Constant Properties Research Articles

Viscoelastic free vibration analysis of in-plane functionally graded orthotropic plates integrated with piezoelectric sensors: Time-dependent 3D analytical solutions

This paper proposes an accurate three-dimensional framework for elastic and viscoelastic free vibration investigation of in-plane functionally graded (IPFG) orthotropic rectangular plates integrated with piezoelectric sensory layers. The developed analytical framework is capable of considering layer-wise unidirectional linear functional gradation in both stiffness and density of the orthotropic composite layers. 3D piezoelasticity-based governing equations of motion are formulated in mixed form by employing Hamilton’s principle, and further solved analytically for Levy-type support conditions using the power-series-based extended Kantorovich method (EKM) jointly with Fourier series. The displacements, stresses, and electrical variables (electric field and electric potential) are solved as the primary variables that ensure the point-wise interlayer continuity and electro-mechanical support conditions. The viscoelastic property of the orthotropic interlayer is defined by employing Biot model, which is similar to the standard linear viscoelastic model. The correctness and efficacy of the present mathematical model are established by comparing the present numerical results with published literature and 3D finite element results, obtained by utilizing user material subroutine in the commercial FE software ABAQUS. An extensive numerical study is performed for various configurations and thickness ratios to investigate the influences of in-plane gradation, viscoelasticity and their coupled effects on the free-vibration response of hybrid laminated plates. It is found that in-plane gradation of stiffness and density remarkably alters the flexural frequencies and corresponding mode shapes of the hybrid intelligent rectangular plates. The flexural frequencies and stresses in the plate can be modified by selecting suitable grading indexes. Another interesting observation is that the in-plane gradation shows a considerably less effect on the electrical response of piezoelectric layers, which can play a vital role in the design of sensors and actuators for dynamic applications. Further, the numerical study demonstrates a potential time-dependent structural behaviour based on the present viscoelastic modelling. The consideration of viscoelasticity could be crucial for analysing the mechanical behaviour of a wide range of polymer composites more realistically and for prospective temporal programming in smart structural systems by exploiting the viscoelastic effect. Although the present analytical solution has been proposed for the free-vibration investigation of smart in-plane functionally graded (IPFG) viscoelastic plates, it can also be utilized directly to analyze the symmetric and asymmetric laminated piezoelectric smart plates with constant properties.

Recent progress of Ga2O3-based gas sensors

In recent years, gas sensors fabricated from gallium oxide (Ga 2 O 3 ) materials have aroused intense research interest due to the superior material properties of large dielectric constant, good thermal and chemical stability, excellent electrical properties, and good gas sensing. Over the past decades, Ga 2 O 3 -based gas sensors experienced rapid development. The long-term stable Ga 2 O 3 -based gas sensors for detecting oxygen and carbon monoxide have been commercialized and renowned with extremely good gas sensing characteristics. Recent pioneering studies also exhibit that the Ga 2 O 3 -based gas sensors possess great potentials in applications of detecting nitrogen oxides, hydrogen, volatile organic compounds and ammonia gases. This article presents recent advances in gas sensing mechanism, device performance parameters, influence factors, and applications of Ga 2 O 3 -based gas sensors. The impacts of influence factors, doping, material structure and device structure on the performance of gas sensors are discussed in detail. Finally, a brief overview of challenges and opportunities for the Ga 2 O 3 -based gas sensors is presented.

Scrutiny of physico‐chemical properties of extractant‐diluent phase: Keystone of extraction systems

AbstractSolvent extraction is one of the hydro metallurgical techniques adopted due to its ease for efficient separation of metal ions. The separation and extraction of metals are enabled using privileged metal distribution between the aqueous and organic phase. Commercially available solvent extractants and recently the designer solvents like ionic liquids have gained adequate attention in the area of separation science for the retrieval of different metal ions. Diluents play an important role by ensuring the improved hydrodynamics of the extraction system. The physico‐chemical characteristics of the organic phase solution need to be scrutinized thoroughly in order to optimize the extraction conditions. Investigation on the interaction between extractant and diluent at molecular level is vital for the assessment of extraction efficiency. Density, viscosity, dielectric constant, refractive index, conductivity, and acoustic properties provide evidence on the molecular organizations between these unlike molecules. The aim of this review is to project on the importance of physical, chemical, and thermodynamic properties for fabricating an efficient combination of extractants‐diluents to achieve maximum extraction output.

