Steady-state Temperature Research Articles

Mitigation of thermal artifacts in 100kHz ultrafast 2D IR spectroscopy.

Ytterbium lasers make possible shot-to-shot data collection of two-dimensional infrared (2D IR) spectra at 100kHz and higher repetition rates. At those rates, the power absorbed by the sample is appreciable and creates a steady state temperature rise and an accumulated thermal grating artifact in the spectra that can obscure weak or low concentration IR chromophores. We report the magnitude of the temperature rise, the pulse ordering by which it is created, and ways to mitigate it. Using a calibrant molecule, we measured a steady-state temperature up to 32.5 and 45 °C for laser light at 4 µm in H2O and 6 µm in D2O, respectively, for a typical optical density used in 2D IR experiments. The temperature reached a steady state in ∼60s. The temperature rise scales with the integrated optical density of the sample across the laser spectrum. By cooling the sample cell, we returned the steady state temperature to room temperature within the laser focus. For samples that undergo rotation, the accumulated thermal grating artifact is removed using a perpendicular ⟨XXYY⟩ polarization because the permuted time-orderings of the thermal grating artifact has the orientational response ⟨XYXY⟩, which decays to zero during the delay between consecutive laser pulses. The procedure described in this study can be used to characterize and minimize the thermal effects in experiments where repetition rate and/or pulse energy cause an appreciable temperature rise.

Experimental study on dynamic flow and heat transfer performance of silicon-based microchannel under variable thermal load

The issue of high power density in chips has become one of the bottlenecks restricting the improvement of chip performance. Silicon-based microchannel heat sinks (Si-MCHS) can guide the cooling fluid close to the chip junction, significantly enhancing the cooling capability. Due to the rapid changes in chip power consumption, understanding the flow and heat transfer performance of Si-MCHS, especially their dynamic heat transfer performance, is crucial. This paper introduces the fabrication of Si-MCHS and experimentally tests its static and dynamic performance. The microchannels can handle a maximum thermal flux of 71.3 W/cm2. It was found that the temperature response process of Si-MCHS mirrors that of a first-order system’s step response or zero-input response. Upon a sudden change in power consumption, the thermal response can reach 90 % of the steady-state temperature difference (ΔT) within 4 s and 50 % ΔT within 1 s. Increasing the pump speed significantly reduces the response time, while different power step changes have minimal impact on the response time. Consequently, we have formulated a graded flow rate control strategy based on the flow and heat transfer performance of Si-MCHS, which achieves effective flow rate control.

Theoretical model for predicting the yield strength of metal materials under electrically-assisted deformation

In this paper, based on the Force-Heat equivalence energy density principle, considering the thermal and athermal effects caused by current, the theoretical model for the current density dependent yield strength of metallic materials is developed. The novelty of this work lies in the fact that no adjustable fitting parameters were introduced during the modeling process, and both the Joule heating effect and the energy changes brought about by free electrons were considered in the contribution to the yield behavior of metallic materials, on which basis a critical energy density related to yield under the action of electric current was proposed. This model reveals the quantitative relationships between elastic modulus, steady-state temperature, electrical resistivity, thermal conductivity, current density, and yield strength under the action of current. The theoretical prediction results have achieved good consistency with experimental results. Furthermore, based on the principles of energy conservation and the assumption of steady-state, a theoretical expression was derived to predict the steady-state temperature caused by Joule heating. In addition, the results of the model analysis indicate that increasing the electrical resistivity of the material or decreasing its thermal conductivity can both facilitate plastic deformation and processing in electrically-assisted forming processes, especially at high current densities. This work provides an effective method for quantitatively evaluating the yield strength of metallic materials under the action of electric current, which can offer theoretical basis and optimization guidance for the extensive application and further development of electrically-assisted processes.

