Small Flat Surfaces Research Articles

Influence of Thermal Boundary Conditions and Number of Channels on the Performance of Heat Sinks with Rectangular Minichannels.

This paper aims to contribute to the analysis of a heat sink designed for the active cooling of small flat surfaces. The heat transfer device investigated here consists of a flat square substrate and a cover, separated by parallel channels with a rectangular cross-section. The cold air flowing in the channels is sucked from the environment, and the bottom of the substrate adheres closely to the hot surface of the device to be cooled. The thermal problem is tackled by considering two different conditions: the first one assuming one long side of the channel is heated and the three other sides are adiabatic (version 1L) and the second one assuming high conductivity of the walls (version 4), in both the H1 and H2 boundary conditions. Moreover, to investigate the effect of the number of channels on the performance of the heat sink, the number of channels is changed between 1 and 20. The results, presented in terms of the f Re product, Nusselt number, maximum surface temperature, and thermal resistance, reveal that both the thermal boundary conditions and the number of channels significantly affect the performance of the investigated heat transfer device.

Model eye tool for retinal optical coherence tomography instrument calibration

Optical coherence tomography (OCT) has been extensively used as noninvasive tool for biological tissues owing to its three-dimensional imaging ability and high axial resolution. OCT quality assurance is vital in these occasions to keep the reliability and accuracy in medical diagnosis. It is necessary to develop a calibration tool for OCT product manufacture, calibration, and quality control. A practical tool is demanded in the OCT quality control and calibration of OCT. So far, there is no such a practical tool that can test all the key parameters of OCT. We design and fabricate a model eye tool, which has this function. The model eye comprises a doublet lens, a single filament, a piece of glass plate and the microsphere-embedded phantom. The doublets lens is bonded by two pieces of planoconvex lenses in the plane position. The first lens focuses parallel light onto the rear surface of the second lens. The rear surface marked with concentric circles serves as retina to measure the angular field of view (FOV). The small flat surface on the peak of the second lens is used to test signal to noise ratio (SNR). The single filament with 125[Formula: see text][Formula: see text]m diameter is used to check the co-alignment of preview and OCT scan. The empty chamber between the small plane of the second lens and the first surface of glass plate is used to measure the depth scaling of the OCT. The microspheres of 1[Formula: see text][Formula: see text]m diameter distributed uniformly in the phantom, which can test the lateral and the axial resolution of OCT equipment. Experimental results are presented to show the validity of the proposed tool. It is shown that the tool is able to be used in the calibration and quality control of retinal OCT.

Liquid film thickness measurements on a plate based on brightness curve analysis with acute PLIF method

Normal planar laser induced fluorescence (N-PLIF) method has been widely applied in liquid film imaging and thickness measurements in circular tubes with large curvatures, but meets great challenges in liquid film thickness measurements in circular tubes with small curvatures or at plates. An alternative method is to place both the incident laser sheet and the camera below the bottom interface of a plate, forming the acute PLIF (A-PLIF) method with an acute laser optical path and camera alignment. However, the liquid film thickness measurements based on direct imaging with the A-PLIF method are still challenged by the decrease of image contrast and indistinct interfaces. This work further explores the A-PLIF method with a novel image processing approach through both static liquid film and moving liquid film measurements. In static liquid film measurements, brightness curves along the liquid film thickness direction are extracted to compare with numerical simulation results based on ray-tracing approach, in which the laser intensity attenuation, laser sheet thickness, fluorescence spectrum and top interface reflection are considered. The comparison indicates that out-of-focus imaging is the dominant factor for the expanding of measured brightness curves. Three distinct regions, i.e. the increasing region, slowly decreasing region and rapidly decreasing region, are identified on the brightness curves and the main fluorescence source of each region is analyzed theoretically. It is concluded that the total width of the two decreasing regions shows strong correlation to the liquid film thickness, which facilitates the evaluation of liquid film thickness through peak position determination of the brightness curve and linear fitting of the rapidly decreasing region. This method is further tested in the moving liquid film thickness measurement in a cross-flow tunnel at various cross-sections, which shows that it can be applied to the liquid film imaging and thickness measurements on small curvature or flat surfaces.

