Reconstructed Temperature Distributions Research Articles

Numerical and Experimental Reconstruction of Temperature Distribution and Soot Concentration Field for Thin-Slice Flames Using a Charge Coupled Device Camera

This work proposed a novel model to simultaneously reconstruct temperature distribution and soot volume fraction field for two-dimensional thin-slice flames using the knowledge of monochromatic radiation intensities at two wavelengths using a CCD camera. The deduction process and numerical analysis of the model were described. Effects of wavelength combinations and measurement errors on reconstruction accuracy were considered in detail. Numerical results have proven the model’s accuracy and showed that the temperature and soot volume fraction fields can be reconstructed well even with noisy input data from flame radiation. In addition, a series of experiments were conducted on a mesoscale combustor to obtain the real thin-slice flames for further experimental reconstruction via the model. The experimental results indicated that the proposed model can successfully reconstruct the flame temperature distribution and soot volume fraction field and the main features of thin-slice flames also can be reasonably reproduced.

A combined inverse prediction and experimental analysis for the frozen ground heat transfer in a structure foundation

This paper takes the representative buried structure in permafrost regions, a transmission line tower foundation, as the research object. An inverse prediction is conducted in a scaled-down experimental system mimicking actual heat conduction of the frozen ground in a tower foundation. In permafrost regions, global warming and the heat transfer through the buried structures bring significantly adverse thermal effects on the stability of the infrastructures. In modeling the thermal effects, it has been a challenge to determine the ground surface boundary condition and heat source strength from the buried structures due to the complex climate and environmental conditions. In this work, based on the improved model predictive inverse method with an adaptive strategy, an inverse scheme is successfully implemented to simultaneously identify the time-varying surface temperature and the time-space-dependent heat source representing the buried structures. In this scheme, an adaptive time-varying predictive model is established by the rolling update of the sensitivity response coefficients according to the predicted temperature field to overcome the influence of nonlinear characteristics in the heat transfer process. The inverse method is verified by simulation and experimental data. According to the experimental inversion results, the reconstructed temperature distribution efficiently predicts the thermal state evolution of the permafrost foundation under seasonal freezing and thawing. It is found that, under the experimental conditions, the intensified thawing and freezing are significantly severe, e.g., the increased area ratio of active layer thickness is as high as 28% after building a tower, and the depth of permafrost table ranges from about 14 mm to about 38 mm, which could be detrimental to the stability and safety of the tower foundation. This study will provide valuable guidance for risk assessments or optimizing the design and maintenance of the real tower foundation and similar buried structures.

Optimum angular arrangement of a multi-light field imaging technique for flame temperature reconstruction

A burner array produces a multi-modal flame temperature field and a compact combustion region. A multi-light field imaging technique can retrieve the multi-modal flame temperature accurately. However, the angular arrangement of the multi-light field imaging technique is a crucial factor that affects the accuracy of the temperature reconstruction. In this study, a method is proposed by integrating a Quantum-behaved Particle Swarm Optimization algorithm to optimise the angular arrangement of the multi-light field imaging technique and to achieve optimal accuracy of the flame temperature reconstruction. The proposed method is evaluated through numerical and experimental studies. The proposed method is also evaluated under different angular arrangements of the multi-light field camera system. Numerical results demonstrate that the optimal angular arrangement provides better reconstruction accuracy in comparison with different angular arrangements. The experimental results of the reconstructed temperature distributions of ethylene–air bimodal diffusion flames show that the proposed method has good applicability.

A Novel Reconstruction Method for Temperature Distribution Measurement Based on Ultrasonic Tomography.

The precise temperature distribution measurement is crucial in many industrial fields, where ultrasonic tomography (UT) has broad application prospects and significance. In order to improve the resolution of reconstructed temperature distribution images and maintain high accuracy, a novel two-step reconstruction method is proposed in this article. First, the problem of solving the temperature distribution is converted to an optimization problem and then solved by an improved version of the equilibrium optimizer (IEO), in which a new nonlinear time strategy and novel population update rules are deployed. Then, based on the low-resolution and high-precision images reconstructed by IEO, Gaussian process regression (GPR) is adopted to enhance image resolution and keep the reconstruction errors low. After that, the number of divided grids and the parameters of IEO are also further studied to improve the reconstruction quality. The results of numerical simulations and experiments indicate that high-resolution images with low reconstruction errors can be reconstructed effectively by the proposed IEO-GPR method, and it also shows excellent robust performance. For a complex three-peak temperature distribution, a competitive accuracy with 3.10% and 2.37% error at root-mean-square error and average relative error is achieved, respectively. In practical experiment, the root-mean-square error of IEO-GPR is 0.72%, which is at least 0.89% lower than that of conventional algorithms.

