Two-layer Configuration Research Articles

Simultaneous measurement of thermal conductivity and heat capacity by flash thermal imaging methods.

Thermal properties are important for material applications involved with temperature. Although many measurement methods are available, they may not be convenient to use or have not been demonstrated suitable for testing of a wide range of materials. To address this issue, we developed a new method for the nondestructive measurement of the thermal effusivity of bulk materials with uniform property. This method is based on the pulsed thermal imaging-multilayer analysis (PTI-MLA) method that has been commonly used for testing of coating materials. Because the test sample for PTI-MLA has to be in a two-layer configuration, we have found a commonly used commercial tape to construct such test samples with the tape as the first-layer material and the bulk material as the substrate. This method was evaluated for testing of six selected solid materials with a wide range of thermal properties covering most engineering materials. To determine both thermal conductivity and heat capacity, we also measured the thermal diffusivity of these six materials by the well-established flash method using the same experimental instruments with a different system setup. This paper provides a description of these methods, presents detailed experimental tests and data analyses, and discusses measurement results and their comparison with literature values.

Natural convection of the oxide pool in a three-layer configuration of core melts

We investigated the natural convection of the oxide layer in a three-layer configuration of core melts in a severe accident. In order to achieve high modified Rayleigh numbers of 1012–1013, mass transfer experiments were performed using a copper sulfate electroplating system based upon the analogy between heat and mass transfer. Four different cooling conditions of the top and the bottom plates were tested. The upward heat ratios were 14% higher for three-layer than for two-layer due to the reduced heights and the downward heat ratios were lower the same amount. The local Nusselt numbers for the top and the bottom plates were measured and compared with the two layer configuration. To explore the heat load to the reactor vessel, the angle-dependent heat fluxes at the side wall, were measured and compared with the two-layer configuration. Heat load to the side wall and peak heat at the uppermost location were intensified for the three-layer configuration.

Analytical and experimental determination of the parasitic parameters in high-frequency inductor

Abstract The paper presents the results of calculations, simulations, and measurements of parasitic capacitance of winding in ferrite inductor suitable for cooperating with 2 kW DC-DC boost converter built using SiC JFET transistors, operating with a switching frequency of 100 kHz. The inductor winding is made of litz wire in a two-layer configuration. The lumped model of inductor winding was adopted. The results of analytical calculations have been compared with the results obtained from experimental investigations based on the resonance effect.

Ultra-broadband and omnidirectional enhanced absorption of graphene in a simple nanocavity structure

In this study, we developed a simple approach, using a nanocavity structure, to increase the light absorption of graphene in an ultra-broadband and omnidirectional manner. We determined the light absorption of graphene by calculating the surface electric fields (E-fields) of various underlying substrates. Although the surface E-field was maximized for both one-dimensional photonic crystals and a metal/dielectric nanocavity structure, the much simpler two-layer nanocavity configuration also provided ultra-broadband and omnidirectional enhancement of absorption. By selecting a suitable metal as the back reflector and controlling the thickness of the single-layer dielectric spacer in the nanocavity structure, we found experimentally that the light absorption of graphene could be enhanced approximately fivefold, with full widths at half maximum of 200 nm in the ultraviolet, 400 nm in the visible, and greater than 1000 nm in the infrared regime. Moreover, we observed a significantly enhanced photo–heat response from the greater light absorption of graphene in the nanocavity structure. The absorbance spectrum of graphene in the nanocavity structure perfectly matched the air mass 1.5 solar spectrum, suggesting that such systems might be very useful for harvesting solar energy in optoelectronic devices.

