Measurement Of Temperature Distribution Research Articles

Experimental and numerical study of combustion characteristics in a liquid fuel CAN micro-combustor

In the present study, combustion characteristics of a CAN type combustor of a micro gas turbine working with liquid fuel are evaluated. First, an experimental work is conducted to measure the combustion chamber temperature values. The goal of the experimental study is to determine the experimental behavior of the chamber at one of its operating points. Then, numerical simulation is done to investigate the details of combustion phenomenon in the combustor. The measured temperature distribution by experiment is well predicted by the results of numerical calculation. However, there are points making a difference between experimental and numerical results in few regions due to the two-dimensional axisymmetric simulation error. The results show that the IRZ (Inner Recirculation Zone) and recirculation zones around the liner walls increase forces applying to the droplets and promote breakup and droplet evaporation rates, due to the instability and high turbulence kinetic energy. These zones play an influential role in the evaporating liquid fuel droplets, creating a homogeneous mixture of fuel and air and forming and stabilizing the flame, by providing high residence time for the mixture of vaporized fuel droplets and air. Zones where the fuel-air mixing is such that the mixture fraction is equal to the stoichiometric amount, in addition to forming and stabilizing flame, the species of complete combustion such as CO2 and the species of incomplete combustion such as CO have the highest and lowest values, respectively. Finally, the chamber performance in the operating point is found to be at an acceptable level, by investigating the chamber's performance parameters such as evaporation efficiency, combustion efficiency, pattern factor and the entropy generation.

Reconstruction of 3D flame temperature and absorption coefficient field by the hybrid light-field imaging and laser extinction technique

A hybrid method based on combining the light-field imaging and laser extinction techniques is proposed to reconstruct the 3D temperature and absorption coefficient fields in the pure absorbing flame. The inhomogeneous absorption coefficient distribution can be recovered based on the exit laser signals according to Beer-Lambert law firstly. According to the attained absorption coefficient distribution, the temperature field can be retrieved accurately with high efficiency by utilizing the light-field imaging technique. Besides, the influence of two types of measured signal noises, i.e. the laser signal noise and the light-field image signal noise, on the reconstructed quality have been investigated thoroughly. The Landweber method is adopted to solve the inverse analysis. All the results showed that the 3D temperature and absorption coefficient distribution can be reconstructed accurately and efficiently with different measurement noises, which proves the feasibility of the proposed method for the non-contact measurement of 3D temperature and absorption coefficient distributions of absorbing flame.

Real-time in-situ distributed fiber core temperature measurement in hundred-watt fiber laser oscillator pumped by 915/976\u2009nm LD sources

In this manuscript, we studied the thermal properties of hundred-watt fiber laser oscillator by real-time in-situ distributed temperature measurement. Optical frequency domain reflectometry (OFDR) was introduced to measure the temperature distribution of gain fiber core. The fiber laser oscillator operated at 1080 nm and the wavelength of detecting signal from OFDR was ~1550 nm. The maximum output power of this fiber oscillator was 100 W. The fiber core temperature distributions in experiment agree well with our theoretical simulation. The temperature measurement of gain fiber core in oscillator has always been a problem because the backward laser from the oscillator may reduce the signal-to-noise ratio in OFDR. To the best of our knowledge, this is the first temperature distribution measurement of fiber core in hundred-watt oscillator. By the experimental measurement and theoretical model, we also analyzed the thermal properties of laser oscillator respectively pumped by 915 nm and 976 nm LD sources. We found fiber laser oscillator pumped by 976 nm LD sources experienced not only higher maximum thermal load but also higher average thermal load than that pumped by 915 nm LD sources at the same level output power. We also analyzed the fiber core temperature of other components in system, such as combiners and fiber Bragg gratings (FBG). These results are meaningful for us to improve the thermal design and management in fiber lasers.

Measurement of indoor air temperature distribution using acoustic travel-time tomography: Optimization of transducers location and sound-ray coverage of the room

Abstract Acoustic travel-time TOMography (ATOM) allows the measurement and reconstruction of air temperature distributions. Due to limiting factors, such as the challenge of travel-time estimation of the early reflections in the room impulse response, which heavily depends on the position of transducers inside the measurement area, ATOM is applied mainly outdoors. To apply ATOM in buildings, this paper presents a numerical solution to optimize the positions of transducers. This optimization avoids reflection overlaps, leading to distinguishable travel-times in the impulse response reflectogram. To increase the accuracy of the measured temperature within tomographic voxels, an additional function is employed to the proposed numerical method to minimize the number of sound-path-free voxels, ensuring the best sound-ray coverage of the room. Subsequently, an experimental set-up has been performed to verify the proposed numerical method. The results indicate the positive impact of the optimal positions of transducers on the distribution of ATOM-temperatures.