Фазовий метод виявлення обривів в статорних обмотках асинхронних двигунів

The paper considers the specific features of the technical operation of asynchronous motors in hoisting machines and typical damages to stator windings. It is established that one promising approach to motor protection is the use of computer monitoring systems. These systems' algorithmic and application software includes measuring and controlling stator winding currents. A method for calculating the operating modes of asynchronous motors with a break in one of the parallel branches of the stator phase winding is developed. Based on the derived equations, a computer simulation scheme was compiled using the graph method in the MatLab software environment with the Simulink extension to calculate the symmetric and asymmetric operating modes of an asynchronous motor, considering the current distribution in the parallel branches of the phase windings, and the results of theoretical studies are experimentally confirmed. As a result, graphs are provided to show the relationship between the steady-state temperatures of the stator windings' frontal sections and the values of the phase currents. It is shown that current overload of the operating branch of the damaged phase winding can occur even at the nominal linear current. At the same time, in the operating parallel branch of the phase winding with a break, there is a significant thermal overload, which leads to rapid degradation of the winding insulation materials and the development of a malfunction to a more serious one. A characteristic feature of the operating mode of an asynchronous motor with a break in the parallel branch of the stator phase winding is that at a reduced load, the motor can operate for an extended period without overheating. It is demonstrated that the nature of the asymmetry of linear currents by phase can be used as a diagnostic indicator. Keywords: asynchronous motor, lifting machine, stator winding, break of parallel branch, protection, current overload, diagnostics.

Loss calculation and temperature prediction method for High-Speed amorphous alloy PMSM considering the coupling effect of Multi-Physical field factors

The correct prediction of the loss of amorphous alloy stator cores (AASC) is challenging due to factors such as temperature fluctuations, interference fit stress, and skin effect in high frequency environments. In the complicated operating conditions of high-speed amorphous alloy permanent magnet synchronous motor (HSAAPMSM), an accurate prediction of AASC loss is accomplished by introducing a refined modeling approach of iron loss that considers the interaction of several physical field components. This approach combines with the 3D lumped-parameter thermal network model to generate bidirectional iterative coupling between the temperature distribution of the entire machine and different forms of losses in HSAAPMSM. A steady-state temperature rise result from Maxwell-Fluent bidirectional magnetothermal coupling simulation and test validates the effectiveness and computational superiority of the temperature model that considers the coupling effect of multi-physical field variables.

Thermal Characterization of Ferroelectric Al1-xBxN for Nonvolatile Memory.

Boron (B)-substituted wurtzite AlN (Al1-xBxN) is a recently discovered wurtzite ferroelectric material that offers several advantages over ferroelectric Hf1-xZrxO2 and PbZr1-xTixO3. Such benefits include a relatively low growth temperature as well as a thermally stable, and thickness-stable ferroelectric polarization; these factors are promising for the development of ferroelectric nonvolatile random-access memory (FeRAM) that are CMOS-compatible, scalable, and reliable for storing data in harsh environments. However, wurtzite ferroelectric materials may undergo exacerbated self-heating upon polarization switching relative to other ferroelectric materials; the larger energy loss is anticipated due to the higher coercive field and remanent polarization. This work provides insight into the polarization switching-induced self-heating of future FeRAM based on Al1-xBxN. It was experimentally observed that the thermal conductivity of Al1-xBxN thin films drops from 40.9 W m-1 K-1 to 4.35 W m-1 K-1 (which is 2 orders of magnitude lower than that of bulk AlN) when the B composition (x) increases from 0 to 0.18. The transient thermal response of an Al0.93B0.07N metal-ferroelectric-metal (MFM) capacitor was investigated using micro-Raman thermometry and validated via device thermal modeling. Further simulation studies reveal that the large heat generation rate and the low thermal conductivity is predicted to induce an instantaneous temperature rise that may exceed 150 °C in a FeRAM device based on a 5 nm thick Al1-xBxN film at GHz frequency switching. In addition, thermal crosstalk within a FeRAM cell array exacerbates the self-heating, resulting in a predicted steady-state temperature rise that is an order of magnitude higher than that of a single bit-cell.

