Measured Temperature Rise Research Articles

Automated Measurement System of High Accuracy for Shunt Reactors

System for automated transformer tests (ATT) enables different measurements on power transformers, from simple to the most complex, with a high degree of automation. ATT system is now expanded with modules for measurements on shunt reactors. The measurements related to shunt reactors that are covered with the system are: measurement of losses, impedance measurement, linearity test, zero impedance measurement, winding resistance measurement, temperature rise test and measurement of mutual reactance. Besides the measurement, ATT enables data analysis and report generation, all in accordance with [1,2]. Measurement of shunt reactor losses with satisfactory accuracy is a big challenge due to power factors of the reactors as low as 0,001. A system for loss measurements with high accuracy, consisting of measuring bridge, current comparator and standard capacitor is integrated into ATT. In the paper, a comparison in terms of loss measurement accuracy on shunt reactor is given for two measurement systems – a newly integrated system for shunt reactors and standard system used for transformer measurements.

Core loss determination in electric machines using short‐time transient thermal measurements

AbstractThis paper introduces a novel application of the inverse modelling method, which is designed to estimate core losses in both the stator and rotor regions of an electrical machine. The technique focuses on the use of short‐term transient temperature measurements obtained from the stator core of a slotless induction machine, with a focus on validating the measured temperature rise through a forward model. The measurement setup involves two primary approaches: (i) the use of thermal sensors embedded in a printed circuit board inside the stator core and (ii) surface sensors embedded on the stator yoke. Through the use of this innovative approach, the results indicate that the inverse modelling technique is highly effective in predicting core losses based on short‐time transient temperature rise measurements.

Top-down constitutive modelling to capture nanoscale shear localization

Deformation localization as exemplified by earthquakes, landslides, shear banding in solids, and failure of engineering components is of utmost importance. In practice, differentiating the mechanical behavior in such generative narrow bands from the rest part, with difference by orders of magnitude in characteristic size, flow strength, temperature, and shearing rate, is both experimentally and computationally formidable. Here we propose a machine-learning-based constitutive modeling framework to overcome this barrier borne from conventional top-down continuum modelling approach. The model enables us to realize ultra-fine resolutions for deformation in those narrow bands with high efficiency. Taking metallic glasses (MGs) as an example, our model captures well shear localization in BMGs across a broad range of temperatures (0 K to its melting point of ∼1000 K) and strain rates (10−4 to 108/s). We verify through this model the width of shear bands (SBs) in MGs is on the order of 5–8 nanometers, which is resulted from a cascade of (intervening) events, from localized shearing to plastic heating, subsequent temperature rise to thermal softening, and accelerated flow rate to strain-rate hardening. Temperature rise in SBs is a resultant of heat flow and plastic dissipation, but strongly depend on thermal conductivity: Low thermal conductivity facilitates strain localization and great temperature rise. It helps understanding the current controversy upon experimentally measured temperature rise ranging from several K to ∼1000 K. Lastly, strain rates within SBs are approximately one to two orders of magnitude higher than externally applied strain rates, and in general shearing in adiabatic SBs is faster than that in isothermal condition.

Numerical simulation of laser heating effect in optical temperature measurement based on Kubelka-Munk theory

The fluorescence intensity ratio (FIR) technique is widely used in many fields as one of the sensing methods of phosphor thermometry. In the gas turbine field, the rare earth ions are often doped to thermal barrier coating (TBC). When excited by laser pulses TBC glows phosphorescent, and it can be utilized for thermometry. The laser energy absorbed by the TBC is not only used to generate the luminescence but also introduces heat into the TBC and causes a temperature rise further increasing optical temperature measurement error. Therefore, it’s essential to predict the temperature rise and the temperature measurement error, and take measures to reduce the error due to the laser heating effect. However, there are few researches concerning this problem, and most of them focus on the relationship between the laser energy and the point temperature measured by the FIR technique. Here we show a method for evaluating the effect of laser heating on temperature fields and optical temperature measurement errors by establishing thermal equivalent model and discrete model of body luminescence, considering laser and phosphorescence scattering in coatings made of YSZ based on Kubelka-Munk theory. We found that continuous pulsed laser heating caused severe temperature rise and significant temperature measurement error. Furthermore, the temperature rise can be decreased to the level of a single pulsed laser heating by decreasing the frequency of laser. In addition, the main influencing factors of the temperature measurement error are the density of laser energy and coating thickness.