The development of the simultaneous reconstruction of 2D temperature and concentration using a 6-peaks algorithm for CT-TDLAS

A new reconstruction algorithm for a computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS) proposed for the measurements of two-dimensional temperature and concentration distribution of a gas flame. The characteristic wavelengths near 1388 nm where water vapor was detected, it used for the performance test of the proposed algorithm. The new algorithm is a 6-peaks algorithm, in which the absorptions at 6 representative wavelengths are used for the construction of the actual absorption spectra at a certain temperature of gas flame. Multiplicative algebraic reconstruction technique (MART) and scale & least mean squares (LMS) algorithms were adopted for data reconstructions. Mean squared error (MSE) was calculated during the iterative calculations for data reconstructions. In order to evaluate the performances of the new algorithm, a numerical test was performed by the use of phantom data in which two-dimensional distribution of temperature and concentration fields were set at 22 × 22 square mesh with Gaussian distribution. Further, the proposed algorithm has been adopted to calculate an actual temperature distribution inside a combustion engine, through which the performance of the newly proposed 6-peaks algorithm has been demonstrated theoretically and experimentally. It is highly expected that the proposed algorithm will be the most appropriate approach for calculating the temperature and concentration fields in CTTDLAS.

Development of electrochemical-thermal modelling for large-format Li-ion battery

Considering the non-homogeneous microstructure due to materials and fabrication process of large-format lithium-ion batteries, an effective electrochemical-thermal model is necessary for modern Li-ion battery (LIB) industry. In this work we developed a simplified model by using parallel method to study large-format Li-ion batteries. In particular, an approach in a combination of Maxwell-Cattaneo-Vernotte theory and Marcus-Hush-Chidsey kinetics was developed to determine the effect of lithium ion transport inertia and electron transfer behavior within 3D electrodes. To clearly verify the effectiveness of the developed model, temperature distribution measurements of a 155 Ah prismatic-type Li-ion batteries were carried out by using four built-in temperature sensors during charge and discharge process at different current densities. The simulation error of the studied model is only within 1.7 °C at 1.0C discharge, for 2.0C discharge, the error is 3.9 °C, which provide very strong verifications. We found that the hottest zone inside the battery is around the positive connector. The simulation studies also found that the internal currents of large-format batteries are unstable during constant current discharge process. During a discharge process at 2.0C, local internal current in some areas even reached 6.0C and negative current is also detected as well. This means that the local redox direction can be significantly changed in a large-format LIB. This phenomenon can be explained by the nonuniform distribution of reactant concentration and temperature inside the studied batteries. This work introduced an effective approach to establish a model for LIB industry, which can be used as a fast and accurate diagnosis method to design optimal parameters for large-format LIB batteries.

Decomposition Reactions of Fe(CO)5, Fe(C5H5)2, and TTIP as Precursors for the Spray-Flame Synthesis of Nanoparticles in Partial Spray Evaporation at Low Temperatures

Flame spray pyrolysis is an important method of nanoparticle manufacturing. Reactions of the precursor and the solvent determine which intermediates can contribute to particle formation. To investigate the chemical interaction between the solvent and the precursor during the partial evaporation of the spray preceding ignition, precursor solutions were sprayed into an externally heated flow reactor. The thermal decomposition of the precursors Fe(CO)5, Fe(C5H5)2, and Ti(i-OC3H7)4 in solutions of xylene and ethanol was investigated. Decomposition products were analyzed by mass spectrometry. The relevance of reactions at these low temperatures for the spray-flame process is substantiated by measurements of the spatial temperature distribution of the spray flame. Depending on the relative thermal stabilities of the precursor and the solvent, the less stable component can initiate decomposition of the more stable component, resulting in different reaction patterns of the solutions. The results are discussed with regard to their potential influence on particle formation pathways.

