Direct Current Heating Research Articles

Pulse-Driven MEMS NO2 Sensors Based on Hierarchical In2O3 Nanostructures for Sensitive and Ultra-Low Power Detection

As the mainstream type of gas sensors, metal oxide semiconductor (MOS) gas sensors have garnered widespread attention due to their high sensitivity, fast response time, broad detection spectrum, long lifetime, low cost, and simple structure. However, the high power consumption due to the high operating temperature limits its application in some application scenarios such as mobile and wearable devices. At the same time, highly sensitive and low-power gas sensors are becoming more necessary and indispensable in response to the growth of the environmental problems and development of miniaturized sensing technologies. In this work, hierarchical indium oxide (In2O3) sensing materials were designed and the pulse-driven microelectromechanical system (MEMS) gas sensors were also fabricated. The hierarchical In2O3 assembled with the mass of nanosheets possess abundant accessible active sites. In addition, compared with the traditional direct current (DC) heating mode, the pulse-driven MEMS sensor appears to have the higher sensitivity for the detection of low-concentrations of nitrogen dioxide (NO2). The limit of detection (LOD) is as low as 100 ppb. It is worth mentioning that the average power consumption of the sensor is as low as 0.075 mW which is one three-hundredth of that in the DC heating mode. The enhanced sensing performances are attributed to loose and porous structures and the reducing desorption of the target gas driven by pulse heating. The combination of morphology design and pulse-driven strategy makes the MEMS sensors highly attractive for portable equipment and wearable devices.

Enhanced migration and degradation of nitrobenzene in heterogeneous porous media using pulsed direct current electrical resistance heating with hydraulic circulation

Electrical resistance heating (ERH) is a promising in-situ technology for heterogeneous organic contaminated site remediation, yet may have low efficiency when treating semi-volatile organic contaminant (SVOC) of relatively high boiling point. Herein, we chose nitrobenzene as a representative SVOC, and proposed an ERH system powered by pulsed direct current (PDC) with simple hydraulic circulation for improved remediation efficiency in heterogeneous media. The proposed PDC-ERH with hydraulic circulation showed overall improvement in heating performance and energy efficiency, as well as migration and removal of nitrobenzene. This new system improved the uniformity of PDC heating and achieved a temperature increase of ~15°C compared to that using conventional alternating current (AC) of same voltage. Nitrobenzene migration out of the low permeability zone (LPZ) was intensified by the dual effects of heat-induced diffusion enhancement and electric field-induced electroosmotic flow, while subsequent removal was enhanced by electrochemical degradation and volatilization. After 96h, the proposed system has a higher nitrobenzene removal from LPZ (> 97.1%) compared to that using AC (84.0%–95.9%). These results suggest PDC heating coupled with hydraulic circulation was a promising approach for heterogeneous site remediation.

Spatiotemporal dynamic temperature variation dominated by ion behaviors during groundwater remediation using direct current

Direct current (DC) electric field has shown promising performance in contaminated site remediation, in which the Joule heating effect plays an important role but has been previously underappreciated. This study focuses on the spatiotemporal characteristics and mechanism of temperature change in heterogeneous porous media with applied DC. The heating process can be divided into four phases: preferential heating of the low permeability zone (LPZ), rapid heating in the middle region, temperature drop and hot zone shift, and reheating. The dynamic ion behaviors with complex interplays among reactions, electrokinetic-driven migration, and mixed convection induced an uneven redistribution of ions and dominated the heating rate and temperature distribution. The concentration of major ions near the pH jump decreased to 1% of the initial value, even though ions were continuously pumped into the heating zone. This ion depletion caused a drop in current, heating rate, and temperature. Here ions cannot be delivered rapidly into the ion-depleted zone by electromigration due to the potential flattening in the surrounding region. The presence of LPZ intensified the nonuniformity of ion redistribution, where a regional focusing of water-soluble ions was observed, and weakened the temperature rebound compared with that using homogeneous sand. These results provide a new perspective on the regulation of DC heating in site remediation.

