Transient Temperature Measurements Research Articles

C-type two-thermocouple sensor design between 1000 and 1700 °C.

At the present stage of transient ultra-high-temperature energy release of boron-containing warm-pressure explosives, single thermocouples are often used for multi-point measurements in the process of their temperature field changes, and the results of their temperature field reconstruction are not satisfactory due to the limited consistency of the thermocouples. Aiming at the above-mentioned problems, a C-type two-thermocouple suitable for transient temperature measurement in high-temperature environments is designed; the system characterization of the two-thermocouple is carried out by using the blind system identification method of the inter-relationships; the identification process is evaluated by a new cost function; and the optimal solution on the new cost function is realized by using the gradient descent method. The temperature reconstruction of the two-thermocouple output excited by the simulated heat source is carried out by using the auto-regressive with extra inputs model, and the feasibility of the reconstruction results is verified. In the experimental part, a thermocouple dynamic characteristic calibration system based on a high-temperature furnace is constructed and experimental validation is carried out in the high-temperature furnace to compare the effects of different exposure lengths and different wire diameters on the output of the two-thermocouple, and as a result, the outputs are corrected and analyzed. The results show that two-thermocouple methods with different combinations of wire diameters are better for temperature measurement, with a reconstructed root mean squared error of 0.0162 and a goodness of fit of 89.13%.

Facemask vapor trapping, condensation, and thermoregulation

The widespread adoption of facemasks in various contexts has highlighted challenges associated with prolonged mask-wearing. Despite their effectiveness in preventing the spread of pathogens, issues such as discomfort, stuffiness, and fogging of eyeglasses can deter individuals from wearing masks consistently. Understanding the mechanisms of thermal and humidity regulation during facemask use is crucial for addressing these challenges. This study investigates the impact of face mask-wearing on facial thermoregulation and moisture accumulation, comparing conditions with and without masks. An integrated computational model was developed to consider respiratory flows, tissue heat generation, skin convective heat dissipation, the influence of inhaled cool air and exhaled warm air, and their interactions with the mask media. Model validation was conducted using complementary Schlieren imaging and transient temperature measurements. Results reveal significant increases in facial temperature with well-fitted masks and highlight the role of trapped moisture inside the mask. Thermo-humidity variations beneath the mask and condensations in the mask were quantified, providing insights into facemask-wearing thermoregulation. The effects of moist vs. dry air, steady vs. tidal breathing, and with vs. without buoyancy were quantitatively compared. These findings have implications for improving mask design and promoting adherence in diverse environmental settings. Addressing these discomfort-related challenges is crucial for enhancing mask adherence and ensuring adequate protection.

Dynamic phase change materials with extended surfaces

Phase change materials (PCMs) present opportunities for efficient thermal management due to their high latent heat of melting. However, a fundamental challenge for PCM cooling is the presence of a growing liquid layer of relatively low thermal conductivity melted PCM that limits heat transfer. Dynamic phase change material (dynPCM) uses an applied pressure to pump away the melt layer and achieve a thin liquid layer, ensuring high heat transfer for extended periods. This paper investigates heat transfer during dynPCM cooling when the heated surface has extended features made from high thermal conductivity copper (Cu). Using experiments and finite element simulations, we investigate the heat transfer performance of dynPCM paraffin wax on finned Cu surfaces. A total of 102 transient temperature measurements characterize the performance of dynPCM with extended surfaces and compare the performance with other cooling methods including hybrid PCM and air cooling. The study examines the effects of fin geometry, applied power (20–65 W), and pressure (0.97–12.5 kPa). For dynPCM on a finned surface and a heating power of 65 W, the thermal conductance is 0.45 W/cm2-K, compared to 0.22 W/cm2-K for dynPCM on a flat surface and 0.10 W/cm2-K for hybrid PCM. The heat transfer is highest at the fin tips where the melt layer is thinnest, providing valuable design guidelines for future high performance dynPCM cooling technologies.

Transient temperature measurement of silicon carbide Schottky barrier diode based on thermal reflection.

In this article, we present a transient temperature detection device for silicon carbide (SiC) Schottky barrier diodes (SBDs) based on thermal reflection theory. We constructed a thermal reflection temperature measurement device based on a 530-nm green laser. This device is more suitable for transient temperature measurement of SiC SBDs than previous thermal reflection equipment. The accuracy of temperature measurement by our device was confirmed by comparison with the results of infrared thermal imaging. The high temporal resolution characteristics of the thermal reflection technology allowed the detection of millisecond-level transient temperature changes in SiC SBDs. In addition, we investigated the complementarity of transient temperature change curves during heating and cooling processes, as well as the reasons for the differences between these curves. Finally, we used the structural function method combined with the Bayesian deconvolution algorithm to obtain the thermal resistance along the heat flow path of the device and validated the results using an established thermal resistance testing method.

