Measurement Of Temperature Field Research Articles

Obtaining velocity and pressure distributions in natural convection flows using experimental temperature fields

New hybrid simulation technique is proposed for natural convection flows, which combines experimental measurements of the instantaneous temperature fields with numerical integration of the fluid dynamics equations. Experimental temperature distributions are used to determine the buoyancy term, which enables one to obtain the velocity and pressure fields without extra measurements. Solution of the energy equation is replaced with experimental data, hence the technique can be used even if the energy equation contains unknown source terms or if the boundary conditions for temperature are unknown. The approach is demonstrated for Background Oriented Schlieren (BOS) measurements of three natural convection flows: natural convection near a heated vertical plate, convective plume from a heated horizontal wire and horizontal convection driven by nonuniform radiative heating of liquid surface. The velocity fields, obtained by reconstruction in steady and unsteady flows, exhibit good agreement with numerical simulations if the input temperature data are accurate. Moreover, the hybrid simulation takes into account the flow asymmetries in a particular experimental run. However, spatially limited measurement region or underestimation of the peak temperature, typical for BOS measurements of the thin thermal layers in liquids, lead to underprediction of the velocity and pressure disturbances in hybrid simulation. • Velocity and pressure fields are determined from the measured temperature fields. • The proposed approach is validated for three different natural convection flows. • Instantaneous temperature fields are measured using Background Oriented Schlieren. • The proposed approach can be used if the problem contains unknown heat sources. • Influence of temperature uncertainty and limited measurement region is analyzed.

Observation of room temperature d0 ferromagnetism, bandgap narrowing, zero dielectric loss, dielectric enhancement in highly transparent p-type Na-doped rutile TiO2 compounds for spintronics applications

The Na-doped TiO2 compounds, i.e Ti1−xNaxO20≤x≤0.12 were synthesized via the solid-state synthesis method. The formation of single rutile phase with tetragonal structure was identified through the structural study by recording the XRD patterns. The analyses of the XRD patterns further indicate that Na+ ions are likely being substituted at the interstitial site of Ti4+ ions. The microstructural study using SEM revealed the homogeneous morphology of all compounds, with the particle size in the range of 1–2 μm. The room temperature magnetization versus field measurement reveals a ferromagnetic behavior for all Na-doped compounds with coercivity values ranging from 100 to 930 Oe. The saturation magnetization was observed to be maximum for Ti0.97Na0.03O2 compound but thereafter it decreases. According to optical property measurements, the bandgap reduces from 2.94 to 2.71 eV as the concentration of Na doping increases. The maximum transmittance value 91% was noted for Ti0.97Na0.03O2 compound. The Hall effect measurements indicate that the carrier concentration of all Na-doped TiO2 ranged from 1.077×1015 to 7.579×1015/cm3, and it grew monotonically with the increase of Na-doping concentration. The value of the ac conductivity and dielectric constant were observed to enhance with increasing Na-doping concentration; indicating that transport occurs via hopping of the charge carrier. Further, the dielectric properties observation reveals lossless nature in the produced sample, which suggests that this material could be employed in high-frequency optoelectronic devices.

Field measurement and numerical investigation of artificial ground freezing for the construction of a subway cross passage under groundwater flow

Artificial ground freezing is an environmentally friendly and reliable method to provide temporary ground improvement and groundwater isolation under adverse geological and hydrological conditions. Groundwater flow supplies a substantial source of heat which has an undesirable impact on the closure of frozen soil body. Furthermore, the phenomenon of frost heave and thaw settlement may threaten the surrounding structures. In terms of a ground freezing case in Beijing Metro Line 19, field measurement of ground temperature and deformation were conducted for the prediction of the formation of frozen curtain and the site stability. A hydro-thermal coupling model considering the effect of groundwater flow and phase transition was proposed to quantify the temperature distribution. The numerical model considers the soil particles, crystal ice and liquid water as separate phases, and thermal parameters as variable values related to temperature. Through two basic physical laws and corresponding governing equations, the model captures the relevant coupled relationship in heat and mass transfer. The proposed model is validated by means of the field measured data. Furthermore, the influence of groundwater velocities on the closure of frozen curtain was investigated. The results indicate groundwater flow has an adverse influence on the formation of freezing curtain, even leading to a failure to the closure. The thickness and temperature of frozen curtain with a groundwater velocity of 2 m/d can attain the design values after freezing for 50 days. Moreover, the ground and tunnel deformation in the process of freezing construction were well controlled.

Three-dimensional dynamic measurement of unstable temperature fields by multi-view single-shot phase-shifting digital holography.