A virtual thermometer for ultrahigh-temperature–pressure experiments in a large-volume press

Ultrahigh-temperature–pressure experiments are crucial for understanding the physical and chemical properties of matter. The recent development of boron-doped diamond (BDD) heaters has made such melting experiments possible in large-volume presses. However, estimates of temperatures above 2600 K and of the temperature distributions inside BDD heaters are not well constrained, owing to the lack of a suitable thermometer. Here, we establish a three-dimensional finite element model as a virtual thermometer to estimate the temperature and temperature field above 2600 K. The advantage of this virtual thermometer over those proposed in previous studies is that it considers both alternating and direct current heating modes, the actual sizes of cell assemblies after compression, the effects of the electrode, thermocouple and anvil, and the heat dissipation by the pressure-transmitting medium. The virtual thermometer reproduces the power–temperature relationships of ultrahigh-temperature–pressure experiments below 2600 K at press loads of 2.8–7.9 MN (∼19 to 28 GPa) within experimental uncertainties. The temperatures above 2600 K predicted by our virtual thermometer are within the uncertainty of those extrapolated from power–temperature relationships below 2600 K. Furthermore, our model shows that the temperature distribution inside a BDD heater (19–26 K/mm along the radial direction and <83 K/mm along the longitudinal direction) is more homogeneous than those inside conventional heaters such as graphite or LaCrO3 heaters (100–200 K/mm). Our study thus provides a reliable virtual thermometer for ultrahigh-temperature experiments using BDD heaters in Earth and material sciences.

Determination of Annealing Temperature Regimes for Ferromagnetic Amorphous Wires Prepared by the Ulitovsky–Taylor Method with Direct Current Heating

Determination of Annealing Temperature Regimes for Ferromagnetic Amorphous Wires Prepared by the Ulitovsky–Taylor Method with Direct Current Heating

Effect of Cu or Ni addition to ZnO nanostructures on their n-butanol sensing performance

ZnO nanostructures with two shapes were routinely synthesised using a direct-current heating technique. These structures were coated with metals such as Cu and Ni to enhance the sensor response to n-butanol vapour. The surface modification approach associated with semiconductor materials used in gas sensor applications is essential for improving sensing performance, including the sensor response, selectivity, and stability for specific gases. Previously investigated surface modification approaches mostly involved the addition of noble metals, such as Pd, Pt, and Au. However, these metals are expensive for commercial applications. Herein, surface modification by the addition of non-noble metals is presented as a p–n junction for sensor fabrication. Cu and Ni sputter-coated onto ZnO nanostructures were transformed into CuO and NiO, respectively. The results of the gas-sensing characteristics show that the p–n junction formation of the ZnO–CuO and ZnO–NiO sensors remarkably enhanced the sensor response toward n-butanol. The sensor response of the ZnO–NiO sensor upon exposure to n-butanol at a concentration of 1000 ppm was 1400.0 at a working temperature of 450 °C, whereas that of the ZnO–CuO sensor was 775.9 at the optimum working temperature of 400 °C and an n-butanol concentration of 1000 ppm. Furthermore, these sensors exhibited excellent selectivity toward n-butanol compared to other gases. The sensing mechanism is explained by the large depletion layer width at the boundary of the p–n junction, which improves the sensor response. These results demonstrate a viable approach for manufacturing n-butanol sensors and possibly for constructing a functional active layer in e-nose applications.