Cooling high power electronics using dynamic phase change material

Phase change materials (PCMs) offer effective transient cooling due to their high latent heat of fusion and energy density. Unfortunately, PCMs generally have relatively low thermal conductivity, impeding effective heat dissipation from the heat source and limiting their power density. This work uses dynamic PCM (dynPCM) cooling for thermal management of high power electronics. DynPCM cooling uses pressure-enhanced close-contact melting of a PCM. The applied pressure causes liquid PCM to be pumped away from the heat transfer surface, maintaining a thin melt layer and high heat transfer. Through experimental investigations with a circuit board mounted 2 × 2 array of gallium nitride (GaN) power transistors integrated with heat spreaders of different thicknesses, we evaluate the cooling performance of dynPCM across various device heat dissipation levels (4.4 W/cm² to 46.6 W/cm²) and under both homogeneous and heterogeneous heating conditions. Using paraffin as the PCM, we explore the effects of different pressures (0 Pa, 750 Pa, and 7.5 kPa) on dynPCM cooling effectiveness. DynPCM significantly enhances cooling for electronics operating at high power, achieving over a 50 % reduction in steady-state junction temperature when compared to both traditional air-cooled and hybrid PCM-cooled systems at a 32.4 W/cm² individual GaN device power loss. We developed a reduced-order thermal resistance model to assess heat transfer from the electronic devices through the heat spreader into the dynPCM. The model helps to illustrate the critical role of the heat spreader design and PCM geometry on cooling performance, offering design guidelines for dynPCM thermal management systems. This work highlights the potential of dynPCM as a thermal management strategy for high-power electronic devices, facilitating the advancement of more effective cooling methods for a variety of applications.

Steady-State Temperature Prediction for Cluster-Laid Tunnel Cables Based on Self-Modeling in Natural Convection

Accurate temperature prediction of the operating tunnel cable is crucial for its safe and efficient function. To achieve a rapid and accurate prediction of the steady-state temperature of the tunnel cable, the self-modeling pattern in natural convection on the cable surface in the rectangular tunnel is investigated, and the self-modeling method for the convective heat transfer coefficient calculation is proposed. A thermal circuit model for single cables is further established to predict the cable core temperature, and the model is extended to predict the cluster-laid cable core temperature based on the combined method. The results show that when the tunnel size is neglected, the maximum relative deviation of the convective heat transfer coefficient between the self-modeling method and the finite element simulation is only 1.78% in the studied cases, indicating that the natural convection on the cable surface approximately satisfies the self-modeling method. Additionally, applying the self-modeling method to the thermal circuit can accurately predict the temperature of the single cable core. Furthermore, for the three-phase four-circuit cable, the maximum deviation between the temperature prediction results and the finite element results is within 2 K in the studied cases, which verifies the predictive accuracy of the combined method for the cluster-laid tunnel cable.

A steady-state numerical approach for the thermo-structural analysis of a cryogenic piston pump

Abstract The process of liquefaction of gaseous fuels, such as natural gas or hydrogen, is an essential technology that helps reduce transportation costs over long distances. Cryogenic piston pumps play a critical role in these systems, as they compress the fuel up to 700 bar before vaporization and storage in high-pressure vessels. Due to the extreme temperatures and pressures involved, the design of these machines poses a significant challenge from the thermal and structural point of view. This work presents the application of a simplified numerical approach for evaluating the thermally induced stresses and deformations through a de-coupled thermo-structural three-dimensional analysis of a prototype cryogenic piston pump. Thermal simulations of the solid domain are carried out to assess the steady-state temperature distribution of the pump. The heat transfer between the pump and cryogenic liquid is computed using three-dimensional steady-state CFD simulations of the suction and discharge phases. Heat generated by friction during the working cycle of the pump and external natural convection are calculated and imposed as a heat source in the simulations. The steady-state temperature distribution is imposed in a finite-element steady-state three-dimensional structural simulation to evaluate the combined effect of thermal loads induced by the cryogenic temperatures and loads induced by the high working pressures. Results show how the proposed methodology can assist in the design of cryogenic piston pumps by offering valuable insights into the most critical aspects of these machines.