Research on a dedicated thin-film thermocouple testing system for transient temperature measurement

The thin-film thermocouple (TFTC) is featured on small heat capacity and rapid response speed for transient temperature measurements under narrow space and difficult installation. Consequently, we propose a novel transient temperature testing system specifically designed for TFTC. This system features signal conditioning circuits with extended bandwidth and superior transfer speeds, a cold junction compensation method that supports customizable indexing tables, and an adaptive data filtering approach that precisely balances the smoothing of steady-state data with rapid responsiveness to transient data. This approach effectively mitigating the measurement distortion of transient temperature signals and the nonlinear phenomenon in cold junction compensation for TFTC. Utilizing NiCr/NiSi TFTC, we evaluated the system’s accuracy, demonstrating a precision range of −0.5 °C–0.25 °C within 20 °C–100 °C, and a response delay under 0.1 ms. Compared to traditional thermocouple measurement systems, our system exhibits a finer time-domain resolution. Lastly, we successfully applied this system to observe the response of TFTC under the thermal load of short-pulse laser shocks, measuring a time constant of only 1.16 ms for the TFTC. This novel transient temperature testing system provides a new approach for TFTC to achieve online dynamic measurement and online calibration, and provides technical support for TFTC measurement technology towards engineering applications.

A protocol for accurately calibrating thermocouples at cryogenic temperatures

To study the quenching characteristics of materials in a cryogenic liquid bath transient temperature measurements of high accuracy are necessary. Thermocouple is an ideal tool for this application because of its low self-heat capacity. However, they require calibration before usage that require multiple fixed-point temperatures. The common fixed-point temperatures are the water-ice melting temperature, the dry ice sublimation temperature, and the boiling temperature of liquid nitrogen. It is important to note that there are uncertainties associated with dry ice sublimation and liquid nitrogen boiling temperature inherent to the heat and mass transport phenomenon at their phase-changing interface or inside the bulk medium. The dry ice temperature is influenced by the mass transport phenomenon occurring at the interface between the dry ice and the ambient surrounding it. In a typical lab environment, dry ice temperature is significantly lower than the commonly quoted sublimation temperature of -78.5 °C at 1.013 bar. In the case of liquid nitrogen stored in a cryostat, temperature gradients develop in the liquid bath. This paper describes a protocol for calibrating thermocouples by accurately defining and using fixed-point temperatures of dry ice in a saturated environment and a liquid nitrogen slush.

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.

Numerical modeling and experimental validation of heat and mass transfer within decomposing carbon fibers/epoxy resin composite laminates

CFRP composite laminates decompose by pyrolysis/oxidation when exposed to high heat fluxes. While gaseous and solid residues created within the composite material are ignored in most models, a multi-species approach is proposed to describe transient decompositions from the virgin to the final charred state of the material. The model is based on a porous medium description that includes gas creation and transport within the laminate, respectively driven by Arrhenius and Darcy’s laws. Orthotropic heat transfer and decomposition gas transport within the laminate up to the surface remain often uninvestigated while it can drastically act upon the dynamics of a fire event. An experiment is carried out to analyze multi-dimensional heat and mass transfer during the charring processes of a composite laminate exposed to a high power laser beam. Transient temperature measurements on the unexposed surface of the material are confronted to 3D unsteady numerical results to validate the model formulation.

Variations of skin thermal diffusivity on different skin regions.

Skin thermal diffusivity plays a crucial role in various applications, including laser therapy and cryogenic skin cooling.This study investigates the correlation between skin thermal diffusivity and two important skin parameters, melanin content and erythema, in a cohort of 102 participants. An in-house developed device based on transient temperature measurement was used to assess thermal diffusivity at different body locations. Melanin content and erythema were measured using a colorimeter. Statistical analysis was performed to examine potential correlations. The results showed that the measured thermal diffusivity values were consistent with previous reports, with variations observed among subjects. No significant correlation was found between thermal diffusivity and melanin content or erythema. This suggests that other factors, such as skin hydration or epidermis thickness, may have a more dominant influence on skin thermal properties. This research provides valuable insights into the complex interplay between skin thermal properties and physiological parameters, with potential implications for cosmetic and clinical dermatology applications.

