Temperature Coefficient Research Articles

AP-1000 fuel assembly performance with UO2 and UO2/U3Si2 fuels and silicon carbide cladding from the viewpoint of neutronics

ABSTRACT Accident Tolerate Fuels have been highly researched since the Fukushima disaster. To improve the safety of the AP-1000 fuel assembly, an advanced fuel, UO2/U3Si2, is considered. In addition, the silicon carbide (SiC) cladding that has the capability of reducing oxidation is compared with the baseline Zircaloy for AP-1000 fuel assembly along with the two different fuel cases (UO2 and UO2-U3Si2). The present study focuses on the neutronic performance of the UO2/U3Si2 fuel and thus the main neutronic parameters such as the fuel cycle length, pin power distribution, atom density evolution of main isotopes, and the reactivity feedback coefficients are evaluated. An increase of 6.72% in the criticality period is introduced when 70%UO2-30%U3Si2 fuel with SiC cladding is considered. The pin power peaking factors, fuel temperature coefficients, and moderator temperature coefficients of the proposed fuel result in very few changes. For instance, the maximum pin power distribution difference between 70%UO2-30%U3Si2 and UO2 fuel with SiC cladding is 0.001, which is negligible. Thus, its performance is as good as the traditional UO2 fuel from the neutronic aspects and controlling power distribution.

Sintering behaviors and microwave dielectric properties of BaO–MgO–SiO2 ternary ceramics

AbstractIn the present work, five compositions in the BaO–MgO–SiO2 ternary system were chosen, and ceramics were prepared using the solid‐state reaction method. Single phases were formed easily for the first four compositions, and BaMgSi3O8 ceramics were found to be a mixture of both BaSi2O5 and MgSiO3, according to X‐ray diffraction results. Among all the compositions, Ba2MgSi2O7 ceramic sintered at 1225°C possesses the highest Qf (Q = 1/dielectric loss = 1/tanδ, f = resonant frequency) value ∼55 010 GHz along with relative permittivity ∼8.0 and temperature coefficient of resonant frequency (TCF) ∼−57.5 ppm/°C. With 3 wt.% BCB (BaO–B2O3–CuO) additions, Ba2MgSi2O7 ceramic was well densified at 950°C with a relative permittivity ∼8.1, Qf value ∼28 920 GHz (at 12.37 GHz) and TCF value ∼‒56.6 ppm/°C. These series ceramics with low relative permittivity values might be good candidates for low‐temperature co‐fire ceramic technology substrate applications.

Tracking the maximum power point of solar panels through direct estimation of optimum voltage with temperature

Abstract Electricity production from photovoltaic (PV) panels is maximized when the operating point is located at the maximum power point thanks to dedicated controllers. These controllers are driven to track the maximum power by using various algorithms within distributed or centralized architectures accounting for factors such as partial irradiation and temperature changes. The effect of irradiance on the optimal panel voltage is weak or even negligible, while it is strong and quasi-linear-dependent on temperature. Based on this observation, this article introduces a straightforward method for tracking the maximum power of a PV panel by using an optimizer, focusing solely on its temperature response as an input variable. The proposed approach hinges on linearizing the relationship between panel temperature and operating voltage. This relationship enables the estimation of the maximum power point through temperature measurement alone. Thus, after determination of the linear temperature coefficient of the voltage requiring only the knowledge of two optimal voltages at different temperatures, for example from the datasheet of the panel, the power tracking involves only one temperature sensor placed on the panel alongside a voltage sensor for regulation. The principle, modelling, and validation post-panel ageing of the method are detailed in this paper. Simulation, conducted using real experimental irradiation and temperature data, attests to the effectiveness of the control. Results indicate an average effectiveness of the method of >99.1% in tracking the maximum power, with the panel generating 2.33 kWh out of a possible 2.35 kWh. This performance is comparable to that of tracking devices employing more complex algorithms. The simplicity and efficiency of the method make it a promising option for maximizing the power production at low cost from PV systems in small or residential, on- or off-grid connected applications.

Particle size effect on surface/interfacial tension and Tolman length of nanomaterials: A simple experimental method combining with theoretical.