Micro-Joule heater and temperature sensor array on a suspended silicon nitride membrane for measurement of in-plane thin film thermal diffusivity

In this work, a microfabricated chip device for measurement of in-plane thin film thermal diffusivity by temperature wave analysis (TWA) is presented. The device consists of a suspended silicon nitride (SiNx) membrane with a micro-patterned electric Joule heater in the center and several temperature sensors at different distances from the center. The SiNx membrane serves as a thermally isolated platform for the thin film of interest. The design of the measurement device and its fabrication process are presented. Temperature calibration of the RTDs and measurement of the steady-state temperature rise on the membrane were carried out. Finally, the thermal diffusivity of the bare chip and the bare chip coated with polymeric Parylene C thin films of different thicknesses was measured by a temperature wave method. The steady state temperature and temperature wave measurement were performed in high vacuum (p < 1 ×10−5 mbar). For the 150 nm thick low stress SiNx membrane, a thermal diffusivity of (1.77 ± 0.10)× 10−6 m2 s−1 was measured. The device is sensitive to differences in the thermal diffusivity resulting from changes in Parylene C layer thickness of a few hundred nanometers.

Determination of Small-Region Temperature Variation With RDTS System

A novel measurement scheme is proposed, which is capable of detecting temperature variations in sensing fibers based on Raman scattering with centimeter-level spatial resolution. The problem of inaccuracy in temperature determination when the length of temperature variation region (TVR) is less than the minimum required length of the test fiber is overcome by a procedure including determining the TVR length firstly, calculating the area value from the measured temperature rise curve secondly, and obtaining practical temperature change at small-region TVR from the pre-calibrated relation between the temperature and the area value at different TVR lengths finally. Theoretical analysis and experimental measurement are presented, and the influence of the uncertainty of TVR length on the detectable minimum temperature variation is also discussed. As an example, the experimental result shows that temperature variation of 60 °C can be measured with an accuracy of ± 3 °C when the TVR length is as low as 16 cm. The proposed scheme can greatly increase the spatial resolution of the Raman distributed temperature sensing system and enhance its applications in various fields.

1337 nm Emission of a Nd3+-Doped TZA Glass Random Laser

Random lasers have been studied using many materials, but only a couple have used glass matrices. Here, we present a study of zinc tellurite and aluminum oxide doped with different percentages of neodymium oxide (4 wt.%, 8 wt.%, and 16 wt.%) and demonstrate for the first time random laser action at 1337 nm. Laser emission was verified and the laser pulse’s rise time and input–output power slope were obtained. A cavity composed of the sample’s pump surface and an effective mirror formed by a second, parallel layer at the gain-loss boundary was probably the main lasing mechanism of this random laser system. The reason for the absence of emission at 1064 nm is thought to be a measured temperature rise in the samples’ active volume.

Heat pulse probe design optimization using numerical simulation

Heat pulse (HP) measurements are used as an alternative method for a variety of thermal and hydraulic properties critical for many scientific disciplines and engineering applications. This study investigated factors affecting heat pulse probe (HPP) measurements using COMSOL numerical simulations. We sought to understand the influence of rod support material (e.g., circuit board) and rod length on the measured temperature rise by comparing the parametric model-fitted thermal properties of ice and water with the known reference values. Temperature dynamics near the rod support were significantly impacted by the physical and thermal properties of the rod support material, while temperature changes further away from it were mostly affected by the properties of the surrounding media. In addition, comparing results for soil volumetric water contents of 0.00, 0.20, and 0.40 m3 m−3, thermal variations near the rod support material were greater at lower water contents. Results indicate the rod length should be 60 mm or longer, and the optimal thermistor location is at the midpoint of the rod, where more accurate temperature rise curves were obtained for both measurements and simulations.