A General Non-Lipschitz Infimal Convolution Regularized Model: Lower Bound Theory and Algorithm

The convex infimal convolution model proposed in Chambolle and Lions [Numer. Math., 76 (1997), pp. 167--188] is a fundamental model to extract two useful components from a single input image and has various low level vision applications. In many of them, one target component has an (approximately) piecewise constant structure and the other is a smoothly varying function or repeated texture pattern. In this paper, we propose and study a general non-Lipschitz infimal convolution (GnLIC) regularization model, which covers most existing applications in this type. Therein the non-Lipschitz regularization enforces the piecewise constant property of the first component. For this GnLIC model, we prove a lower bound theory for its local minimizers and a local version for its stationary points. Motivated by these, we naturally extend previous works to design an inexact iterative support shrinking algorithm with proximal linearization for our GnLIC model (InISSAPL-GnLIC). Moreover, we establish the sequence convergence property and a sequence lower bound theory for InISSAPL-GnLIC, provided that an inexact subgradient condition generated by a subsolver holds. The subsolver is constructed by efficient ADMM and a specially designed feasibilization operation. We finally give numerical experiments in two low level vision applications: Retinex and cartoon-texture decomposition. These tests demonstrate that our non-Lipschitz regularization based method can indeed extract the piecewise constant component better than existing approaches, which is consistent with the established lower bound theory.

Evaluation of the Dielectric and Insulating Properties of Newly Synthesized Ethylene/1-Hexene/4-Vinylcyclohexene Terpolymers

Terpolymerizations of newly synthesized ethylene (E), vinylcyclohexene (VCH), and 1-hexene were carried out with symmetrical metallocene catalysts rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (catalyst A) and rac-Et(Ind)2ZrCl2 (catalyst B). X-ray diffractometry (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), high-temperature gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) spectroscopy were used to evaluate the behavior and microstructure of the polymers. The activity of catalyst B was 1.49 × 106 gm/mmolMt·h), with a Tm of 73.45 (°C) and ΔHm of 43.19 (J/g), while catalyst A produced first higher 1-hexene, 19.6 mol %, and VCH contents with a narrow molecular weight distribution (MWD). In previous reports, ethylene propylene monomer dienes (EPDM) had a low content and were used for dielectric and insulating properties with nanomaterials. Second, this paper presents a kind of elastomeric polymers based on E/1-hexene and VCH with a high dielectric constant (k = 6–4) and mechanical properties. In addition, low dielectric loss suggests the suitable application potential of these polymeric materials for the fabrications of capacitors. Also, this work reveals that these polymers can be a better candidate for high-voltage electrical insulation due to their enhanced dielectric, mechanical, and thermal characteristics. To examine the insulating property, the interface characteristics of the polymer were evaluated using electrochemical impedance spectroscopy (EIS) with a frequency range of 1 × 105–0.01 Hz and an amplitude of 5.0 mV. EIS is an effective method to investigate the polymers’ interfacial electron transfer characteristics. The EIS Nyquist plot showed high Warburg impedance features in the low-frequency domain with straight lines without a semicircle, suggesting that the property of the polymer owing to the high electrical resistance and poor conductivity for ionic kinetics in the electrolyte may have surpassed that of the semicircle. Although the slope of low frequencies in polymers holding potent exoelectrogenic bacteria (Shewanella oneidensis MR-1) as a charge carrier in the electrolyte could significantly reduce the Warburg resistance, it still could not improve the conductivity, which demonstrated that the external charge supply could not alter the insulating property in the used polymers.