A multi-view phase measurement system based on single-shot phase-shifting digital holography is proposed to dynamically obtain three-dimensional (3-D) information of an unstable temperature field. The proposed system consists of a laser, three polarization imaging cameras, and the corresponding optical components. The laser beam emitted from the laser is separated by the fibers into three pairs that contain three object beams and three reference beams. The object beams pass through the object in three different directions and interfere with the reference beams at the image sensor plane respectively. The recording of the three cameras is triggered simultaneously, which enables the phase measurement of dynamic objects from different viewpoints. We successfully measured the 3-D distributions of an unstable temperature field in the experiments with the proposed system.

Internal fatigue crack monitoring during ultrasonic fatigue test using temperature measurements and tomography

Very high cycle fatigue fracture is often associated with internal crack propagation and one major problem to study the initiation and the propagation of this internal crack is to detect its initiation and quantify its propagation rate. The objective of the present work is to develop an experimental methodology to follow the initiation and propagation of the internal crack. The experimental technique presented here is based on temperature field measurement on the specimen surface during an ultrasonic fatigue test using infrared thermography. Indeed, plasticity in the reverse cyclic plastic zone near the crack front generates heat sources due to the dissipation of plastic energy rate and thus an increase of the temperature which propagates through the specimen thanks to heat conduction. By considering the heat source located in the reverse cyclic plastic zone and the geometry of the crack obtained by tomographic observations, finite element simulation of the heat transfer problem enables us to establish a relationship between the internal crack growth and the temperature field evolution on the specimen surface. The results obtained for a cast aluminum alloy are presented and analyzed.

Effect of temperature field on the porosity and mechanical properties of 2024 aluminum alloy prepared by direct chill casting with melt shearing

Porosity severely deteriorates the mechanical properties of aluminum alloys. Large-sized and aggregated porosity often occurs in the center of Direct-Chill (DC) cast ingot. The variation of the temperature field in the sump affects the formation of porosity. In the present work, high shear technology was introduced into the DC casting process and the rotation speed and position of the high shear device were precisely controlled based on the measured temperature fields of conventional DC casting to realize the control of the temperature field and study its effects on the microstructure and mechanical properties of DC cast ingot. The results showed that when the temperature of the melt near the shear site (TS) was close to the temperature of the melt near the center of ingot and at starting position of the slow cooling zone of conventional DC casting (TG), forced convection can affect the cooling zone which is below the graphite ring in the sump, resulting in uniform microstructure of the ingot. If TS was above the liquidus and close to TG (temperature field II), the microstructure shows rod grains with fine secondary dendrite arms, refined porosity and second phase particles. For the lower TS which is below the liquidus and close to TG, (temperature field III), the mixed microstructure of spherical grains and small equiaxed was formed. And the increase of size and content of porosity can decrease of mechanical properties of the ingot. The concomitant relationship between floating/spherical grains and porosity was also discovered and discussed.

Quantitative measurement of natural thermal convection temperature field based on color stripe background oriented schlieren (CSBOS)

In this study, a new color stripe background oriented schlieren (CSBOS) was proposed. Through multiple experiments, the oblique stripes with color alternating arrangements were selected to draw the background pattern, and the natural thermal convection temperature fields of premixed flame combustion in butane laminar flow with different equivalence ratios were analyzed and reconstructed. A color stripe background oriented schlieren experimental platform was built to collect images of the natural thermal convection field above the butane flame, which can improve the accuracy and spatial resolution, and analyze the influence of different equivalence ratios on the flow field morphology and temperature distribution. The root mean square error (RMSE) between the temperature reconstructed by CSBOS and the temperature measured by invasive measurement (the flow field is not destroyed) is 5.26 at different equivalence ratios, and the maximum measurement error between the reconstructed flow field temperature distribution and the contact measurement is only 2.7%, indicating that CSBOS can accurately reconstruct the temperature of the natural thermal convection field.

Combined use of blackbody and infrared radiation for accurate measurement of temperature field of aluminum alloys

Temperature is considered a critical factor in improving the quality of workpieces in the manufacturing of aluminum alloys. To improve the temperature measurement accuracy of aluminum alloys and realize on-line measurement, this paper proposes a method for measuring the temperature field of aluminum alloys with infrared radiation combined with blackbody spots calibration. Since the emissivity of aluminum alloys changes with the surface characteristics of an object, there is a certain difference between the directly measured temperature using the infrared thermal imager and the actual temperature of the aluminum alloy surface. For this purpose, a correction method of infrared radiation temperature field of aluminum alloy based on image mapping theory was established. The uniform and non-uniform temperature fields of the aluminum alloy workpiece were designed, and the temperature field of the aluminum alloy plate was reconstructed based on the image mapping theory and the blackbody spots temperature. The study reveals that accurate measurement of the temperature field of aluminum alloys can be achieved based on infrared radiation combined with blackbody spots online calibration, and the maximum error is 1.5 K. Therefore, the method is suitable for industrial applications of aluminum alloys where emissivity varies with temperature.