Surface tension and interfacial tension are crucial to the study of nanomaterials. Herein, we report a solubility method using magnesium oxide nanoparticles of different radii (1.8-105.0nm, MgO NPs) dissolved in pure water as a targeted model; the surface tension and interfacial tension (and their temperature coefficients) were determined by measuring electrical conductivity and combined with the principle of the electrochemical equilibrium method, and the problem of particle size dependence is discussed. Encouragingly, this method can also be used to determine the ionic (atomic or molecular) radius and Tolman length of nanomaterials. This research results disclose that surface/interfacial tension and their temperature coefficients have a significant relationship with particle size. Surface/interfacial tension decreases rapidly with a radius <10nm (while the temperature coefficients are opposite), while for a radius >10nm, the effect is minimal. Especially, it is proven that the value of Tolman length is positive, the effect of particle size on Tolman length is consistent with the surface/interfacial tension, and the Tolman length of the bulk does not change much in the temperature range. This work initiates a new era for reliable determination of surface/interfacial tension, their temperature coefficients, ionic radius, and Tolman length of nanomaterials and provides an important theoretical basis for the development and application of various nanomaterials.

The dynamic of photovoltaic resources on its performance predictability, based on two new approaches

AbstractThe manuscript is a digest, which puts forward findings from previous research papers, combined with new proposals. Approaches comprise two full models' derivation for photovoltaic (PV) systems energy conversion predictability. It brings in several models for key physical observables formulated as functions of the operating conditions. The proposals encompass mean spectral reflectance, coefficient for reflections and spatial geometry, incident angular losses factor, angular losses, and fill factor along with its coefficient of temperature. Applying the superposition principle, these models are integrated into two full approaches for performance predictability. The underlying physics description is mathematically consistent with experimental measurements of the physical observables involved, reported in other studies. To the authors' knowledge, these full models have been reported previously nowhere. Simulation results from the more inaccurate of two full models show good agreement of these findings with the experimental evidence, reported of its performance. The resulting key performance indicators (KPIs), after simulating a grid‐connected PV system located in Cuba, yield 1.61%, 13.10%, −1.61%, 2.02%, and 0.81 of MAE, MAPE, MBE, RMSE, and R2, respectively, which they confirm the model's good behavior. Approaches formulations, as functions of solar irradiance and module temperature, its derivations, applications, and model's simulation results are considered the main manuscript novelties.

A 8.83 ppm/°C temperature coefficient, 75 dB PSRR subthreshold CMOS voltage reference with piecewise curvature compensation

A subthreshold CMOS voltage reference (CVR) with low temperature coefficient (TC) over a wide temperature range and low power is proposed in this paper. The proposed CVR utilizes the ΔVGS of different-threshold and same-threshold nMOS pairs to generate complementary-to-absolute-temperature (CTAT) and proportional-to-absolute-temperature (PTAT) voltages, respectively. To compensate for the low-temperature and high-temperature segments of the temperature characteristic curve, the nonlinear compensation currents generated by the exponential-like relationship between the drain current and the gate-source voltage of two MOSFETs work in the subthreshold region is used. Based on a 0.18-μm CMOS process, post-layout simulation results show that the proposed CVR achieves an average output voltage of 263 mV. The power supply ripple rejection (PSRR) is −75 dB at 10 Hz and the line sensitivity (LS) is 0.0069 %/V when the supply voltage varies from 0.8 V to 2.5 V. The average TC is 8.83 ppm/°C for a wide temperature range of −40 °C–120 °C, and the minimum TC is only 3.65 ppm/°C.

Positive temperature coefficient material based on silicone rubber/ paraffin/ graphite/ carbon nanotubes for wearable thermal management devices

PTC materials provide substantial advantages such as adaptive temperature control performance and excellent safety. However, their use in wearable devices has been limited due to the essential requirements for flexibility and stability. This study prepared a new type of flexible PTC material, with a PTC intensity of 6.3 and a resistivity of only 400 Ω·cm in the low-temperature region. The flexibility of the material is evidenced by its 2 mm bending diameter and its ability to maintain structural integrity even after 100 bends. Furthermore, experimental evidence proves that PTC material has excellent thermal stability and can withstand extreme temperatures ranging from −20 °C to 120 °C. In the thermal control experiment, the PTC material maintains a temperature of approximately 25 °C to accommodate the requirements of the human body in a cold environment. When compared to the conventional PI heating sheet, the newly prepared PTC material exhibits advantages such as rapid response, adaptive temperature control performance, and safety. Consequently, it presents a broad application prospect in the field of wearable heating devices.