Development of two-layer multiple transmitter fibre optic bundle displacement sensor and application in structural health monitoring

This paper presents a study of fibre optic bundle displacement sensor with multiple layers of transmitters. By arranging the transmitter of two-layers in certain ratio, an enhancement of the linear range as well as sensitivity can be achieved compared to conventional bifurcation arrangement. A theoretical model using the Gaussian beam assumption has been developed to characterise the response curve of the various two-layer configurations. The designed two-layer multiple transmitter fibre optic sensor is fabricated to validate the results. The predicted displacement response shows an enhancement of the linear range and sensitivity of four and two times, respectively, better than the corresponding ranges for the conventional bifurcation configuration and is validated by experimental static calibration. Harmonic excitation test is employed to deduce its dynamic displacement response behaviour. Results show constant sensitivity of about 0.363mV/μm (absolute deviation less than 5%) over a bandwidth up to 2.2kHz with minimum measurable displacement amplitude of about 50nm at 2.2kHz and signal-to-noise ratio of around 26dB. The minimum measurable displacement is found to be 18nm at 3.4kHz with a signal-to-noise ratio of around 6dB. Finally, application of the proposed sensor in structural health monitoring is demonstrated experimentally with comparison of conventional contact and non-contact sensors.

Physical and Numerical Modeling of Irregular Wave Transformation over a Fringing Reef

ABSTRACT Shin, S.; Kim, Y.T., and Lee, J.I., 2016. Physical and Numerical Modeling of Irregular Wave Transformation over a Fringing Reef. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 922–926. Coconut Creek (Florida), ISSN 0749-0208. Two-dimensional laboratory experiments were conducted to investigate cross-shore variations of wave transformation, setup, and breaking phenomena over a fringing reef. Various conditions of irregular waves were generated by changing a water depth, a wave period, and a wave height. A multi-layer Boussinesq model was used to predict the wave transformation and the results were compared to the experimental results. One-layer and two-layer model configurations were selected to figure out and compare the model capability. In the model and data comparisons, both models well predicted the wave transformation characteristic...

Enhanced performance in phenol removal from aqueous solutions by a buoyant composite photocatalyst prepared with a two-layered configuration on polypropylene substrate

A buoyant composite photocatalyst was prepared by immobilizing powdered activated carbon (PAC), followed by TiO2 nanoparticles (P25), in a two-layered configuration on the polypropylene granule (PPG) substrate. The PAC layer was anchored onto PPG surface through a thermal bonding process, and then the P25 layer was loaded on the PAC layer by a suspension deposition method. The PAC layer not only served as a protection layer for PPG but also provided the composite photocatalyst with adsorptive property to enhance its capability of collecting organic pollutants from the solution and thus enhance the photocatalytic degradation efficiency. The performance of the prepared composite photocatalyst was evaluated through a series of experiments, including its stability against mechanical attrition and photocatalytic degradation, its adsorptive performance and photocatalytic degradation efficiency in phenol removal. The results showed that the developed composite photocatalyst (denoted as PPG-PAC-P25) was much more mechanically and photocatalytically stable, as compared to those composite photocatalysts prepared from immobilizing a mixture of PAC and P25 together on the PPG, and also showed better photocatalytic degradation performance in phenol removal. A synergistic effect was clearly observed with the composite photocatalyst that had the two layered PAC and P25 configuration. PPG-PAC-P25 was also tested for 20 recycles in a batch process for phenol removal and the overall photocatalytic degradation performance was only slightly decreased by less than 7%, indicated that the developed buoyant composite photocatalyst in this study has a great prospect for possible actual applications in the removal of organic pollutants from water or wastewater.

Thermo-Fluid-Stress-Deformation Analysis of Two-Layer Microchannels for Cooling Chips With Hot Spots

Two-layer single phase flow microchannels were studied for cooling of electronic chips with a hot spot. A chip with 2.45 × 2.45 mm footprint and a hot spot of 0.5 × 0.5 mm in its center was studied in this research. Two different cases were simulated in which heat fluxes of 1500 W cm−2 and 2000 W cm−2 were applied at the hot spot. Heat flux of 1000 W cm−2 was applied on the rest of the chip. Each microchannel layer had 20 channels with an aspect ratio of 4:1. Direction of the second microchannel layer was rotated 90 deg with respect to the first layer. Fully three-dimensional (3D) conjugate heat transfer analysis was performed to study the heat removal capacity of the proposed two-layer microchannel cooling design for high heat flux chips. In the next step, a linear stress analysis was performed to investigate the effects of thermal stresses applied to the microchannel cooling design due to variations of temperature field. Results showed that two-layer microchannel configuration was capable of removing heat from high heat flux chips with a hot spot.

