Inhomogeneous Temperature Research Articles

Thermal Interference When Recording Turbulent Pressure Fluctuations on the Surface of a Floating Device

Thermal interference is studied when recording turbulent pressure fluctuations on the surface of a floating device at specified experimental parameters of temperature stratification of an aquatic medium. The effect of distortion of the spectral levels of pressure fluctuations recorded by a sound receiver in the field of temperature inhomogeneities is studied using the example of measurements of turbulent pressure fluctuations in the boundary layer during the vertical ascent of a device from a specified depth. At moderate flowvelocities exceeding 1–2 m/s, the temperature susceptibility of a piezoceramic receiver is shown to be decisively determined by its characteristic “thermal” frequency. The parameters of the threshold critical frequency, below which the temperature signal (thermal interference) prevails over the useful signal generated by pressure fluctuations, are determined. With respect to the receivers used in experiments on a floating device [7], the values of the threshold critical frequency are 130 and 215 Hz.

Influence of Interface Morphology on the Thermal Stress Distribution of SOFC under Inhomogeneous Temperature Field

Excessive thermal stress can cause the failure of a solid oxide fuel cell (SOFC), and an inhomogeneous temperature field is one of the reasons for thermal stress in the cell. In the present work, the bi-dimensional thermo-mechanical coupling models of SOFCs with different interface morphologies including planar and corrugated cells are proposed. The temperature distribution of two types of cells under the action of heat conduction is analyzed. Further, the inhomogeneous temperature field caused by gas flow is used as the thermal load to compare the thermal stress distribution of planar and corrugated cells. The influence of interface morphology on the temperature distribution, stress distribution and the contribution of the temperature gradient to stress distribution are investigated. This research provides a reference for reducing thermal stress and improving the stability of SOFC.

Estimation of 2D profile dynamics of electrostatic potential fluctuations using multi-scale deep learning

Abstract Dynamics in magnetically confined plasmas are dominated by turbulence driven by spatial inhomogeneities in density and temperature. Simultaneous measurement of velocity field and density fluctuations is necessary to observe the particle transport, but the measurement of the velocity field fluctuations is often challenging. Here, we propose a method to estimation velocity field fluctuations from density fluctuations by using plasma turbulence simulations and a deep technique learning. In order to take multi-scale characteristics into account, the several number of spatial filters are used in the convolutional neural network. The velocity field fluctuations are successfully predicted, and the particle transport estimated from the predicted velocity field fluctuations is within 93.1% accuracy. The deep learning could be used for the prediction of physical variables which are difficult to be measured.

Investigation on the effectiveness of transpiration cooling under the influence of shock wave

As an advanced active cooling method, transpiration cooling can be used for thermal protection of high-temperature wall. The change of cooling effect caused by the incident shock wave on the transpiration cooling boundary layer is sufficient to affect the safe flight of the aircraft. In this paper, the interaction mechanism between shock wave and transpiration cooling is studied based on the thermal equilibrium model. The effects of shock wave incident angle, coolant injection ratio, Mach number of high enthalpy airflow and coolant type on thermal protection effect were studied respectively. Shock wave incidence in the boundary layer of transpiration cooling can cause the change of coolant flow and heat sink distribution in porous media, and cause the fluctuation of fluid parameters in the boundary layer. The temperature inhomogeneity on the porous wall and the inhomogeneity of the total enthalpy difference are markedly affected by the shock wave intensity. The heat insulation effect of the coolant on the solid surface limits the improvement effect of the increase of the injection ratio on the effective heat absorption power. Hydrogen as a coolant can form a better cooling effect and has less resistance to the mainstream.