Computational Fluid Dynamics Studies in the Drying of Industrial Clay Brick: The Effect of the Airflow Direction

The manufacture of ceramic brick goes through the stages of raw material extraction, clay homogenization, material conformation, drying and firing. Drying is the phase that needs greater care, as it involves removing part of the moisture from the brick, in order to preserve its quality after process. This work aims to predict heat and mass transfer in the drying of ceramic bricks in oven using computational fluid dynamics. Considering the constant thermophysical properties, a transient three-dimensional mathematical model was used to predict mass and energy transfer between the material and air during the process. Drying simulations at temperature of 100°C were performed with the air flow in the frontal direction to the ceramic brick holes and the results were compared with those obtained for the air flow in the perpendicular direction to the brick holes reported in the literature. It was found that the position of the brick in relation to the direction of air flow inside the oven affected directly the drying and heating kinetics, and the distribution of temperature and moisture content inside the brick. The positioning of the holes in the brick parallel to the direction of the air flow resulted in reduction at the drying time and, consequently, in energy savings in the process, more uniform drying, and improvement in the product quality.

Effect of transverse magnetic field on wake dynamics and heat transfer through a porous circular cylinder

AbstractA two‐dimensional numerical simulation using the commercial computational fluid dynamics package ANSYS Fluent 15.0 is performed to investigate the effect of a transverse magnetic field on the wake dynamics around a heated porous circular cylinder. The study is conducted considering a Newtonian, incompressible, and electrically conductive fluid with constant properties for the low Reynolds number laminar regime. In the range of Reynolds number (Re = 10–40), recirculating vortices are observed to penetrate (or detach) into (from) the porous cylinder surface depending on the Darcy number, Da (10−6 to 10−2). The effect of the magnetic field parameter (Hartmann number) Ha (0–10) on the detachment and penetration characteristics of a porous cylinder is reported for the first time. A steady separated flow behind the cylinder turns into an attached flow at a critical magnetic field strength. Accordingly, the critical Hartmann number (Hacr) is estimated for the complete suppression of the flow separation behind the porous cylinder. Hacr is found to decrease with an increase in Da and a decrease in Re. The wake behind the cylinder is also found to be detached from the cylinder surface at a particular value of the magnetic field strength termed as the detachment Hartmann number (Had). Had also decreased with an increase in Da and decrease of Re. In addition, the effect of Ha on the separation angle, recirculation length, detachment length, and drag coefficient is also discussed. Furthermore, the effect of the magnetic field on the forced convective heat transfer characteristics is also studied considering various fluids (Prandtl number, Pr = 0.02, 0.71, and 7) past the circular permeable cylinder. At a particular Pr, the heat transfer rate is almost invariant for low permeability, whereas it increases significantly at higher permeability with an applied magnetic field. The rate of heat transfer increases with the Prandtl number for all Hartmann and Darcy numbers. Finally, a correlation is developed to predict the average heat transfer as a function of Re, Pr, Da, and Ha.

High-k Lead-Free Ferroelectric KNN as an Electron Blocking Layer toward Efficient Hybrid Piezoelectric–Triboelectric Nanogenerators

Lead-free ferroelectric one-dimensional nanostructures exhibit great potential in building micro/nanoenergy harvesters owing to their high dielectric constant and piezoelectric properties. Herein, potassium sodium niobate (KNN) nanostructures are embedded into a poly(dimethylsiloxane) (PDMS) film to develop a hybrid piezoelectric–triboelectric nanogenerator (PTENG) that scavenges mechanical energy efficiently. By comparing different structures with and w/o the functional KNN layer, the spontaneous polarized electric field produced by the KNN-Mn film is systematically investigated, and its function as an electron blocking layer to hinder electron transfer is also well illustrated. Furthermore, after embedding KNN-Ca nanorods into PDMS to enhance relative permittivity, we find that the induced polarized electric field initiated by KNN-Ca nanorods binds free electrons and acts as a charge retention transition layer to further boost surface charge density. This work brings ideas to prepare high-performance PTENGs by applying ferroelectric materials with high permittivity.