Experimental study on vertical temperature distribution of the two-layer smoke flow in tunnel during construction

For a tunnel fire during construction, the formation of two-layer smoke flow underneath the ceiling accelerates the smoke descent threatening the personnel evacuation. As an important indicator of smoke diffusion, the gas temperature distribution inside tunnel is worthy of analysis in depth. However, the vertical temperature profiles within this kind of two-layer smoke flow inside tunnel have not been experimentally studied. To fill the gap, this paper conducts a series of fire experiments in a 1/20 reduced-scale tunnel model. Multi-variables including fire heat release rate, fire position, lifting-up height of fire source, inclined shaft slope, are considered. The visible flame shape, O2 volume fraction and gas temperature are recorded and measured. The burning of the propane gas persists steadily for 20 mins without the occurrence of self-extinction. The structural evolutions of the smoke layer are predicted by FDS simulation and traced by the laser sheet. The smoke descent process in the main tunnel is divided into three stages. The effects of fire source position, inclined shaft slope, fire heat release rate and lifting-up height on the gas temperature distributions inside tunnel are analyzed. The measured temperature rise and the perpendicular distance from the ceiling are normalized by ΔTmax and LT, respectively. At various longitudinal positions (1.82 ≤ │X-dm│/Hef ≤ 10.68), the normalized temperature distributions follow the same curve, independent of the values of Qm, dm and hm. The self-similarity of the vertical temperature distribution within the two-layer smoke flow are sufficiently proved. It is found that ΔT/ΔTmax with z/LT shows a two-regional variation. Based on over 1,740 temperature data from 36 experimental cases, an experimental equation is proposed to describe the gas temperature rise in the region between the fire source and the closed end. The proposed model shows good agreement with the measured data, which can help the researchers to better assess the smoke layer height inside tunnel.

Multi-echo MR thermometry in the upper leg at 7T using near-harmonic 2D reconstruction for initialization.

The aim of this work is the development of a thermometry method to measure temperature increases in vivo, with a precision and accuracy sufficient for validation against thermal simulations. Such an MR thermometry model would be a valuable tool to get an indication on one of the major safety concerns in MR imaging: the tissue heating occurring due to radiofrequency (RF) exposure. To prevent excessive temperature rise, RF power deposition, expressed as specific absorption rate, cannot exceed predefined thresholds. Using these thresholds, MRI has demonstrated an extensive history of safe usage. Nevertheless, MR thermometry would be a valuable tool to address some of the unmet needs in the area of RF safety assessment, such as validation of specific absorption rate and thermal simulations, investigation of local peak temperatures during scanning, or temperature-based safety guidelines. The harmonic initialized model-based multi-echo approach is proposed. The method combines a previously published model-based multi-echo water/fat separated approach with an also previously published near-harmonic 2D reconstruction method. The method is tested on the human thigh with a multi-transmit array at 7T, in three volunteers, and for several RF shims. Precision and accuracy are improved considerably compared to a previous fat-referenced method (precision: 0.09 vs. 0.19°C). Comparison of measured temperature rise distributions to subject-specific simulated counterparts show good relative agreement for multiple RF shim settings. The high precision shows promising potential for validation purposes and other RF safety applications.

Research on Transient Temperature Rise Measurement Method for Semiconductor Devices Based on Photothermal Reflection

In this article, a transient temperature rise measurement method for semiconductor devices based on photothermal reflection is proposed. The relationship between the reflectivity of a 360 nm laser beam and the device temperature is studied. Through the appropriate design of the optical circuit and the data acquisition system, measurement of the transient temperature rise characteristics of GaN-based microwave power devices is realized. In combination with resistor-capacitor network impulse response theory, the transient temperature rise curve is processed using the Bayesian iterative deconvolution method. By extracting the thermal time constant, nondestructive characterization of the temperature increase and thermal resistance characteristics of each material layer in the heat flow path is achieved, and the complementary relationship between the temperature change in the active region during heating and the device heat dissipation characteristics is verified. Additionally, the forward Schottky junction characteristics method and infrared thermal imaging are used to measure the channel temperature for verification of the proposed thermal reflection method. These measurements indicate that the proposed method can provide accurate results.