Development of a solar-powered vapour absorption cooling system

In this paper, performance evaluation of a developed Solar-Powered Vapor Absorption Refrigeration (VAR) System using the NH3-H2O solution as working fluid is done. The cooling system has total storage space of 0.038 m3 with capacity to accommodate about 0.04 metric tonnes (40kg) of items such as to cool water and other drinks for human comfort applicable in rural regions where electricity is unreliable or non-existent. A solar Photovoltaic (PV) panel of 300W, 40W Direct Current (DC) heating element with a 20A solar controller were designed to power the developed cooling system. Measurements of important operational parameters such as the generator, ambient, evaporator, cabinet and condenser temperatures were studied and measured from the system. Performance evaluation of the system refrigerating capacity was determined in terms of its cooling performance (COP) and the system efficiency ratio (ƞ) based on no load and on load conditions. The system when tested has COP of 0.1275 at an average cabinet temperature (Tr) of 9.0 ℃ against an average room temperature of 25.8 ℃. Additionally, the system had an overall refrigerating efficiency ratio of 8.25. The performance test results revealed that the developed cooling system performed well in terms of temperature regulation for refrigeration purposes

Bi-objective topology optimization for direct current concentration and heat flux cloaking using adaptive weighting method

Bi-objective topology optimization for direct current concentration and heat flux cloaking using adaptive weighting method

Recycle and Reuse of Continuous Carbon Fibers from Thermoset Composites Using Joule Heating.

This study demonstrates a new and sustainable methodology for recycling continuous carbon fibers from end-of-life thermoset composite parts using Joule heating. This process addresses the longstanding challenge of efficiently recovering carbon fibers from composite scrap and reusing them to make fresh composites. The conductive carbon fibers volumetrically heat up when an electric current is passed through them, which in turn rapidly heats up the surrounding matrix sufficiently to degrade it. Fibers can be easily separated from the degraded matrix after the direct current (DC) heating process. Fibers reclaimed using this method were characterized to determine their tensile properties and surface chemistry, and compared against both as-received fibers and fibers recycled using conventional oven pyrolysis. The DC- and oven-recycled fibers yielded similar elastic modulus when compared against as-received fibers; however, an around 10-15 % drop was observed in the tensile strength of fibers recycled using either method. Surface characterization showed that DC-recycled fibers and as-received fibers had similar types of functional groups. To demonstrate the reusability of recycled fibers, composites were fabricated by impregnation with epoxy resin and curing. The mechanical properties of these recycled carbon fiber composites (rCFRCs) were compared against conventional recycling methods, and similar modulus and tensile strength values were obtained. This study establishes DC heating as a scalable out-of-oven approach for recycling carbon fibers.

High-surface-area corundum nanoparticles by resistive hotspot-induced phase transformation

High-surface-area α-Al2O3 nanoparticles are used in high-strength ceramics and stable catalyst supports. The production of α-Al2O3 by phase transformation from γ-Al2O3 is hampered by a high activation energy barrier, which usually requires extended high-temperature annealing (~1500 K, > 10 h) and suffers from aggregation. Here, we report the synthesis of dehydrated α-Al2O3 nanoparticles (phase purity ~100%, particle size ~23 nm, surface area ~65 m2 g−1) by a pulsed direct current Joule heating of γ-Al2O3. The phase transformation is completed at a reduced bulk temperature and duration (~573 K, < 1 s) via an intermediate δʹ-Al2O3 phase. Numerical simulations reveal the resistive hotspot-induced local heating in the pulsed current process enables the rapid transformation. Theoretical calculations show the topotactic transition (from γ- to δʹ- to α-Al2O3) is driven by their surface energy differences. The α-Al2O3 nanoparticles are sintered to nanograined ceramics with hardness superior to commercial alumina and approaching that of sapphire.