Materials Selection and Tests for Precise Execution of Foundry Molds Designed to Geopolymer Casts

The paper presents the results of research on the selection of material for molds intended for geopolymer castings as well as an appropriate technological process for the preparation of such castings. Three silicons with different elasticity and hardness of 30, 40 and 60Sh were tested. The above-mentioned rubbers were used to make one-piece open molds and test the performance of each material. A model having several details and a small flat surface was chosen for the replica. Based on this variation in the wall structure, it was possible to assess the accuracy of mapping, both small elements and straight cast planes. In the prepared forms 10 tests of geopolymer casting were carried out to develop the best technological process. The appropriate result was achieved when the molds covered with the divider were flooded with raw material by vibrating them on a vibrating table, and then allowed to react for an hour for free mass components and leaking gases to the surface. After a set time, the compaction was carried out again to more accurately eliminate the resulting air bubbles. The effect of this method is to obtain a cast with precisely mapped details and a smooth even surface, and almost complete elimination of air bubbles from representative surfaces.

Effects of SiO2 interlayers on the phase change behavior in the multilayer Zn15Sb85/SiO2 materials

In this study, the multilayer Zn15Sb85/SiO2 materials were investigated for phase change memory application with the intention of improving thermal stability and switching speed. The Zn15Sb85/SiO2 materials exhibited a high crystallization temperature (Tc∼230 °C), good data retention (T10 ∼ 160 °C), small density change (∼3.3%), flat surface and rapid amorphization speed (∼1.34 ns). T-shaped phase change devices based on Zn15Sb85/SiO2 materials achieved low RESET voltage (VRESET∼1.3 V) in programming operation. The results showed that the multilayer Zn15Sb85/SiO2 material was a promising phase change material with high thermal ability, low power consumption and rapid switching speed.

Predicting the critical heat flux in pool boiling based on hydrodynamic instability induced irreversible hot spots

A new model, based on the experimental observation reported in the literature that CHF is triggered by the Irreversible Hot Spots (IHS), has been developed to predict the Critical Heat Flux (CHF) in pool boiling. The developed Irreversible Hot Spot (IHS) model can predict the CHF when boiling methanol on small flat surfaces and long horizontal cylinders of different sizes to within 5% uncertainty. It can also predict the effect of changing wettability (i.e. contact angle) on CHF to within 10% uncertainty for both hydrophilic and hydrophobic surfaces. In addition, a linear empirical correlation has been developed to model the bubble growth rate as a function of the system pressure. The IHS model with this linear bubble growth coefficient correlation can predict the CHF when boiling water on both flat surfaces and long horizontal cylinders to within 5% uncertainty up to 10 bar system pressure, and the CHF when boiling methanol on a flat surface to within 10% uncertainty up to 5 bar. The predicted detailed bubble grow and merge process from various sub-models are also in good agreement with the experimental results reported in the literature.

Verification and in situ calibration of large-aperture null correctors for convex aspheric mirrors

Interferometric test of large convex aspheres with high accuracy is still an urgent problem. Adopting a large-aperture null corrector is usually inevitable, and it is imperative to certify the large-aperture null optics in case incorrect final shape of the aspheric mirror is obtained. Moreover, it is necessary to calibrate and remove errors of the large-aperture null lens and trace errors to surfaces that are easy to obtain high accuracy. For these purpose, this paper presents an in situ calibrated null test method. The large-aperture null corrector for convex aspheric mirror is verified and calibrated by a wisely designed small aperture certifying null whose surfaces are either flat or spherical which are easy to be fabricated, measured and assembled. A redundant test is implemented by a Zygo VeriFire Asphere interferometer for cross test. Compared with existing methods of certificating null correctors which utilize an expensive CGH or a self-aligning aspherical mirror, the presented method finally traces errors of a large-aperture null corrector to small aperture flat and spherical surfaces thus costs are expected to be saved dramatically.

