bluuebunny/crossref_metadata_2025 huggingface dataset:
Liquid Slippage in Confined Flows: Effect of Periodic Micropatterns of Arbitrary Pitch and Amplitude
Authors: Kumar Avinash , Datta Subhra , Kalyanasundaram Dinesh
Published: March 2016

The recently confirmed violation of the no-slip boundary condition in the flow of small-molecule liquids through microchannels and nanochannels has technological implications such as friction reduction. However, for significant friction reduction at low cost, the microchannel wall needs to be chemically inhomogeneous. The direct fluid dynamic consequence of this requirement is a spatial variation in the local degree of liquid slippage. In this work, the pressure-driven flow in a channel with periodically patterned slippage on the channel walls is studied using a spectrally accurate semi-analytical approach based on Fourier decomposition. The method puts no restrictions on the pitch (or wavelength) and amplitude of the pattern. The predicted effective slip length in the limits of small pattern amplitude and thick channels is found to be consistent with previously published results. The effective degree of slippage decreases with the patterning amplitude. Finer microchannels and longer pattern wavelengths promote slippage.
Mesoscopic Analysis of Droplet Spreading Behaviour on Wetted Surface for Low Viscosity Ratio
Authors: Bhardwaj Saurabh , Dalal Amaresh
Published: March 2016

In the present study, the interfacial dynamics of displacement of three dimensional spherical droplet on a rectangular microchannel wall considering wetting effects are studied. The two-phase lattice Boltzmann Shan-Chen model is used to explore the physics. The main focus of this study is to analyse the effect of wettability, low viscosity ratio and capillary number on the displacement of spherical droplet subjected to gravitational force. The hydrophobic and hydrophilic nature of wettabilities on wall surface are considered to study with capillary number, Ca=0.1, 0.35 and 0.66 and viscosity ratio, M ≤ 1. The results are presented in the form of temporal evolution of wetted length and wetted area for combined viscosity ratios and wettability scenario. In the present study, it is observed that in dynamic droplet displacement, the viscosity ratio and capillary number play a significant role. It is found that as viscosity ratio increases, both the wetted area and the wetted length increase and decrease in the case of hydrophilic and hydrophobic wettable wall respectively.
Numerical Simulation of Microflows by a DOM With Streaming and Collision Processes
Authors: Yang L. M. , Shu C. , Wu J.
Published: March 2016

Inspired from the idea of developing lattice Boltzmann method (LBM), a discrete ordinate method (DOM) with streaming and collision processes is presented for simulation of microflows in this work. The current method is quite different from the conventional discrete ordinate method (DOM), unified gas kinetic scheme (UGKS) and discrete unified gas kinetic scheme (DUGKS), in which the finite volume method (FVM) or the finite difference method (FDM) is usually utilized to discretize the discrete velocity Boltzmann equation (DVBE). Due to the application of FVM or FDM, the evaluation of the flux of distribution function at the cell interface becomes an essential step for these approaches. Besides that, for the UGKS and DUGKS, not only the flux of distribution functions but also the conservative variables at the cell interface are needed to be computed. These processes require a lot of computational efforts. In contrast, for the developed method, it only needs interpolations within the cell to perform the streaming process. Thus, the computational efficiency can be improved accordingly. To compare the accuracy and efficiency of present scheme with those of DSMC and/or UGKS, several numerical examples including the Couette flow, pressure driven Poiseuille flow and thermal transpiration flow are simulated. Numerical results showed that the solution accuracy of current scheme is comparable to that of DSMC and UGKS. However, as far as the computational efficiency is concerned, the present scheme is more efficient than UGKS.
Experimental Investigation of Ultrasonic Frequency Effect on an Oscillating Heat Pipe
Authors: Zhao Nannan , Fu Benwei , Ma Hongbin , Su Fengmin
Published: March 2016

The heat transport capability in an oscillating heat pipe (OHP) significantly depends on the oscillating frequency. An external frequency directly affects the natural frequency in the system. In this investigation, the ultrasound sound effect on the heat transport capability in an OHP was conducted with focus on the ultrasonic frequency effect on the oscillating motion and heat transfer capacity in an OHP. The ultrasonic sound was applied to the evaporating section of the OHP by using the electrically-controlled piezoelectric ceramics. The heat pipe was tested with or without the ultrasonic sound with different frequencies. In addition, the effects of operating temperature, heat load from 25 W to 150 W were investigated. The experimental results demonstrate that the heat transfer capacity enhancement of the OHP depends on the frequency of the ultrasound field, and there exists an optimum combination of the frequencies which will lead to the largest enhancement of the heat transfer capacity of the OHP.
Artificial Opals: Reflection Spectra and Distribution Laws of Energy Transfer
Authors: Liu Yuan Bin , Qiu Jun , Jin Rong , Liu Lin Hua
Published: March 2016