Experimental and numerical investigation on thermal management of an outdoor battery cabinet

Many forms of electronic equipment such as battery packs and telecom equipment must be stored in harsh outdoor environment. It is essential that these facilities be protected from a wide range of ambient temperatures and solar radiation. Temperature extremes greatly reduce lead-acid based battery performance and shorten battery life. Therefore, it is important to maintain the cabinet temperature within the optimal values between 20 °C and 30 °C to ensure battery stability and to extend battery lifespan. To this end, cabinet enclosures with proper thermal management have been developed to house such electronic equipment in a highly weather tight manner, especially for battery cabinet.In this paper, the flow field and temperature distribution inside an outdoor cabinet are studied experimentally and numerically. The battery cabinets house 24 batteries in two configurations namely, two-layer configuration and six-layer configuration respectively. The cabinet walls are maintained at a constant temperature by a refrigeration system. The cabinet's ability to protect the batteries from an ambient temperature as high as 50 °C is studied. An experimental facility is developed to measure the battery surface temperatures and to validate the numerical simulations. The differences between the experimental and computational fluid dynamic (CFD) results are within 5%.

The Role of Whitecapping in Thickening the Ocean Surface Boundary Layer

AbstractThe effects of wind-driven whitecapping on the evolution of the ocean surface boundary layer are examined using an idealized one-dimensional Reynolds-averaged Navier–Stokes numerical model. Whitecapping is parameterized as a flux of turbulent kinetic energy through the sea surface and through an adjustment of the turbulent length scale. Simulations begin with a two-layer configuration and use a wind that ramps to a steady stress. This study finds that the boundary layer begins to thicken sooner in simulations with whitecapping than without because whitecapping introduces energy to the base of the boundary layer sooner than shear production does. Even in the presence of whitecapping, shear production becomes important for several hours, but then inertial oscillations cause shear production and whitecapping to alternate as the dominant energy sources for mixing. Details of these results are sensitive to initial and forcing conditions, particularly to the turbulent length scale imposed by breaking waves and the transfer velocity of energy from waves to turbulence. After 1–2 days of steady wind, the boundary layer in whitecapping simulations has thickened more than the boundary layer in simulations without whitecapping by about 10%–50%, depending on the forcing and initial conditions.

Tapered Two-Layer Broadband Vibration Energy Harvesters

Two-layer piezoelectric vibration energy harvesters using convergent and divergent tapered structures have been developed for broadband power output. The harvesters consist of a base cantilevered beam, which is attached to an upper beam by a spacer to develop a two-layer configuration. Two masses are attached to each layer to tune the resonance frequencies of each harvester and one of these masses also serves as the spacer. By varying the positions of the masses, the convergent and divergent tapered harvesters can generate close resonance frequencies and considerable power output in the first two modes. A broadband harvester design strategy is introduced based on a modal approach, which determines the modal performance using mass ratio and modal electromechanical coupling coefficient (EMCC). The required modal parameters are derived using the finite element method. Mass ratio represents the influence of the modal mechanical behavior on the power density directly. Since the dominant mode causes the remaining modes to have smaller mass ratios, smaller EMCC, and poor performance, the design strategy involves the selection of the harvester configurations with close resonances and favorable values of mass ratio initially, and deriving the EMCC and power density of those selected configurations.

Transport phenomena in polymer electrolyte membrane fuel cells via voltage loss breakdown

This study presents a voltage loss breakdown method based on in-situ experimental data to systematically analyze the different overpotentials of a polymer electrolyte membrane fuel cell. This study includes a systematic breakdown of the anodic overpotentials via the use of a reference electrode system. This work demonstrates the de-convolution of the individual overpotentials for both anode and cathode side, including the distinction between mass-transport overpotentials in cathode porous transport layer (PTL) and electrode, based on in-situ polarization tests under different operating conditions. This method is used to study the relationship between mass-transport losses inside the cathode catalyst layer (CL) and the PTL for both a single layer and two-layer PTL configuration. We conclude that the micro-porous layer (MPL) significantly improves the water removal within the cell, especially inside the cathode electrode, and therefore the mass transport within the cathode CL. This study supports the theory that the MPL on the cathode leads to an increase in water permeation from cathode to anode due to its function as a capillary barrier. This is reflected in increased anodic mass-transport overpotential, decreased ohmic losses and decreased cathode mass-transport losses, especially in the cathode electrode.