Effect of thermal gradients on inhomogeneous degradation in lithium-ion batteries

Understanding lithium-ion battery degradation is critical to unlocking their full potential. Poor understanding leads to reduced energy and power density due to over-engineering, or conversely to increased safety risks and failure rates. Thermal management is necessary for all large battery packs, yet experimental studies have shown that the effect of thermal management on degradation is not understood sufficiently. Here we investigated the effect of thermal gradients on inhomogeneous degradation using a validated three-dimensional electro-thermal-degradation model. We have reproduced the effect of thermal gradients on degradation by running a distributed model over hundreds of cycles within hours and reproduced the positive feedback mechanism responsible for the accelerated rate of degradation. Thermal gradients of just 3 °C within the active region of a cell produced sufficient positive feedback to accelerate battery degradation by 300%. Here we show that the effects of inhomogeneous temperature and currents on degradation cannot and should not be ignored. Most attempts to reproduce realistic cell level degradation based upon a lumped model (i.e. no thermal gradients) have suffered from significant overfitting, leading to incorrect conclusions on the rate of degradation.

Thermal–Fluid–Solid Coupling Analysis on the Effect of Cooling Gas Temperature on the Fatigue Life of Turbine Blades with TBCs

The application of thermal barrier coatings (TBCs) can increase the blade’s operating temperature and fatigue life. Previous studies have neglected the effects of cooling gas temperature variations on the temperature field, stress field, and fatigue life of blades and TBCs. For this reason, this paper considers the inhomogeneity of the high-temperature gas inlet temperature, the internal cooling gas temperature, the periodicity of the external flow field, etc., and establishes a finite element model of the gas turbine blade with TBCs. Then, the life of the blade and the TBCs is predicted based on the Ncode 2020R2. Finally, the effect of the cooling gas temperature on the temperature, stresses, and life of the blade and the TBCs is analyzed. The results show that the fatigue life of the TBCs is lower than that of the blade, and the low-life region of the TBCs is located at the leading edge of the blade, which is consistent with the TBCs shedding region of the real blade and verifies the accuracy of the life prediction method in this paper. The fatigue life of the blade and TBCs firstly increases and then decreases with the increase in the cooling gas temperature, and the trend of the stress changes in the opposite direction. When the cooling gas temperature is increased from 573 K to 873 K, the minimum life of the blade is increased by 358.5%, and that of the TBCs is increased by 138.7%. The conclusions can provide guidance for the design of long-life turbine blades with TBCs.

Refuelling tests of a hydrogen tank for heavy-duty applications

A transition towards zero-emission fuels is required in the mobility sector in order to reach the climate goals. Here (green) renewable hydrogen for use in fuel cells will play an important role, especially for heavy duty applications such as trucks. However, there are still challenges to overcome regarding efficient storage, infrastructure integration and optimization of the refuelling process. A key aspect is to reduce the refuelling duration as much as possible, while staying below the maximum allowed temperature of 85 °C. Experimental tests for the refuelling of a 320 l type III tank were conducted at different operating conditions and the tank gas temperature measured at the front and back ends. The results indicate a strongly inhomogeneous temperature field, where measuring and verifying the actual maximum temperatures proves difficult. Furthermore, a simulation approach is provided to calculate the average tank gas temperature at the end of the refuelling process.

Microwave-assisted, performance-advantaged electrification of propane dehydrogenation.

Nonoxidative propane dehydrogenation (PDH) produces on-site propylene for value-added chemicals. While commercial, its modest selectivity and catalyst deactivation hamper the process efficiency and limit operation to lower temperatures. We demonstrate PDH in a microwave (MW)-heated reactor over PtSn/SiO2 catalyst pellets loaded in a SiC monolith acting as MW susceptor and a heat distributor while ensuring comparable conditions with conventional reactors. Time-on-stream experiments show active and stable operation at 500°C without hydrogen addition. Upon increasing temperature or feed partial pressure at high space velocity, catalysts under MWs show resistance in coking and sintering, high activity, and selectivity, starkly contrasting conventional reactors whose catalyst undergoes deactivation. Mechanistic differences in coke formation are exposed. Gas-solid temperature gradients are computationally investigated, and nanoscale temperature inhomogeneities are proposed to rationalize the different performances of the heating modes. The approach highlights the great potential of electrification of endothermic catalytic reactions.