Janus-inspired alternating architecture CNF/MXene/ZnFe2O4@PANI composite films with outstanding electromagnetic interference shielding and Joule heating

With the continuous advancement of electronic devices, flexible thin films with both thermal management functions and excellent electromagnetic interference (EMI) shielding properties have received much attention. Hence, inspired by Janus, a CNF/MXene/ZnFe2O4@PANI composite film with an asymmetric gradient alternating structure was successfully prepared by adjusting the filler content of the conductive and magnetic layers using a vacuum-assisted filtration method. Benefiting from the magnetic resonance and hysteresis loss of ZnFe2O4@PANI, conductive loss and dipole polarization of MXene, as well as the exclusive “absorption-reflection-reabsorption” shielding feature in the alternating multilayered films, CM&CZFP-4G film has superior EMI shielding performance, with an EMI SE of up to 45.75 dB and shielding effectiveness of 99.99%. Surprisingly, the composite film maintains reliable EMI shielding properties even after prolonged erosion in harsh environments such as high/low temperatures, high humidity, acids and alkalis. Furthermore, the CM&CZFP-4G responded quickly within about 50 s and reached a maximum steady-state temperature of 235.8 °C at an applied voltage of 9.0 V, indicating the obtained film acquired outstanding and controllable Joule heating performance. This result was attributed to the homogeneous dispersion of MXene to build up a conductive network and endow the CNF/MXene with high conductivity. Meanwhile, the fire resistance of CM&CZFP-4G was significantly improved compared to pure CNF, which guaranteed fire safety during its application. Additionally, contributed by long fiber entanglement of CNF, extensive hydrogen-bonding interactions and multilayer structural design, the CM&CZFP-4G film exhibits excellent mechanical characteristics, with the tensile strength and fracture strain of 27.74 MPa and 6.21%, separately. This work offers a creative avenue to prepare multifunctional composite films with electromagnetic shielding and Joule heating for various application environments.

Graphene Microflower by Photothermal Marangoni-Induced Fluid Instability for Omnidirectional Broadband Photothermal Conversion.

2-D carbon-based materials are well-known for their broadband absorption properties for efficient solar energy conversion. However, their high reflectivity poses a challenge for achieving efficient omnidirectional light absorption. Inspired by the multilevel structures of the flower, a Graphene Microflower (GM) material with gradient refractive index surface was fabricated on polymer substrates using the UV-intense laser-induced phase explosion technique under the synergistic design of the photothermal Marangoni effect and the fluid instability principle. The refractive index gradient reduces light reflection and absorbs at least 96% of light at incident angles of 0-60° across the entire solar wavelength range (200-2500 nm). Over 90% absorption even at 75° angle of incidence. The light absorption is enhanced by the multiple interferometric phase cancelation and localized surface plasmon resonance, resulting in a steady-state temperature 60 °C higher than ambient conditions under one solar irradiation. The max rate of temperature rise can reach up to 62 °C s-1. The device is then integrated at the hot end of the temperature difference generator at high altitude to ensure continuous and efficient power generation, producing a steady-state power of 196 mW.

Thermal Analysis of HCSB Blanket Concept for a Moderate Sized Tokamak Fusion Reactor

The conceptual design of a helium-cooled solid breeder blanket for a moderate sized tokamak fusion reactor is presented to explore the feasibility of heat extraction for power conversion. A compact reactor is considered with a major radius of 3 m, fusion power of 200 MW, and modular blankets. A configuration of radially stacked breeder units with a nested C-shaped helium flow scheme that enables nearly uniform high temperatures of the helium outlet is proposed. A detailed thermal analysis of the central module of the blanket is presented. A model is developed to carry out the one-dimensional thermal transient analysis of the breeder unit, which is benchmarked with ANSYS simulation. This can be used as a tool for rapid scan of the conceptual design for a wide range of parameters. The calculations show that a minimum pulse length of 2000s or above is required to achieve a steady-state blanket temperature for efficient heat extraction.

High phenotypic diversity correlated with genomic variation across the European Batrachochytrium salamandrivorans epizootic.

Recognizing the influence of pathogen diversity on infection dynamics is crucial for mitigating emerging infectious diseases. Characterising such diversity is often complex, for instance when multiple pathogen variants exist that interact differently with the environment and host. Here, we explore genotypic and phenotypic variation of Batrachochytrium salamandrivorans (Bsal), an emerging fungal pathogen that is driving declines among an increasing number of European amphibian species. For thirteen isolates, spanning most of the known temporal and geographical Bsal range in Europe, we mapped phenotypic diversity through numerous measurements that describe varying reproductive rates in vitro across a range of temperatures. Bsal isolates are revealed to have different thermal optima and tolerances, with phenotypic variation correlating with genomic diversity. Using a mechanistic niche model of the fire salamander (Salamandra salamandra) as an example, we illustrate how host steady-state body temperature and Bsal thermal range variation may influence pathogen growth through space and time across Europe. Our combined findings show how the identity of emergent pathogen variants may strongly influence when and which host populations are most at risk.