Thermal behavior analysis of lithium-ion capacitors at transient high discharge rates

As one of the prospective high-rate energy storage devices, lithium-ion capacitors (LICs) typically incorporate non-Faradaic cathodes with Faradaic pre-lithiated anodes. LICs that deliver power density at high-rate discharging process can be accompanied by overheating problems which result in capacity deterioration and lifetime reduction. Therefore, it is essential to conduct a comprehensive analysis of the heat generation of LICs. The thermal behavior of pouch lithium-ion capacitors in this work is systematically investigated at transient high-rates from 1C to 550C. The heat transfer mechanisms of each part in the overall thermal behavior are quantified in detail during discharging processes. As the discharge rate increases, the temperature curve shows an upward parabolic trend at the end of discharge, with a maximum temperature of 33.68 °C at 200C.The proportion of irreversible heat to total heat generation is close to 80 % at 550C, but the temperature at the end of discharge decreases owing to the reduced discharge time. The actually measured temperature rise is compared with the one calculated using the intermittent current method, the voltage-current (VI) characteristic method and the alternating current impedance method. It can be found that the intermittent current method calculated temperature trends are in good agreement with the measured values better than other methods, because the polarization internal resistance is significantly related to the discharge time interval. These results would provide the basis for further development of a thermal model of the cell, in order to rationally design the cooling system to avoid overheating and degradation of the cells.

Subfascial versus extrafascial ultrasound-guided stellate ganglion block in patients with post-mastectomy sympathetically mediated pain: A randomized clinical trial.

Despite being a well-described intervention, the optimal anatomical approach to perform a stellate ganglion block (SGB) has been disputed. We compared the subfascial and extrafascial ultrasound-guided (USG) SGB. A randomised clinical trial was conducted, consisting of 50 patients in two groups. Group I received SGB via the subfascial approach while Group II received an SGB via the extrafascial approach. The primary endpoint was successful sympathetic blockade (as indicated by a measured temperature rise of ≥2°C). Secondary endpoints included analgesic efficiency (extent of early onset of pain relief as indicated by >50% improvement in Visual Analogue Scale (VAS) score at 300's post-procedure); occurrence of Horner's syndrome; extent of local anaesthetic distribution; and adverse events. The mean increase in sympathetic blockade was significantly higher in the subfascial group (2.6 ± 0.6°C; p = .003). Analgesic efficacy was also significantly higher in the subfascial group (p < .001). The difference in the average dermatomal spread of local anaesthetic down to T2 and up to C4 between the groups was also statistically significant (p = .021 and p = .019, respectively). The degree of temperature rise, pain relief and occurrence of Horner's syndrome were higher in the subfascial than the extrafascial group. The subfascial approach to SGB, with a limited volume of local anaesthetic agent, is a more reliable technique when compared to the extrafascial approach.

Feasibility and Error Analysis of Using Fiber Optic Temperature Measurement Device to Evaluate the Electromagnetic Safety of Hot Bridge Wire EEDs.