Wavefront error measurement of the concave ellipsoidal mirrors of the METIS coronagraph on ESA Solar Orbiter mission

The paper describes the alignment technique developed for the wavefront error measurement of ellipsoidal mirrors presenting a central hole. The achievement of a good alignment with a classic setup at the finite conjugates when mirrors are uncoated cannot be based on the identification and materialization at naked eye of the retro-reflected spot by the mirror under test as the intensity of the retro-reflected spot results to be ≈1E−3 of the intensity of the injected laser beam of the interferometer. We present the technique developed for the achievement of an accurate alignment in the setup at the finite conjugate even in condition of low intensity based on the use of an autocollimator adjustable in focus position and a small polished flat surface on the rear side of the mirror. The technique for the alignment has successfully been used for the optical test of the concave ellipsoidal mirrors of the METIS coronagraph of the ESA Solar Orbiter mission. The presented method results to be advantageous in terms of precision and of time saving also when the mirrors are reflective coated and integrated into their mechanical hardware.

Time-Resolved Nanometer Scale AFM Imaging of Antimicrobial Peptide Activity on Live Escherichia coli Cells

Bacterial membranes have a much more complex structure than mammalian cell membranes. As such, knowledge of bacterial membrane composition and organization, as well as characterization of the molecular-level responses to drug interactions, is critical to the development and assessment of effective antibacterial drug formulations. Cellular drug responses involve highly dynamic processes. However, the ability to image live cells with nanometer resolution on timescales relevant to dynamic cellular events has proven challenging. With traditional AFM systems, the typically longer image acquisition times required to obtain a single high-resolution image (~minutes) has limited the ability to investigate dynamic biological processes. While recent years have shown significant progress in the development of high-speed atomic force microscopy (HS-AFM), the nature of the instrumentation that has been developed has several drawbacks in specimen size, requiring small scan sizes and flat sample surfaces. As such, the majority of biologically-related HS-AFM studies have concentrated on imaging single biomolecules with little focus on using HS-AFM to examine cellular processes.

Ductility improvement of aluminum 1050A rolled sheet by a newly designed ball burnishing tool device

Conventional ball burnishing processes using a roller or a ball pressed against round or small flat surfaces have long been used to improve hardness, fatigue strength, and wear resistance of mechanical parts by plastic deformation. However, the treatment of large flat surfaces using conventional techniques is rarely considered because of its time consumption. In the present work, the optimal burnishing parameters of rolled sheets of aluminum 1050A are determined by means of a newly developed burnishing tool device especially designed to treat large flat surfaces with orders of magnitude reduction in burnishing time. Experiments were designed and performed on a machining center based on response surface methodology with central composite design. The burnished specimens were then tested to find the burnishing condition under which ductility was improved. This study has resulted in significant new insights into the effect of burnishing on the surface quality and workpiece properties of aluminum 1050A plates. A second-order mathematical model, validated using data obtained from atomic force microscopy, was developed to predict the surface roughness as functions of speed, force, and feed rate. The results indicate that burnishing of aluminum 1050A plates improves its ductility, but not its micro-hardness. Following the various burnishing conditions, the micro-hardness measurements range from 40 to 43 HV (50 g), indicating that there is little or no hardening. Although a moderate effect with varied degrees is found on the surface roughness as functions of the investigated parameters, the burnishing force has a significant effect on ductility. The results also indicate that lower values of roughness do not guarantee better ductility for aluminum 1050A plates. Furthermore, the effect of the burnishing loads on the residual stresses was found to depend on the feed direction.