The effects of driving time scales on coronal heating in a stratified atmosphere

Aims. We investigate the atmospheric response to coronal heating driven by random velocity fields with different characteristic time scales and amplitudes. Methods. We conducted a series of three-dimensional magnetohydrodynamic simulations of random driving imposed on a gravitationally stratified model of the solar atmosphere. In order to understand differences between alternating current (AC) and direct current (DC) heating, we considered the effects of changing the characteristic time scales of the imposed velocities. We also investigated the effects of the magnitude of the velocity driving. Results. In all cases, complex foot point motions lead to a proliferation of current sheets and energy dissipation throughout the coronal volume. For a given driving amplitude, DC driving typically leads to a greater rate of energy injection when compared to AC driving. This ultimately leads to the formation of larger currents, increased heating rates, and higher coronal temperatures in DC simulations. There is no difference in the spatial distribution of energy dissipation across simulations; however, energy release events in AC cases tend to be more frequent and last for less time than in DC cases. This results in more asymmetric temperature profiles for field lines heated by AC drivers. Higher velocity driving is associated with larger currents, higher temperatures, and the corona occupying a larger fraction of the simulation volume. In all cases, the majority of heating is associated with small energy release events, which occur much more frequently than larger events. Conclusions. When combined with observational results that highlight a greater abundance of oscillatory power in lower frequency modes, these findings suggest that energy release in the corona is more likely to be driven by longer time scale motions. In the corona, AC and DC driving occur concurrently and their effects remain difficult to isolate. The distribution of field line temperatures and the asymmetry of temperature profiles may reveal the frequency and longevity of energy release events and therefore the relative importance of AC and DC heating.

Consolidation and high‐temperature strength of monolithic lanthanum hexaboride

AbstractIn this study we explored the densification, microstructure evolution, and high‐temperature properties of bulk lanthanum hexaboride. LaB6 bulks were consolidated using spark‐plasma sintering only in the temperature range between 1400°C and 1700°C. We adopted flash spark plasma sintering (SPS) of LaB6 using a direct current heating without a graphite die. We observed a peculiar grain‐size gradient when coarse grains exceeding 300 μm were observed on the top side of the specimen, while the bottom side had a grain size of 15–20 μm. Such large grain was not observed using SPS at 2000°C, suggesting that these might originate from a local overheating.Based on the three‐point flexural tests, it was observed that the toughness and strength of the LaB6 were acceptable at room‐temperature (3.1 ± 0.2 MPa m1/2, 300 ± 20 MPa). However, at 1600°C, these parameters would decrease to 1.3 ± 0.1 MPa m1/2 and 120 ± 40 MPa, respectively.

Определение температурных режимов отжига ферромагнитных аморфных проводов, полученных методом Улитовского – Тейлора, при нагреве прямым пропусканием тока

The direct current (dc) heating effect of ferromagnetic amorphous wires (AW) on the electromagnetic properties of the serial Co-based alloy, Co – Fe – Cr – Si – B, is investigated. The Ulitovsky – Taylor method was used to produce AW with diameters D = 40, 70, 82, 98, 123, and 145 μm in a glass shell, that was removed mechanically by elastic bending on a laboratory bench. The developed in situ method of stepwise cyclic dc heating of AW of various diameters enables to choose the optimal values of the current (Ia) for carrying out the selected modes that maximize the magnetic properties. AW electromagnetic properties were monitored by registering the amplitude of the intrinsic electromagnetic signal of electromotive force (EMF) of the AW sample under study. Since reliable direct measurements of AW temperature (Ta) when passing the current (Ia) quite an undertakings, we used indirect method of AW heating temperature estimation by establishing the relationship Ta = f (Ia). For the AW specified diameters, the direct current values were experimentally determined, which ensure optimal heat treatment in the range of temperature stability of the amorphous phase, up to the crystallization temperature, Tx. A calibration curve was constructed using reference temperature points, i.e. Tx and the Curie temperature (Tc). The proposed technique for calibration graph construction I = f(D) may be used for different AWs that have different diameters and same composition; it allows one to determine the modes of current annealing required for the best EMF amplitude values of amorphous wires of the given diameter, up to 100 μm.