Most studies assessing the safety of hot bridge wire EEDs employ temperature sensors that directly use the measurements of the temperature measurement device without analyzing the accuracy of the temperature measurement. This study establishes the response function of the exposed bridge and exposed bridge temperature rise system of hot bridge wire EEDs through the Rosenthal’s temperature rise equation and Laplace transformation as well as experimental tests, and through the response function, the response law and numerical characteristics of the two are compared and analyzed under four typical excitations. Under steady current injection and continuous-wave radiation, both exposed bridge and exposed bridge temperature measurement systems can reach thermal equilibrium, and the equilibrium temperature of both are the same. However, under pulse excitation, the temperature rise measurement value is significantly different from the actual value due to the large difference in response time of the exposed bridge (1 ms) and the exposed bridge temperature measurement device (0.82 s). Studies have shown that under steady current injection and continuous-wave radiation, temperature rise measurements can be directly applied to the safety assessment of hot bridge wire EEDs, while under pulsed conditions, temperature rise measurements cannot be directly applied.

Effect of temperature and heat generation on martensitic phase transformation in DH steels

Transformation induced plasticity (TRIP) phenomenon and mechanical behavior of TRIP-aided steels are influenced by the ambient as well as local temperature which raises due to plastic deformation and latent heat of transformation. In order to study this effect, tensile tests with samples made of DH800 steel were carried out at various temperatures, while the temperature rise was monitored during the test. In parallel, a physically-based model was applied to predict the change in material behavior as a consequence of the TRIP effect. In this model, martensitic transformation is mainly stress-driven, and the self-consistent scheme was adopted to achieve a homogenized material behavior. In addition, temperature rise as a result of plastic energy dissipation and latent heat of mechanically-induced retained austenite-martensite transformation was taken into account. Empirical flow curves at various temperatures indicated that at sub-zero values, the hardening of material due to the TRIP effect is much more pronounced. It was observed that a temperature change between +80 °C and −40 °C increases the flow stress by 200 MPa. Measured temperature rise, especially at sub-zero levels, showed an initial sharp increase at low strain stages due to phase transformation that flattens afterward. The numerical results are in agreement with experimental measurements of material flow curves and retained austenite fraction.

Determination of Core Losses Using an Inverse Modeling Technique

This paper presents an inverse thermal modeling technique to determine the core losses from the temperature rise inside the transformer core. For this purpose, initially, a customized printed circuit board (PCB) with thermal sensors is used to measure the temperature rise. Afterward, a 3D magneto-thermal forward model is developed to validate the temperature rise. The accuracy of the forward model is checked by comparing the simulated core losses and temperature rise of the transformer with experimental measurements for different supply conditions. The results show that the forward model can accurately estimate the core losses with a maximum relative error of less than 2.7&#x0025; and predict the temperature rise in the core with a maximum relative error of less than 6.2&#x0025;. Lastly, after ensuring the accuracy of the forward model, an inverse modeling technique is applied to the 3D thermal model to predict the core losses of the transformer directly from the measured temperature rise. The accuracy of the inverse model in estimating the core losses is checked by comparing the results with experimental measurements. The novel approach for the PCB design besides the inverse model shows that the technique can be applied to estimate the core losses directly from the measured temperature rise inside the core with a relative error of 2.7&#x0025; compared to experiments.

Temperature-Rise Measurement of Plastics under Rolling-Sliding Conditions through Twin-Disc Tests

Mechanical properties of plastics greatly depend on temperature, which follows that the temperature rise in meshing gear teeth must be crucial to the load capacity of a gear pair. The present study will provide a method for estimating it. For this purpose, twin-disc tests with plastic test roller and steel roller allowed temperature-rise in test rollers to be measured. The twin-disc tests under the various applied loads and surface sliding velocities defined the change in the surface temperature of test rollers. The measured surface temperature gradually increased during the twin-disc test and converged to a certain level after some minutes. The difference between the initial temperature and the converged one is temperature-rise. The temperature rise depended on contact stress and sliding velocity. As a result, the temperature rise in test rollers has an approximately linear relationship with the PV value, which is the product of the maximum contact pressure (P) and the sliding velocity (V) between roller surfaces. This result could be fundamental data for estimating the temperature rise in meshing gear teeth.