Analytical solution of steady state heat equation in nonlinear thermal-lensing effect

The main interaction of laser beam with materials is to create a temperature distribution, which is the introduction to investigating effects such as thermal-lensing, nonlinear absorption and refraction, and laser-induced damage effects. The correct prediction of this temperature profile can be important in the accurate calculation of thermal expansion volumetric stresses that cause optical aberrations in optical devices and photonic and laser materials. In this letter, new approach has been used to solve the heat equation of laser beam radiation to a thin sample and an exact solution for the time-independent heat equation in a laser-irradiated sample was obtained. Considering appropriate boundary conditions, the steady-state temperature distribution without any approximation was obtained which includes the lower incomplete gamma function. Based on the temperature distribution, the nonlinear changes of absorption and refractive indexes resulting from thermal effects can be accurately calculated. This model was extended for both Gaussian and top-hat beams.

Symmetry Breaking and Modal Localization in a System of Parametrically Excited Microbeam Resonators

In this work, we study the nonlinear dynamics of parametrically excited bending vibrations of two weakly coupled beam microresonators under electrothermal excitation. A steady-state harmonic temperature distribution in the volume of the resonators in the frequency domain was obtained. A system of equations for mechanically coupled beam resonators is derived, considering the deposited particle on one of them. Using asymptotic methods of nonlinear dynamics, equations in slow variables were obtained, which were studied by methods of the theory of bifurcations. It is shown that in a perfectly symmetrical system in a certain frequency range, the effect of symmetry breaking is observed – the emergence of a mode with different amplitudes of oscillations of two beam resonators, which can be the basis for a new principle of high-precision measurements of weak disturbances of various physical natures, in particular – measurements of ultra-low masses of deposited particles.

Estimation and research of the temperature field models of large space spherical mesh shell structures under localized fire

This paper firstly investigated fire dynamics characteristics and the temperature field distributions of large space spherical mesh shell (SMS) structures under localized fire in FDS, and divided the temperature fields into plume region, smoke accumulation region and ceiling jet region. Based on the classical axisymmetric plume model, the predictive models for the steady-state and transient temperature fields in different fire regions for large space SMS structures were proposed in this paper. Thereafter, the proposed temperature models were compared with the simulated results and experimental test results by other scholars, and they were in good agreement. In order to further discover the realistic fire development progress and temperature distribution of large space fire, and validate the proposed temperature field models, this paper designed and conducted three full-scale large space fire tests (Test-1 ∼ Test-3) with different fire source powers in a large space building. Results showed that temperature fields of large space fires could be consisted of near-fire region (Flame region) and far-fire region (Plume region and Ceiling jet region). The steady-state fire source powers were tested for 443 kW, 886 kW, 1090 kW for Test-1, Test-2 and Test-3, respectively, while their maximum temperatures of the roof reached 75 °C, 105 °C and 120 °C. Based on McCaffrey plume model, we further proposed the transient temperature model in flame region for large space structures, and its accuracy was verified by the test results. Moreover, the proposed steady-state and transient temperature fields for large space SMS structures were compared with the tested temperature field data, and the tested and predicted temperature curves were generally in good agreement in plume and ceiling jet regions. Finally, the test results aimed to provide a scientific basis and reference for the fire safety and structural fire-resistant design of large space buildings.

Optimization of cooling process under varied pulsed conditions in multi-stage thermoelectric systems

This paper addresses the issue of thermoelectric cooling in a pulsed quasi-steady state (repetitive) condition. This situation occurs, for example, for an electronic integrated circuit performing demanding tasks in a discontinuous manner. Using heat reservoirs of selected capacity that are part of the thermoelectric system and appropriate shaping of the time profile of the supplied electrical current, cooling temperatures not achievable in the steady state for the system can be reached in a pulsed manner for a specified period. This process is subject to optimization. The analysis was carried out for a two-stage system with an internal (interstage) heat reservoir of a given thermal capacity. The aim of the study was to find the relationship between the level of the supercooling temperature, its repeatability and the ability to maintain this temperature for a given time. To this end, two supply current waveforms were adopted and optimized both without and with contact thermal resistance in the system. The lowest supercooling temperature of about 7 K lower than the steady-state temperature was obtained for a very long period and a very short holding time. Decreasing the period or increasing the holding time results in a non-linear increase in temperature. Similar effects are obtained for the contact thermal resistance present in each layer. A full map of the “period-thermal resistance–temperature” relationship was determined, as well as the supercooling potential curves.