Experimental study on evolution of longitudinal vortex rolls subject to the duct tilted in the spanwise direction

An experiment was performed in this study to investigate the effect of duct spanwise inclinations on the longitudinal vortex pattern in an air mixed convective flow. Key parameters, including Reynolds (Re) numbers from 20 to 30 and Grashof (Gr) numbers from 4071 to 10,855, are investigated. The spatial and temporal attributes of longitudinal vortex rolls (LVRs) are examined via flow field visualization and transient temperature measurement in details. Compared with the corresponding non-sloping case, the duct inclination significantly influences the LVR evolution. Due to the non-zero spanwise buoyancy, the vortex roll tends to be asymmetrical across the span and causes the delayed onset of lower LVRs. The temperature fluctuates significantly with time adjacent to the upper sidewall at the larger tilt angle. In an inclined duct, lower LVRs will stretch spanwise to squeeze upper vortex rolls with a decrease in Re number. Increasing the Gr number is beneficial to LVR formation for a smaller spanwise-inclined angle. However, the increase in either Gr number or tilt angle makes the vortex flow relatively unstable. We also provide an empirical expression to determine the vortex onset as a function of Re, Pr, Gr numbers, and the tilted angle.

Droplet freeze-thawing system based on solid surface vitrification and laser rewarming

Ultra-rapid cooling and rewarming rate is a critical technical approach to achieve ice-free cells during the freezing and melting process. A set of ultra-rapid solid surface freeze-thaw visualization system was developed based on a sapphire flim, and experiments on droplet freeze-thaw were carried out under different cryoprotectant components, volumes and laser energies. The results showed that the cooling rate of 1 μL mixed cryoprotectant [1.5 mol/L propylene glycol (PG) + 1.5 mol/L ethylene glycol (EG) + 0.5 mol/L trehalose (TRE)] could be 9.2×10 3 °C/min. The volume range of 1-8 μL droplets could be vitrified. After comparing the proportions of multiple cryoprotectants, the combination of equal proportion mixed permeability protectant and trehalose had the best vitrification freezing effect and more uniform crystallization characteristics. During the rewarming operation, the heating curve of glassy droplets containing gold nanoparticles was measured for the first time under the action of 400-1 200 W laser power, and the rewarming rate was up to the order of 10 6 °C/min. According to the droplet images of different power rewarming processes, the laser power range for ice-free rewarming with micron-level resolution was clarified to be 1 400-1 600 W. The work of this paper simultaneously realizes the ultra-high-speed temperature ramp-up, transient visual observation and temperature measurement of droplets, providing technical means for judging the ice free droplets during the freeze-thaw process. It is conducive to promoting the development of ultra-rapid freeze-thaw technology for biological cells and tissues.

Precise estimation of dynamic junction temperature of SiC transistors for lifetime prediction of power modules used in three-phase inverters

Precise transient temperature measurement is fundamental to estimate lifetime of power modules, especially those made with SiC transistors having very low thermal capacitance. This paper shows a precise method to estimate dynamic temperature of SiC components composing a power module used in three-phase inverters. This method is based on the use of a fast thermal camera to precisely measure thermal impedance of each die. Results of thermal camera measurements are validated by comparison with classical on-state resistance measurements to estimate junction temperature. Thermal impedance model is then coupled with precise loss calculation in order to predict dynamic die temperature during operation in a three-phase inverter. Measurements of the temperature variation of SiC dies conducting typical currents of a 540 V/7.5 kW three-phase inverter for aeronautical applications show the accuracy of the developed model for dynamic junction temperature estimation.

Simultaneous estimation of reference temperature and heat transfer coefficient in transient film cooling problems

This paper aims to simultaneously estimate the reference temperature and heat transfer coefficient in film cooling situations from transient temperature measurements. The exist-ing steady-state technique is a tedious process and employs distinct boundary conditions to evaluate each parameters of the film cooling. Applying different boundary conditions may lead to errors in the estimated parameters due to differences in aerodynamic condi-tions. On the other hand, a transient technique can estimate both parameters in a single test by utilizing short-duration transient temperature data. Hence, the present study uses a novel approach for solving transient film cooling problems based on the inverse heat con-duction approach, which can simultaneously estimate heat transfer coefficient and refer-ence temperature. The present method employs an optimization technique known as the Levenberg-Marquardt Algorithm. The objective function for the inverse algorithm is con-structed using the analytical solution of a transient one-dimensional semi-infinite body. The transient surface temperature data required for the present analysis is obtained through a numerical simulation of film cooling arrangement over a flat surface. Laterally averaged effectiveness and heat transfer coefficient for blowing ratios of 0.5, 0.8, and 1.0 are analyzed using the present technique and compared against the steady-state simulation results to demonstrate the methodology. An average deviation of around 7% for the estimated effec-tiveness and 4% for the heat transfer coefficient values are observed between the present IHCP method and the steady state simulation results. The deviation in heat transfer coeffi-cient predominately occurred near the film hole exit of x/d < 5, which might have occurred due to the conjugate solution employed in the present work.