Orthodontic shear bond strength and ultimate load tests of CAD/CAM produced artificial teeth

ObjectivesTo investigate whether artificial CAD/CAM processed (computer-aided design/manufacturing) teeth could be a feasible option for the production of dental in vitro models for biomechanical testing.Material and methodsDisks (n = 10 per group) made from two different CAD/CAM-materials, one fiber-reinforced composite (FRC; Trinia, Bicon) and one polymethylmethacrylate-based resin (PMMA; Telio CAD, Ivoclar Vivadent), as well as bovine teeth (n = 10), were tested for their shear bond strength (SBS) and scored according to the adhesive remnant index (ARI). In addition, CAD/CAM-manufactured lower incisor teeth were tested for their ultimate load (Fu).ResultsWith regard to SBS, both PMMA (17.4 ± 2.2 MPa) and FRC (18.0 ± 2.4 MPa) disks showed no significant difference (p = 0.968) compared to bovine disks (18.0 ± 5.4 MPa). However, the samples differed with regard to their failure mode (PMMA: ARI 4, delamination failure; FRC: ARI 0 and bovine: ARI 1.6, both adhesive failure). With regard to Fu, FRC-based teeth could withstand significantly higher loads (708 ± 126 N) than PMMA-based teeth (345 ± 109 N) (p < 0.01).ConclusionUnlike PMMA-based teeth, teeth made from FRC showed sufficiently high fracture resistance and comparable SBS. Thus, FRC teeth could be a promising alternative for the production of dental in vitro models for orthodontic testing.Clinical relevanceCAD/CAM-processed teeth made from FRC enable the use of standardized geometry and constant material properties. Using FRC teeth in dental in vitro studies has therefore the potential to identify differences between various treatment options with rather small sample sizes, while remaining close to the clinical situation.

Mechanistic model of combined pressure drop and heat transfer for the entire growth stage of an elongated bubble in a rectangular microchannel

A one-dimensional flow-boiling model for the slug-flow regime is formulated to describe the pressure drop and heat transfer mechanism in a microchannel of rectangular cross-section. The pressure drop model considers three stages of bubble growth namely: (i) partial confinement, (ii) full confinement and (iii) vapour venting. The heat transfer coefficient at any particular location is obtained by assuming the periodic passage of four zones: (i) liquid slug zone, (ii) elongated bubble zone, (iii) partially dryout zone, and (iv) fully dryout zone. The model is evaluated using constant fluid properties, to study the parametric variation of channel pressure drop and heat transfer coefficient. The effects of variation in channel dimension, flow velocity, heat flux and properties of working fluid on pressure drop and heat transfer coefficient have been studied using the model. The model is capable of simulating all the transport processes for a single bubble from its inception till it leaves the microchannel and thereby it can estimate the pressure drop in the channel along with the heat transfer coefficient i.e. spatially averaged over the channel length and at any location from channel upstream to the downstream end.

MyElas: An automatized tool-kit for high-throughput calculation, post-processing and visualization of elasticity and related properties of solids