Four-Dimensionally Printed Continuous Carbon Fiber-Reinforced Shape Memory Polymer Composites with Diverse Deformation Based on an Inhomogeneous Temperature Field.

Four-dimensionally printed continuous carbon fiber-reinforced shape memory polymer composite (CFSMPC) is a smart material with the ability to bear loads and undergo deformation. The deformation of CFSMPC can be driven by the electrothermal effect of carbon fibers. In this study, the effect of temperature on the shape memory recovery performance of polylactic acid (PLA) was first studied experimentally. Continuous carbon fibers were incorporated into PLA to design CFSMPCs with thickness gradients and hand-shaped structures, respectively. The distribution strategy of the carbon fibers was determined based on simulations of the electrically driven shape recovery process of the aforementioned structures. Both the simulations and experiments demonstrated that the electrification of the CFSMPC structures resulted in an inhomogeneous temperature field, leading to distinct deformation recovery processes. Eventually, a precise unfolding was achieved for the thickness gradient structure and the five fingers in the hand-shaped structure by utilizing a safe voltage of 6 V. This demonstrates that the 4D-printed CFSMPC with diverse deformations based on an inhomogeneous temperature field has potential applications in actuators, reconfigurable devices, and other fields.

A Multi-Yield-Surface Plasticity State-Based Peridynamics Model and its Applications to Simulations of Ice-Structure Interactions

Due to complex mesoscopic and the distinct macroscopic evolution characteristics of ice, especially for its brittle-to-ductile transition in dynamic response, it is still a challenging task to build an accurate ice constitutive model to predict ice loads during ship-ice collision. To address this, we incorporate the conventional multi-yield-surface plasticity model with the state-based peridynamics to simulate the stress and crack formation of ice under impact. Additionally, we take into account of the effects of inhomogeneous temperature distribution, strain rate, and pressure sensitivity. By doing so, we can successfully predict material failure of isotropic freshwater ice,iceberg ice, and columnar saline ice. Particularly, the proposed ice constitutive model is validated through several benchmark tests, and proved its applicability to model ice fragmentation under impacts, including drop tower tests and ballistic problems. Our results show that the proposed approach provides good computational performance to simulate ship-ice collision.

Flow and thermal mixing characteristics of a multi-jet bypass flue with main flue baffles

The decrease of inlet flue temperature of denitrification reaction unit is a major challenge that restricts the low load operation of thermal power units. In this study, a new bypass flue heating technology based on multi-pipe and multipoint was proposed. The effect of different baffle openings (RA), directions and position distance (Db) on the mixing characteristics of multiple jets was quantitatively investigated by the experimental system. Combined with the simulation, the changes of the baffle on the multi-jet flow and mixing are revealed. The results show that the mixing temperature increases with increasing RA, but high RA leads to a significant increase in the thermal mixing temperature inhomogeneity (ζT). As RA increases from 0.4 to 0.7, ζT rises from the minimum 0.368 to the maximum 0.559. The mixing temperature and ζT of the baffle in the +x direction are higher than those in the −x direction. When Db increases from 70 mm to 130 mm, the maximum heating effect decreases from 25.97 °C to 18.89 °C, and ζT decreases gradually at y/Dh = 1.25. The findings provide guidance for bypass flue modification and low load denitrification in engineering.

Secondary flows induced by two-dimensional surface temperature heterogeneity in stably stratified channel flow