Temperature Field Measurement of Photovoltaic Module Based on Fiber Bragg Grating Sensor Array.

Studying the temperature field of photovoltaic modules is important for improving their power generation efficiency. To solve the problem of traditional sensors being unsuitable for measuring the spatial temperature field, we designed a real-time detection scheme of the photovoltaic module temperature field based on a fiber Bragg grating (FBG) sensor array. In this scheme, wavelength division multiplexing and space division multiplexing technologies were applied. The multi-channel FBG sensor strings were arranged on the surface and in the near field of the photovoltaic module. Different FBG strings were selected through optical switches, and the wavelength of the FBG string was addressed and demodulated using the tunable laser method and a peak-seeking algorithm. A measurement experiment of the photovoltaic module temperature field was carried out in an outdoor environment. The experimental results showed that the fluctuation law of the photovoltaic module surface and near-field temperature is basically consistent with that of solar radiation power. The temperature of the photovoltaic module decayed from the surface to space. Within 6 mm of the photovoltaic module surface, the temperature sharply dropped, and then the downward trend became flat. The lower the solar radiation power and the higher the wind speed, the faster the temperature decay. This method provides technical support for measuring the temperature field of a photovoltaic module and other heat source equipment.

Thermal Characterization of a Gas Foil Bearing-A Novel Method of Experimental Identification of the Temperature Field Based on Integrated Thermocouples Measurements.

Maintenance of adequate thermal properties is critical for correct operation of a gas foil bearing. In this work, the authors present the results of the experimentally conducted thermal characterization of a prototype installation of the bearing. A novel method of temperature identification, based on integrated thermocouples readings, has been employed to determine the thermal properties of the specialized sensing top foil mounted in the tested bearing. Two measurement campaigns have been subsequently completed, applying freely-suspended and two-node support configurations, to gather complementary knowledge regarding the bearing’s operation. Apart from the rotational speed and temperature field measurements, the authors have also studied the friction torque and the shaft’s journal trajectories based on its radial displacements. The temporal courses for the above-mentioned quantities have enabled inference on the effects present during run-up, run-out and stable state operation at a constant speed. As confirmed, the applied distribution of the integrated sensors allows for temperature readings on the entire outer surface of the foil, and therefore, provides useful data for the bearing characterization. The work is concluded with presentation of the recommended directions regarding future improvements of the proposed measurement technique and more comprehensive study of the bearing’s characteristics.

Numerical and Experimental Study of Polymers Microwaves Heating

Heating polymers by microwaves is not common. In order to quantify the ability of micro-wives to heat different type of polymers, a bench measuring the dielectrics characteristics of polymers is built, and a numerical modeling of the waves-polymers interaction is achieved. Finite elements method is introduced to solve the Maxwell equations [6-8] and the energy equation. A series of numerical simulations test are performed: convergence tests are realized and the heating power distribution in the sample is obtained. Using the power distribution, we studied a transient heating process of a polymer (CAPA) sample by microwave. In order to validate the numerical approach, we set-up an experimental bench to heat the sample by microwave and measure temperature distribution, using optical fiber and pyrometers. A vector analyzer (VNA). [6, 9-12] is used to check the quality of the microwave cavity The results of the numerical simulations of the wave propagation are presented and the amplitude of the electric field is compared to the experimental measurement: good agreement is observed. In terms of polymer heating, numerical results of temperature field and experimental measurements are also compared: an efficient heating is observed.

Physics-informed neural networks for modelling power transformer’s dynamic thermal behaviour

This paper focuses on the thermal modelling of power transformers using physics-informed neural networks (PINNs). PINNs are neural networks trained to consider the physical laws provided by the general nonlinear partial differential equations (PDEs). The PDE considered for the study of power transformer’s thermal behaviour is the heat diffusion equation provided with boundary conditions given by the ambient temperature at the bottom and the top-oil temperature at the top. The model is one dimensional along the transformer height. The top-oil temperature and the transformer’s temperature distribution are estimated using field measurements of ambient temperature, top-oil temperature and the load factor. The measurements from a real transformer provide more realistic solution, but also an additional challenge. The Finite Volume Method (FVM) is used to calculate the solution of the equation and further to benchmark the predictions obtained by PINNs. The results obtained by PINNs for estimating the top-oil temperature and the transformer’s thermal distribution show high accuracy and almost exactly mimic FVM solution.