High–performance copper–substituted La0.5Sr0.5CoO3 ceramics as economical functional materials for thick film resistors

The demand for cost–effective materials for thick film resistors has driven the exploration of alternative functional materials to replace the traditionally used ruthenium oxides. This study investigates the synthesis and properties of copper–substituted La0.5Sr0.5CoO3 (La0.5Sr0.5Co1-xCuxO3, LSCCu, x = 0.02–0.10) ceramics as a potential economical substitute. The crystal structure, electrical performance, and sintering behavior of LSCCu with varying Cu2+ contents were characterized through solid–state reactions and first–principles simulations. The results indicate that the perovskite structure is maintained with increasing Cu2+, while the densification temperature, crystallinity, and conductivity decrease. Moreover, Cu2+ substitution reduced the DOS across the Fermi level and weakened the electron transport in LSCCu. The sample with x = 0.06 exhibited a promising conductivity of 2609 S/cm after sintering at 1150 °C, comparable to commercial thick film resistor materials. The temperature coefficient of resistance (TCR) of LSCCu showed a metallic behavior with a low value of 1148 ppm/°C for the x = 0.06 sample. Additionally, the LSCCu ceramics possess good long–term stability and frequency stability of resistance. These findings suggest that LSCCu ceramics are a promising economical material for thick film resistor applications.

Substitution of Sn in the high-permeability MnZn ferrite for wide temperature applications

To meet the challenge of varied working temperatures of inductance components in new energy vehicle and 5G communication, the high-TC high-permeability MnZn ferrite with excellent temperature stability was developed by the addition of SnO2. In this series of samples, initial permeability μi maintains large values in a wide temperature range. With increasing the SnO2 content, the temperature of the second permeability peak Tsp decreases and meanwhile Curie temperature TC maintains as high as 160 °C. For the best sample with 6000 ppm SnO2, μi at 25 °C is 7244 and exhibits the excellent temperature stability with the low specific temperature coefficient of 0.35 × 10−6 °C−1 between 25 and 130 °C. The addition of SnO2 generates Fe2+ and adjusts the magneto-crystalline anisotropy constant K1 = 0 point, which is responsible for the wide-temperature high permeability. The effect of SnO2 addition on magnetization process has also been clarified.

Effect of high pressure torsion on magnetic properties and corrosion resistance of MnBi/NdFeB composite magnets

The MnBi/NdFeB composite magnets have been fabricated by high pressure torsion (HPT). The effects of NdFeB content, torsional pressure and torsional degree on the microstructures, magnetic properties, and corrosion resistance of the MnBi/NdFeB composite magnets are systematically investigated. The results show that the remanent magnetization (Mr) of MnBi/NdFeB composite magnets increases with the Nd2Fe14B content. A peak value of the maximum energy product ((BH)max) = 5.61 MGOe is obtained while the Nd2Fe14B content is 75 wt%. Addition of MnBi increases the coercivity temperature coefficient and the density of MnBi/NdFeB composite magnets. The MnBi/NdFeB composite magnets prepared by HPT show perpendicular anisotropy, which can be explained by the (0kl) texture in the perpendicular direction observed by TEM. With the increase of degree of HPT, the intrinsic coercivity (Hcj) difference between perpendicular direction and parallel direction is more obvious, the (0kl) texture is enhanced by the degree of HPT. The first-order reversal curve (FORC) demonstrates that MnBi/NdFeB composite magnets exhibits weaker exchange coupling compared with pure MnBi magnet. Besides, a remarkably improvement in electrochemical stability for the MnBi/NdFeB composite magnet is achieved with the MnBi added.

