Estimation Of Temperature Distribution Research Articles

Numerical modeling on the sensitivity of directional dependent interface heat transfer on thermal transport in a coupled fracture-matrix system

The conventional dual-porosity model has been modified by considering the heat exchange term at the fracture-matrix interface in the governing equation for thermal transport within the low permeable rock-matrix as against its conventional consideration within the high permeable fracture. A finite volume numerical model has been developed in order to analyze the influence of the source/sink term which defines the heat transfer at the fracturematrix interface. The comparison of the spatial distribution for temperature within the fracture and within the reservoir matrix for two different models, (1) conventional model in which the source/sink heat transfer term included in the equation for thermal transport within the fracture; (2) proposed model in which the source/sink heat transfer term included in the equation for thermal transport within the rock-matrix, have been performed. In addition, the sensitivity of the reservoir matrix thermal conductivities, both horizontal and vertical, on thermal energy extraction from the reservoir matrix has also been analyzed using the proposed model. Numerical results suggest that the estimation of temperature distribution in the fracture and rock-matrix and thus quantifying the heat extraction from the reservoir matrix is underestimated in a fracture-matrix system by using the conventional thermal transport model. It has been also observed that the temperature distribution obtained in the fracture and the rock-matrix by considering the heat transfer term in the thermal transport equation within the fracture shows significant variation from the temperature distribution obtained by considering the heat transfer term in the equation for thermal transport within the rock-matrix.

Prediction of Fatigue Strength of Motorcycle Exhaust System Considering Vibrating and Thermal Stresses

<div class="section abstract"><div class="htmlview paragraph">A method applicable in the design stage to predict fatigue strength of a motorcycle exhaust system was developed. In this prediction method, a vibrating stress, thermal stresses, stresses resulting from the assembling of the exhaust system components and a deterioration of fatigue strength of materials originated from high temperature were simultaneously taken into account. For the prediction of the vibrating stress, flexible multibody dynamics was applied to get modeling accuracy for vibration characteristics of the entire motorcycle and the exciting force delivered from engine vibrations. The thermal conduction analysis and the thermal deformation analysis based on finite element method (FEM) were applied for the prediction of thermal stresses in the exhaust system components. The temperature distribution on the surfaces of the exhaust system components is required for calculations of the thermal stresses. The heat transfer analysis, which was composed by combing a one-dimensional (1D) engine cycle simulation and an air flow simulation around the vehicle by 3D-CFD, was used for the estimation of temperature distributions. To validate the developed method, the correlations between the simulations and the actual measurements were analyzed for the vibrating stress, the temperature distribution, the thermal stresses and the fatigue safety factor. High correlations were yielded between them proving the validity of the new method.</div></div>

Nanofocus diamond X-ray windows: Thermal modeling of nano-sized heat source systems

An analytical thermal model is proposed to study heat transfers occurring at high power density in X-ray tubes with micron to submicron sized source. The use of a simple analytical approach instead of a complex numerical simulation allows readily modeling of more and more challenging systems such as multi-source X-ray tubes. By significantly reducing the computing time, it enables a wider parameter range evaluation for engineering phase. We focused our work on tubes integrating a transmission window that is mainly edge-cooled. Our approach can be generally used in cylindrical lateral heat spreaders with distributed small sized source systems. The model enables an efficient estimation of temperature distributions for a large range of parameters and source designs and is, for instance, well-suited to described nanosized heat source systems. It is developed from an electrostatic analogy with the point charge particle model and uses of a series of virtual sources. A multiscale resolution of the heat equation is proposed, hence providing the temperature distribution at any point within the whole system. Moreover, the non-linearity of equations caused by temperature-dependent thermal conductivities is solved by using Kirchhoff's transformation, giving a more realistic approach of heat conduction in diamond X-ray windows, where temperature in excess of 1000°C can be encountered. The influence of convective and radiative transfers has been discussed and the physical accuracy of the predicted temperature is controlled by adjusting the number of virtual sources of the model.