Comparative analysis of two-level and three-level multilevel inverter for electric vehicle application using BLDC motor drive

PurposeThe conventional two-level inverter suffers from harmonics, higher direct current (DC) link voltage requirement, higher dv/dt and heating of the rotor. This study aims to overcome by using a multilevel inverter for brushless DC (BLDC) drive.Design/methodology/approachThis paper presents a comparative analysis of the conventional two-level and three-level multilevel inverter for electric vehicle (EV) application using BLDC drive.FindingsA three-level Active Neutral Point Clamped Multilevel inverter (ANPCMLI) is proposed in this paper which provides DC link voltage control. Simulation studies of the multilevel inverter and BLDC motor is carried out in MATLAB.Originality/valueThe ANPCMLI fed BLDC simulation results shows that there is the significant reduction in the BLDC motor torque ripple, switching stress and harmonic distortion in the BLDC motor fed ANPCMLI compared to the conventional two-level inverter. A prototype of ANPCMLI fed BLDC drive along with field programmable gate array (FPGA) control is built and MATLAB simulation results are verified experimentally.

Thermoelectric building temperature control: a potential assessment

This study focuses on thermoelectric elements (TEE) as an alternative for room temperature control. TEE are semi-conductor devices that can provide heating and cooling via a heat pump effect without direct noise emissions and no refrigerant use. An efficiency evaluation of the optimal operating mode is carried out for different numbers of TEE, ambient temperatures, and heating loads. The influence of an additional heat recovery unit on system efficiency and an unevenly distributed heating demand are examined. The results show that TEE can provide heat at a coefficient of performance (COP) greater than one especially for small heating demands and high ambient temperatures. The efficiency increases with the number of elements in the system and is subject to economies of scale. The best COP exceeds six at optimal operating conditions. An additional heat recovery unit proves beneficial for low ambient temperatures and systems with few TEE. It makes COPs above one possible at ambient temperatures below 0 ^circ C. The effect increases efficiency by maximal 0.81 (from 1.90 to 2.71) at ambient temperature 5 K below room temperature and heating demand dot{Q}_h={100} W but is subject to diseconomies of scale. Thermoelectric technology is a valuable option for electricity-based heat supply and can provide cooling and ventilation functions. A careful system design as well as an additional heat recovery unit significantly benefits the performance. This makes TEE superior to direct current heating systems and competitive to heat pumps for small scale applications with focus on avoiding noise and harmful refrigerants.

Evolution of the Microstructure of a CuCr1Zr Alloy during Direct Heating by Electric Current

Round tensile test specimens of an age-hardened CuCr1Zr alloy were subjected to direct electrical current heating in a Gleeble thermal–mechanical simulator at 800 °C. The mechanical properties were monitored by the Vickers hardness test, and the changes in the grain structure were examined by light metallography. A quantitative analysis of the size and distribution of fine precipitates during annealing was carried out using transmission electron microscopy (TEM). The grain structure showed a gradient corresponding to the gradient of the temperature on the test piece. Annealing for 60 s at 800 °C resulted in a partially (~50%) recrystallized structure with new grains about 45 μm in diameter. In the as-delivered condition, TEM documented tiny (1 to 4 nm) coherent chromium precipitates inducing strain fields in the matrix. During overaging, the particles lost their coherence and gradually coarsened up to a mean diameter of 40 nm after 300 s at 800 °C. The coarsening kinetics obeys Lifshitz, Sloyzov, and Wagner’s theory.

Instantaneous nanowelding of ultra‐high temperature ceramics for hypersonics

AbstractUltra‐high temperature ceramics (UHTCs) are a group of advanced ceramic materials that possess excellent high temperature capabilities, which make them especially suitable for extreme environment engineering applications. As an effective assembling method, joining is frequently required for fabricating sophisticated structures for such applications due to the excessive challenges and costs in producing near‐net shapes. Here, we introduce a promising new joining technique to effectively join UHTCs called Instantaneous Nanowelding, which uses direct electric current assisted rapid Joule heating to instantaneously bond hafnium diboride (HfB2) to zirconium diboride (ZrB2) in 1 s down to atomic scale. Our approach is analogous to high temperature spot welding, and the entire process is complete in 10 min, and the instant diffusion occurs in 1 s. Seamless HfB2/ZrB2 interfaces are formed at 1750 for a duration of 1 s. A series of characterizations are done at the interfaces using techniques including SEM, WDS, EBSD, and S/TEM to observe ZrxHf1−xB2 solid solution formation. Highly coherent transition with perfect lattice alignment at atomic scale from ZrB2 to HfB2 is observed using S/TEM, meaning that the two materials are brought to atomic contact.