Fast and Calibration-Free Temperature Imaging of Dynamic Flames via Wavelength Modulated Lateral Shearing Interferometry

Temperature distributions of dynamical flames were measured by using a proposed calibration-free wavelength modulated lateral shearing interferometry. A distributed feedback (DFB) laser was modulated in the wavelength as a sawtooth profile. The wrapped flame phase in the images was obtained pixel by pixel by calculating the phase shift between the interference light intensity profiles before and after flame ignition. Phase unwrapping and recovery were adopted to solve the flame phase distribution. The refractive index distribution was reconstructed with the help of Inverse Abel transform. The temperature imaging was further achieved by the ideal gas law and Gladstone-Dale model. Numerical simulations were conducted for performance evaluations. The flame phase, refractive index and temperature distributions were reconstructed with errors of 0.0094, 0.0154 and 0.0958, respectively. Standard deviations were in the magnitude of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> at the presence of Gaussian random noises and showed the noise immunity of the proposed method. In actual experiments, reconstructed temperature distribution of a steady flame generated on a Bunsen burner agreed well with the thermocouple measurements. A dynamical process of flame extinguishment was portrayed at one kilo frames per second. Temporal variation of the flame temperature distribution well reflected the extinguishing process. The entire measurement process did not require prior calibration of the modulated wavelength, and the imaging speed was more than ten times faster than the existing phase modulated interferometer. The proposed method can be used for on-line evaluation of dynamic flames.

Improved Two-Color Method for Temperature Measurement of Soot Flames

An improved two-color method, which originates from an approximate emissivity ratio model based on the empirical emissivity formula by Hottel and Broughton, was developed to measure the temperature field of soot flames generated on a McKenna burner in the present study. In conjunction with the onion-peeling method and Tikhonov regularization, the reconstructed temperature fields of rich soot flames under varied equivalence ratios were obtained by calculating the 550 and 650 nm spontaneous emission signal images, which were recorded by an intensified charge coupled device, respectively. At the same time, an autoscanning R-type thermocouple was used to measure flame temperature for validating the reconstructed data. The results show that the reconstructed temperature distributions agreed well with the measured data by thermocouple, and the reconstructed temperature is more precise by the present improved two-color method than by the classic two-color method based on a constant emissivity assumption.

Multi-scale simulation of temperature on braided fibers reinforced composite plate considering the fluctuations

The direct simulation based on the braided model of a whole fibers reinforced composite (FRC) component puts forward too high request on the calculating ability. So a multi-scale simulating method of the temperature on braided FRC plate is built in this paper, considering the temperature fluctuations of braided structures. The effective model of braided plate and the periodic braided structure are built, to obtain the homogenized temperature field and the fluctuations of temperature, respectively. The Fourier series is applied to build the functions of temperature fluctuations. Then the reconstructed temperature field of braided FRC plate could be obtained based on the homogenized temperature field and the functions of temperature fluctuations. Finally, the temperature field with fluctuations based on the braided model of whole plate is also simulated and compared with the reconstructed temperature field, to validate the accuracy of multi-scale thermal analysis method. Additionally, the experiment of temperature test on the braided FRC plate is also carried out to validate the accuracy of simulation, which presented good accuracy. The results show that, the temperature distribution of the braided FRC plate has significant fluctuating characteristics, the temperature in the region with braided yarns is relatively lower comparing with that in the matrix region, and the distributions of fluctuations are highly similar to the braided structures. The homogenized model based on the effective thermal conductivities could not obtain the temperature fluctuations of braided FRC plate. The maximum temperature difference between the braided model and the homogenized model reaches 25.37 K. Finally the maximum relative variation between the reconstructed temperature distribution and the temperature distribution based on the braided model is 3.18%, so the multi-scale thermal analysis method in this paper has good accuracy in simulating the temperature distribution of braided FRC plate with fluctuations.