Measurement of temperature and wavelength-dependent emissivity distributions using multi-wavelength radiation thermometry

A multi-wavelength radiation thermometry method used to determine the temperature and wavelength-dependent emissivity according to spectroscopic radiation intensities is presented. Over a predetermined temperature range, with a set step size, the method traverses the temperature range, and for each temperature, inversely fits a spectral line according to the intensity in the middle of the wavelength region, based on the Rayleigh approximation. The temperature with the spectral line closest to the measured spectral line is considered to be the optimum temperature at that accuracy level. Then, near that optimum temperature, the temperature range and step size are narrowed, to determine the optimum temperature at higher levels of accuracy. Iterating on this method until reaching the required accuracy level, the temperature can be achieved, and the wavelength-dependent emissivity can also be determined. Simulation verification was conducted showing good anti-noise performance and rapid processing capacity. Temperature and emissivity distributions for six heights of an axisymmetric laminar diffusion flame with 194 mL/min ethylene and 240 L/min air were given. Results show that along the line of sight, the radiation temperatures exhibit an average effect of the local temperatures, while the emissivity exhibits a cumulative effect of the absorption coefficients.

Simultaneous measurement of gas-liquid interface motion and temperature distribution on heated surface using temperature-sensitive paint

We developed a simultaneous measurement technique for temperature distribution on a heated surface and gas-liquid interface motion of two-phase flows in microgap channel using temperature-sensitive paint (TSP). Since the TSP layer is optically transparent, the proposed method enables us to simultaneously measure the temperature distribution and the motion of gas-liquid interface through the TSP layer using an in-house stereoscope-like device. Since the refractive index of gas-phase differs from that of liquid-phase, the luminescent intensity of TSP in gas-phase varies from that in liquid-phase even though the temperatures are same in both phases. Then, we proposed a correction method for temperature distribution in gas-phase. To validate the proposed method, the temperature distribution measurements were conducted in liquid single-phase flow. The Nusselt numbers calculated from the measured temperatures were in good agreement with the Sieder-Tate equation. Then, we measured the temperature distributions for the boiling flows under several heated temperature conditions. The temperature distributions at growing bubble and bubble coalescence were successfully measured. TSP is useful method for investigating the temperature distribution in two-phase flows.

Development and Modeling of Differentially Heat-Strengthened Rail Welding: Welding and Local Heat Treatment Modeling

During the manufacturing of continuous welded rail track, the problem of the local hardened points in the welded joint during rail joint welding is resolved by using local heat treatment of the welded joint. As a result, the quenching structure formation is excluded. However, the appearance of new heat-affected zones with reduced hardness is possible. During operation, such rails are characterized by increased tread surface wear in these areas and rail flattening at the welded joint, which is the main reason for retiring the rails from service earlier than the guaranteed service life. A new technology based on the dependence of the structural component dispersion (primarily perlite and carbide particles formed in the process of rail butt welding) is proposed for the steel composition and cooling conditions. The cooling rate has a decisive influence on the dispersion degree of the ferrite-cementite structure formed during the austenite decomposition. During the welding rail process, the granular perlite formation is possible in a butt weld in areas with a temperature ranging within points Ac1 and Acm. To determine these critical temperatures, thermodynamic calculations were performed using the Thermo–Calc® software (TCFE database) allowing the chemical composition of the samples obtained by spectrometry. The iron–carbon state diagrams for rail steel 76KhSF with the minimum and maximum alloying element content according to GOST R 51685–2013 are modeled. To obtain the minimum number of sections with reduced hardness, it is possible to weld rails using shot discontinuous flash welding. In order to eliminate the formation of defective areas with a quenching structure, it is possible to control the cooling of the welded joint by contact heating. Temperature distribution measurement during welding according to given modes and controlled cooling confirms the theoretical conclusions.

Pulverized coal combustion application of laser-based temperature sensing system using computed tomography – Tunable diode laser absorption spectroscopy (CT-TDLAS)

The investigation of combustion phenomena in pulverized coal flames is significant for combustion optimization related to energy conservation and emission reduction. Real-time two dimensional (2D) temperature and concentration distributions play an important role for combustion analysis. The non-contact and fast response 2D temperature and concentration distribution measurement method was developed in this study. The method is based on a combination of computed tomography (CT) and tunable diode laser absorption spectroscopy (TDLAS). The accuracy evaluation of developed 32-path CT-TDLAS demonstrated its feasibility of 2D temperature measurement. 32-path CT-TDLAS was applied to CH4 and 5 kg/h coal combustion fields for 2D temperature measurement. The time-series 2D temperature distribution in coal combustion furnace was measured using 32-path CT-TDLAS measurement cell with kHz time resolution. The transient temperature field of combustion flame directly reflects the combustion mode and combustion stability. The measurement results demonstrate its applicability of CT-TDLAS to various types of combustor, especially the combustion fields with coal and ash particles. CT-TDLAS method with kHz response time enables the real-time 2D temperature measurement to be applicable for combustion analysis.