In this work, we investigated the reflection properties of artificial opals composed of submicron silica spheres with diverse structural parameters and under the effect of light in different states. Furthermore, the primary rules how the reflection properties of artificial opals convert as these factors changing have been revealed clearly. These factors can take effects in changing the shape, value, and position of the peak of the hemispherical reflectance of artificial opals. Then we got the distribution and propagation process of the Poynting vectors corresponding to the positions of the diffraction peak and the low reflectance in the artificial opals at normal and oblique incidence of P-polarization. Comparing with the theoretical interpretation which is a little complicated and nonobjective, this paper will provide a visual result to explain the reason why the structure has high reflectance in some spectral ranges.
Analysis of the Optical and Thermal Properties of Transparent Insulating Materials Containing Gas Bubbles
Authors: Cai Qilin , Ye Hong
Published: March 2016

Transparent insulating materials combine high visible light transmission and excellent thermal insulation, and have potential applications in solar energy utilization, building energy conservation and commercial freezers. As a medium of low absorption and low thermal conduction, introducing gas bubbles into transparent mediums such as glass and polycarbonate (PC) may improve simultaneously their light transmission and thermal insulation performances through decreasing the absorption and thermal conduction in the materials. However, gas bubbles can also enhance the scattering which is a competition to the effect of the absorption decrease. Moreover, the material design should also consider the balance between the visible light transmittance and effective thermal conductivity. Therefore, a radiative transfer model for the transparent medium containing large gas bubbles (with a diameter much larger than the wavelengths concerned) with the assumption of independent scattering and the Maxwell–Eucken thermal conduction model were adopted to calculate the transmittance, reflectance and effective thermal conductivity. Subsequently, the effects of the volume fraction of gas bubbles (fv) and bubble radius (r) were discussed, and the two balances mentioned above were analyzed. The results showed that the transmittance always decreases when fv increases with fixed r or when r decreases with fixed fv. The transmittance includes two components, named as the collimated transmittance and bulk transmittance due to the forward scattering. The collimated transmittance depends on the effects of absorption decrease and scattering increase, whereas in the weak absorption region, the effect of the scattering increase dominates, making the collimated transmittance decrease, and the decreasing rate is larger than the increasing rate of the bulk transmittance as only the forward scattering contributes to the bulk transmittance. Therefore, the transmittance decreases when fv increases with fixed r or when r decreases with fixed fv. In addition, as fv increases from 0 to 0.5, the effective thermal conductivity (ke) of the glass decreases from 1.4 to 0.58 W/(m·K), and ke of the PC decreases from 0.236 to 0.113 W/(m·K). At the same time, the transmittances of both materials at 0.55 μm can be kept larger than 50% for fv=0.5 as long as the bubble radius is larger than 0.7 mm. To elucidate the application performance, a heat transfer model of a freezer adopting glass or PC as a cover was analyzed. Although the decrease percentage of ke for glass is higher than that of PC, the effect of the energy saving is more significant for PC, as the cooling load can be saved by 9.6% when fv increases from 0 to 0.5, while the corresponding value for glass is only 2.7% because that the decreasing rate of the cooling load with ke is higher at a lower ke.
Confined Jet Array Impingement Cooling Using NEPCM Nanofluids
Authors: Hong F. J. , Zhang C. Y. , Chen D. H. , Chen G.
Published: March 2016

The confined jet array impingement cooling using NEPCM (nano-encapsulated phase change material) slurry was investigated numerically using a homogeneous model based on effective heat capacity method. The nanofluids consists of the carrier fluid of polyalphaolefin (PAO) and the NEPCM particles of Polystyrene shell and paraffin core. The distributed slot jet array with the jet width W=100 μm, confinement height H=300 μm, jet-to-jet distance S=400 μm was investigated at first under different jet velocity, inlet temperature and NEPCM volumetric concentration. It was found that for a fixed jet velocity, there is an optimal NEPCM volumetric concentration and an optimal inlet temperature to achieve the maximum average heat transfer coefficient. The larger the jet velocity, the higher the optimal NEPCM concentration and the closer the optimal inlet temperature to the midpoint of melting temperature range of PCM where the peak of effective heat capacity achieves. The local heat transfer on the heating surface under the exit slot is the weakest, because of stagnant zone formed by the head-to-head collision of the two adjacent jets. The pressure drop and average heat transfer coefficient of six jet arrays with different H/W (=2, or 3) and S/W (=3, 4 or 5) were also compared.
Effect of Surface Wettability on Dropwise Condensation Using Lattice Boltzmann Method
Authors: Pawar Nilesh D. , Kondaraju Sasidhar
Published: March 2016

Understanding the condensation mechanism is crucial to enhance the heat transfer performance of numerous industrial applications such as power generations, fog harvesting, water desalination, cooling of nuclear reactor, and thermal management of electronic device. In the present study, simulations are performed to investigate the effect of surface wettability on droplet growth dynamics during dropwise condensation. To simulate droplet growth dynamics involving phase change heat transfer, thermal lattice Boltzmann method has been employed with two distribution function for fluid and temperature field. Simulations performed in this work are used to analyze the effect of surface wettability on nucleation time and the evolution of average droplet radius, height, base diameter, and contact angle of the droplet. It is observed that nucleation time increases exponentially with the contact angle. The growth rate of droplet is higher for smaller droplets compared to larger droplets.
Visualization of Two-Phase Flow in Serpentine Heat Exchanger Passages With Microscale Pin Fins
Authors: Hoysall Dhruv C. , Keniar Khoudor , Garimella Srinivas
Published: March 2016

