Volume-averaged Temperature Research Articles

Multi-objective optimization design for a double-direction liquid heating system-based Cell-to-Chassis battery module

Sub-zero temperature causes performance degradation, lifespan shortage, and even some safety issues of Li-ion battery cells, such as the internal short circuit. Preheating has become a critical issue for electric vehicle (EV) promotion in the high-latitude area or cold temperatures. To address this issue, a double-direction liquid heating-based Cell-to-Chassis (CTC) battery module is proposed for an extreme low-temperature environment (-40°C). Two cooling plates and the battery module are embedded in the chassis to reduce the component number. Besides, the volume energy density gets increased by 26.3%. The numerical calculation indicates that the proposed system is more efficient than the commonly utilized battery thermal management system (BTMS) in EVs. Moreover, the preheating effect with different heating intervals is compared; eight-minutes-preheating is proved to be more effective in preheating the battery module to 0°C with less energy consumption. Furthermore, a multi-objective optimization design is further carried out considering the heating rate, thermal safety, thermal uniformity, and energy cost. The impact of the mass flow rate in the mini-channels and the PTC heating film power are analysed through sensitivity analysis. Finally, the optimal design scheme is selected. The minimum, maximum, and volume average temperatures of the battery module are 273.2K, 296.7K, and 286.9K, respectively. Moreover, the temperature standard deviation is further reduced to 8.8K without much energy cost increment. This study guides for combing the efficient BTMS with the EV chassis for all-climate applications, especially with integrated preheating/cooling functions, which is feasible for the fast charging and cold environment applications, both the thermal management efficiency and the volume energy density can be effectively enhanced.

Optimal temperature sensor placement in buildings with buoyancy-driven natural ventilation using computational fluid dynamics and uncertainty quantification

Natural ventilation and cooling can significantly reduce building energy consumption, but inherent variability in the boundary and operating conditions makes robust design and operation a challenging task. Computational models can be leveraged to evaluate the effects of these uncertainties and support robust design; however, the model accuracy should be thoroughly assessed, ideally through validation with carefully designed full-scale measurements. This study presents a novel approach for using computational fluid dynamics (CFD) simulations with uncertainty quantification to optimize temperature sensor placement in buildings with buoyancy-driven natural ventilation, such that the measurements are representative of the volume-averaged temperature, while also supporting analysis of the spatial variability in the temperature field. The approach uses a polynomial chaos expansion method to quantify the effect of the variability in the boundary and initial conditions on the predicted buoyancy-driven flow and indoor temperature field. Results for an operational building that employs night-time cooling are analyzed to identify sensor locations that will support robust observation of the time series of the volume-averaged temperature and the temperature range. The approach is shown to significantly reduce the potential error between the temperature recorded at a random location and the true volume-average temperature, while also providing a representative measure of the temperature range in the building. The results indicate that this approach can also support identifying optimal locations for temperature sensors used for operational control.

Simulation of an industrial cheese chilling process

A computational fluid dynamics (CFD) simulation was developed to simulate an industrial cheese chilling process. Forced air chilling experiments were performed on blocks of agar (cheese analogue) to simulate the airflow and product arrangement in a section of an industrial cheese chilling tunnel. The flow field was solved at steady-state and decoupled from the heat transfer processes. The six blocks of agar were placed in a polystyrene test chamber that was in turn placed in an environmental testing chamber. Temperatures were measured at the surfaces and the geometric centre of the tested blocks of agar. Good agreement was observed between predicted and experimental data. Having been validated, the model was used to generate simple correlation models for predicting the volume-averaged temperature of blocks of cheddar cheese and mozzarella cheese during industrial chilling

Orbital and thermal modelling of a 3U CubeSat equipped with a high-temperature superconducting coil

High-temperature superconductor (HTS) based devices have the potential to be useful technologies for space applications, allowing very high current transfer and magnetic field generation. However, HTS technology requires cryogenic temperatures (<90 K) to operate, and it is not well understood if and how this can be achieved for HTS devices integrated into space vehicles. In this study, the thermal and power performance of a hypothetical 3U CubeSat equipped with an HTS magnetic coil is explored over a range of orbits around the Earth. After eliminating the possibility of passive cooling this close to a planetary body, a cryocooler was deemed necessary to maintain the required temperatures and was included in the simulations. The results show that the best strategy for maintaining the cryogenic operating environment is to maximise the power availability to the cryocooler from solar panels. This approach increases the volume-averaged temperature of the satellite, but the benefits of increased power outweigh the cost of a decreased cryocooler efficiency. This work demonstrates that a 1 T magnetic field can be generated with an HTS electromagnet in a space environment on a small satellite, enabling the use of HTS for space applications such as electric propulsion and energy storage.