Dosimetric Assessment of Two-Layer Cell Culture Configurations for Fertility Research at 1950MHz

Dosimetric Assessment of Two-Layer Cell Culture Configurations for Fertility Research at 1950MHz

Experimental and numerical studies on wave breaking characteristics over a fringing reef under monochromatic wave conditions.

Fringing reefs play an important role in protecting the coastal area by inducing wave breaking and wave energy dissipation. However, modeling of wave transformation and energy dissipation on this topography is still difficult due to the unique structure. In the present study, two-dimensional laboratory experiments were conducted to investigate the cross-shore variations of wave transformation, setup, and breaking phenomena over an idealized fringing reef with the 1/40 reef slope and to verify the Boussinesq model under monochromatic wave conditions. One-layer and two-layer model configurations of the Boussinesq model were used to figure out the model capability. Both models predicted well (r 2 > 0.8) the cross-shore variation of the wave heights, crests, troughs, and setups when the nonlinearity is not too high (A 0/h 0 < 0.07 in this study). However, as the wave nonlinearity and steepness increase, the one-layer model showed problems in prediction and stability due to the error on the vertical profile of fluid velocity. The results in this study revealed that one-layer model is not suitable in the highly nonlinear wave condition over a fringing reef bathymetry. This data set can contribute to the numerical model verification.

Design and study of a multi-funtional electromagnetic device with functions of field rotating and concentrating

A novel multi-functional electromagnetic (EM) device named rotary-concentrator is designed based on transformation optics theory. For its ability to manipulate the EM wave in a special manner, it can rotate the propagation direction of the EM field in the core region to a fixed angle, as well as concentrate the EM energy into the core region simultaneously. For the proposed three equivalent configurations of the rotary-concentrator, the corresponding constitutive parameter expressions are derived respectively, and the full-wave simulations using the finite element software are also carried out. The simulated results validate the derived constitutive parameter expressions. For the three different kinds of configurations, the first two kinds consist of three layers of media, and the last one is simplified to a two-layer configuration. For a given arbitrary rotating angle and an energy concentration ratio, the three configurations can perform propagation direction rotating and energy concentrating in equivalent effect. These results contribute to further understanding of the mechanism of rotator and concentrator, and provide a fuller theoretical basis for the design of multi-functional devices. The proposed rotary-concentrator has potential applications in the design of high efficient receiving antennas and special circuit package interconnecting devices.

The onset of convection in a porous layer with multiple horizontal solid partitions

The principal objective of the present paper is to investigate the onset of convection in a horizontal layer heated from below which consists of distinct porous sublayers which are separated by solid heat-conducting partitions. Each of the porous sublayers are identical as are the solid partitions. The present analysis employs linearised stability theory and a dispersion relation is derived from which neutral curves may be computed. For two-layer configurations the dispersion relation may be written explicitly, but for larger numbers of sublayers a simple systematic numerical procedure is used to compute the dispersion relation which, while it may also be written analytically, rapidly becomes increasingly lengthy as the number of sublayers increases. It is found that neutral curves are always unimodal and each has a well-defined single minimum. We attempt to give a comprehensive physical understanding of the effect of the number of layer, the relative thickness of the partitions and the conductivity ratio on the onset of convection and the form taken by the onset modes. Our results are compared with those of Rees and Genç (2011) [1] who considered the special case where the partitions are infinitesimally thin.