Multiphase flow phenomena in single micro- and minichannels have been widely studied. Microchannel heat exchangers offer the potential for high heat transfer coefficients; however, implementation challenges must be addressed to realize this potential. Maldistribution of phases among the microchannels in the array and the changing phase velocities associated phase change present design challenges. Flow maldistribution and oscillatory instabilities can severely affect heat and mass transfer rates as well as pressure drops. In components such as condensers, evaporators, absorbers and desorbers, changing phase velocities can change prevailing flow regimes from favorable to unfavorable. Geometries with serpentine passages containing pin fins can be configured to maintain favorable flow regimes throughout the length of the component for diabatic phase-change heat and mass transfer applications. Due to the possibility of continuous redistribution of the flow across the pin fins along the flow direction, maldistribution can also be reduced. These features enable the potential of high heat transfer coefficients in microscale passages to be fully realized, thereby reducing the required transfer area, and achieving considerable compactness. The characteristics of two-phase flow through a serpentine passage with micro-pin fin arrays with diameters 350 μm and height 406 μm are investigated here. An air-water mixture is used to represent two-phase flow through the serpentine test section, and a variety of flow features are visually investigated using high-speed photography. Improved flow distribution is observed in the serpentine geometry. Distinct flow regimes, different from those observed in microchannels are also established. These observations are used to obtain void fraction and interfacial area along the length of the serpentine passages and compared with the corresponding values for straight microchannels. Models for the two-phase frictional pressure drops across this geometry are also developed.
Numerical Investigation of Thermoelectric Topping Cycle in Coal Fired Power Plant Boiler
Authors: Silaen Armin , Wu Bin , Zhou Chenn
Published: March 2016

Traditional fossil fuel power generation process typically has low efficiency. Large amount of the energy loss in Rankine cycle steam turbines (ST) is due to the temperature difference between the combustion flame temperature ∼2250 K (adiabatic) and the high pressure steam temperature up to 900 K. This paper investigates the potential of harvesting this energy to produce additional electrical power using solid-state thermoelectric (TE) power generators placed into the gap between the flame temperature and the steam temperature. Three dimensional (3D) numerical model of a simplified TE module is developed. Different dimensions of fin added to the TE module were investigated to maximize the additional electrical power generation without sacrificing the boiler efficiency.
High Performance Beam Steering via Tunable Liquid Prisms
Authors: Clement Carlos Enrico , Park Sung-Yong
Published: March 2016

The use of liquids for the manipulation of light has many advantages over their conventional solid counterparts. With the emergence of microfluidic technologies to control fluid interfaces, various devices capable of replacing conventional optical components have been developed. Because liquids are intrinsically smooth and can change shape or form, they have been utilized for highly versatile components to manipulate light with high degrees of control using optofluidic technologies. Liquid lenses and beam steering devices are among the typical optofluidic devices that have gained much interest over recent years. In this work, we present high-performance tunable liquid prisms capable of wide beam steering of incoming light. By using the electrowetting phenomena, we are able to modulate the fluid-fluid interface at which beam steering occurs. Optical analyses were conducted to study the effect of liquid selection in the effectiveness of our prisms. Furthermore, the double-stacked prism configuration is proposed to achieve wide beam steering and its performance is compared with that of a single prism for different liquid selections. Finally, our analytical studies have been experimentally demonstrated. We successfully fabricated the tunable liquid prism filled with water and 1-bromonaphthalene (1-BN). Due to large refractive index difference between two liquids (nwater = 1.33 and n1−BN = 1.65 at λ = 532 nm), high-performance beam steering was enabled. With an apex angle of 25°, we were able to experimentally demonstrate a beam steering of β ≤ 8.82° with the single prism configuration. It was significantly improved up to β ≤ 17.04° for the double-stacked prism.
Study on a Novel Selective Solar Absorber With Surface Ultrathin Metal Film
Authors: Fang Xing , Zhao C. Y. , Bao Hua
Published: March 2016

In this paper, simple selective solar absorbers with three layers are investigated, and their selective absorptivity spectra are quite appropriate for high performance solar absorbers. The simple solar absorber contains top ultrathin tungsten (W) layer, middle silica layers and W substrate. The thickness of silica can determine the location of absorptivity peak while the thickness of top W layer affects the intensity of absorptivity. Considering the total conversion efficiency, optimized thicknesses in solar absorbers are determined by genetic algorithm. This optimized thin film solar absorber keeps high absorptivities when incident direction varies from 0 degree to 60 degree in both TE and TM polarizations. Experiments validate the effectivity of thin film solar absorbers, and the deviation from simulations comes from increscent refractive index and surface non-uniform.
Conjugate Heat Transfer in Single-Phase Wavy Microchannel
Authors: Tiwari Nishant , Moharana Manoj Kumar , Sarangi Sunil Kumar
Published: March 2016