Elasticity is one of the most fundamental mechanical properties of solid. In high-throughput design of advanced materials, there is an imperative demand for the capability to quickly calculate and screen a massive pool of candidate structures. A fully automatized pipeline with minimal human intervention is the key to provide high efficiency to achieve the goal. Here, we introduce a tool-kit MyElas that aims to address this problem by forging all pre-processing, elastic constant and other related property calculations, and post-processing into an integrated framework that automatically performs the assigned tasks to drive data flowing through parallelized pipelines from input to output. The core of MyElas is to calculate the second and third order elastic constants of a solid with the energy-strain method from first-principles. MyElas can auto-analyze the elastic constants, to derive other related physical quantities. Furthermore, the tool-kit also integrates a visualization function, which can, for example, plot the spatial anisotropy of elastic modulus and sound velocity of monocrystalline. The validity and efficiency of the toolkit are tested and bench-marked on several typical systems. Program summaryProgram title: MyElasCPC Library link to program files:https://doi.org/10.17632/jbz2s9xsmv.1Code Ocean capsule:https://codeocean.com/capsule/4149434Licensing provisions: GNU General Public License 3Programming language: Python 3.XExternal routines/libraries: Numpy [1], Spglib [2], Matplotlib [3]Nature of problem: Through the first-principal calculation, the second-order and third-order elastic constants of solid materials are automatically calculated, and the post-processing and visualization of single crystal and polycrystalline physical properties are carried out.Solution method: Firstly, the required strain structure is automatically generated through the space group of materials and the corresponding strain matrix. Secondly, the energy of the structure is calculated by first-principles calculation software such as VASP [4]. Thirdly, the relationship between energy and strain is polynomial fitted to deduce the elastic constant of the material. Fourth, automatically derive the relevant physical properties. Finally, the distribution of mechanical modulus and sound velocity in spherical space is visualized.Additional comments including restrictions and unusual features: Many modules of the software can be embedded into other software through simple modification, such as visualization module. The software supports finite temperature calculation with electronic temperature. In addition, the software supports the derivation of corresponding elastic constants from phonon spectrum data generated by Phonopy [5], Alamode [6] and TDEP [7] software through long-wave limit approximation and Christoffel equation.

Risk in Risk Aversion

Behind every investment portfolio, there are sources and uses of its funds, each with their own risks. Though funding risks are pervasive, their implication for setting appropriate risk aversion for portfolio construction is too little exploited. In this article, the authors extend single-period decision making to combine risk in assumed funding supply and uses with risk in investment returns to provide a joint optimization. Their approach uses expected utility maximization based either on the constant relative risk aversion property or on the generalized logarithmic utility model, the latter somewhat sharper in controlling tail risk. Mathematics is greatly simplified by matrix calculation using discrete preference states. The authors also employ investment leverage on surplus over subsistence requirements to estimate the need for conservatism. Examples are given for both the generic moderate errors in judging appropriate risk aversion and the more extreme funding risk arising from uncertainty as to retirement longevity.

High optical performance of Gd2O3-doped PVA/PVP composite films for electronic and laser CUT-OFF filters

Developing new composite materials with significant features is required for essential research and applications in many fields. The blend of the hydrophilic polymeric composites was considered as host carriers for significant rare-earth sources of Gd2O3 at various concentrations (0.05–9.87 wt. %) using the solution casting method. X-ray diffraction (XRD) ascertained the structural behavior of the prepared polymeric films, while the impressive Fourier transform-infrared (FT-IR) analysis landmark the existence of the O-H group on the PVA/PVP polymers. The extraordinary effects of different ratios of Gd2O3 dopants on the optical characteristics of the synthesized composite films were investigated using a UV–vis spectrophotometer. The transmittance spectra of pure PVA/PVP polymeric composites have been recorded to be 90 % in the visible region, then decreased to 66 %, increasing the Gd2O3 concentrations. Also, the absorption spectra of the examined Gd2O3-doped PVA/PVP films peak at 212 nm, revealing the π-π transition of blend segments. Furthermore, adding the Gd2O3 rare-earth dopants to the PVA/PVP polymers raised the bandgap energy and extinction coefficient values. Several theoretical models were applied to accurately evaluate the linear refractive index (n) and nonlinear optical parameters based on the prepared polymeric films' optical energy bandgaps (Eg). This research highlighted some outcome advantages of the semi-crystalline structure, outstanding linear optical energy bandgaps, refractive indexes, dielectric constant, optical limiting, and nonlinear optical properties of the proposed Gd2O3-doped PVA/PVP nanocomposite polymeric films. In conclusion, the synthesized Gd2O3 rare-earth source with a blend of PVA/PVP composites has vital influential and promising roles in practical optoelectronics and cut-off filters.