Microstructural and Micro-Chemical Evolutions in Irradiated UCO Fuel Kernels of AGR-1 and AGR-2 TRISO Fuel Particles

AGR-1 and AGR-2 tristructural-isotropic (TRISO) fuel particles were fabricated using slightly different fuel kernel chemical compositions, modified fabrication processes, different fuel kernel diameters, and changed 235U enrichments. Extensive microstructural and analytical characterizations were conducted to correlate those differences with the fuel kernels’ responses to neutron irradiations in terms of irradiated fuel microstructure, fission products’ chemical and physical states, and fission gas bubble evolutions. The studies used state-of-the-art transmission electron microscopy (TEM) equipped with energy-dispersive x-ray spectroscopy (EDS) via four silicon solid-state detectors with super sensitivity and rapid speed. The TEM specimens were prepared from selected AGR-1 and AGR-2 irradiated fuel kernels exposed to safety testing after irradiation. The particles were chosen in order to create representative irradiation conditions with fuel burnup in the range of 10.8 to 18.6% fissions per initial metal atom (FIMA) and time-average volume-average temperatures varying from 1070 to 1287°C. The 235U enrichment was 19.74 wt.% and 14.03 wt.% for the AGR-1 and AGR-2 fuel kernels, respectively. The TEM results showed significant microstructural reconstructions in the irradiated fuel kernels from both the AGR-1 and AGR-2 fuels. There are four major phases: fuel matrix of UO2 and UC, U2RuC2, and UMoC2—in the irradiated AGR-2 fuel kernel. Zr and Nd form a solid solution in the UC phase. The UMoC2 phase often features a detectable concentration of Tc. Pd was mainly found to be located in the buffer layer or associated with fission gas bubbles within the UMoC2 phase. EDS maps qualitatively show that rare-earth fission products (Nd et al.) preferentially reside in the UO2 phase. In contrast, in the irradiated AGR-1 fuel kernel, no U2RuC2 or UMoC2 precipitates were positively identified. Instead, there was a high number of rod-shaped precipitates enriched with Ru, Tc, Rh, and Pd observed in the fuel kernel center and edge zone. The differences in irradiated fuel kernel microstructural and micro-chemical evolution when comparing AGR-1 and AGR-2 TRISO fuel particles may result from a combination of irradiation temperature, fuel geometry, and chemical composition. However, irradiation temperature probably plays a more deterministic role. Limited electron energy-loss spectroscopy (EELS) characterizations of the AGR-2 fuel kernel show almost no carbon in the UO2 phase, but a small fraction of oxygen was detected in the UC/UMoC2 phase.

Numerical Investigation of a Radially Cooled Turbine Guide Vane Using Air and Steam as a Cooling Medium

Gas turbine performance is closely linked to the turbine inlet temperature, which is limited by the turbine guide vanes ability to withstand the massive thermal loads. Thus, steam cooling has been introduced as an advanced cooling technology to improve the efficiency of modern high-temperature gas turbines. This study compares the cooling performance of compressed air and steam in the renowned radially cooled NASA C3X turbine guide vane, using a numerical model. The conjugate heat transfer (CHT) model is based on the RANS-method, where the shear stress transport (SST) k−ω model is selected to predict the effects of turbulence. The numerical model is validated against experimental pressure and temperature distributions at the external surface of the vane. The results are in good agreement with the experimental data, with an average error of 1.39% and 3.78%, respectively. By comparing the two coolants, steam is confirmed as the superior cooling medium. The disparity between the coolants increases along the axial direction of the vane, and the total volume average temperature difference is 30 K. Further investigations are recommended to deal with the local hot-spots located near the leading- and trailing edge of the vane.