A three-dimensional numerical study has been carried out to understand the effect of axial wall conduction in a conjugate heat transfer situation in a wavy wall square cross section microchannel engraved on solid substrate whose thickness varying between 1.2–3.6 mm. The bottom of the substrate (1.8 × 30 mm2) is subjected to constant wall heat flux while remaining faces exposed to ambient are assumed to be adiabatic. The vertical parallel walls are considered wavy such that the channel cross section at any axial location will be a square (0.6 × 0.6 mm2) and length of the channel is 30 mm. Wavelength (λ) and amplitude (A) of the wavy channel wall are 12 mm and 0.2 mm respectively. Simulations has been carried out for substrate thickness to channel depth ratio (δsf ∼ 1–5), substrate wall to fluid thermal conductivity ratio (ksf ∼ 0.34–646) and flow rate (Re ∼ 100 to 500). The results show that with increase in flow rate (Re), the hydrodynamic and thermal boundary layers are thinned due to wavy passage and they shifted from the centerline towards the peak which improves the local heat transfer coefficient at the solid-fluid interface. It is also found that after attaining maximum Nuavg at optimum ksf, the slope goes downward with increasing ksf for all set of δsf and flow rate (Re) considered in this study.
Rarefaction Effects on Gas Mixing in Micro- and Nanoscales
Authors: Darbandi Masoud , Sabouri Moslem
Published: March 2016

We present the rarefaction effects on diffusive mass transport in micro- and nanoscales using the results of direct simulation Monte Carlo DSMC method. Unlike the previous investigations, the momentum and heat contributions are eliminated from the computations via uniform velocity, pressure, and temperature field considerations. The effects of global Knudsen number on the diffusion phenomenon are studied for the same Peclet number and a unique mixer shape. The results indicate that there is considerable weakening in diffusion mechanism for high Knudsen number cases. As a result, the non-dimensional diffusive mass fluxes would decrease and the non-dimensional mixing length would increase as the Knudsen number increases. The effective diffusion coefficient is calculated throughout the mixer using the diffusive mass fluxes and the species mass fraction gradients. It is observed that the effective diffusion coefficient can vary considerably as a result of local rarefaction variations. It reaches to the lowest value at the point of confluence, where the maximum mass fraction gradient magnitude would occur for the species. Moving away from this point, the local rarefaction effects would weaken and the effective diffusion coefficient would reinforce subsequently. All the presented results indicate that there would be a convergent to a limiting behavior, which corresponds to the continuum mass diffusion case. Despite this, the local rarefaction level decreases continuously. Unfortunately, because of a considerable increase in the statistical fluctuations at very low rarefaction levels, the simulations do not provide reliable results in the limit of continuum regime.
Nano-PCMs for Electronics Cooling Applications
Authors: Colla Laura , Fedele Laura , Mancin Simone , Bobbo Sergio , Ercole Davide , Manca Oronzio
Published: March 2016

The present work aims at investigating a new challenging use of Aluminum Oxide (Al2O3) nanoparticles to enhance the thermal properties (thermal conductivity, specific heat, and latent heat) of pure paraffin waxes to obtain a new class of Phase Change Materials (PCMs), the so-called nano-PCMs. The nano-PCMs were obtained by seeding 0.5 and 1.0 wt% of Al2O3 nanoparticles in two paraffin waxes having melting temperatures of 45 and 55 °C, respectively. The thermophysical properties such as specific heat, latent heat, and thermal conductivity were then measured to understand the effects of the nanoparticles on the thermal properties of both the solid and liquid PCMs. Furthermore, a numerical comparison between the use of the pure paraffin waxes and the nano-PCMs obtained in a typical electronics passive cooling device was developed and implemented. A numerical model is accomplished to simulate the heat transfer inside the cavity either with PCM or nano-PCM. Numerical simulations were carried out using the ANSYS-Fluent 15.0 code. Results in terms of solid and liquid phase temperatures and melting time were reported and discussed.
The Enhancement of Boiling Heat Transfer in a Minichannel Heat Sink With Saw-Tooth Structure on Channel Surface
Authors: Chung Shan-Yu , Pan Chin
Published: March 2016

The dimension of electronic devices becomes smaller and smaller and, thus, it is of crucial importance to enhance the heat dissipation from such tiny devices. The present study investigates the boiling heat transfer in a minichannel heat sink with saw-tooth structure on channel surface. The heat sink is comprised of four minichannels with hydraulic diameter of 0.8 mm and made of copper. The dimensions of the base area of the heat sink are 90 mm (length) × 5 mm (width). The saw-tooth topology on the bottom surface of minichannel was manufactured by wire-cut electrical discharge machining (EDM). The height, tip angle, and pitch of the saw-tooth structure are 0.5 mm, 45°, and 1mm, respectively. This study employed refrigerant HFE-7100, which is of low global warming potential (GWP), as a working fluid to investigate the boiling heat transfer in three kinds of surface structures (i.e., plain, parallel saw-tooth, and counter saw-tooth). The mass flux of the HFE-7100 ranged from 64 to 285 kg/m2s. The experimental results showed that the critical heat flux (CHF), compared to the plain minichannel, is improved by 46.7% and 40.2%, respectively, in the parallel and counter saw-tooth minichannels for a low mass flux of 127 kg/m2s. This result indicated that the CHF is considerably enhanced by the saw-tooth structure with both parallel and counter flow designs for the low mass flux. However, the CHF in the parallel and plain minichannels is nearly the same for a large mass flux of 285 kg/m2s. But for a saw-tooth structure with counter flow design, the CHF increases by 17.1% compared to the plain minichannel. Consequently, the experimental results demonstrated that the CHF can be enhanced by using saw-tooth structure on the channel surface.
Heat Transfer Characteristics of CuO-Water Nanofluids Jet Impingement on a Hot Surface
Authors: Chougule Sandesh S. , Modak Mayank , Gharge Prajakta D. , Sahu S. K.
Published: March 2016