The structure and impact of thermally induced secondary motions in stably stratified channel flows with two-dimensional surface temperature inhomogeneities is studied using direct numerical simulation (DNS). Starting from a configuration with only spanwise varying surface temperature, where the streamwise direction is homogeneous (Bon & Meyers, J. Fluid Mech., 2022, pp. 1–38), we study cases where the periodic temperature strip length $l_x/h$ (with $h$ the half-channel height) assumes finite values. The patch width ( $l_y/h =\{{\rm \pi} /4, {\rm \pi}/8$ }) and length are varied at fixed stability and two different Reynolds numbers. Results indicate that for the investigated patch widths, the streamwise development of the secondary flows depends on the patch aspect ratio ( $a=l_x/l_y$ ), while they reach a fully developed state after approximately $25l_y$ . The strength of the secondary motions, and their impact on momentum and heat transfer through the dispersive fluxes, is strongly reduced as the length of the temperature strips decreases, and becomes negligible when $a\lesssim 1$ . We demonstrate that upward dispersive and turbulent heat transport in locally unstably stratified regions above the high-temperature patches lead to reduced overall downward heat transfer. Comparison to local Monin–Obukhov similarity theory (MOST) reveals that scaled velocity and temperature gradients in homogeneous stably stratified channel flow at $Re_\tau =550$ agree reasonably well with empirical correlations obtained from meteorological data. For thermally heterogeneous cases with strips of finite length, the similarity functions only collapse higher above the surface, where dispersive fluxes are negligible. Lastly, we show that mean profiles of all simulations collapse when using outer-layer scaling based on displacement thickness.

Modeling and Analysis of Temperature-Dependent Capacity Degradation in Large Format Lithium-Ion Batteries

The large-format lithium-ion batteries, widely used for electric vehicle applications, are generally characterized by spatial non-uniformities in temperature. The presence of thermal gradients and temperature-dependence of cell parameters are responsible for non-uniform degradation within the battery that leads to poor performance of the battery packs and also poses safety risks. In this work, we aim to develop a detailed physics-based simulation framework to model non-uniform, temperature-dependent capacity degradation within these large format batteries based on the classical pseudo two-dimensional (p2D) battery model. The electrochemical model will be coupled with degradation mechanisms to capture solid-electrolyte interface layer growth, reversible lithium plating, structural disintegration, and volume change within the electrodes on the cell level signatures and usable capacity over charge/discharge cycles. The effects of temperature inhomogeneities will be accounted in the multi-cell simulations at different operating temperatures for individual cells with dynamic currents and temperature and concentration dependent battery parameters as the model inputs.Overall, the primary focus of this study is to capture the effect of spatial temperature variation on battery capacity over cycles and help identify an improved design for the battery module. The model is implemented in an efficient equation-based form for the p2D model and degradation mechanisms with dynamic cell inputs using the mathematical modules in the finite element based solver, COMSOL Multiphysics. This approach enables an easier model development and analysis of the detailed physics and allows an easier implementation of any additional side reaction. The relative contributions of various fade modes have also been compared to understand their competitive interplay over cell cycles. The model predictions are validated with the available experimental data and in-house codes for each case. We believe that this simple yet detailed model can be further developed to be computationally feasible for adoption and implementation in a battery thermal management system.

Effects of temperature and composition inhomogeneity on the ignition characteristics of NH3/H2 co-firing fuels under HCCI operating conditions

The application of ammonia (NH3) in combustion devices, such as internal combustion engines (ICEs), is expected to largely reduce the greenhouse gas (CO2) emission. NH3/H2 cofiring fuels in homogeneous charge compression ignition (HCCI) engines may provide a potential way to deal with zero carbon requirements. However, in HCCI engines, the ignition process needs to be moderated since the ignition is only controlled by the chemical kinetics of the fuel. Therefore, this study investigates the effects of temperature and composition stratification strategies on the auto-ignition characteristics of NH3/H2/air mixtures under HCCI engine operating conditions with direct numerical simulation (DNS). 12 cases with different stratification strategies have been set under turbulent conditions. The chemical kinetics of NH3/H2/air was verified with the laminar flame speeds and ignition delay times. Results show that the temperature stratification can reduce the peak value of heat release rate (HRR), advance the ignition time and extend the combustion duration. In this case, the chemical reaction front is dominated by the deflagration or flame propagation mode. However, in contrast, composition stratification shows very limited effect on the overall combustion process, which is similar to homogeneous ignition and denoted as the spontaneous ignition mode. When increasing the hydrogen content in the fuel, the ignition time is obviously advanced and the peak of HRR is slightly increased. Higher NO emission is also observed which is mainly due to the increase of O, H, and OH intermediates to enhance the fuel NO production. Temperature stratification degree can improve the ignition process under both negatively correlated or unrelated T-Φ fields. However, the improvement is more evident for unrelated T-Φ condition when increasing the stratification degree.