Simultaneous estimation of reference temperature and heat transfer coefficient in transient film cooling problems

This paper aims to simultaneously estimate the reference temperature and heat transfer coefficient in film cooling situations from transient temperature measurements. The exist-ing steady-state technique is a tedious process and employs distinct boundary conditions to evaluate each parameters of the film cooling. Applying different boundary conditions may lead to errors in the estimated parameters due to differences in aerodynamic condi-tions. On the other hand, a transient technique can estimate both parameters in a single test by utilizing short-duration transient temperature data. Hence, the present study uses a novel approach for solving transient film cooling problems based on the inverse heat con-duction approach, which can simultaneously estimate heat transfer coefficient and refer-ence temperature. The present method employs an optimization technique known as the Levenberg-Marquardt Algorithm. The objective function for the inverse algorithm is con-structed using the analytical solution of a transient one-dimensional semi-infinite body. The transient surface temperature data required for the present analysis is obtained through a numerical simulation of film cooling arrangement over a flat surface. Laterally averaged effectiveness and heat transfer coefficient for blowing ratios of 0.5, 0.8, and 1.0 are analyzed using the present technique and compared against the steady-state simulation results to demonstrate the methodology. An average deviation of around 7% for the estimated effec-tiveness and 4% for the heat transfer coefficient values are observed between the present IHCP method and the steady state simulation results. The deviation in heat transfer coeffi-cient predominately occurred near the film hole exit of x/d < 5, which might have occurred due to the conjugate solution employed in the present work.

Measurement of thermal properties of ferro siliceous sacrificial radiation shielding concrete using semi-infinite transient heat conduction model

The accurate measurement of thermal properties of ferro siliceous sacrificial concrete (FSSC) is quite difficult but essential to study the radiation shielding behavior and molten core corium interaction (MCCI). The present study aims to propose a step-wise transient method based on a semi-infinite medium principle to measure the different thermal properties of FSSC using transient temperature measurement and a simple data processing approach. Various thermophysical properties such as specific heat, thermal conductivity, thermal diffusivity and thermal effusivity are determined, which can be helpful to understand the ablation behavior of the FSSC during molten core-corium interaction in nuclear power plants. The results of specific heat of the FSSC vary from 760 to 770 J/kg.K, while the value of thermal conductivity lies in the range of 7.0–7.4 W/m.K. The average value of thermal diffusivity and thermal effusivity is found to be 2.51 × 10−6 m2/s and 3900.5 Jm−2K−1s−1/2, respectively. The specific heat obtained using semi-infinite assumptions is predicted well by the rule of mixture. The results of thermal conductivity obtained from the present model are compared with the results of the Serial, Parallel and Lichtnecker models available in the literature. These models under predict the value of thermal conductivity obtained from the experimental results.

Fast response characteristics of fiber Bragg grating temperature sensors and explosion temperature measurement tests

Transient temperature measurement technology with fast response, harsh measurement environment, and high technical challenges has attracted research interest in the field of temperature measurement. Based on the differential equation of heat conduction at the interface of an optical fiber, the dynamic-response-time formula of the optical fiber was derived, the dynamic response capability of the optical fiber with different diameters was analyzed, and the transient thermal response simulation of the optical fiber was conducted. The theoretical dynamic test response times of optical fibers with diameters of 80, 125, and 145 µm were 30.21, 60.78, and 85.97 ms, respectively. Fast-response fiber Bragg grating (FR-FBG) temperature sensors were designed and manufactured by femtosecond-fabricated FBGs with diameters of 80 and 125 µm. The average response times of the 80 and 125 µm-FR-FBG temperature sensors were 33.2 and 65.3 ms, and the errors between the data and theoretical values were 9.89 % and 7.44 %, respectively. From explosion experiments, it is concluded that the femtosecond grating can be applied to the monitoring of rapid temperature response during explosion, and the response time is related to the diameter of the grating.