In present study, an experimental investigation has been carried out to analyze the heat transfer characteristics of CuO-water nanofluids jets on a hot surface. A rectangular stainless steel foil (AISI-304, 0.15 mm thick) is used as a test surface is electrically heated to obtain the required initial temperature. The distribution of heat flux on the target surface is evaluated from the recorded thermal images during transient cooling. The effect of nanoparticle concentration and Reynolds number of the nanofluids jet impingement heat transfer characteristics is studied. Tests were performed for an initial surface temperature of 500°C, Reynolds number (5000≤Re≤13000), CuO-water nanofluids concentration (Φ= 0.15%, 0.6%) and nozzle to plate distance was l/d= 4.
A Computational Simulation of Using Tungsten Gratings in Near-Field Thermophotovoltaic Devices
Authors: Watjen J. I. , Liu X. L. , Zhao B. , Zhang Z. M.
Published: March 2016

Near-field thermophotovoltaic (NFTPV) devices have received much attention lately as attractive energy harvesting systems, whereby a heated thermal emitter exchanges super-Planckian near-field radiation with a photovoltaic (PV) cell to generate electricity. This work describes the use of a grating structure to enhance the power throughput of NFTPV devices, while increasing thermal efficiency by ensuring that a large portion of the radiation entering the PV cell is above the bandgap. The device is modeled as a one-dimensional high-temperature tungsten grating on a tungsten substrate that radiates photons to a room-temperature In0.18Ga0.82Sb PV cell through a vacuum gap of several tens of nanometers. Scattering theory is used along with the rigorous coupled-wave analysis to calculate the radiation exchange between the grating emitter and the PV cell. A parametric study is performed by varying the grating depth, period, and ridge width in the range that can be fabricated using available fabrication technologies. By optimizing the grating parameters, it is found that the power output can be improved by 40% while increasing the energy efficiency by 6% as compared with the case of a flat tungsten emitter. Reasons for the enhancement are investigated and found to be due to the surface plasmon polariton resonance, which shifts towards lower frequencies. This work shows a possible way of improving NFTPV and sheds light on how grating structures interact with thermal radiation at the nanoscale.
Numerical Simulation on the Performance of Nanofluid-Based Direct Absorption Solar Collector With Parabolic Trough Concentrator
Authors: Chen Wei , Xu Guoying , Zhao Sainan , Zhang Xiaosong
Published: March 2016

Nanofluids obtain high stability, improved heat transfer capability and excellent optical properties, the low-temperature nanofluid-based direct absorption solar collector (NDASC) has been previously investigated. However, the detailed radiation absorption and heat transfer mechanism for a NDASC with a solar concentrator operated on medium-temperature conditions were seldom researched. Therefore, this paper presents a numerical study on the solar collection characteristics of NDASC with a parabolic trough concentrator. CuO/oil nanofluids with various weight concentration from 0.05% to 0.1% were prepared, and used as working fluids of NDASCs, respectively. Using the developed heat transfer model, operating characteristics of NDASCs were simulated. Furthermore, the influences of weight concentration of nanofluids on the heat transfer characteristics in the NDASCs were analyzed and optimum weight concentration used for the designed NDASC obtained.
Laser Flash Raman Spectroscopy Method for Characterizing Thermal Diffusivity of Suspended and Supported 2D Nanomaterials
Authors: Li Qin-Yi , Zhang Xing
Published: March 2016

2D nanomaterials have been attracting extensive research interests due to their superior properties and the accurate thermophysical characterization of 2D materials is very important for nanoscience and nanotechnology. Recently, a noncontact technique based on the temperature dependent Raman band shifts has been used to measure the thermal conductivity of 2D materials. However, the heat flux, i.e. the absorbed laser power, was either theoretically estimated or measured by a laser power meter with uncertainty, resulting in large errors in thermal conductivity determination. This paper presents a transient “laser flash Raman spectroscopy” method for measuring the thermal diffusivity of 2D nanomaterials in both the suspended and supported forms without knowing laser absorption. Square pulsed laser instead of continuous laser is used to heat the sample and the laser absorption can be eliminated by comparing the measured temperature rises for different laser heating time and laser spot radii. This method is sensitive for characterizing typical 2D materials and useful for nanoscale heat transfer research.
Research on R245fa Condensation Heat Transfer Characteristic Inside Horizontal Tubes
Authors: Liu Shengchun , Zhang Wenkai , Dong Ziteng
Published: March 2016