Combination of conformal mapping with variable discrete ordinates method for solving the radiation heat transfer in concentric spherical media

The radiation problem in one-dimensional participating media between two concentric spheres is solved by mapping the concentric spherical domain into the plane-parallel domain, where the radiative rays propagate along curved paths. The computational plane-parallel domain is discretized into slices with constant radiative properties and the angular domain for each control volume is discretized into variable polar angles. To validate the accuracy of the present method, comparisons are made with the previous studies in literature.

Assessment of constant force properties for various superelastic shape memory alloy structure

In the biomedical materials applications, biocompatibility of implanted prostheses and clamped medical devices leads to devices failures that frequently occur. Embedding constant force elements based on superelastic shape memory alloys in implanted prostheses and clamped medical devices to achieve constant force clamping of soft tissues can improve biocompatibility issues. This paper proposes combining shape memory alloy superelasticity and structural optimization to design constant force elements with special stress-strain relationships. The design criteria for constant force element and evaluation method for constant force characteristics are proposed. According to the design criteria and evaluation methods of in-vivo constant force elements, I-shaped structure, heart-shaped structure, M-shaped structure, V-shaped structure, O-shaped structure and C-shaped structure were designed based on shape memory alloy. Then the finite element models of various structures are established to compare and analyze their constant force characteristics. The results show that the C-shaped may obtain a force-displacement curve with large constant force region by changing their geometric parameters, and it is easier to find the characteristics geometric parameters with a large constant force range.

Characterization and Modelling of Sheet Material with Graded Strength for more Accurate Finite Element Analysis

Many sheet materials do not exhibit constant properties over the sheet thickness. On the one hand, this can be caused by a rolling process with a pass reduction of 1-2%, the so-called skin pass rolling. This is mainly used for deep drawing steel grades to eliminate the pronounced yield strength of the base material. Another possibility is abrasive blasting or shot peening of sheet metal. This causes plastic deformation of the sheet surface and material strengthening. The grading can be used to locally strengthen components or locally adapt the roughness. Since many production processes today are designed numerically, the mapping of such a grading is necessary but currently not implemented in FE code. Aim of this research is, to correlate the material hardness to a plastic pre-strain with a newly developed characterization method. For this purpose, graded material properties are generated by means of abrasive blasting as an example process. The resulitng locally varying work hardening over the sheet thickness is further integrated in finite element analysis by the assignment of a starting condition of a 2d-shell element formulation. With this approach, it is possible to map the graded material properties easily in FE simulations with a very good accuracy.

Forced vibration mechanism and suppression method for thin-walled workpiece milling

Thin-walled workpieces are widely used in aerospace applications, but their weak stiffness characteristic leads to forced vibration during milling, which reduces the quality of the milled surface. To solve the forced vibration problem in milling thin-walled workpieces, this paper proposes a forced vibration mechanism for the thin-walled workpiece under the influence of various factors and a corresponding suppression method. First, the response characteristics of the thin-walled workpiece excitation features correlated with the mode shape are given. Then, the vibration shapes of the thin-walled workpiece are combined with the cutting position, and the effects of the cutting force frequency and cutting force magnitude are also considered. Finally, the different vibration characteristics are associated with the time constant properties of the shear thickening fluid (STF), and the corresponding forced vibration effects are suppressed by the STF. After a series of experimental modal analyses and cutting experiments, the results show that the proposed theory can explain the forced vibration phenomenon of the thin-walled workpiece, and the vibration suppression effect of the STF is consistent with the theory. The method is also applicable to vibration suppression at the weak position during the machining of the large workpiece.