Operation up to 225°C of NiO/ β-(Al0.21Ga0.79)2O3 /Ga2O3 Heterojunction Lateral Rectifiers

The characteristics of NiO/ β-(Al0.21Ga0.79)2O3 /Ga2O3 heterojunction lateral geometry rectifiers with the epitaxial layers grown by Metal Organic Chemical Vapor Deposition were measured over the temperature range from 25-225°C. The forward current increased with temperature, while the on-state resistance decreased from 360 Ω•cm2 at 25°C to 30 Ω.cm2 at 225°C. The forward turn-on voltage was reduced from 4 V at 25°C to 1.9 V at 225°C. The reverse breakdown voltage at room temperature was ~4.2 kV, with a temperature coefficient of -16.5 V/K. This negative temperature coefficient precludes avalanche being the breakdown mechanism and indicates that defects still dominate the reverse conduction characteristics. The corresponding power figures-of-merit were 0.27-0.49 MW.cm-2. The maximum on/off ratios improved with temperature from 2105 at 25°C to 3107 at 225°C when switching from 5 V forward to 0 V. The high temperature performance of the NiO/ β-(Al0.21Ga0.79)2O3 /Ga2O3 lateral rectifiers is promising if the current rate of optimization continues.

Post-Fire Mechanical Properties of Half-Grouted Sleeve Connectors with Grouting Defects

Half-grouted sleeve connectors are a primary method for connecting rebar in prefabricated concrete structures. However, due to limitations in the construction environment, all kinds of grouting defects are inevitable, especially grouting voids. Additionally, fire disasters, among the most common types of disasters, significantly threaten the structural performance and safety of these prefabricated structures. Therefore, it is imperative to determine the mechanical properties of half-grouted sleeve connectors with grouting voids after high temperatures. This study designed and prepared 48 groups of half-grouted sleeve specimens with different grouting voids and defect locations. These specimens were heated to the specified temperature (25 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C), followed by unidirectional tensile testing after natural cooling. The experimental results showed that rebar fracture failure and rebar pulled-out failure were the failure modes of specimens. With the increase in temperature, bearing capacity, safety factor and ductility coefficient of specimens all decreased. When the temperature was lower than 400 °C, the specimen with void length less than twice the diameter of the rebar (i.e., 2d) had sufficient connection performance. For specimens with the same total void lengths, the bearing capacity of discrete voids is lower than concentrate voids at the same temperature. The load-displacement curve, safety coefficient, ductility coefficient and grey correlation degree of half-grouted sleeve specimens with grouting voids at different temperatures are analyzed and discussed, and the bond stress slip constitutive model is given. Grouting defects have greater influence on specimens after grey correlation analysis. Findings from this study provide valuable references for the safety performance evaluation of prefabricated structures with half-grouted sleeve connectors after exposure to fire.

Semiconductor Nanoparticle Anchored Single-Walled Carbon Nanotubes for a Bolometer.

The bolometer is developed using single-walled carbon nanotubes (SWCNT) anchored with semiconductor nanoparticles of cadmium sulfide, stannous disulfide, and zinc oxide (ZnO). The bolometric responses were recorded at varying temperatures from 10 K to room temperature. The anchored SWCNTs provided a higher temperature coefficient of resistance (TCR) than pristine SWCNTs. The largest TCR is recorded from SWCNTs/ZnO (-0.11%/K) at room temperature, which is 200% higher than pristine SWCNTs. The largest photoresponsivities of SWCNTs/ZnO under near-infrared (NIR) and wide wavelength source (200-1200 nm) illuminations are 5.06 and 37.51 mV/W, respectively. The extraordinary performance of SWCNTs/ZnO stands out at ∼17 × 104% under IR illumination. The study presents a significant advancement in the development of high-performance SWCNT bolometric materials by anchoring with semiconductor nanoparticles.