Condensation heat transfer of R245fa in horizontal copper pipe is studied in this paper. In the experimental study, the pipe inner diameter is 4.38 mm, the condensing temperature range from 50∼60°C, mass flow rate ranges from 3.132kg/h to 11.988kg/h, and inlet ranges from 0.89∼1. The research results indicate that the condensation coefficient is rose with the condensing; and it will rise when the inlet quality ranges from 0.89 to 1. Experimental value and the existing two-phase flow correlation are compared in this paper. It shows that the condensation heat transfer coefficient predicted by Haraguchi correlation has a high accuracy relatively. The research provides a foundation to promote development of microchannel high efficiency heat exchanger and it is useful to practical engineering.
Simulation and Experiment Study on Water Vapor Condensing Heat Transfer Characteristics in Horizontal Tubes
Authors: Liu Shengchun , Zhang Jiahui
Published: March 2016

Water vapor condensing process inside horizontal tube has been studied in the paper. A CFD simulation model has been developed with Fluent software. An experimental investigation has also been conducted with an 8-mm inside diameter horizontal tube. As well as the heat transfer correlations available in literatures, the CFD model has been validated against the experimental results. The discrepancy of the simulation model is within 15%. The effect of wall temperature, inlet vapor velocity and inlet superheating degree on local heat transfer coefficient has been analyzed. The simulation model can be employed in future work to develop a condensation heat transfer correlation in horizontal tube.
Study on Heat Transfer Performance Affected by Structural Parameters of Multi-Channel Cylinder Dryer
Authors: Yan Yan , Jixian Dong , Wei Tang , Shiyuf Feng
Published: March 2016

An approach to design multi-channel cylinder dryer was proposed. The heat transfer performance and flow characteristic under various structural parameters were analyzed. First, an experiment was designed and set up to measure the condensing heat transfer coefficient and the pressure drop in order to verify the applicability of the Cavallini’s correlation. Then, the relationship among the count of channels, aspect ratio, spacing ratio, width, height and hydraulic diameter of a channel was given. Finally, the correlation of condensing heat transfer and the homogeneous model were introduced in order to observe the heat transfer performance and flow characteristic of the multi-channel cylinder dryer affected by different structures. The study reveals that the structural parameters including count of channels, aspect ratio, spacing ratio of a channel dramatically influence the condensation heat transfer coefficient and frictional resistance of the steam. Based on the selected paper machine, it is suggested that the overall performance of the multi-channel cylinder dryer is best if the count of channels is 150–200, the aspect ratio is 1:3 and the spacing ratio is 1:1–1:3.
The Uncertainties of Continuum-Based CFD Solvers to Perform Microscale Hot-Wire Anemometer Simulations in Flow Fields Close to Transitional Regime
Authors: Darbandi Masoud , Ghorbani Mohammad Reza , Darbandi Hamed
Published: March 2016

In this study, we simulate the flow and heat transfer during hot-wire anemometry and investigate its thermal behavior and physics using the Computational Fluid Dynamics (CFD) tool. In this regard, we use the finite-volume method and solve the compressible Navier-Stokes equations numerically in slightly non-continuum flow fields. We do not use any slip flow model to include the transitional flow physics in our simulations. Using the CFD method, we simulate the flow over hot–wire and evaluate the uncertainty of CFD in thermal simulation of hot-wire in low transitional flow regimes. The domain sizes and the mesh distributions are carefully chosen to avoid boundary condition error appearances. Following the past researches, we do not take into account the conduction heat transfer passing through hot-wire mounting arms in our simulations. Imposing a fixed temperature condition at the face of hot-wire, we simulate the flow over and the heat transfer from hot-wire and calculate the convection heat transfer coefficient and the local Nusselt number values. To be sure of the accuracy of our CFD code, we simulate a number of similar test cases and compare our numerical solutions with the available numerical solutions and/or experimental data.
Improved Thermal Emitters for Thermophotovoltaic Energy Conversion
Authors: Stelmakh Veronika , Chan Walker R. , Joannopoulos John D. , Soljacic Marin , Celanovic Ivan , Sablon Kimberly
Published: March 2016

Thermophotovoltaic (TPV) energy conversion enables millimeter scale power generation required for portable microelectronics, robotics, etc. In a TPV system, a heat source heats a selective emitter to incandescence, the radiation from which is incident on a low bandgap TPV cell. The selective emitter tailors the photonic density of states to produce spectrally confined selective emission of light matching the bandgap of the photovoltaic cell, enabling high heat-to-electricity conversion efficiency. The selective emitter requires: thermal stability at high-temperatures for long operational lifetimes, simple and relatively low-cost fabrication, as well as spectrally selective emission over a large uniform area. Generally, the selective emission can either originate from the natural material properties, such as in ytterbia or erbia emitters, or can be engineered through microstructuring. Our approach, the 2D photonic crystal fabricated in refractory metals, offers high spectral selectivity and high-temperature stability while being fabricated by standard semiconductor processes. In this work, we present a brief comparison of TPV system efficiencies using these different emitter technologies. We then focus on the design, fabrication, and characterization of our current 2D photonic crystal, which is a square lattice of cylindrical holes fabricated in a refractory metal substrate. The spectral performance and thermal stability of the fabricated photonic crystal thermal emitters are demonstrated and the efficiency gain of our model TPV system is characterized.
Spectral Control of Thermal Radiation Using Metal-Dielectric Multilayers for High-Temperature Usage Over 1000°C
Authors: Shimizu Makoto , Kohiyama Asaka , Iguchi Fumitada , Yugami Hiroo
Published: March 2016