Long-term evolution of mechanical performance of solid oxide fuel cell stack and the underlying mechanism

Mechanical performance analysis is important for ensuring the long-term reliability of solid oxide fuel cells (SOFCs). Thermal-mechanical models are constructed to conduct time-dependent mechanical performance analysis of SOFC stack with temperature field obtained by multiphysics modeling. The volume-averaged temperature field is used as comparison. The creep strains are examined with a time step of 10 h for 10,000 h. It reveals: (1) Uniform temperature significantly decreases the stresses, strains, failure probabilities of all stack components. (2) The failure probability of sealant reduced rapidly and the sealant becomes mechanically safer for long-term operation. (3) Creep strain is dominant for anode/sealant/interconnect, but negligible for electrolyte/cathode. All components are predictably safe against strain failure for 100,000 h (4) Creep strains of stack components interact with each other. Coupled analysis of creep strains of anode/sealant/interconnect is mandatory, but the creep strains of electrolyte/cathode may be neglected for studying mechanical evolutions.

Transient convection experiments in internally-heated systems

Radioactive decay of unstable isotopes is one of the main heat sources in the early stages of planetary formation as well as in the mantle of terrestrial planets. Laboratory studies characterized by Rayleigh and Prandtl numbers in the range relevant for planetary bodies had remained beyond the ability of the experimental approach until the development of a new technique based on microwave heating. Using this technique, we performed a series of experiments focused on the thermal evolution of an internally heated viscous fluid cooled from above. We established a steady-state scaling law relying the internal temperature variation to the Rayleigh number and we showed that this scaling law remains valid during the transitory regime provided both internal heating and secular evolution of the temperature are taken into account. The result is a parameterized model describing the average internal temperature of the fluid as a function of time in terms of experimental conditions and fluid properties.•We generated a uniform and stable volume heat source in a large volume tank, based on absorption of microwaves guided through an innovative design of microwave circuits.•Automatic laser scanning of the tank coupled with image acquisition and processing enables us the measurement of the 3D temperature field in the convective fluid from which we extracted the volume average temperature and surface heat flux evolution in time.•We validated a transient scaling law for the time evolution of the volume average temperature in an internally-heated convective system.

DINVESTIGATION OF CONTACT HEATING OF FRUIT AND VEGETABLES WITH SATURATED WATER STEAM

The purpose of this research was to study the modes of heating different types of plant raw materials in model technological environments that imitate the blanching of raw materials under factory conditions. The research aimed at expanding the range of canned products made from fruit and vegetables. To this end, new methods were searched for, in addition to the existing ones, allowing heating various plant raw materials and increasing the energy efficiency of canned fruit and vegetables production. Saturated water steam was selected as the treatment medium. The experimental studies included determining the volume-average temperature of the fruit layer in the container. A pulse method of supplying the heating media has also been investigated. It allows using the inertial properties of raw materials and significantly reducing the expenditure of the heating media. The objects selected for study were various species of pomes and drupes, in particular, apples, plums, cherries, sweet cherries, as well as a vegetable crop of the gourd family, or Cucurbitaceae. The following characteristics have been studied: the dynamics of heating individual fruit and vegetables in the saturated water steam environment at atmospheric pressure; the dependence of the heating and cooling rates of individual fruit and vegetables on the geometric index; the dependence of the heating rate of individual fruit and vegetables on the value of the characteristic dimension; the dependences of changes in the volume-average temperature of the fruit layer on the duration of treatment with saturated water steam. It has been established that the volume-average temperature in the centre of a fruit is also influenced by the shape of the fruit itself. To characterise the anomalous shapes of plant raw materials, the geometric index G has been calculated. This index characterises the elliptical shape of a fruit, and allows determining parameters in two mutually perpendicular planes. Also, to compare fruit of the elliptical and the spherical shapes, a special concept of characteristic dimension was used, which is applicable to fruit of different shapes. The experimental data on the change in the dependences of the heating and cooling rates of individual elliptical fruit have been analysed. The analysis has shown that the size of a fruit significantly affects the volume-average temperature in the fruit layer. It has been suggested to use pulsed heating of the fruit layer with saturated water steam, which will appreciably increase the energy efficiency of production due to a significant reduction in heating media consumption