Tensile and compressive properties of bamboo scrimber under different temperature conditions

AbstractBamboo scrimber demonstrates vulnerability to environmental temperature fluctuations, such as exposure to cold or fire, when deployed in structural applications. Consequently, its mechanical properties can substantially diverge from the intended design values under varying thermal conditions. This study aims to study the tensile and compressive properties of bamboo scrimber under different temperatures to provide data support for studying bamboo scrimber under low and high temperatures. The compressive properties of bamboo scrimber under temperatures ranging from −30°C to 250°C and the tensile properties under −20°C to 250°C were determined by a series of tests with a total of 125 specimens. The results show that the mass loss of bamboo scrimber increases gradually with the increase in temperature, and the increasing trend intensifies after 120°C. With the increase of temperature, the failure mode of the specimens under compression changes from the bottom compression cracking damage to the local destabilization of longitudinal fibers, while the tensile damage modes aren't influenced by temperature, and both “straight‐line” and “folded‐line” types of damage modes occur at different temperatures. The tensile and compressive strengths and elastic modulus of the specimens decreased with the increase in temperature, and the strength was more susceptible to the temperature than the elastic modulus: a rise in temperature from 20°C to 250°C resulted in a reduction of compressive strength and tensile strength by 80.80% and 84.11%, respectively, the compressive modulus and tensile modulus experienced decreases of 49.51% and 53.28%. Furthermore, equations of temperature influence coefficients of strength and elastic modulus were established based on the test results.Highlights Bamboo scrimber's mechanical properties under different temperatures are studied. Tendency and explanation of temperature influence coefficients are analyzed. Temperature coefficient equations for strength and elastic modulus are proposed.

High-performance GeSi/Ge multi-quantum well photodetector on a Ge-buffered Si substrate.

This work demonstrates a high-performance photodetector with a 4-cycle Ge0.86Si0.14/Ge multi-quantum well (MQW) structure grown by reduced pressure chemical vapor deposition techniques on a Ge-buffered Si (100) substrate. At -1 V bias, the dark current density of the fabricated PIN mesa devices is as low as 3 mA/cm2, and the optical responsivities are 0.51 and 0.17 A/W at 1310 and 1550 nm, respectively, corresponding to the cutoff wavelength of 1620 nm. At the same time, the device has good high-power performance and continuous repeatable light response. On the other hand, the temperature coefficient of resistance (TCR) of the device is as high as -5.18%/K, surpassing all commercial thermal detectors. These results indicate that the CMOS-compatible and low-cost Ge0.86Si0.14/Ge multilayer structure is promising for short-wave infrared and uncooled infrared imaging.

Improvement of magnetic performance of Nd-Ce-Fe-B sintered magnets via Pr-Co-Ga grain boundary reconstruction

Grain boundary reconstruction is a commonly used method to improve the coercivity of Nd-Ce-Fe-B magnets but at the expense of a notable reduction in remanence. In this study, we present an effective approach to achieving a balance between remanence and coercivity of Nd-Ce-Fe-B magnets through Pr-Co-Ga grain boundary reconstruction. Compared to the original Nd0.7-Ce0.3-Fe-B magnet, the remanence of the magnet with 4 wt% Pr-Co-Ga addition decreased only from 13.09 kGs to 12.8 kGs, while the coercivity remarkably increased from 10.95 kOe to 14.84 kOe. Additionally, the coercivity temperature coefficient (20–150 °C) was improved from − 0.606 %/°C to − 0.547 %/°C, and the Curie temperature was increased from 278.4 °C to 285.1 °C, demonstrating excellent thermal stability. XRD refinement analysis showed a slight decrease in the main phase ratio, accompanied by a slight increase in orientation, resulting in a slight decrease in remanence. SEM and EPMA observations revealed that Pr preferentially replaced Ce on the grain surface, forming a “Pr-rich” shell with an enhanced anisotropy field. TEM analysis showed that the magnets with PCG addition exhibit a continuous Fe-lean grain boundary phase, weakening the exchange coupling of the adjacent grains. The synergistic effect of the “Pr-rich” shell formation and grain boundary optimization effectively enhanced the coercivity.