On‐line monitoring device for dry zone formation in the soil surrounding underground power cables

Formation of dry zones around power cables is an important factor affecting the cable loading and may lead to cable failure. This phenomenon is ignored by some standards in the calculation of power cables capacity. Numerous efforts have been done by many researchers for cable monitoring. In this study, monitoring system based on measurements of temperature distribution surrounding the cable route is suggested. When reaching the temperature of the dry zone formation the system will produce a warning alarm. To the best of the authors knowledge, the invention of a device that gives a warning in the case of drying layers formation around the power cables has not received attention so far. The proposed device is characterised by cheap price, high accuracy and its simplicity in the design. The system is tested in the laboratory using different soil types. Field tests are done to verify the reliability of the device.

Thermal comfort and virtual reality headsets

This study proposed to investigate the thermal properties and subjective thermal discomfort of five virtual reality headsets, and their relationships. Twenty-seven university students used each of the five headsets for 45 min. Microclimate temperature and relative humidity were measured by miniature dataloggers. Infrared thermography was used to measure temperature distribution on the contact points between user's face and the headsets. Participants reported subjective thermal discomfort associated with using each headset.The average microclimate temperature and relative humidity increased by 7.8 °C and 3.5% respectively after headset use. Overall subjective thermal discomfort increased along with duration of use and came primarily from the display. Applying the linear mixed-effects model showed that subjective thermal discomfort is positively correlated with duration of use, microclimate temperature, relative humidity and display coverage area. Conversely, thermal discomfort is negatively correlated with total coverage area, with microclimate temperature acting as the most significant contributing factor. The headsets were ranked by pairing the objective measurements with subjective evaluations.

Simultaneous estimation of heat flux and heat transfer coefficient in irregular geometries made of functionally graded materials

Abstract A numerical inverse analysis based on explicit sensitivity coefficients is developed for the simultaneous estimation of heat flux and heat transfer coefficient imposed on different parts of boundary of a general irregular heat conducting body made of functionally graded materials with spatially varying thermal conductivity. It is assumed that the thermal conductivity varies exponentially with position in the body. The body considered in this study is an eccentric hollow cylinder. The heat flux is applied on the cylinder inner surface and the heat is dissipated to the surroundings through the outer surface. The numerical method used in this study consists of three steps: 1) to apply a boundary-fitted grid generation (elliptic) method to generate grid over eccentric hollow cylinder (an irregular shape) and then solve for the steady-state heat conduction equation with variable thermal conductivity to compute the temperature values in the cylinder, 2) to propose a new explicit sensitivity analysis scheme used in inverse analysis, and 3) to apply a gradient-based optimization method (in this study, conjugate gradient method) to minimize the mismatch between the computed temperature on the outer surface of the cylinder and simulated measured temperature distribution. The inverse analysis presented here is not involved with an adjoint equation and all the sensitivity coefficients can be computed in only one direct solution, without the need for the solution of the adjoint equation. The accuracy, efficiency, and robustness of the developed inverse analysis are demonstrated through presenting a test case with different initial guesses.

Temperature Field Measurement in a Cutting Tool by Laser Interferometry

To increase machining efficiency, in addition to determining the temperature distribution on the tool surface, it is also necessary to determine the internal temperature distribution. The existing methods for determining the cutting tool temperature distribution and temperature field measurement have significant disadvantages, which limit their applicability and accuracy. The purpose of this study is to develop and test a novel cutting tool temperature field measurement method. The method involves recording the cutting tool thermal expansion fields by laser interferometry and calculating the tool material temperatures with its coefficient of thermal expansion (CTE). Compared with the methods employing infrared thermometry, the method developed in the present study has a higher spatial resolution and a lower achievable field of view due to its usage of light in the visible region. In addition, since the oxidation film has a higher reflection coefficient for visible light, the present method is less sensitive to the thin-film interference on an oxidized tool surface than those using infrared thermometry, eliminating the false shift of the measured temperature. Moreover, by utilizing cheaper optical components and equipment for interference fringe pattern registration, this method is more affordable. Unlike the emissivity coefficient in infrared thermometry, CTE is independent of changes in the surface quality and can be measured with high accuracy by modern dilatometry. Therefore, the developed method, which employs CTE to calculate the temperature, has a higher reliability. In the present study, the efficiency of this method is tested by the orthogonal turning of difficult-to-cut martensitic heat-treated steel with a cemented tungsten carbide tool. Through the experiment, the temperature distributions along the rake face and flank of the tool, as well as the temperature field inside the tool, were obtained. The results can improve the temperature field measurement in machining cutting tools.