Temperature Field Measurements In The Cross-Section Of Falling Liquid Films By Laser-Induced Fluorescence

Thin wavy liquid films a reused in many applications as heat a nd mass transfer promoters thanks to their great performances for a small liquid consumption. To further understand the exact mechanisms of coupling between the wavy fluid dynamics and the heat transfer, a laser-induced fluorescence technique has been developed. The technique enables a measurement of the temperature field inside of a wavy film flowing down an inclined plane with a high spatial resolution. This paper reports on the development of the technique. Water liquid films were investigated under two-dimensional waves conditions. The measurements reveal the regions where mixing is enhanced by convective circulation zones and enables the evaluation of the intensification of the heat transfer due to the waves.

Time-resolved multi-parameter flow diagnostics by filtered Rayleigh scattering: system design through multi-objective optimisation

The measurement of the time-resolved three-component (3C) velocity field together with scalar flow quantities such as temperature or pressure by laser-optical diagnostics is a challenging task. Current approaches usually employ combinations of different methods relying on tracer particles or molecules. This typically requires usage of at least two laser systems and detection units as well as elaborate calibration of the luminous properties of the applied tracer species with regard to the specific thermodynamic conditions anticipated for the flow case at hand. In contrast to this, the tracer-free filtered Rayleigh scattering (FRS) technique has been proven to obtain combined time-averaged velocity and scalar fields and might offer a viable alternative for unsteady flow diagnostics. By applying multiple perspective views, two detection system variants are presented, combining (1) six observation branches with one camera/molecular filter and (2) three camera views with two cameras and molecular filters of differing vapour densities. Both configurations in principle allow for the simultaneous measurement of instantaneous 3C velocity, temperature and pressure fields. Multi-objective optimisation is used to enhance the detection setups for different sets of experimental configurations. It is shown that a higher number of observation positions and the associated dynamics of the FRS signal prove to be advantageous compared to the use of less views in combination with two acquisition channels equipped with different molecular filters. It is also shown that the use of circularly polarised laser light offers no advantage over linear polarisation. By demonstrating a moderate sensitivity of the optimised observation arrangement to alignment errors, the presented FRS concept provides a practical solution for the simultaneous measurement of time-resolved 3C flow velocity and scalar fields.

Direct background-oriented schlieren tomography using radial basis functions.

Background-oriented schlieren tomography (BOST) is effective for flow field measurement; however, different from general computed tomography (CT), the BOST utilizes the deflection of rays passing through an inhomogeneous field for measurement. It is sensitive to the refractive index gradient. Therefore, an additional integration step is typically employed to obtain the refractive index. In this article, a calculation method of projection matrix is proposed based on the radial basis function (RBF). The 3D distribution of the refractive index can be reconstructed directly. This method was first verified by numerical simulation. Then, the 3D instantaneous refractive index field above a candle flame was measured. The reprojection error was calculated by ray tracing. The results illustrate the accuracy and stability of the proposed method. This research provides a new and complete solution for the 3D instantaneous flow field (refractive index, density, or temperature) measurement.

In-Fiber Integrated Quasi-Distributed Temperature Sensor Array With High Spatial Resolution for Silicon Nitride Igniter

As a key component in the engine system, silicon nitride igniter’s stable and reliable operation is a necessary condition for the proper functioning of the engine system. However, an online high temperature sensor of silicon nitride igniter inside the engine is absent. This paper presents and demonstrates a novel in-fiber integrated high temperature sensor array with high spatial resolution for online temperature field measurement on a silicon nitride igniter. The sensor array with a series of weak reflectors is written by a femtosecond laser in the core of single-mode fiber. The reflectivity of each reflector can be controlled from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−8</sup> by adjusting the written power of femtosecond laser. Two adjacent weak reflectors form a compact fiber sensor. The size of a single sensor can be as small as 3–5 mm, so it is able to measure the temperature fluctuation in a space down to several millimeters. The five-sensor-array, with the help of a white light interference demodulation system, can measure high temperature up to 1000°C. Due to the advantages of high reliability, compact construction and simple fabrication, this high temperature sensor array can be widely applied in high temperature sensing applications with space constrains.