Development and characterization of the Portable Ice Nucleation Chamber 2 (PINCii)

Abstract. The Portable Ice Nucleation Chamber 2 (PINCii) is a newly developed continuous flow diffusion chamber (CFDC) for measuring ice nucleating particles (INPs). PINCii is a vertically oriented parallel-plate CFDC that has been engineered to improve upon the limitations of previous generations of CFDCs. This work presents a detailed description of the PINCii instrument and the upgrades that make it unique compared with other operational CFDCs. The PINCii design offers several possibilities for improved INP measurements. Notably, a specific icing procedure results in low background particle counts, which demonstrates the potential for PINCii to measure INPs at low concentrations (<10 L−1). High-spatial-resolution wall-temperature mapping enables the identification of temperature inhomogeneities on the chamber walls. This feature is used to introduce and discuss a new method for analyzing CFDC data based on the most extreme lamina conditions present within the chamber, which represent conditions most likely to trigger ice nucleation. A temperature gradient can be maintained throughout the evaporation section in addition to the main chamber, which enables PINCii to be used to study droplet activation processes or to extend ice crystal growth. A series of both liquid droplet activation and ice nucleation experiments were conducted at temperature and saturation conditions that span the spectrum of PINCii's operational conditions (-50≤ temperature ≤-15 ∘C and 100 ≤ relative humidity with respect to ice ≤160 %) to demonstrate the instrument's capabilities. In addition, typical sources of uncertainty in CFDCs, including particle background, particle loss, and variations in aerosol lamina temperature and relative humidity, are quantified and discussed for PINCii.

Numerical simulation of rice drying process in a deep bed under an angular air duct

AbstractThe deep‐bed drying process of rice grains was investigated through numerical simulation, employing the porous medium flow field theory and the local thermal nonequilibrium method. Moisture field of rice grains described using thin‐layer equations. On this basis, the deep‐bed drying of rice grains modeled with COMSOL, and verified its plausibility. The results showed that the drying rate of rice grains was significantly accelerated when the hot air temperature was increased from 40°C to 70°C, but the inhomogeneity of rice grains temperature increased by 29.79%, 22.31%, and 17.41% for every 10°C increase. Drying grains faster with vertically arranged an angular air duct, with a 4.88% increase in drying speed in 300 min. The temperature difference between the top and the bottom of an angular air duct with a small width is smaller, about 11°C, and the heating efficiency is better at the top, by 31.28%.Practical ApplicationsGrain dryers are often used in high‐volume grain drying operations and it has been a great challenge to save the energy consumption of the drying process. It is necessary to use numerical simulation to design a reasonable structure of the heating section to improve the energy utilization efficiency of the heating section of the grain dryer. The numerical model proposed in this article can effectively simulate the spatial distribution of moisture content of rice under different structures of grain drying units, which can be used not only for the prediction of drying time but also for analyzing the optimal heating structure from it. A technical basis is provided for the design of grain dryers.

Exergy destruction comparison of facial area ratio on dehumidification performance of the rotary desiccant wheel system under conventional and deep dehumidification

The rotary desiccant wheel has been extensively applied for humidity control in air conditioning systems, and it is also capable of deep dehumidification processes in various areas. The differences in the exergy destruction characteristics of the desiccant wheel between deep dehumidification and conventional dehumidification were still unclear. This study conducted numerical investigations to illustrate the impact of operating parameters, especially the facial area ratio, on the transfer exergy destruction and the mixing exergy destruction of the desiccant wheel components. The results revealed that the desiccant wheel with a facial area ratio of 1 has a higher exergy efficiency in conventional dehumidification due to low transfer and mixing exergy destruction. However, it shows a lower exergy efficiency than that of 3 under the deep dehumidification depth when operated at a high regeneration air humidity ratio. In the deep dehumidification process, the mixing exergy destruction caused by the distribution inhomogeneity of temperature and humidity ratio becomes a prominent factor to influence the exergy efficiency along with the transfer exergy destruction. It is concluded that the efficient design of the desiccant wheel dehumidification system highly depends on the dehumidification depth, the operating parameters, and the proper facial area ratio.