The spectrally selective coating technology which can be applicable for solar-thermophotovoltaic (solar-TPV) generation systems is described in this paper. In solar-TPV system, the spectrally selective absorber plays a key role to obtain high-efficiency. The technologies of controlling thermal radiation spectrum at temperature over 1000°C, however, have not been established yet. We focus on metal-dielectric multi-layer coating. This selective coating shows enormously high absorptance at short wavelength range and sharp cutoff property. Thermal stability test confirms that this multi-layer structure can be one of the candidates for the selective coatings for solar-TPV systems.
Force Analysis of Bubble Dynamics in Flow Boiling Silicon Nanowire Microchannels
Authors: Alam Tamanna , Li Wenming , Yang Fanghao , Khan Ahmed Shehab , Tong Yan , Khan Jamil , Li Jing , Wang Zuankai , Li Chen
Published: March 2016

In microchannel flow boiling, bubble nucleation, growth and flow regime development are highly influenced by channel cross-section and physical phenomena underlying this mechanism are far from being well-established. Relative effects of different forces acting on wall-liquid and liquid-vapor interface of a confined bubble play an important role in heat transfer performances. Therefore, fundamental investigations are necessary to develop enhanced microchannel heat transfer surfaces. Force analysis of vapor bubble dynamics in flow boiling Silicon Nanowire (SiNW) microchannels has been performed based on theoretical, experimental and visualization studies. The relative effects of different forces on flow regime, instability and heat transfer performances of flow boiling in Silicon Nanowire microchannels have been identified. Inertia, surface tension, shear, buoyancy, and evaporation momentum forces have significant importance at liquid-vapor interface as discussed earlier by several authors. However, no comparative study has been done for different surface properties till date. Detailed analyses of these forces including contact angle and bubble flow boiling characteristics have been conducted in this study. A comparative study between Silicon Nanowire and Plainwall microchannels has been performed based on force analysis in the flow boiling microchannels. In addition, force analysis during instantaneous bubble growth stage has been performed. Compared to Plainwall microchannels, enhanced surface rewetting and critical heat flux (CHF) are owing to higher surface tension force at liquid-vapor interface and Capillary dominance resulting from Silicon Nanowires. Whereas, low Weber number in Silicon Nanowire helps maintaining uniform and stable thin film and improves heat transfer performances. Moreover, force analysis during instantaneous bubble growth shows the dominance of surface tension at bubble nucleation and slug/transitional flow which resulted higher heat transfer contact area, lower thermal resistance and higher thin film evaporation. Whereas, inertia force is dominant at annular flow and it helps in bubble removal process and rewetting.
Study of Micro-Structure Based Effective Thermal Conductivity of Graphite Foam
Authors: Chai Yue , Yang Xiaohu , Meng Xiangzhao , Zhang Qunli , Jin Liwen
Published: March 2016

As a new type of functional material, porous graphite foam exhibits unique thermal physical properties and geometric characteristics in heat transfer applications. It has the advantages of low density, high specific surface area, high porosity and high bulk thermal conductivity, which can be used as the core component of small, lightweight, compact and efficient heat sinks. Effective thermal conductivity serves one of the key thermophysical properties for foam-cored heat sinks. The complex three-dimensional topology and interstitial fluids significantly affect the heat conduction through such kind of porous structures, reflecting a topologically based effective thermal conductivity. This paper presents a novel geometric model for representing the microstructure of graphite foams, with simplifications and modifications made on the actual pore structure of graphite foam. For calculation simplicity, we convert the realized geometry consisting of complex surfaces and tortuous ligaments into a simplified geometry with circular ligaments joined at cuboid nodes, on the basis of the volume equivalency rule. The multiple-layer method is used to divide the proposed geometry into solvable areas and the series-parallel relations are used to derive the analytical model for effective thermal conductivity. To physically explore the heat conduction mechanisms at pore scale, direction numerical simulations were conducted on the reconstructed geometric model. Achieving good agreement with experimental data, the present analytical model (based on the simplified geometry) is validated. Further, the numerically simulated conductivities follow the model prediction, favoring thermally that the two geometries are equal. The present geometry model is more realized and capable of reflecting the internal microstructure of graphite foam, which will benefit the understandings for the thermo-physical mechanisms of pore-scaled heat conduction and micro structures of graphite foam.
Technical Note: Development and performance of a software tool for quality assurance of online replanning with a conventional Linac or MR‐Linac
Authors: Chen Guang‐Pei , Ahunbay Ergun , Li X. Allen
Published: March 2016

Purpose:

To develop an integrated quality assurance (QA) software tool for online replanning capable of efficiently and automatically checking radiation treatment (RT) planning parameters and gross plan quality, verifying treatment plan data transfer from treatment planning system (TPS) to record and verify (R&V) system, performing a secondary monitor unit (MU) calculation with or without a presence of a magnetic field from MR‐Linac, and validating the delivery record consistency with the plan.