Uniformity Improvement in Carrier Concentration on 150 mm Diameter C-Face Epitaxial Growth of 4H-SiC

The guidelines necessary to improve the n-type doping uniformity on C-face epitaxial growth of 4H-SiC have been examined as far as the practical throughput is maintained, e.g. 3×150 mm wafers with the growth rate higher than 20 μm/h. The flow-channel enlargement was carried out and the effect was estimated by temperature distribution estimation performed by hydrogen etching. Also, effective C/Si was simulated with the temperature distribution obtained from the hydrogen etching experiments. As a result, positional agreement was found between the region where carrier concentration begins to increase and the drastic drop in temperature and the effective C/Si ratio.

Surface temperature measurement for space charge distribution measurements with thermal methods

The implementation of space charge measurements based on thermal perturbation on thin films requires an improvement of the temperature distribution estimation at the surface and in the depth of dielectric materials for getting reliable space charge profile measurements. Absolute temperature variations are needed, both in time and space. The present contribution addresses surface temperature measurements based on either thermoelectric or bolometric effects. Both responses have been measured on coppercoated silicon nitride layers and gold-coated polypropylene films heated with a Nd:YAG laser pulse. It is shown that high temporal resolution thermal response can be obtained through the bolometric response and that the information appears nearly independent on the nature of the coating electrode. The setup developed provides good signal to noise ratio for heated electrodes of a few ohm resistance. Strategies are still to develop to get the temperature profile in the insulating sample layer.

Model-Based Virtual Thermal Sensors for Lithium-Ion Battery in EV Applications

Continuous monitoring of temperature distribution in lithium-ion (Li-ion) batteries is critical in preventing rapid degradation, mismatch in cell capacity, and potentially thermal runaway. A model based on virtual thermal sensor (VTS) for automotive grade Li-ion batteries is presented in this paper. This model, using a small number of physical sensors, is able to estimate temperature distribution throughout the battery in real time. First, the thermal model of the battery is developed and the characteristic parameters of the battery are tuned using the prediction error minimization method. Then, the tuned model is combined with a Kalman filter to estimate the temperature distribution of the battery under unknown initial values and model uncertainty. The proposed model-based VTS has been experimentally validated on an automotive grade 70-Ah lithium iron phosphate $(\hbox{LiFePO}_{4})$ battery.

Optimal Carbon Abatement in a Stochastic Equilibrium Model with Climate Change

This paper studies a dynamic stochastic general equilibrium model involving climate change. Our model allows for damages on output resulting from global warming. We compare two approaches (level and growth rate impact) and provide results for both. Our calibration captures several effects of climate change and feedback effects on the temperature dynamics. In particular, we are able to match estimates of future temperature distributions provided in the fifth assessment report of the IPCC (2014). We solve for the optimal abatement policy and find that this policy is considerably state-dependent. We also study the effect of risk aversion and elasticity of intertemporal substitution. It turns out that risk aversion matters more if climate change has a level impact on output, whereas the elasticity of intertemporal substitution has a significant effect for both specifications. Similar results hold for the social cost of carbon.

Real-time conductivity imaging of temperature and tissue property changes during radiofrequency ablation: an ex vivo model using weighted frequency difference.

We demonstrated the feasibility of time difference and weighted frequency difference conductivity imaging for real-time monitoring of temperature distribution and ablation region estimation during radiofrequency (RF) ablation. The electrical conductivity spectrum of biological tissue reflects mobility of ions in intra- and extra-cellular fluids and changes in cellular morphology induced by heating. The time series conductivity spectra were measured in an ex vivo bovine liver by a high-speed electrical impedance tomography (EIT) system. The EIT system was protected by filters to suppress RF energy and allow interleaved real-time imaging. We recorded time and weighted frequency-difference conductivity images and direct temperature variations at the ablation region and control region during 8 min ablation and for the following 66 min of cooling. Conductivity variation in regions of interest was compared with temperature recordings. Contours of conductivity change were visualized and compared to estimate the ablation area. EIT images confirmed increase of conductivity at all frequencies and loss of frequency conductivity change associated with loss of cellular structure. Time difference conductivity images showed changes due to both heating during ablation and heat dissipation following ablation together with tissue property changes. Weighted frequency-difference images presented persistent changes following heating due to the morphological change in the ablation zone.