Improving the Efficiency of the Furnace Process of Low-Temperature Low-Capacity Furnaces

A review of studies of furnace processes in industrial furnaces has shown that there is a sufficient number of studies for high-temperature and medium-temperature furnaces. However, there is an insufficient understanding of furnace processes in low-temperature low-power furnaces. One of the most important factors in the working process of low-temperature ovens, in contrast to high-temperature and medium-temperature ovens, is a significantly lower level of temperature inhomogeneity. For example, in heating ovens in the machine-building industry, the temperature inhomogeneity is 30 °С…50 °C, while in baking ovens, temperature fluctuations of 5 °C…10 °C are permissible.The aim of this article is to analyze the efficiency of the organization of combustion processes in industrial baking ovens operating on natural gas, which are organized by two different combustion technologies: in a cupcake baking oven, the combustion process is organized using a vortex-type burner device operating in a pulse mode; in a wafer sheet baking oven, microflame gas combustion technology is implemented. Some disadvantages of using the above-mentioned technologies for the studied furnaces have been identified and ways to eliminate them by organizing furnace processes in these furnaces using jet-niche gas combustion technology have been proposed. Namely, the modernization of these furnaces with the replacement of standard burners with burners that implement the principles of jet-niche technology.

Sniffer worm, C. elegans, as a toxicity evaluation model organism with sensing and locomotion abilities.

Additive manufacturing, or 3D printing, has revolutionized the way we create objects. However, its layer-by-layer process may lead to an increased incidence of local defects compared to traditional casting-based methods. Factors such as light intensity, depth of light penetration, component inhomogeneity, and fluctuations in nozzle temperature all contribute to defect formations. These defective regions can become sources of toxic component leakage, but pinpointing their locations in 3D printed materials remains a challenge. Traditional toxicological assessments rely on the extraction and subsequent exposure of living organisms to these harmful agents, thus only offering a passive detection approach. Therefore, the development of an active system to both identify and locate sources of toxicity is essential in the realm of 3D printing technologies. Herein, we introduce the use of the nematode model organism, Caenorhabditis elegans (C. elegans), for toxicity evaluation. C. elegans exhibits distinctive 'sensing' and 'locomotion' capabilities that enable it to actively navigate toward safe zones while steering clear of hazardous areas. This active behavior sets C. elegans apart from other aquatic and animal models, making it an exceptional choice for immediate and precise identification and localization of toxicity sources in 3D printed materials.

Numerical Assessment of the Inhomogeneous Temperature Field and the Quality of Heat Extraction of Nb3Sn Impregnated Magnets for the High Luminosity Upgrade of the LHC

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN foresees the installation of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn-based quadrupole magnets at selected interaction points of the accelerator. The precise knowledge of each magnet's thermal characteristics and heat extraction performance in response to power depositions during both nominal and ultimate conditions is essential in determining safe operating margins. A 2D numerical framework has been developed to systematically assess the temperature distribution in the combined magnet structure-superfluid He system of each magnet and enveloping cold mass using open-source software. Here a full cross-section of a magnet cold mass is modelled, under the power density distribution expected at the most exposed longitudinal position during accelerator operation at an instantaneous luminosity of 5.0x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , corresponding to the nominal conditions for HL-LHC. Temperature maps and margins are presented for the inner triplet magnets (MQXF) for both horizontal and vertical beam crossing conditions, along with the validation of the design of cold mass cooling channels for heat extraction.