Low Dielectric Constant and Anisotropic Mechanical Properties of Dispenser‐Printed Polyetherimide Films Using Two‐Step Thermal Treatment

AbstractAlthough polyetherimide (PEI) has attracted attention owing to its good dielectric properties, superior mechanical properties, and thermal/chemical stabilities, there is still a lack of methodology to fabricate PEI films in desired shapes directly on devices. In this study, a dispenser printing method to fabricate sophisticated 2D PEI structures is introduced. As dispenser printing is a solution‐based process, PEI ink is prepared by dissolving PEI in N‐methyl pyrrolidone (NMP). The printing conditions are controlled by optimizing the pneumatic pressure and viscosity of the inks with various ratios of PEI and NMP, followed by a two‐step heat treatment to develop fine PEI films. The dielectric constant of the PEI film increases from 2.28 to 2.61 with the corresponding secondary heating time of 1–5 h, which is much lower than the theoretical value owing to the free volume and loosely entangled polymer chains generated from the shear forces in printing and solvent evaporation. Furthermore, the film exhibits anisotropic mechanical properties in different printing directions, stemming from the alignment effect of the polymer molecules. It is believed that the developed PEI films and the facile methodology can be diversely tuned to provide new insights into material utilization, further extending the application fields.

Efficiency Measurement and Modeling of a High‐Performance Mg2(Si,Sn)‐Based Thermoelectric Generator

Mg2(Si,Sn) is an attractive material class due to its excellent thermoelectric (TE) properties, its eco‐friendly constituents, its low mass density, and its low price. A lot of research has been done on optimizing its TE properties; however, works on its use in thermoelectric generators (TEG) are scarce. Herein, the first conversion efficiency measurement of a functional, fully Mg2(Si,Sn)‐based TEG, approaching a maximum value of 4% for an applied = 375 °C, is shown. A maximum power density of 0.9 W cm−2 (related to the cross‐sectional area of the TE legs) at =375 °C is also reported, which is among the highest performance of silicide‐based modules reported in literature. Efficiency measurements can be tricky due to the uncertainty of heat flow measurement and parasitic heat losses; therefore, assessing the measurement reliability by confronting it to theoretical calculations is necessary. TEG device simulation in a constant property model is used to compare measured data to expected values and a good match is found (&lt;1% deviation for current at maximum power, &lt;4% difference for maximum power output, deviation within measurement uncertainty range for heat flows and efficiency). The significant discrepancy between measurement and calculations of the inner electrical resistance reveals room for improvement. Cracks form due to thermally induced mechanical stress, which dramatically increase the inner electrical resistance. It is shown that by avoiding those cracks, the maximum power output and conversion efficiency of the TEG could be improved by 30%.

Effects of surface properties on wall superheat at the onset of microbubble emission boiling

Boiling heat transfer (BHT) is a promising technology for cooling the high heat flux emitted from next generation electronic devices. Pool boiling represents an eco-friendly cooling technology because its pumps do not require an external electronic power source. To increase the maximum heat flux of pool boiling beyond the critical heat flux, microbubble emission boiling (MEB) can be implemented with highly subcooled water. However, conventional MEB experiments use a copper heating surface, which can easily be oxidized in air. Thus, copper heating surfaces do not retain constant surface properties, especially when the BHT boiling pool is open to air. Applying a coating to the copper surface can enable further investigations of the MEB phenomenon and improve the reliability of MEB-based cooling devices. However, it is unclear which surfaces are suitable for promoting the onset of MEB. Herein, we experimentally investigated a stable hydrophilic black chrome plating on copper by performing subcooled pool boiling with water at atmospheric pressure. The results confirmed that the black chrome plating did not interrupt the onset of MEB, but rather, it enabled constant wall superheat during repeated experiments spanning the transition from nucleate boiling to MEB. Moreover, the threshold of liquid subcooling for the onset of MEB with the black chrome plating (20 K) was similar to that with a copper heat transfer surface.