Estimation of Transient Temperature Distribution during Quenching, via a Parabolic Model

A material-independent model to estimate the transient temperature distribution in a test probe quenched by immersion is presented in this study. This model is based on the assumption that, under one-dimensional unsteady heat conduction, the radial temperature distribution at the end of an interval belongs to the equation of a parabola. The model was validated using AISI 304 stainless steel test probes (Φ8×40 mm and Φ12×60 mm) quenched from 850 to 900 °C in water and in water-based NaNO 2 solutions at 25 °C and in canola oil at 50 °C. Additionally, square test probes (20×20×100 mm) were quenched from 550 °C in water. The test probes were equipped with embedded thermocouples for temperature-versus-time data logging at the core, one-quarter thickness and 1 mm below the surface. In each experiment, the data recordings from the core and near-surface thermocouples were employed for the temperature calculations while the data from the one-quarter thickness thermocouple were employed for model validity verifications. In all cases, the calculated temperature distributions showed good correlations with the experimentally obtained values. Based on the results of this work, it is concluded that this approach constitutes a simple, quick and efficient tool for estimating transient surface and radial temperature distributions and represents a useful resource for quenchant cooling rate calculations and heat transfer characterizations.

Optimal Carbon Abatement in a Stochastic Equilibrium Model with Climate Change

This paper studies a dynamic stochastic general equilibrium model involving climate change. Our frame- work allows for feedback effects on the temperature dynamics. We are able to match estimates of future temperature distributions provided in the fifth assessment report of the IPCC (2014). We compare two approaches to capture damaging effects of temperature on output (level vs. growth rate impact) and combine them with two degrees of severity of this damage (Nordhaus vs. Weitzman calibration). It turns out that the choice of the damage function is crucial to answer the question of how much the distinction between level and growth rate impact matters. The social cost of carbon is similar for frameworks with level or growth rate impact if the potential damages of global warming are moderate. On the other hand, they are more than twice as large for a growth rate impact if damages are presumably severe. We also study the effect of varying risk aversion and elasticity of intertemporal substitution on our results. If damages are moderate for high temperatures, risk aversion only matters when climate change has a level impact on output, but the effects are relatively small. By contrast, the elasticity of intertemporal substitution has a significant effect for both level and growth rate impact. If damages are potentially severe for high temperatures, then the results also become sensitive to risk aversion for both damage specifications.

B122 液体中の発熱マイクロ粒子周りの温度分布推定(OS-8:マイクロ・ナノ熱工学(2))

B122 液体中の発熱マイクロ粒子周りの温度分布推定(OS-8:マイクロ・ナノ熱工学(2))

Hierarchical design principles of selective laser melting for high quality metallic objects

Selective laser melting (SLM) is becoming a powerful additive manufacturing technology for different industries: automotive, medical, chemical, aerospace, etc. SLM could dramatically narrow the time frames to optimize production, providing extraordinary freedom to validate design and to develop new materials. The extension of applications requires different materials with specific properties and therefore tailored properties of the final product. In this article, a hierarchical approach including mutual analysis of SLM parameters necessary to control the final product quality on every level – the track, the layer and the final 3D object – is suggested and discussed. Numerical simulation allowed the estimation of temperature distribution during laser melting and predicted final microstructures and properties of a 3D SLM object. A series of single tracks, layers and 3D objects were manufactured from AISI 420 stainless steel to validate a proposed algorithm. The efficiency of the approach was illustrated by the manufacturing of fully dense samples from AISI 420 stainless steel widely used in the plastics-moulding industry. The results show that based on the proposed systematic hierarchical approach, optimal process parameters can be efficiently established for high-quality SLM parts from metal powders.