Plasmonic stimulation of gold nanorods for the photothermal control of engineered living materials

Engineered living materials (ELMs) encapsulate microorganisms within polymeric matrices for biosensing, drug delivery, capturing viruses, and bioremediation. It is often desirable to control their function remotely and in real time and so the microorganisms are often genetically engineered to respond to external stimuli. Here, we combine thermogenetically engineered microorganisms with inorganic nanostructures to sensitize an ELM to near infrared light. For this, we use plasmonic gold nanorods (AuNR) that have a strong absorption maximum at 808 nm, a wavelength where human tissue is relatively transparent. These are combined with Pluronic-based hydrogel to generate a nanocomposite gel that can convert incident near infrared light into heat locally. We perform transient temperature measurements and find a photothermal conversion efficiency of 47 %. Steady-state temperature profiles from local photothermal heating are quantified using infrared photothermal imaging and correlated with measurements inside the gel to reconstruct spatial temperature profiles. Bilayer geometries are used to combine AuNR and bacteria-containing gel layers to mimic core-shell ELMs. The thermoplasmonic heating of an AuNR-containing hydrogel layer that is exposed to infrared light diffuses to the separate but connected hydrogel layer with bacteria and stimulates them to produce a fluorescent protein. By tuning the intensity of the incident light, it is possible to activate either the entire bacterial population or only a localized region.

Transient thermal analysis of gas insulated switchgear modules using thermal network approach

Abstract Thermal analysis of Gas Insulated Switchgear (GIS) modules is of utmost important to optimize their dimensions for higher current ratings. Temperature rise test simulation has to be carried out on GIS modules to ensure that the temperature rise of modules shall not exceed the allowable temperature limits. The analyses also help to estimate the time duration required for GIS modules to reach steady state temperature as per IEC 62271-102 and IEC 61869-2. In the present study, to conduct transient thermal analysis, a novel Thermal Network Model (TNM) has been proposed for gas insulated switchgear equipment of two important modules i.e., disconnector switch (DS) and current transformer (CT). GISmodules.m program is developed in the study to analyze effect of various parameters like type of material being used for HT conductor and enclosure, rated voltage, rated current and enclosure current on time varying behavior of temperature rise of conductor and enclosure. Finally, the temperature rise test has also been carried out on 245 kV and 420 kV GIS modules at rated current ranging from 3150 A to 4000 A. When the transient temperature measurements conducted on 420 kV DS and compared with the results obtained through proposed TNM based analyses, it is clear that temperatures are within difference of 3.3 °C for conductor and 1.2 °C for enclosure. Further, it is evident that the time taken for conductor and enclosure to reach steady state temperature is about 8–10 h depending on enclosure current magnitude and GIS configuration.

Research of transient temperature measuring based on thin-film thermocouple and Wi-Fi wireless DAQ method

The thin-film thermocouple temperature sensor is a new type of temperature sensor which was emerged with the development of thin-film materials. It features on a small heat capacity and a rapid response speed for transient temperature measurement on the surface of objects. The existing temperature data acquisition systems for filamentary thermocouples do not yet meet the conditions for distortion-free measurement of transient temperature signals in terms of sampling frequency and transmission rate. In addition, it is less flexible in terms of data transmission methods, while the cold end of the thermocouple compensation method has not yet compensated for the non-linear phenomenon of thermocouples, which affects the final measurement accuracy. This paper devised a wireless temperature data acquisition system for K-type thin-film thermocouples using a Wi-Fi wireless network to transmit sampling data, then applied the devised system as a data acquisition method to investigate the measurement of transient temperatures in conjunction with thin-film thermocouple sensors. The results of performance test indicated that the devised system is capable of transient temperature measurement of K-type thin-film thermocouples in the range of 0–650°C with a maximum sampling rate of 100 kHz, a temperature resolution of 0.16 degrees Celsius, an accuracy of 0.2% after non-linear compensation and the ability to measure transient temperature signals with a maximum frequency component of 25 kHz. Taken advantage of the devised wireless data acquisition system to measure the impulse response of a thin-film thermocouple sensor specimen, the meausured response curve is consistent with the law of first-order system, and the time constant of the sensor was obtained as approximately 1.16 ms. A comparison between the existing data acquisition apparatuses of type K thermocouple was made. The limitations of the devised system are also discussed.

Measurement of transient temperature using laser-induced breakdown spectroscopy (LIBS) with the surface temperature effect

A method based on LIBS technology for measuring transient surface temperatures had been proposed with an ultra-high time resolution of several μs.