Results of the AGR-2 TRISO fuel performance demonstration irradiation experiment in the Advanced Test Reactor

UCO and UO2 tristructural isotropic fuel compacts were irradiated in the AGR-2 experiment, conducted in the Advanced Test Reactor for 559.2 effective full power days. UCO and UO2 compacts reached calculated peak burnups of 13.15 and 10.69% fissions per initial heavy-metal atom, and fast fluences of 3.47 × 1025 and 3.53 × 1025 n/m2 (E > 0.18 MeV), respectively. The time-average volume-average temperatures ranged from 987 to 1296 °C in UCO compacts and from 996 to 1062 °C in UO2 compacts. Fission product release-to-birth (R/B) ratios remained below 2 × 10−6 in UCO compacts and 10−7 in UO2 compacts during the first three irradiation cycles. R/B data then became unreliable due to mixing of the capsule gas flows which hindered the evaluation of fuel performance for the later portion of the irradiation. Post-irradiation examination of the irradiation capsules and fuel compacts is underway and will provide additional information on fuel performance.

Large-scale simulations of H and He reionization and heating driven by stars and more energetic sources

ABSTRACT We present simulations of cosmic reionization and reheating from z = 18 to z = 5, investigating the role of stars (emitting soft UV-photons), nuclear black holes (BHs, with power-law spectra), X-ray binaries (XRBs, with hard X-ray dominated spectra), and the supernova-associated thermal bremsstrahlung of the diffuse interstellar medium (ISM, with soft X-ray spectra). We post-process the hydrodynamical simulation MassiveBlack-II (MBII) with multifrequency ionizing radiative transfer. The source properties are directly derived from the physical environment of MBII, and our only real free parameter is the ionizing escape fraction fesc. We find that, among the models explored here, the one with an escape fraction that decreases with decreasing redshift yields results most in line with observations, such as of the neutral hydrogen fraction and the Thomson scattering optical depth. Stars are the main driver of hydrogen reionization and consequently of the thermal history of the intergalactic medium (IGM). We obtain 〈xH ii〉 = 0.99998 at z = 6 for all source types, with volume-averaged temperatures $\langle \, T \rangle \sim 20\,000$ K. BHs are rare and negligible to hydrogen reionization, but conversely they are the only sources that can fully ionize helium, increasing local temperatures by ∼104 K. The thermal and ionization state of the neutral and lowly ionized hydrogen differs significantly with different source combinations, with ISM and (to a lesser extent) XRBs, playing a significant role and, as a consequence, determining the transition from absorption to emission of the 21-cm signal from neutral hydrogen.

Molecular dynamics simulation on the phase change of argon molecules between two plates in a wide range of temperature variation

Understanding the complex physical mechanisms of phase change phenomena such as solidification, evaporation and condensation at the nanoscale depending on the temperature variation in a wide range is very important. This study carried out molecular dynamics simulation to investigate the motion of the argon molecules and their phase changes between the bottom cold and top hot walls whose temperatures cover a wide range of variation from the freezing temperature to the supercritical temperature. The motion of argon molecules and their corresponding final phases of solid, liquid, liquid-gas and supercritical fluid formed in the domain depend on the temperature values at the bottom cold and top hot walls, and were classified into seven different processes. The characteristics of final phases of solid, liquid, liquid-gas and supercritical fluid were analyzed by using the radial distribution function, the surface-averaged temperature distribution along the vertical direction and the volume-averaged temperature in the domain for different phases of argon molecules obtained at the final stage of the non-equilibrium simulation. Furthermore, the time history of the average density of argon molecules at the upper domain has also been reported.