Extreme learning machine based spatiotemporal modeling of lithium-ion battery thermal dynamics

Due to the overwhelming complexity of the electrochemical related behaviors and internal structure of lithium ion batteries, it is difficult to obtain an accurate mathematical expression of their thermal dynamics based on the physical principal. In this paper, a data based thermal model which is suitable for online temperature distribution estimation is proposed for lithium-ion batteries. Based on the physics based model, a simple but effective low order model is obtained using the Karhunen–Loeve decomposition method. The corresponding uncertain chemical related heat generation term in the low order model is approximated using extreme learning machine. All uncertain parameters in the low order model can be determined analytically in a linear way. Finally, the temperature distribution of the whole battery can be estimated in real time based on the identified low order model. Simulation results demonstrate the effectiveness of the proposed model. The simple training process of the model makes it superior for onboard application.

A nonlinear sliding mode observer for the estimation of temperature distribution in a planar solid oxide fuel cell

Compliance to certain temperature constraints is essential for the long life and stable operation of solid oxide fuel cells (SOFCs). However, it is difficult and costly to measure the temperature inside a high temperature, well-sealed cell directly. A nonlinear sliding mode observer has been designed in this paper for estimating the temperature distribution in a hydrogen fed SOFC stack. The observer design is based on a finite-volume parameter SOFC model, which is simplified by quasi-static mass balance assumption. In the observer design, a decoupling pole placement method that applies to multi-timescale systems is proposed to obtain a suitable observer gain. And a quasi-sliding mode control method is adopted to eliminate the chatter caused by the discontinuous control actions of sliding mode control. Theoretical analysis and simulation results are presented to prove the convergence and good performance of the designed observer for estimating the temperature distribution in a SOFC stack during steady-state and transient operation.

A Spatiotemporal Estimation Method for Temperature Distribution in Lithium-Ion Batteries

Effective thermal management is crucial to the optimal operation and health management of lithium-ion batteries. The online estimation of the temperature distribution in vehicle battery systems is not easy, as there are only a few sensors available on site. Furthermore, the thermal behaviors of batteries are difficult to predict, as their dynamics are strongly time-varying. In this paper, a hybrid model is developed for spatiotemporal estimation of temperature distribution in lithium-ion batteries. A simple but effective nominal model is first developed for real-time thermal management using a time/space separation method. Subsequently, a data-based neural model is proposed to compensate the model-plant mismatch caused by the spatial nonlinearity and other model uncertainties. The developed algorithm is simple and can be readily integrated into existing battery management systems. Simulation studies demonstrate the effectiveness of the proposed method.

The Estimation of Temperature Distribution in Cylindrical Battery Cells Under Unknown Cooling Conditions

The estimation of temperature inside a battery cell requires accurate information about the cooling conditions even when the battery surface temperature is measured. This paper presents a model-based approach for estimating temperature distribution inside a cylindrical battery under unknown convective cooling conditions. A reduced-order thermal model using a polynomial approximation of the temperature profile inside the battery is used. A dual Kalman filter (DKF), a combination of a Kalman filter and an extended Kalman filter, is then applied for the identification of the convection coefficient and the estimation of the battery core temperature. The thermal properties are modeled by volume averaged lumped-values under the assumption of a homogeneous and isotropic volume. The model is parameterized and validated using experimental data from a 2.3 Ah 26650 lithium-iron-phosphate battery cell with a forced-air convective cooling during hybrid electric vehicle drive cycles. Experimental results show that the proposed DKF-based estimation method can provide an accurate prediction of the core temperature under unknown cooling conditions by measuring battery current and voltage along with surface and ambient temperatures.