A Computational Fluid Dynamic Investigation of a Data Centre Employing Rear Door Heat Exchangers

As the global demand for data services expands, cooling in data centres continues to evolve towards more efficient and cost-effective systems. Incorporating active rear door heat exchangers has become a popular and reliable method that increases the capability of data centres to operate at higher power densities. This study conducts a thermal analysis of a data centre employing active rear door heat exchangers with the use of computational fluid dynamic (CFD) techniques. The data centre under investigation contains seventy-seven cooled racks with three additional uncooled racks operating in the centre of the hall. The main purpose of this study is to understand how the uncooled racks affect the temperature distribution in the data centre. This study presents a modelling technique which uses temperature and velocity field measurements to facilitate the modelling of rear door heat exchangers. Computer server modelling server was carried out at varying inlet temperature and load. Server simulation results have been utilized with field measurements to create four data centre scenarios. Scenarios were created to show how inlet temperature and load affect the temperature distribution in the data centre. Data centre scenarios have been used to validate and compare with field measurements performed. It was found that heat dissipation in the server was directly related to the server’s velocity profile. From the data centre scenarios created it was found that when higher loaded racks are isolated amongst lower loaded racks the distribution of heat is less significant than if the higher loaded racks were situated in clusters of three or more. It was also found that higher loaded racks could be positioned strategically to diminish the effect of the untreated air produced by the uncooled racks in the data centre. The findings from this paper help to understand the thermal behaviour in data centres and suggests areas to consider when reviewing pre-existing data centre designs.

Temperature field measurements between a Bunsen flame and flat a cold plate by using PLIF

The present experimental work reports on the temperature measurements in a Bunsen flame, covered by a flat cooled plate from the top. The temperature field is measured based on the planar laser-induced fluorescence method for hydroxyl radical (OH) during the excitation of excitation Q1(8) line of the (1-0) band of the A2Σ+-X2Π electronic system. Thermometry was based on the imaging of the ratio of the fluorescence intensity for the band (2-0) and bands (0-0), (1-1). The paper presents the obtained temperature fields for the distances between the plate and the burner of 1, 2 and 3 calibres. The paper also concludes that the used method can be implemented using a single-pulse laser illumination and is effective for the detection of cold zones.

Development of a multi-spectral thermal imager for measurement of the laser-induced damage temperature field

In order to analyze the damage effectiveness of the high-energy laser beam damage to the target, it is important to accurately measure the laser-induced damage temperature field. However, the obtained data cannot meet the requirements of damage effectiveness evaluation, as most of these data are from simulated temperature measurements in the laser-induced damage temperature field. Moreover, traditional temperature measuring instruments can only measure temperature points, and cannot obtain the multi-spectral temperature field of the laser-induced damage. In response to the above problems, this paper has developed a multi-spectral thermal imager for measurement of the laser-induced damage temperature field. Using a five-channel four-wavelength filter photometer, the instrument makes the fifth channel as a calibration channel so that the infrared thermal imager can accurately collect data under multi-spectral channels. Temperature fields corresponding to the spectral data can be inverted by multi-spectral thermometry method. The temperature results of the multi-spectral thermal imager are compared with that of thermocouples, and the measurement error is<1.5%. According to the experimental data of laser-induced damage field measurements, it is shown that the laser-induced damage temperature field can be acceptably measured with the multi-spectral thermal imager.

Computational Fluid Dynamics Modeling of a Broiler House Microclimate in Summer and Winter.

Simple SummaryMicroclimate conditions in broiler housing are significant for maximizing poultry production and ensuring the welfare of the birds. In the present study, we modeled summer and winter microclimates in a mechanically ventilated broiler house. Validation of the simulated values was accomplished through comparison to field measurements. In visual simulations, the results were used to reconstruct microclimate conditions such as stagnant and stress zones of broiler houses. In conclusion, simulation techniques can be used as an alternative method for analyzing poultry house indoor environments.Appropriate microclimate conditions in broiler housing are critical for optimizing poultry production and ensuring the health and welfare of the birds. In this study, spatial variabilities of the microclimate in summer and winter seasons in a mechanically ventilated broiler house were modeled using the computational fluid dynamics (CFD) technique. Field measurements of temperature, relative humidity, and airspeeds were conducted in the house to compare the simulated results. The study identified two problems of high temperature in summer, which could result in bird heat stress and stagnant zones in winter, and simulated possible alternative solutions. In summer, if an evaporative cooling pad system was used, a decrease in temperature of approximately 3 °C could be achieved when the mean air temperature rose above 25 °C in the house. In winter, adding four 500-mm circulation fans of 20-m spacing inside the house could eliminate the accumulation of hot and humid air in the stagnant zones in the house. This study demonstrated that CFD is a valuable tool for adequate heating, ventilation, and air conditioning system design in poultry buildings.