3D high-quality temperature-field reconstruction method in furnace based on acoustic tomography

Reconstructed 3D high-quality temperature distribution in furnace can provide important information to better control boiler operations and to optimize the combustion process. Acoustic travel-time tomography is considered to be a promising method that uses the dependence of sound speed on temperature to reconstruct the temperature field. In this paper, a new 3D temperature field reconstruction method based on radial basis function approximation with polynomial reproduction (RBF-PR) and truncated generalized singular value decomposition (TGSVD) is proposed to solve the inverse problem. To improve the reconstruction quality, we consider the refraction effect of sound waves in the non-uniform temperature field and estimate the sound wave propagation path model in the reconstruction method. The shooting method with improved Powell algorithms is used to solve the propagation path model and obtain the relationship between the acoustic travel-time over the propagation path and temperature distribution. Simulations are implemented to evaluate the effectiveness of the proposed reconstruction method. The results indicate that compared with other methods, the new reconstruction method that considers the refraction effect can reconstruct temperature distribution with higher accuracy and better anti-noise ability. Experimental results also demonstrate that the temperature distribution can be reconstructed effectively by the proposed method.

Application of 2D temperature measurement to a coal-fired furnace using CT-TDLAS

The measurement of temperature and species concentration in combustion fields is very significant for the development of highly efficient combustion technologies for energy conservation and emission reduction. There are various measurement technologies, including contact and non-contact measurement. Tunable diode laser absorption spectroscopy (TDLAS) technology is a proven non-contact method for detection of the temperature and species concentration by absorption measurement. To enable two-dimensional (2D) representation of temperature and species concentration in combustion fields, the TDLAS technology is usually combined with computed tomography (CT). The latter is, however, considerably new in combustion research, especially in the solid fuel reaction environment. In this paper, a 32-path 2D CT-TDLAS system for temperature measurement in a pilot-scale coal-fired furnace was developed. The accuracy of the CT algorithm in the reconstruction of 2D temperature distributions in different laser-path arrangements was first analyzed using the sum of squared difference (SSD) and zero-mean normalized cross-correlation (ZNCC) by comparing it to the 2D temperature distribution of a full-scale coal-fired furnace simulated using computational fluid dynamics (CFD). The accuracy was improved by 32-path reconstruction. The study was then progressed to investigate its measurement accuracy in a simple CH4–air burner configuration with rounded and rectangular cells as well as sensitivity for flame shift detection, whereby the reconstructed temperature distribution was compared to the temperature measured using a thermocouple. It is verified that this CT reconstruction was feasible for various measurement areas, even if the center of the flame was shifted. Finally, a 32-path 2D CT-TDLAS system with a rectangular-structured cell was developed and applied for temperature measurement in a Tenaga Nasional Berhad (TNB) Research’s pilot-scale coal-fired furnace. The 2D temperature distribution in the coal-fired furnace was reconstructed according to the experimental results. The potential of the CT-TDLAS for online 2D temperature measurement for actual applications is demonstrated.

Reconstruction of thermal field in target tissue during the therapy of high intensity focused ultrasound

High intensity focused ultrasound (HIFU) is a minimally invasive medical procedure, obtaining the transient temperature field of the target tissue is a key to study HIFU ablation. In this work, an inverse heat transfer scheme is proposed to investigate thermal effect of HIFU and further reconstruct the transient temperature field of the target tissue. In the inverse scheme, a prediction model is established between the measured temperature and heat source in the target tissue. Then, based on the prediction model, a model predictive inverse scheme is established to estimate heat source induced by HIFU in the target tissue. Finally, the inversed heat source is used to solve biological heat transfer equation to reconstruct temperature distribution in the target tissue of HIFU ablation. Numerical experiments are performed to study the effects of the form of heat source, the number of future time steps and measured error on the inverse results. The results have shown that the inverse scheme can significantly reduce the sensitivity of the inverse results on measurement noise, and the temperature distribution in the target tissue can be obtained by the inverse scheme, which provides theoretical guidance for treatment planning and efficacy evaluation of HIFU.

Joint method for reconstructing three-dimensional temperature of flame using Lucy-Richardson and nearest neighbor filtering using light-field imaging

The real-time measurement and reconstruction of three-dimensional temperature are essential when studying the combustion process inside a flame. In the proposed sectioned flame light field imaging model, flame sections are reconstructed based on the characteristics identified using the Lucy-Richardson or nearest neighbor filtering methods, or a joint method involving a combination of both, to improve on the accuracy of two-dimensional temperature reconstruction. Compared to the results of a previous work, the proposed method increases the resolution in the depth of field direction and the extraction of the flame temperature of all sections from the same height ensures the accuracy of the reconstructed temperature distribution across the cross-section of the flame. The relative error when compared to the actual flame is less than 10%. Thus, this approach allows the accurate estimation of the three-dimensional temperature distribution inside a flame, and enables the rapid and effective reconstruction of the three-dimensional temperature field.