Compound self-heating strategies and multi-objective optimization for lithium-ion batteries at low temperature

Rapid and effective battery preheating for thermal management is particularly significant to overcome the performance limitation of batteries and guarantee the efficient operation of electric vehicles in cold environments. A low-temperature compound self-heating (CSH) strategy integrating the inner-battery direct-current heating and outer-battery electric heating is proposed to enhance heating efficiency and shorten heating duration without the requirement of extra power supplies. Computationally efficient distributed thermal equivalent circuit models, to capture the temperature distribution within batteries, are developed and experimentally validated with good accuracy. Four typical CSH methods are systematically discussed and compared in terms of the heating rate, temperature uniformity, energy consumption, capacity fade, and fabrication and safety challenge. The CSH method with electric heaters installed on the largest battery surfaces is found preferable due to its relatively easy implementation and low safety risk, and slightly small temperature gradient within the battery. Three crucial yet competing objectives, the heating time, temperature gradient, and capacity fade, are formulated for the favorable CSH method, and the Pareto front is obtained using the multi-objective optimization algorithm. An optimal low-temperature CSH method is thus proposed, where the battery is heated from −30 °C to 2 °C within 62.1 s. Compared with the direct-current heating method, the proposed optimal CSH method strengthens the heating rate by 60.8%, reduces energy consumption by 54.8%, and relieves battery degradation by 45.2%.

Bio-inspired deposition of electrochemically exfoliated graphene layers for electrical resistance heating applications

Electrochemically exfoliated graphene (eeG) layers possess a variety of potential applications, e.g. as susceptor material for contactless induction heating in dynamic electro-magnetic fields, and as flexible and transparent electrode or resistivity heating elements. Spray coating of eeG dispersions was investigated in detail as a simple and fast method to deposit both, thin conducting layers and ring structures on polycarbonate substrates. The spray coating process was examined by systematic variation of dispersion concentration and volume applied to heated substrates. Properties of the obtained layers were characterized by UV-VIS spectroscopy, SEM and Confocal Scanning Microscopy. Electrical conductivity of eeG ring structures was measured using micro-four-point measurements. Modification of eeG with poly(dopamine) and post-thermal treatment yields in the reduction of the oxidized graphene proportion, an increase in electrical conductivity, and mechanical stabilization of the deposited thin layers. The chemical composition of modified eeG layer was analyzed via x-ray photoelectron spectroscopy pointing to the reductive behavior of poly(dopamine). Application oriented experiments demonstrate the direct electric current heating (Joule-Heating) effect of spray-coated eeG layers.

Investigating the effect of load on tribological behaviour of Cu composite reinforced with Ti2SnC particles

Purpose This paper aims to study the effect of load on the tribological behaviour of Cu-based composites, so as to obtain a suitable applied load on these composites. Design/methodology/approach Cu-based composites were prepared by powder sintering with direct current electric current heating and tested by Universal Mechanical Test-3 with a ball-on-disk at room temperature. Findings The results showed that Cu-based composites are might suitable for working under low load. There is only mild damage on the surface under a load of 2 N. While it has microcracks and shows signs of cavitation at a certain depth at 20 N and 50 N. In addition, it is evident that there are three zones in the cross-section of the matrix, namely, a mechanical mixing layer, ceramic layer and substrate, respectively. Originality/value There are two wear mechanisms at different loads, and the evolution of worn surfaces with sliding time is also involved. Thus, the developed material can be used for light load sliding electrical contact material applications.