Performance of one-dimensional hydrodynamic lake models during short-term extreme weather events

Numerical lake models are useful tools to study hydrodynamics in lakes, and are increasingly applied to extreme weather events. However, little is known about the accuracy of such models during these short-term events. We used high-frequency data from three lakes to test the performance of three one-dimensional (1D) hydrodynamic models (Simstrat, GOTM, GLM) during storms and heatwaves. Models reproduced the overall direction and magnitude of changes during the extreme events, with accurate timing and little bias. Changes in volume-averaged and surface temperatures and Schmidt stability were simulated more accurately than changes in bottom temperature, maximum buoyancy frequency, or mixed layer depth. However, in most cases the model error was higher (30–100%) during extreme events compared to reference periods. As a consequence, while 1D lake models can be used to study effects of extreme weather events, the increased uncertainty in the simulations should be taken into account when interpreting results.

Study of the Spectrumof Low-Frequency Current Fluctuations in Filaments of Electric Lamps

We study experimentally the spectral characteristics of low-frequency current fluctuations in tungsten filaments of lighting lamps in the ranges of frequencies 2.5・10−4 – 5・10−1 Hz and temperatures 1260 – 2600 K. To decrease the influence of the edge effects and increase the measurement accuracy, we use subtraction (compensation) of the constant component of the current. Application of special schemes allowed decreasing significantly the influence of the inherent noise of power supplies which are used to feed the lamp filaments. It is found that low-frequency current fluctuations are a randomly time-interleaved aggregate of four random processes: relaxation, pulsed, stepwise, and quasi-continuous ones. We show that relative fluctuations do not exceed 3 ・ 10−4 in the entire range of the studied frequencies, and the frequency dependence of the spectral power density is well approximated by a function having the form 1/fγ and the index γ of the power spectral density within the (1.6 – 1.8) ± 0.2 limits. The dependence of the parameters of the power spectral density of low-frequency current fluctuations on the average value of the current and the volume-average temperature is studied. In our opinion, the revealed features of low-frequency fluctuations are related to the electron, atomic, and degradation processes in lamp filaments.

Istraživanje simulacije sagorevanja kod benzinskog motora korišćenjem softvera OpenFOAM

The open source Field Operation and Manipulation (OpenFOAM) software was used to investigate the performance of a fully premixed, modern high-performance 4-valve, ISO-octane, dual overhead cam (DOHC) engine with quasi-symmetric pent roof combustion chamber running at 1500 revolutions per minute. The peak pressure occurred at the TDC and had a value of about 30 bar. The results from this study show that the maximum combustion temperature occurred at approximately 95 degrees crank angle ATDC and has a volume averaged value of about 2700°K , whereas the actual computed peak temperature was found to be about 3000ºK and it occurred at grid point 12630. The other temperatures which were found to be higher than the volume averaged temperature were found to be in the range 2968.81 ° K to 2974.01 ° K and correspond to grid point positions 12630 to 12633.The flame-wrinkling factor, X = St / Su was found to be in the range 1.0 ≤ X ≤ 3.8. The dynamics of the regress variable b was accurately predicted.

Numerical simulation of a flow mixer for a radial type chemical reactor

In this work, we performed mathematical modeling of internal elements for mixing the reaction flows. The reactor of the dehydrogenation of ethylbenzene to styrene process was studied. A variant of a radial type reactor in which the gas flow is from the bottom up is considered. Ethylbenzene and steam were selected as components for mixing. Ethylbenzene is supplied to the mixer at a temperature of about 600°C, and steam at a temperature of about 700°C. Three design cases for the internal devices of the mixer are considered. The analysis of the gas mixture parameters, such as volume fraction and average temperature, at the outlet of the mixer was carried out. The cases with the best mixing of the components are determined.

Combined Experimental and Numerical Study of Charcoal Injection in a Blast Furnace: Effect of Biomass Pretreatment