Wind-tunnel experiments on cross-ventilative cooling in a generic isolated building with one heated wall: Impact of opening size

This paper presents wind-tunnel experiments of cross-ventilative cooling in a generic isolated building with an interior heated side wall. Two different sizes of openings are considered: large and small openings. Particle image velocimetry (PIV) is used to determine velocities in the vertical centerplane. Air temperatures in the vertical centerplane are measured using negative temperature coefficient (NTC) sensors. Surface temperatures on the heated wall are measured using an infrared camera. Surface heat fluxes are obtained using heat flux sensors. In both cases the indoor airflow is dominated by the jet through the openings, with higher velocities in the building with large openings. The air temperatures measured with small openings are up to 7.5 % larger than those with large openings. The surface heat fluxes are up to 20 % higher in the building with large openings. The interior convective heat transfer coefficients vary considerably across the heated wall for both opening sizes and can be very different (up to 5 times higher) from those obtained by existing internal convective heat transfer coefficient correlations. The measurement results give insight into the complexity of ventilative cooling and can be used to validate computational fluid dynamics (CFD) simulations of cross-ventilative cooling.

Structure and physical properties of multicomponent films based on the Fe-Si-B system

The influence of modernized three-electrode ion-plasma sputtering of a complex Fe–Si–B– (Cu, Nb)/(Ni, Mo) target on the structure and properties of sputtered films was studied. The formation of amorphous and nanocrystalline phases in Fe73Si15.8B7.2-(Cu, Nb)4 and Fe78.5Si6B14-(Ni, Mo)1.5 films with a coherent scattering region size of 1.6 nm and 12 nm, respectively, was established as a result of a modernized three-electrode ion - plasma sputtering. The thermal stability of metastable states of films as well as electrical and magnetic properties of freshly prepared and heat-treated films has been investigated. The conditions for obtaining films with low values of the temperature coefficient of electrical resistance (−0.9∙10−5 K−1) and coercive force (HC ∼11 A/m) have been determined.

Characterization of Magnetoresistive Shunts and Its Sensitivity Temperature Compensation.

The main purpose of the paper is to show how a magnetoresistive (MR) element can work as a current sensor instead of using a Wheatstone bridge composed by four MR elements, defining the concept of a magnetoresistive shunt (MR-shunt). This concept is reached by considering that once the MR element is biased at a constant current, the voltage drop between its terminals offers information, by the MR effect, of the current to be measured, as happens in a conventional shunt resistor. However, an MR-shunt has the advantage of being a non-dissipative shunt since the current of interest does not circulate through the material, preventing its self-heating. Moreover, it provides galvanic isolation. First, we propose an electronic circuitry enabling the utilization of the available MR sensors integrated into a Wheatstone bridge as sensing elements (MR-shunt). This circuitry allows independent characterization of each of the four elements of the bridge. An independently implemented MR element is also analyzed. Secondly, we propose an electronic conditioning circuit for the MR-shunt, which allows both the bridge-integrated element and the single element to function as current sensors in a similar way to the sensing bridge. Third, the thermal variation in the sensitivity of the MR-shunt, and its temperature coefficient, are obtained. An electronic interface is proposed and analyzed for thermal drift compensation of the MR-shunt current sensitivity. With this hardware compensation, temperature coefficients are experimentally reduced from 0.348%/°C without compensation to -0.008%/°C with compensation for an element integrated in a sensor bridge and from 0.474%/°C to -0.0007%/°C for the single element.

A Study of the Thermal Management and Discharge Strategies of Lithium-Ion Batteries in a Wide Temperature Range

The performance of lithium-ion batteries is greatly influenced by various factors within their operating environment, which can significantly impact their overall efficiency and effectiveness. In this paper, a multi-physics field electrochemical thermal model is established to measure the physical parameters of a battery module during the charge/discharge process. The effects of working temperature, current rate, and convective heat transfer coefficient are investigated by establishing an electrochemical and thermal model. The results are obtained by conducting numerous parameterized scans to analyze the system’s state across various operating conditions, enabling the determination of its temperature and the selection of appropriate cooling measures accordingly. Based on the internal and external conditions of battery operation, parameter selection corresponding to the operating range is divided into several stages, with thermal management strategies provided for each stage. The existing framework facilitates the design of battery packs equipped with efficient thermal management strategies, thereby enhancing the battery systems’ reliability and performance. Furthermore, it aids in establishing optimal operational and safety boundaries for batteries.