Methods:

The software tool, named ArtQA, was developed to obtain and compare plan and treatment parameters from both the TPS and the R&V system database. The TPS data are accessed via direct file reading and the R&V data are retrieved via open database connectivity and structured query language. Plan quality is evaluated with both the logical consistency of planning parameters and the achieved dose–volume histograms. Beams in between the TPS and R&V system are matched based on geometry configurations. To consider the effect of a 1.5 T transverse magnetic field from MR‐Linac in the secondary MU calculation, a method based on modified Clarkson integration algorithm was developed and tested for a series of clinical situations.

Results:

ArtQA has been used in their clinic and can quickly detect inconsistencies and deviations in the entire RT planning process. With the use of the ArtQA tool, the efficiency for plan check including plan quality, data transfer, and delivery check can be improved by at least 60%. The newly developed independent MU calculation tool for MR‐Linac reduces the difference between the plan and calculated MUs by 10%.

Conclusions:

The software tool ArtQA can be used to perform a comprehensive QA check from planning to delivery with conventional Linac or MR‐Linac and is an essential tool for online replanning where the QA check needs to be performed rapidly.
The Singing Cymbal: Is It Really Photon Momentum?
Authors: Collin Samantha , Etchenique Nikki , Moore Thomas R.
Published: March 2016

A simple demonstration that is occasionally used in the classroom to show that light carries momentum involves making an orchestral cymbal audibly ring using light from a common photoflash. A metal plate or a piece of foil can also be used; however, it appears that many people use a cymbal because the sound is easily heard at a reasonable distance. It is such an impressive example of the effects attributable to photon momentum that it is posted on the CERN website for educational resources under the name “singing cymbal.” Although it is an impressive demonstration, a series of simple classroom experiments can show that the sound of the singing cymbal is not due to the transfer of photon momentum.
A Connector Between Active Laboratory Probes and Computer Interfaces of Different Brands
Authors: Hui Kaleonui J. , Coney John P. , Binder P.-M.
Published: March 2016

In PASCO's Technical Article # 763, it is stated that “PASCO [also] makes sensors with an 8-pin DIN connector. These sensors cannot be used with the Vernier interfaces, as they have different power requirements.” Recently we had the need to make such connections in a 10-station freshman lab. Since the Vernier input is a 6-way BT 631A plug also used in TI and Casio equipment, our experience may be of interest to a broad audience of lab coordinators.
The Inverse-Square Law and the Exponential Attenuation Law Used to the Shielding Calculation in Radiotherapy on a High School Level
Authors: de Paiva Eduardo
Published: March 2016

Every year millions of people contract cancer in the world, and according to prediction of the World Health Organization by the year 2030 there will be about 27 million new cases. Because of these figures and the resulting social and economic implications of this disease, radiotherapy, which is one form of treatment that uses ionizing radiation, has a great importance. In the classroom the teacher can introduce the subject of the use of ionizing radiation in medicine and the basic physical principles to calculate the thickness of the walls of the rooms that house ionizing radiation sources.
Evaluating multipulse integration as a neural-health correlate in human cochlear-implant users: Relationship to forward-masking recovery
Authors: Zhou Ning , Pfingst Bryan E.
Published: March 2016

The present study evaluated the slopes of threshold-versus-pulse-rate functions (multipulse integration, MPI) in humans with cochlear implants in relation to recovery from 300-ms forward maskers. MPI has been correlated with spiral ganglion cell density in animals. The present study showed that steeper MPI functions were correlated with faster recovery from forward masking. The findings suggested that the variations in the MPI slopes are explained not only by the quantity of neurons contributing to the integration process but also by the neurons' temporal response characteristics and possibly central inhibition.
Great Expectations: How Role Expectations and Role Experiences Relate to Perceptions of Group Cohesion
Authors: Benson Alex J. , Eys Mark A. , Irving P. Gregory
Published: March 2016

Many athletes experience a discrepancy between the roles they expect to fulfill and the roles they eventually occupy. Drawing from met expectations theory, we applied response surface methodology to examine how role expectations, in relation to role experiences, influence perceptions of group cohesion among Canadian Interuniversity Sport athletes (N = 153). On the basis of data from two time points, as athletes approached and exceeded their role contribution expectations, they reported higher perceptions of task cohesion. Furthermore, as athletes approached and exceeded their social involvement expectations, they reported higher perceptions of social cohesion. These response surface patterns—pertaining to task and social cohesion—were driven by the positive influence of role experiences. On the basis of the interplay between athletes’ role experiences and their perception of the group environment, efforts to improve team dynamics may benefit from focusing on improving the quality of role experiences, in conjunction with developing realistic role expectations.