Three-vortex quasi-geostrophic dynamics in a two-layer fluid. Part 1. Analysis of relative and absolute motions

AbstractThe results presented here examine the quasi-geostrophic dynamics of a point vortex structure with one upper-layer vortex and two identical bottom-layer vortices in a two-layer fluid. The problem of three vortices in a barotropic fluid is known to be integrable. This fundamental result is also valid in a stratified fluid, in particular a two-layer one. In this case, unlike the barotropic situation, vortices belonging to the same layer or to different layers interact according to different formulae. Previously, this occurrence has been poorly investigated. In the present work, the existence conditions for stable stationary (translational and rotational) collinear two-layer configurations of three vortices are obtained. Small disturbances of stationary configurations lead to periodic oscillations of the vortices about their undisturbed shapes. These oscillations occur along elliptical orbits up to the second order of the Hamiltonian expansion. Analytical expressions for the parameters of the corresponding ellipses and for oscillation frequencies are obtained. In the case of finite disturbances, vortex motion becomes more complicated. In this case we have made a classification of all possible movements, by analysing phase portraits in trilinear coordinates and by computing numerically the characteristic trajectories of the absolute and relative vortex motions.

Numerical simulations and experimental measurements of dense-core vortex rings in a sharply stratified environment

We present three-dimensional direct numerical simulations of a vortex ring settling in sharply stratified miscible ambient fluids for near two-layer configurations, and comparisons of these simulations with the results from laboratory experiments. The core fluid of the vortex rings has density higher than both the top and the bottom layers of the ambient fluid, and is fully miscible in both layers. This setup ensures a rich parameter space that we partially explore in this study. In particular, a critical (bifurcation) phenomenon is identified that distinguishes the long-time behavior of the settling vortex ring as either being fully trapped at the ambient density layer or continuing through the layer in its downward motion. This critical behavior is determined by the initial conditions (e.g. the size and speed of the vortex ring, the initial distance to the layer, etc). The numerical simulations are able to provide evidence for this in qualitative agreement with an experimental phase diagram. Our setup isolates essential elements of mixing, trapping and escape through stratified fluids in a variety of situations, such as the mixing and dispersion of pollutants and plankton in the ocean.

Shear instability of internal solitary waves in Euler fluids with thin pycnoclines

AbstractThe stability with respect to initial condition perturbations of solitary travelling-wave solutions of the Euler equations for continuously, stably stratified, near two-layer fluids is examined numerically and analytically for a set of parameters of relevance for laboratory experiments. Numerical travelling-wave solutions of the Dubreil–Jacotin–Long equation are first obtained with a variant of Turkington, Eyland and Wang’s iterative code by testing convergence on the equation’s residual. In this way, stationary solutions with very thin pycnoclines (and small Richardson numbers) approaching the near two-layer configurations used in experiments can be obtained, allowing for a stability study free of non-stationary effects, introduced by lack of numerical resolution, which develop when these solutions are used as initial conditions in a time-dependent evolution code. The thin pycnoclines in this study permit analytical results to be derived from strongly nonlinear models and their predictions compared with carefully controlled numerical simulations. This brings forth shortcomings of simple criteria for shear instability manifestations based on parallel shear approximations due to subtle higher-order effects. In particular, evidence is provided that the fore–aft asymmetric growth observed in all simulations requires non-parallel shear analysis. Collectively, the results of this study reveal that while the wave-induced shear can locally reach unstable configurations and give rise to local convective instability, the global wave/self-generated shear system is in fact stable, even for extreme cases of thin pycnoclines and near-maximum-amplitude waves.

Dielectric characterization of materials using a modified microstrip ring resonator technique

The goal of this study is to present a simple model based on the ring-resonator technique to measure nondestructively the permittivity and loss tangent of dielectric materials. The proposed measurement model utilizes a modified ring-resonator technique in one-layer and two-layer microstrip configurations. This method eliminates the requirement to metalize the samples and enables characterization of permittivity and dielectric loss from 2 to 40 GHz. The effects of conductor and radiation losses that may introduce significant errors in the calculation of the loss tangent, especially at very high frequencies, are minimized. The measurement precision is evaluated by comparing the results with those obtained by using two well-known standard techniques. Uncertainties associated with the proposed model are addressed.