Experimental and numerical analysis of radiative entropy generation in industrial and boiler furnaces

In this paper, based on the radiative entropy generation formula and the inverse radiation analysis, experimental and numerical analysis of the radiative entropy generation in an oil-fired industrial furnace and a coal-fired boiler furnace is presented. The radiative entropy generation in two-dimensional enclosure solved by Discrete Ordinates method was verified by the second-law thermodynamics analysis. With the reconstructed temperature distribution and radiative properties through the inverse radiation analysis, the radiative entropy generation in the furnace and total net radiative heat on the wall were given. The effects of temperature distribution and optical thickness on total net radiative heat and radiative entropy generation in the furnaces were analyzed. Numerical and experimental results proved, when the optical thickness is small, with the decrease of non-uniformity of temperature distribution of medium, the radiative entropy generation due to radiative processes of medium decreases, and total net radiative heat on the wall also decreases which causes the decrease of the radiative entropy generation due to radiative process on the wall. However, when the optical thickness is large, with the decrease of non-uniformity of temperature distribution of medium, the radiative entropy generation due to radiative processes of medium decreases, but total net radiative heat on the wall increases which causes the increase of the radiative entropy generation due to radiative process on the wall.

Development of an Algorithm for Predicting the Thermal Distribution by using CT Image and the Specific Absorption Rate

During hyperthermia therapy, cancer cells are heated to a temperature in the range of 40 ~ 45 °C for a defined time period to damage these cells while keeping healthy tissues at safe temperatures. Prior to hyperthermia therapy, the amount of heat energy transferred to the cancer cells must be predicted. Among various non-invasive methods, the thermal prediction method using the specific absorption rate (SAR) is the most widely used method. The existing methods predict the thermal distribution by using a single constant for the mass density in one organ through assignment. However, because the SAR and the bio heat equation (BHE) vary with the mass density, the mass density of each organ must be accurately considered. In this study, the mass density distribution was calculated using the relationship between the Hounsfield unit and the mass density of tissues in preceding research. The SAR distribution was found using a quasi-static approximation to Maxwell’s equation and was used to calculate the potential distribution and the energy distributions for capacitive RF heating. The thermal distribution during exposure to RF waves was determined by solving the BHE with consideration given to the considering contributions of heat conduction and external heating. Compared with reference data for the mass density, our results was within 1%. When the reconstructed temperature distribution was compared to the measured temperature distribution, the difference was within 3%. In this study, the density distribution and the thermal distribution were reconstructed for the agar phantom. Based on these data, we developed an algorithm that could be applied to patients.

Application of Landweber Method for Three-Dimensional Temperature Field Reconstruction Based on the Light-Field Imaging Technique

Combined with the light-field imaging technique, the Landweber method is applied to the reconstruction of three-dimensional (3D) temperature distribution in absorbing media theoretically and experimentally. In the theoretical research, simulated exit radiation intensities on the boundary of absorbing media according to the computing model of light field are employed as inputs for inverse analysis. Compared with the commonly used iterative methods, i.e., the least-square QR decomposition method and algebraic reconstruction technique (ART), the Landweber method can produce reconstruction results with better quality and less computational time. Based on the numerical study, an experimental investigation is conducted to validate the suitability of the proposed method. The temperature distribution of the ethylene diffusion flame is reconstructed by using the Landweber method from the flame image captured by a light-field camera. Good agreement was found between the reconstructed temperature distribution and the measured temperature data obtained by a thermocouple. All the experimental results demonstrate that the temperature distribution of ethylene flame can be reconstructed reasonably by using the Landweber method combined with the light-field imaging technique, which is proven to have potential for the use in noncontract measurement of temperature distribution in practical engineering applications.

Research on Temperature Field Reconstruction Based on RBF Approximation with Polynomial Reproduction Considering the Refraction Effect of Sound Wave Paths

The temperature field distribution directly reflects the combustion condition in a furnace．In this paper, acoustic thermometry to reconstruct temperature distribution is investigated. A method based on radial basis function... | Find, read and cite all the research you need on Tech Science Press

Influence of tool material and tool wear on tool temperature in hard turning reconstructed via inverse problem solution

In this work the cutting tool temperature distribution that develops during turning of hardened cold-work tool steel is modeled on the basis of experimental data. The data obtained from a series of thermocouples, placed on a PCBN insert, into an anvil, and into a toolholder, were used as the input for the model. An inverse problem was solved, where the heat fluxes were computed. The temperature distribution was modeled for the case of new tools, as well as for the case of its development in the course of a tool wear. The reconstructed temperature distributions were in good agreement with the measured data. The heat flux through rake face was found to be reducing with the decrease of thermal conductivity of the tool material.