Surface Effects on the Atomic and Electronic Structure of Unpassivated GaAs Nanowires

On the basis of accurate ab initio calculations, we propose a model for predicting the stability of III-V nanowires (NW) having different side walls and ridge configurations. The model allows us to obtain the NW formation energies by performing calculations only on relatively "small" systems, small diameter NWs and flat surfaces, to extract the contributions to the stability of each structural motif. Despite the idea illustrated here for the case of hexagonally shaped GaAs NWs grown along the [111]/[0001] direction, the method can also be applied generally to other differently shaped and oriented III-V NWs. The model shows that NW surfaces (side walls plus ridges) mainly determine the NW stability, so the changes to the surface structure (e.g., induced by defects or different growth conditions) would modify the final NW structure in a remarkable way. We find that wurtzite and zinc blende nanowires have similar energies over a wide diameter range, thus explaining the observed polytypism. Furthermore, new more stable ridge reconstructions are proposed for zinc blende nanowires. The surface-related structural motifs also have clear fingerprints on the NW electronic structure. We find that the more stable nanowires are all semiconducting. The band gaps are ruled by surface states and do not follow the trend mandated by the quantum confinement effect. Small diameter wurtzite nanowires have an indirect band gap, but for some of them, an indirect to direct transition can be foreseen to occur at larger diameters. Surface states have a larger impact on the zinc blende NW band gaps than on the wurtzite NW ones. Zinc blende nanowire band gaps reduce significantly with increasing nanowire radius, reaching the bulk value at a diameter of about 30 Å. The surface structure and the high surface related DOS below the conduction band are going to affect the nanowire dopant incorporation and efficiency when doping is carried out during the NW growth.

Porous polymer coatings: a versatile approach to superhydrophobic surfaces.

We present a facile and inexpensive approach to superhydrophobic polymer coatings. The method involves the in-situ polymerization of common monomers in the presence of a porogenic solvent to afford superhydrophobic surfaces with the desired combination of micro- and nano-scale roughness. The method is applicable to a variety of substrates and is not limited to small areas or flat surfaces. The polymerized material can be ground into a superhydrophobic powder, which, once applied to a surface, renders it superhydrophobic. The morphology of the porous polymer structure can be efficiently controlled by composition of the polymerization mixture, while surface chemistry can be adjusted by photografting. Morphology control is used to reduce the globule size of the porous architecture from micro down to nanoscale thereby affording a transparent material. The influence of both surface chemistry as well as the length scale of surface roughness on the superhydrophobicity is discussed.

Studies on a novel bioactive glass and composite coating with hydroxyapatite on titanium based alloys: Effect of γ-sterilization on coating

A novel silicate based bioactive glass coating composition containing B 2O 3 and TiO 2 having matching thermal properties with that of Ti 6Al 4 V implants was developed and characterized. A conventional vitreous enamelling technique was used for coating small flat surface and curved surface of small rods. Hydroxyapatite (HAp) micro and nano-crystalline particles were used to prepare bioactive glass-HAp composite coating. Scratch testing was used to study the coating adhesion and its fracture behaviour under simulated conditions. As observed from scratch testing results, adhesion strength of the coating improved from 21 N normal load to 27 N and 32 N on addition of micro-HAp and nano HAp powder, respectively, to bioactive glass matrix. Further, sterilization of the coated samples with 25 kGy gamma irradiation substantially enhanced the adhesion of glass coating and HAp-composite coating.

Performance of a polymeric heat sink with circular microchannels

The object of this work is the thermal investigation of a polymeric microchannel heat sink designed for the active cooling of small flat surfaces. Its performance, pressure drop, temperature distribution, and thermal resistance are evaluated. A three-dimensional procedure is developed and applied to a geometrical configuration consisting of a circular microduct (with a gas running through it), embedded in a solid substrate with rectangular cross-section. The conjugate heat transfer problem is solved assuming fully developed laminar flow in forced convection. The bottom side of the heat sink receives a uniform heat flux, while the top side is adiabatic. Considering a gas flow with low Prandtl and Reynolds numbers, the temperature distribution is given by the sum of a linear function (in the stream direction) and a numerical solution obtained in 2-D coordinates resorting to a finite element software, based on the Rayleigh–Ritz–Galerkin method, with user-defined error tolerance. Rarefaction, compressibility and viscous dissipation are neglected, i.e., the Knudsen, Mach and Brinkman numbers are low. The theoretical results are shown in some graphs and compared with experimental data concerning helium and nitrogen flows in Nylon circular microducts. The agreement is quite satisfactory.