Characteristics and genesis of geothermal systems in the southern Junggar Foreland Basin, NW China

Complex structural styles of foreland basins and limited temperature data hinder our understanding of the characteristics and genesis of geothermal systems in these basins. Characteristics and genesis of the present thermal regime in the southern Junggar Foreland Basin are discussed and a conceptual model of the geothermal system is established based on steady-state temperatures, well-testing temperatures, thermal conductivities, radiogenic heat production, and thermal structures. Thermal conductivities of mudstone, sandstone, and volcanic rocks exhibit normal distribution patterns, with their average thermal conductivities in a consistent order. Heat production varies according to lithologic assemblages and uranium anomalies, being higher in mudstones and tuffs and lower in sandstones and coal measures. The geothermal characteristics are predominantly controlled by tectonic patterns, including geodynamic process and current basement structure. Surface heat flow is decreased from the first structural belts in the south to the third structural belts in the north and is converged from sub-depressions to sub-uplifts or anticlines, whose distribution matches well with positions of three structural belts. The generally low geothermal characteristics are attributed to thick thermal lithosphere and crust, as well as the thermal structure of “cold crust and cold mantle”. Groundwater and fault activities also influence heat flow. Additionally, uranium anomalies at the Cretaceous and Jurassic strata in the first structural belts enhance radiogenic heat production and result in continuously-distributed high heat flow. The heat generated by uranium anomalies helps explain the heat flow distribution in the first structural belts, which cannot be fully accounted for by tectonic-related thermal genesis alone.

Continuous near-equilibrium operation and model validation of a pilot-scale thermochemical energy storage reactor using CaO/Ca(OH)2

Thermochemical energy storage using the material system CaO/Ca(OH)2 is regarded as one of the most promising technologies for application temperatures between 400 °Cand600 °C. There is still a lack of information concerning the transfer of laboratory results to industrially-relevant conditions. This study addresses this research gap and provides data for a continuously operated pilot-scale fluidized-bed storage reactor (257 mm diameter, up to 31L fluidized bed volume, maximal 700 °C and 6barg). The reactor is operated near the thermodynamic equilibrium at varying space times of the storage material (250 - 400 µm). The bed height is maintained at 390 mm during continuous operation. The results indicate good fluidization quality at steady-state operation for up to 9 h. Based on the results, a CSTR-type reactor model is proposed and validated, giving good results in predicting the fluidized bed’s steady-state conversion and temperature. The model is based on material and fluidization properties, such as the fluidized beds porosity, that are measured in dependence of temperature and superficial gas velocity. The simulation results indicate that the heat transfer characteristics are crucial for adequate storage power.

Neural network-based reconstruction of steady-state temperature systems with unknown material composition

Effective thermal management is crucial for the performance and longevity of devices such as computer chips and batteries. A fundamental challenge in this field is accurately determining temperature distributions, which are often limited by incomplete observations. We introduce a neural-network-based approach to overcome these challenges. Specifically, a physics-informed fully convolutional auto-encoder coupled with a preceding spatial propagator network module is used to reconstruct complete temperature fields from partial observations, without requiring additional information about the spatial distribution of materials with varying thermal properties. This paper details the development and validation of our model, demonstrating its effectiveness in virtual sensing setups for both simulated and real-world thermal systems. The reconstruction capabilities for different sampling strategies are investigated. The most challenging of which is the “grid-edge” sampling where only discrete temperature sensors on the periphery of the systems are taken as input, amounting to a sampling ratio as low as 3.12%. The presented method is able to reconstruct the full temperature field with a relative average error of 1.1%. The NN-based approach outperforms the standard Kriging method in predicting the maximum temperature in a system, and proves more robust when the available measurements contain little information.