Carbonization is a pretreatment process for upgrading biomass to the so-called biochar or charcoal. Charcoal is a suitable alternative to coal in many fossil-based industries, especially carbon-based industries, for example, ironmaking blast furnaces (BFs). In this study, a combined experimental and numerical method is used to investigate the influence of biomass pretreatment schemes on charcoal combustion within a commercial BF. One woody biomass is upgraded to several types of charcoals using several different carbonization temperatures. The charcoal products are characterized and subjected to non-isothermal devolatilization analysis, with their kinetics calculated. The experiments indicated that the carbonization at a lower temperature produces charcoals with a higher pore fraction, larger volatile matter content, and faster devolatilization kinetics. The properties of different charcoals and their kinetic parameters are then applied to an improved three-dimensional computational fluid dynamics model for comparing the thermochemical performance of charcoal injection in the raceway cavity of an industrial-scale BF, to understand the response of the charcoal performance in the BF to the carbonization temperature. It is found out that the charcoals by carbonization at a lower temperature give higher burnouts in the raceway, but it leads to a lower gas temperature along the boundary of the raceway because of the endothermic reaction of coke and the less char combustion. The volume-averaged gas temperature within the raceway is affected by the collected results of the calorific value and burnout of charcoals. This combined experimental and modeling study discovers the impact of the biomass carbonization temperature on charcoal combustion under industrial BF conditions and can be used for charcoal design and pulverized coal injection operation optimization in future applications.

Quantifying human contributions to past and future ocean warming and thermosteric sea level rise

More than 90% of the Earth’s energy imbalance is stored by the ocean. While previous studies have shown that changes in the ocean warming are detectable and distinct from internal variability of the climate system, an estimate of separate contributions by natural and individual anthropogenic forcings (such as greenhouse gases and aerosols) remains outstanding. Here we investigate anthropogenic and greenhouse-gas contributions to past ocean warming, and estimate their contributions to future sea level rise by the year 2100. By applying detection and attribution framework (regularized optimal fingerprinting), we show that ocean warming in the historical period is detectable and attributable to contributions from the aggregate anthropogenic forcing as well as greenhouse gas forcing alone. We also discuss the role of natural forcing on the ocean volume-averaged temperature and examine the impact of volcanic activity from the three main volcanoes occurring in the historical period 1955–2012. Our results suggest that estimated anthropogenic and greenhouse-gas contributions to ocean warming are consistent with observations, and observationally-constrained future thermosteric sea level rise projections support the central and lower part of the multi-model mean projection range distribution.

Metrological Aspects of Measuring the Volume-Average Temperature of Filaments in Illuminating Lamps

We study metrological problems encountered in measuring the volume-average temperature of heated tungsten filaments. The process of heating is realized by electric currents within the temperature range 300–3000 K. The measurements were carried with the use of an improved method of thermal resistance characterized by a weaker influence of the heat losses and contact potential drops in current-supplying wires, a lower error of measurements of the resistance of filament at the initial temperature, and the possibility of taking into account the nonlinearity of temperature dependences of the analyzed resistance near or below the Debye temperature. The relative error of measurements is estimated.

On the transient thermal response of thin vapor chamber heat spreaders: Governing mechanisms and performance relative to metal spreaders

Vapor chambers can offer a passive heat spreading solution for thermal management in electronics applications ranging from mobile devices to high-power servers. The steady-state operation and performance of vapor chambers has been extensively explored. However, most electronic devices have inherently transient operational modes. For such applications, it is critical to understand the transient thermal response of vapor chamber heat spreaders and to benchmark their transient performance relative to the known behavior of metal heat spreaders. This study uses a low-cost, 3D, transient semi-analytical transport model to explore the transient thermal behavior of thin vapor chambers. We identify the three key mechanisms that govern the transient thermal response: (1) the total thermal capacity of the vapor chamber governs the rate of increase of the volume-averaged mean temperature; (2) the effective in-plane diffusivity governs the time required for the spatial temperature profile to initially develop; and (3) the effective in-plane conductance of the vapor core governs the range of the spatial temperature variation, and by extension, the steady-state performance. An experiment is conducted using a commercial vapor chamber sample to confirm the governing mechanisms revealed by the transport model; the model accurately predicts the experimental measurements. Lastly, the transient performance of a vapor chamber relative to a copper heat spreader of the same external dimensions is explored as a function of the heat spreader thickness and input power. The mechanisms governing the transient behavior of vapor chambers are used to explain the appearance of key performance thresholds beyond which performance is superior to the copper heat spreader. This work provides a foundation for understanding the benefits and limitations of vapor chambers relative to metal heat spreaders in transient operation and may inform the design of vapor chambers for improved transient performance.