Pool boiling CHF on a laser heated thin plate

The technique of laser heating a thin metal foil was used to experimentally observe local phenomena in pool boiling CHF on a small flat surface. The experiments were performed with saturated water boiling on 25 μm thick copper and titanium foils with heating surface diameters ranging from 2.27 to 9 mm. The number of simultaneously active nucleation sites depends on the heat flux and the size and material of the laser heated surface. A reduction in the heating surface diameter D H moves the transition between one and several simultaneously active nucleation sites towards higher heat fluxes. CHF for small heating surfaces is lower than that for entirely heated surfaces. The variation of the ratio of bubble/vapour mass diameter to the heating surface diameter, D B/ D H, with D H is similar to the variation of CHF with D H. CHF is significantly influenced by the number of simultaneously active nucleation sites. The influence of heating of the surrounding surface on decreasing D H, which was observed using two laser beams with different diameters was more intense at higher D H on Cu foil than on Ti foil.

833 ねじり疲労における微小き裂の発生・成長に及ぼす磁場の影響

Reversed tortional fatigue test of sandglass type specimen with a small flat surface notch was conducted at room temperature for a pure iron and a reduced activation ferritic steel F-82H in a solenoid coil cooled by water. Specimen was not constrained lonitudinally to avoid the additional stress induced by magnetostriction. Magnetic flux density in specimen, about 0.7 Tesra, was in rotation magnetization condition. Initiation and propagation behavior of large number of small cracks were observed on the flat surface notch by using image processing technique. For pure iron, crack initiation became earlier and crack growth faster in magnetic field. For F-82H steel influence of magnetic field did not observed.

Surface-mounted optical fiber strain sensor design

We develop the theory of surface-mounted interferometric optical fiber strain sensor design for arbitrarily configured fiber paths and present design techniques to select the path of a curved fiber-optic sensor required to isolate predetermined strain components. Several of these gauges are combined to form a rosette that directly measures the state of strain without the need to solve a set of simultaneous equations. We also use the design procedures to develop an optical fiber sensor that measures a single arbitrary stress component in an isotropic body. The design process is guided by a fundamental relationship among path, strain, and phase change for an arbitrarily configured optical fiber. The design theory is restricted to small strains and flat surfaces. All fiber sensor designs are validated with experiments.

Response of a strand with elliptical outer wires

The linearized form of the equilibrium equations for wire rope is used to develop a theory which describes the axial response of a strand, with elliptical outer wire cross-sections, to a static load for two strand configurations. The strand geometries are the same except for a small flat surface on each of the outer wires for the second configuration. The forces, moments, stresses and strains are calculated using the same loading conditions for each strand configuration and varying the ellipticity of the outer wires. The results for both cases are then evaluated and an application of the theory is briefly discussed.

X-ray measurements of the crystal truncation rod scattering from cleavage surfaces of ionic crystals

X-ray diffraction measurements of the crystal truncation rod (CTR) scattering show that the cleavage surfaces of ionic crystals such as NaCl(001) and KBr(001) are divided into several small flat surface regions with normal directions close to the [001] direction but differing slightly from each other like for a mosaic crystal. From the analysis of the intensity distribution of the CTR scattering, the c-axis lattice spacings of the top surface layers of the vacuum-cleaved crystals were found to shrink by about 3% and 6% relative to the bulk lattice spacings for NaCl(001) and KBr(001), respectively.

Transient boiling heat transfer from two different heat sources: Small diameter wire and thin film flat surface on a quartz substrate

Transient boiling heat transfer data are reported for two different heater surface geometries submerged in liquid nitrogen. During the early part of the transient heat pulse, the heat transfer coefficient for both geometries generally agrees with values predicted from classical transient pure conduction equations. The agreement persists until the time for onset of convection which varies approximately as 1 q 2 where q is the heat flux to the fluid.