MEASUREMENT UNCERTAINTY OF WINDING TEMPERATURE RISE ON WASHING MACHINE HEATING-TEST

Evaluation of measurement uncertainty in safety tests is critical for a testing laboratory, especially if many aspects influence the test results, such as in the washing machine heating test. While performing the heating test, the temperature rise of the motor winding was determined to evaluate the safety level of a washing machine. The temperature rise is obtained by the resistance method, which measures the change of winding resistance to assess its temperature rise. In this work, the washing machine was loaded at maximum capacity and supplied with hot water. All factors contributing to the measurement uncertainty originating from both the measurement system and the testing method are evaluated. The expanded uncertainty of the temperature rise measurement obtained in this study is 1.4%. This uncertainty is mainly contributed by the variance of test water temperature (0.54%), calibration uncertainty of RCL meter (0.43%), and calibration uncertainty of temperature logging system (DLS) (0.31%). Therefore, the heating test requires a tight temperature controller, an improved calibration uncertainty of the resistance meter, and a better accuracy of the temperature logger to reduce the measurement uncertainty.

High intensity focused ultrasound and microbubbles induce targeted mild hyperthermia suitable for enhanced drug delivery

High intensity focused ultrasound (HIFU) can elevate the temperature leading to tissue ablation (&amp;gt;60 °C). Mild hyperthermia (39–45 °C) can enhance drug delivery such as in the activation of thermosensitive liposomes for chemotherapy and in radiotherapy. The addition of microbubbles during HIFU could greatly enhance the heating process and increase the treatment area while operating at lower intensities. Here, we present a parametric study of microbubble-enhanced mild hyperthermia with HIFU in ex vivo porcine liver. A 30-s treatment at 0.9 MHz, 372 000 cycles, 82% duty cycle was used, and at estimated non-derated (water) pressures of 0.63, 1.25, 2.50 and 3.75 MPa. The microbubbles were injected locally in the treatment area. The measured temperature rise was greater with microbubbles than without at low acoustic pressures (0.63 and 1.25 MPa). At higher pressures (2.50 and 3.75 MPa), the presence of microbubbles did not have an effect on the measured temperature rise possibly due to inertial cavitation. Our results agree with predictions from a numerical model that solves the coupled acoustic-bubble flow fields with a two-way coupled Euler–Lagrange model. Future work will utilize the numerical model and new measurements to optimize targeted mild hyperthermia before applying it to enhanced drug delivery.

A simple laboratory flash apparatus for thermal diffusivity measurement: Modeling and application for composite material based on clay and straw

In this work. we have developed and tested a flash apparatus for thermal diffusivity measurement of building materials. After the test on homogeneous materials, this very inexpensive apparatus was then used to estimate the thermal diffusivity of some local materials based on clay and straw. To estimate this quantity, the measured temperature rise at the rear face of the sample was processed by solving analytically the transient heat equation based on a one-dimensional model with time-dependent convective boundary conditions. The obtained mathematical model takes into account the temporal shape f(t) of the heat pulse used to excite the front sides of the samples as well as four unknown parameters ie: the thermal diffusivity, the two Biots numbers related to the heat losses on the rear and the front sides and the maximum adiabatic temperature. For this purpose, the excitation form performed via a flashlight was experimentally measured and f(t) properly modeled by a first square form followed by a short exponential waning phase attributed to the thermal inertia of the used halogen lamps. Finally, the simultaneous estimation of the remaining unknown parameters was carried out by minimizing the sum of the quadratic differences between the mathematical model and the measured thermogram on the back faces of the samples. The precision and accuracy of the apparatus results were also examined by measuring the thermal diffusivity of several homogeneous building materials. The standard deviation in thermal diffusivity for the studied samples doesn’t exceed 4.72 %. Then, five samples from clay mixed with different mass fractions of straw are prepared and their thermal diffusivities are measured. The thermal conductivity and the heat capacity of these composite materials are experimentally achieved and their values are reported for comparative purposes. The thermal characterization shows a decrease of about 27.5 % in thermal diffusivity, 43.32 % in thermal conductivity and 4.40 % in heat capacity versus the increase of the straw mass fraction.