Two-Dimensional Flame Temperature and Emissivity Distribution Measurement Based on Element Doping and Energy Spectrum Analysis

Most of the existing non-contact flame temperature measurement methods rely on the ideal thermal-optical excitation model, which has a great influence on temperature measurement accuracy. Therefore, based on element doping and energy spectrum analysis, this study proposes a novel two-dimensional (2-D) estimation method for flame temperature and emissivity distribution. The element doping method and laser-induced breakdown spectroscopy (LIBS) are introduced into the temperature field test. The external doped element whose spectral radiation characteristics are easy to be analyzed, is regarded as the measured particles to describe the flame temperature distribution from the side. And LIBS is used to analyze and select the doped element, and further determine the effective working wavelength of the optical camera. Besides, the relationship between spectral radiance and emissivity (L-ε) of doped samples is obtained by the emissivity calibration experiment. Then, the 2-D temperature and emissivity distributions can be estimated. Infrared thermograph is used to verify the accuracy of temperature measurement, the measurement error between calculated and standard values is not more than 5%. The experimental results of the oxygen-ethanol combustion flame show that this method can be well applied to the similar temperature measurement.

Noninvasive measurement of temperature distribution in pseudo body with tissue distribution using ultrasonic CT

Noninvasive measurement of temperature distribution in pseudo body with tissue distribution using ultrasonic CT

Quantitative temperature distribution measurements by non-contact scanning thermal microscopy using Wollaston probes under ambient conditions.

Temperature measurement using Scanning Thermal Microscopy (SThM) usually involves heat transfer across the mechanical contact and liquid meniscus between the thermometer probe and the sample. Variations in contact conditions due to capillary effects at sample-probe contact and wear and tear of the probe and sample interfere with the accurate determination of the sample surface temperature. This paper presents a method for quantitative temperature sensing using SThM in noncontact mode. In this technique, the thermal probe is scanned above the sample at a distance comparable with the mean free path of ambient gas molecules. A Three-Dimensional Finite Element Model (3DFEM) that includes the details of the heat transfer between the sample and the probe in the diffusive and transition heat conduction regimes was found to accurately simulate the temperature profiles measured using a Wollaston thermal probe setup. In order to simplify the data reduction for the local sample temperature, analytical models were developed for noncontact measurements using Wollaston probes. Two calibration strategies (active calibration and passive calibration) for the sample-probe thermal exchange parameters are presented. Both calibration methods use sample-probe thermal exchange resistance correlations developed using the 3DFEM to accurately capture effects due to sample-probe gap geometry and the thermal exchange radii in the diffusive and transition regimes. The analytical data reduction methods were validated by experiments and 3DFEM simulations using microscale heaters deposited on glass and on dielectric films on silicon substrates. Experimental and predicted temperature profiles were independent of the probe-sample clearance in the range of 100-200 nm, where the sample-probe thermal exchange resistance is practically constant. The difference between the SThM determined and actual average microheater temperature rise was between 0.1% and 0.5% when using active calibration on samples with known thermal properties and between ∼1.6% and 3.5% when using passive calibration, which yields robust sample-probe thermal exchange parameters that can be used also on samples with unknown thermal properties.

Modelling thermal properties of large LED modules

Abstract In this paper a problem of modelling thermal properties of large LED modules is considered. The compact thermal model of such modules is proposed. The form of this model is presented and a method of parameters estimation is described. The practical usefulness of this model is verified experimentally by comparing the results of calculations and measurements of internal temperature of selected LEDs included in LED modules. The modules were fabricated by Fideltronic, Poland and measurements of temperature distribution on the surface of the modules at selected variants of power dissipation were performed at the Gdynia Maritime University. Good agreement between the results of measurements and modelling was obtained.

Measurements of Temperature Distributions and Condensation Heat Fluxes for Downward Flows of Steam-Air Mixture in a Circular Pipe

Measurements of Temperature Distributions and Condensation Heat Fluxes for Downward Flows of Steam-Air Mixture in a Circular Pipe