid layer. A new expression of the Marangoni number (Ma) is derived for the Benard-Marangoni instability in a microchannel. The threshold Ma values are obtained, providing guidance for microfluidic design.
Thermophysical Properties and Pool Boiling Characteristics of Water in Polyalphaolefin Nanoemulsion Fluids
Authors: Xu Jiajun , Yang Bao
Published: July 2013

In this work, thermophysical properties and pool boiling characteristics of water-in-polyalphaolefin (PAO) nanoemulsion fluids and their dependence on water concentration have been investigated experimentally. Water-in-PAO nanoemulsion fluids are formed via self-assembly with surfactant sodium sullfosuccinate (AOT). Thermal conductivity of the fluids is found to increase with water concentration, as expected from the Maxwell equation. However, the measured thermal conductivity increase is very moderate, e.g., a 16% increase for 8.6Vol. %. Unlike thermal conductivity, the dynamic viscosity of these nanoemulsion fluids first increases with water concentration, reaches a maximum, and then decreases. This trend could be attributed to the attractive forces among water droplets. The boiling behavior of these nanoemulsion fluids has been altered due to water nanodroplets. Adding water nanodroplets can lower the nanoemulsion’s boiling point compared to the pure PAO. Another interesting phenomenon observed is that pool boiling of nanoemulsion fluids randomly follows two different curves when the water concentration is in the range of 5.3 Vol. % to 7.8 Vol. %. The mechanism underlying this phenomenon is not understood yet, but it may be related to the evolution of microstructures in the water-in-PAO nanoemulsion fluids.
Micro/Nanochannel Emulsification for Generating Monosize Droplets
Authors: Kobayashi Isao , Nakajima Mitsutoshi
Published: July 2013

Emulsification is an important process in various fields including foods, pharmaceuticals, cosmetics, and chemicals. Emulsification operation is commonly conducted using conventional emulsification devices, such as high-speed blenders, colloid mills, high-pressure homogenizers, and ultrasonic homogenizers. However, these emulsification devices result in the production of polydisperse emulsions with wide droplet size distributions and poor controllability in droplet size and its distribution. In contrast, monodisperse emulsions consisting of monosize droplets have received a great deal of attentions over the past decade due to their high-tech applications, e.g., monosize microparticles as spacers for electronic devices and monosize micro-carriers for drug delivery systems (DDS). Our group proposed microchannel (MC) emulsification as a promising technique to produce monodisperse emulsions in the mid 1990s. Micro/Nanochannel (MNC) emulsification enables generating monosize droplets with the smallest coefficient of variation (CV) of below 5% using MC and nanochannel (NC) arrays of unique geometry. The resultant droplet size, which ranged from 0.5 to 200 μm, can be precisely controlled by channel geometry. Droplet generation for MNC emulsification is very mild and does not require any external shear stress; a dispersed phase that passed through channels is transformed spontaneously into monosize droplets inside a continuous-phase domain. The aim of this paper is to present recent developments in MNC emulsification chips, particularly focusing on asymmetric straight-through MC arrays for large-scale production of monodisperse emulsions. Asymmetric straight-through MC array chips were fabricated using a silicon-on-insulator wafer. Numerous asymmetric straight-through MCs each consisting of a microslot and a narrow MC were positioned in the central region of the chip. Monosize droplets were stably generated via asymmetric straight-through MCs at high production rates. Below a critical droplet production rate, monosize droplets were generated via asymmetric straight-through MCs, with droplet size and size distribution independent of the droplet productivity. The use of a large asymmetric straight-through MC array chip achieved the mass production of monosize tetradecane oil droplets at ∼1 L/h. The simulation results using CFD (computational fluid dynamics) agreed well with the experimental results and provided useful information, such as the movement of the oil-water interface during droplet generation. Monosize submicron droplets were also obtained using NC emulsification chips made of single-crystal silicon.
A Study on the Effects of Ceramic Content of CNT / Metal Composite Surface Coatings Fabricated by Cold Spray for Boiling Heat Transfer Enhancement
Authors: Pialago Edward Joshua , Zheng Xi Ru , Ada Kristian Arvin , Kwon Oh Kyung , Cha Dong An , Park Chan Woo
Published: July 2013

In this study, the enhancement of boiling heat transfer through surface modification of heat transfer materials by surface coating was investigated. Specifically, the study evaluated how the boiling heat transfer performance of CNT/metal composite coatings, fabricated by the cold gas dynamic spray process, was affected by the addition of different ceramic particles on the raw materials of these surface coatings. These raw materials were composite powders of CNT, Cu powder, and ceramic powders (SiC, AlN, and BN) that were mechanically alloyed using an attrition ball mill.

The boiling heat transfer tests were performed in a pool of R134a at a gauge pressure of 2.5 kg/cm2 and liquid temperature of 4.8°C. Test results showed that the addition of ceramic particles in the CNT/Cu composite powders can further augment boiling heat transfer. The augmented boiling heat transfer performance varied with the kind of ceramic powder added and with their quantity. The highest enhancement ratio was 2.57. This was exhibited by a Cu plate specimen that was cold spray coated with (5 vol.% CNT + 95 vol.% Cu) + 20 vol.% AlN composite powder.
Two-Temperature Non-Equilibrium Molecular Dynamics Simulation of Thermal Transport Across Metal-Nonmetal Interfaces
Authors: Wang Yan , Ruan Xiulin
Published: July 2013

We have developed a two-temperature non-equilibrium molecular dynamics method for modeling interfacial thermal resistance across metal-nonmetal interfaces. Non-equilibrium molecular dynamics is used, where a temperature bias is imposed and the heat current is derived. On the metal side, the electron degree of freedom is added, and the electron-phonon coupling is treated with the two-temperature model. Temperature non-equilibrium between electrons and phonons in the metal side is quantitatively predicted, and a temperature drop across the interface is observed. The results agree with experimental data better than those obtained from conventional molecular dynamics simulations, which are only able to model phonons. Our method is capable of taking into account both electron and lattice degrees of freedom in a single molecular dynamics simulation, and is a generally useful tool for predicting metal-nonmetal interfaces.