Transient modeling and validation of lithium ion battery pack with air cooled thermal management system for electric vehicles

A transient numerical model of a lithium ion battery (LiB) pack with air cooled thermal management system is developed and validated for electric vehicle applications. In the battery model, the open circuit voltage and the internal resistance map based on experiments are used. The Butler-Volmer equation is directly considered for activation voltage loss estimation. The heat generation of cells and the heat transfer from cells are also calculated to estimate temperature distribution. Validations are conducted by comparison between experimental results at the cell level and the pack level. After validations, the effects of module arrangement in a battery pack are studied with different ambient temperature conditions. The configuration that more LiB cells are placed near the air flow inlet is more effective to reduce the temperature deviation between modules.

Using pairs of physiological models to estimate temporal variation in amphibian body temperature

Physical models are often used to estimate ectotherm body temperatures, but designing accurate models for amphibians is difficult because they can vary in cutaneous resistance to evaporative water loss. To account for this variability, a recently published technique requires a pair of agar models that mimic amphibians with 0% and 100% resistance to evaporative water loss; the temperatures of these models define the lower and upper boundaries of possible amphibian body temperatures for the location in which they are placed. The goal of our study was to develop a method for using these pairs of models to estimate parameters describing the distributions of body temperatures of frogs under field conditions. We radiotracked green-eyed treefrogs (Litoria serrata) and collected semi-continuous thermal data using both temperature-sensitive radiotransmitters with an automated datalogging receiver, and pairs of agar models placed in frog locations, and we collected discrete thermal data using a non-contact infrared thermometer when frogs were located. We first examined the accuracy of temperature-sensitive transmitters in estimating frog body temperatures by comparing transmitter data with direct temperature measurements taken simultaneously for the same individuals. We then compared parameters (mean, minimum, maximum, standard deviation) characterizing the distributions of temperatures of individual frogs estimated from data collected using each of the three methods. We found strong relationships between thermal parameters estimated from data collected using automated radiotelemetry and both types of thermal models. These relationships were stronger for data collected using automated radiotelemetry and impermeable thermal models, suggesting that in the field, L. serrata has a relatively high resistance to evaporative water loss. Our results demonstrate that placing pairs of thermal models in frog locations can provide accurate estimates of the distributions of temperatures experienced by individual frogs, and that comparing temperatures from model pairs to direct measurements collected simultaneously on frogs can be used to broadly characterize the skin resistance of a species, and to select which model type is most appropriate for estimating temperature distributions for that species.

Estimation of surface heat flux and temperature distributions in a multilayer tissue based on the hyperbolic model of heat conduction

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to solve the inverse hyperbolic heat conduction problem in estimating the unknown time-dependent surface heat flux in a skin tissue, which is stratified into epidermis, dermis, and subcutaneous layers, from the temperature measurements taken within the medium. Subsequently, the temperature distributions in the tissue can be calculated as well. The concept of finite heat propagation velocity is applied to the modeling of the bioheat transfer problem. The inverse solutions will be justified based on the numerical experiments in which two different heat flux distributions are to be determined. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The influence of measurement errors on the precision of the estimated results is also investigated. Results show that an excellent estimation on the time-dependent surface heat flux can be obtained for the test cases considered in this study.

Post-mortem estimation of temperature distribution on a power transformer: Physicochemical and mechanical approaches

Power transformers are electrical machines that allow us to transport electric energy, with reduced losses, from generation stations to consumption points. This definition gives us an idea of the number of transformers that are used in power distribution systems worldwide. The main problem that may affect power transformers is the operation at high temperature. This paper summarizes the results of a postmortem temperature estimation carried out on an 800 kVA distribution transformer. Two methodologies are considered for estimating the temperature distribution in the windings of the machine. The first is based on the calculation of the degree of polymerization and the second is obtained from the tensile strength index. By knowing the value of these two magnitudes for a new and for an aged paper, and the period of operation of a transformer, the temperature distribution along the height of the windings can be estimated. None other previous works have used the tensile strength of winding paper for temperature distribution estimation. With these results and the loading regime records, similar transformers still in operation can be operated in an alternative manner and future designs can be improved.