Tomographic imaging of reacting flows in 3D by laser absorption spectroscopy

This paper describes the development of an infrared laser absorption tomography system for the 3D volumetric imaging of chemical species and temperature in reacting flows. The system is based on high-resolution near-infrared tunable diode laser absorption spectroscopy (TDLAS) for the measurement of water vapour above twin, mixed fuel gas burners arranged with an asymmetrical output. Four parallel laser beams pass through the sample region and are rotated rapidly in a plane to produce a wide range of projection angles. A rotation of 180° with 0.5° sampling was achieved in 3.6 s. The effects of changes to the burner fuel flow were monitored in real time for the 2D distributions. The monitoring plane was then moved vertically relative to the burners enabling a stack of 2D images to be produced which were then interpolated to form a 3D volumetric image of the temperature and water concentrations above the burners. The optical transmission of each beam was rapidly scanned around 1392 nm and the spectrum was fitted to find the integrated absorbance of the water transitions and although several are probed in each scan, two of these transitions possess opposite temperature dependencies. The projections of the integrated absorbances at each angle form the sinogram from which the 2D image of integrated absorbance of each line can be reconstructed by the direct Fourier reconstruction based on the Fourier slice theorem. The ratio of the integrated absorbances of the two lines can then be related to temperature alone in a method termed, two-line thermometry. The 2D temperature distribution obtained was validated for pattern and accuracy by thermocouple measurements. With the reconstructed temperature distribution, the temperature-dependent line strengths could be determined and subsequently the concentration distribution of water across the 2D plane whilst variations in burner condition were carried out. These results show that the measurement system based on TDLAS can be used for 2D temporal or 3D volume imaging of temperature and chemical species concentration in reacting flows.

Estimation of Internal Heat Generation in a Fin Involving All Modes of Heat Transfer Using Golden Section Search Method

ABSTRACTThe present work deals with the application of the golden section search method (GSSM) for predicting the internal rate of heat generation to reconstruct a given temperature distribution within a rectangular fin involving all modes of heat transfer. The thermal conductivity has been assumed to be temperature-dependent. The forward problem is numerically solved using an implicit fourth-order Runge–Kutta method, whereas, an inverse problem has been solved using GSSM. In conjunction with GSSM, for the inverse analysis, the effect of inverse crime has been addressed using a different solver operating on fifth-order accurate Runge–Kutta method than that used for synthesizing the input data. A case study of Hastelloy generally used in gas turbine applications is also presented and the effect of measurement error in the temperature distribution has been reported. For pure temperature data, an exact estimation of the internal heat generation rate is done, whereas, even with noisy data, a satisfactory estimation of the heat generation rate is also achieved which is verified from the reconstructed temperature distributions.

Ultrasonic temperature distribution reconstruction for circular area based on Markov radial basis approximation and singular value decomposition

Temperature distribution reconstruction is of critical importance for circular area, and an ultrasonic technique is investigated to meet this demand in this paper. Considering the particularity of circular area, algorithm based on Markov radial basis approximation and singular value decomposition is proposed, while ultrasonic transducers layout and division of measured area are properly designed. The reconstruction performance is validated via numerical experiments using different temperature distribution models, and is compared with algorithm based on least square method. To study the anti-interference, various noises are adding to the theoretical value of time-of-flight. Experiment results indicate that the proposed algorithm can reconstruct temperature distribution with higher accuracy and stronger anti-interference, while without the problem of algorithm based on least square method that its reconstructions will lose much temperature information near the edge of measured area.

A New Algorithm for Reconstructing Two-Dimensional Temperature Distribution by Ultrasonic Thermometry

Temperature, especially temperature distribution, is one of the most fundamental and vital parameters for theoretical study and control of various industrial applications. In this paper, ultrasonic thermometry to reconstruct temperature distribution is investigated, referring to the dependence of ultrasound velocity on temperature. In practical applications of this ultrasonic technique, reconstruction algorithm based on least square method is commonly used. However, it has a limitation that the amount of divided blocks of measure area cannot exceed the amount of effective travel paths, which eventually leads to its inability to offer sufficient temperature information. To make up for this defect, an improved reconstruction algorithm based on least square method and multiquadric interpolation is presented. And then, its reconstruction performance is validated via numerical studies using four temperature distribution models with different complexity and is compared with that of algorithm based on least square method. Comparison and analysis indicate that the algorithm presented in this paper has more excellent reconstruction performance, as the reconstructed temperature distributions will not lose information near the edge of area while with small errors, and its mean reconstruction time is short enough that can meet the real-time demand.