Measurement Of Temperature Distribution Research Articles

Event-triggered background-oriented schlieren: high-frequency visualization of a heated jet flow.

This Letter reports a novel, to our knowledge, event-triggered background-oriented schlieren (EBOS) technique using a combination of an event-triggered camera and pulsed laser speckle projection. The BOS images are reconstructed using the event data generated by the pulsed laser speckle projection and then processed to obtain the density and temperature distribution of the flow. This technique enables continuous visualization and recording of flows at kFPS frame rates with a very low cost, breaking through the short operating times of existing high-frame-rate BOSs. To examine the event-triggered BOS technique, tests are conducted on a hot air gun. The measured temperature distribution coincides with the thermocouple data with an error of no more than 10.8%. Measurements taken during the start-up of the hot air gun demonstrate that the presented technique can measure the evolution of the jet temperature for at least 150 s, as well as capture the localized unsteady turbulent structure in the heated jet flow.

Multi-point thermometry tool and in-situ measurement of temperature fields

In-situ real-time measurement of instantaneous milling temperature distribution is a key issue to realize efficient machining. For the foregoing reasons, the milling model of Inconel 718 was established, and the cloud diagram of tool temperature distribution during milling was obtained. A multi-point temperature measurement tool for milling temperature with an integrated thin-film temperature sensor was designed. The real-time temperature distribution of the tool during milling was obtained from 27 sets of milling tests. The impact of each milling parameter on the milling temperature was analyzed by ANOVA.

Thermal measurements of boiling granular films.

This study focused on two familiar items in our daily lives: grains and boiling water. Accurately measuring boiling dense granular beds requires specialized instruments and novel techniques. An annular vertical riser was used to boil granular films. The riser was filled with glass beads and then immersed in liquid water. The water is heated by inducing eddy currents at the base of the riser, which is composed of carbon steel. Beyond the critical electric current, Ic, the Lyapunov exponent of the time series of the measured temperature distributions within the granular films became positive. This indicates the chaotic behavior of the films. Slightly above Ic, patterned instabilities with affine fractal-like structures were observed in the boiling granular films. Chaotic boiling granular films manifested percolation and transition to turbulence. Computer simulations of the above system under the guidance of generative AI (GenAI) successfully reproduced many critical features of the experimental observations, which can be considered a significant breakthrough in the modeling and simulation of complex systems. With this success in utilizing GenAI, more accurate instruments can be developed, resulting in the world of tomorrow rapidly becoming today's world.

Temperature imaging inside fluid devices using a ratiometric near infrared (NIR-II/III) fluorescent Y2O3: Nd3+, Yb3+, Er3+ nanothermometer.

Luminescence thermometry is a non-contact method that can measure surface temperatures and the temperature of the area where the fluorescent probe is located, allowing temperature distribution visualizations with a camera. Ratiometric fluorescence thermometry, which uses the intensity ratio of fluorescence peaks at two wavelengths with different fluorescence intensity dependencies, is an excellent method for visualizing temperature distributions independent of the fluorophore spatial concentration, excitation light intensity and absolute fluorescence intensity. Herein, Nd3+/Yb3+/Er3+-doped Y2O3 nanomaterials with a diameter of 200nm were prepared as phosphors for temperature distribution measurement of fluids at different temperatures. The advantages of this designed fluorescent material include non-aggregation in water and the fact that its near-infrared (NIR) fluorescence excitation (808nm) is not absorbed by water, thereby minimizing sample heating upon irradiation. Under optical excitation at 808nm, the ratio of the fluorescence intensities of Yb3+ (IYb; 975nm) and Er3+ (IEr; 1550nm), which exhibited different temperature responses, indicated the temperature distribution inside the fluid device. Thus, this technique using Nd3+/Yb3+/Er3+-doped Y2O3 is expected to be applied for temperature distribution mapping analysis inside fluidic devices as a ratiometric NIR fluorescence thermometer, which is unaffected by laser-induced heating.

Development of thermally assisted OH PLIF temperature measurement method based on a single femtosecond laser

Recently, OH planar laser-induced fluorescence (PLIF) using the broadband, ultrashort femtosecond-duration (fs-duration) and the thermally assisted vibrational transfer in excited state has been investigated in flames. In this present work, we first measured temperature by thermally assisted OH laser-induced fluorescence (TALF) method with a single ultrashort broadband fs laser. In the experiment, the fs excitation of OH at ultraviolet wavelength is followed by fluorescence detection from two different vibrational bands. The ratio of two measured (1–0) and (0–0) band fluorescence is calibrated with calculated temperature using Chemkin PRO PRIMIX. The calibrated results are used in measuring temperature distributions in different laminar flames. It is found that TALF method using the fs laser can detect 2D temperature distribution in the burnt area with high OH fluorescence signal. However, OH chemiluminescence brings inevitable noise at the flame front that the TALF method does not perform well. And because (1–0) band fluorescence is so weak, the noise from the camera sensor and imaging intensifier (I.I.) remains at the measured temperature imaging. In conclusion, quantitative temperature measurement based on OH TALF based on a single broadband, ultrashort fs laser can be applied in laminar flames with high frequency by a simple experiment setup.

High spatial resolution temperature variation detection in one direction with a fiber solenoid and RDTS system

Limited by the large bottom width of the pulsed light and the large sampling spacing of the data acquisition card in conventional Raman distributed temperature sensing (RDTS) systems, short straight fibers cannot acquire temperature measurements with high spatial resolution and high temperature accuracy in a single temperature variation region (TVR). In contrast, winding sensing fiber on a screwed tube as a fiber solenoid for temperature sensing can indirectly improve the spatial resolution of the system. However, as the radius of the screwed tube decreases, the ability of the screwed tube to improve the spatial resolution of the system will deteriorate. To break this limitation, we innovatively propose a signal processing scheme to first construct a three-dimensional surface of the sensing length of screwed tube-temperature-area value, then obtain the length of the TVR and the area value of the temperature rise curve generated from a single TVR, and finally demodulate the temperature of the TVR in the surface. The experimental results show that the proposed scheme improves the spatial resolution of the conventional screwed tube from 8 cm to 1 cm, and the average temperature accuracy of the three TVRs with the interval and length of the TVRs in the order of centimeters is ± 0.63 °C. The screwed tube can be used for axial temperature distribution measurements of liquids as well as solids, and the proposed method can further expand the application prospects of the RDTS system for continuous measurement of multiple TVRs with lengths and intervals of centimeters in one direction without changing the internal hardware.

Study on interface adhesion between EP/IFR/HBPSi epoxy intumescent coating and steel substrate

Interface adhesion is a key factor to systematically understand heat transfer process from intumescent coating to underlying steel substrate. In this paper, epoxy intumescent coating EP/IFR/HBPSi was prepared by adding ammonium polyphosphate (APP), melamine (MEL) and a new organosilicone flame retardant phenyl silicone resin (HBPSi) to epoxy resin (EP). The temperature function was obtained by fitting the interval distance between the intumescent coating and the steel substrate measured from 23 °C to 715 °C with muffle furnace, which showed that the interface adhesion was greatly affected by the heating conditions. At the same time, the effects of incident heat flux, chemical formulation, thicknesses of epoxy intumescent coating, the composition, thickness and surface roughness of steel substrate on interface adhesion were investigated by SEM, energy spectrum analyzer, and temperature distribution measurement and so on. The results indicate that all of these factors have influence on interface adhesion. This work helps to further understand thermal protection mechanism of the intumescent coating for steel structure buildings.

Hot, cold, or just right? An infrared biometric sensor to improve occupant comfort and reduce overcooling in buildings via closed-loop control

To improve occupant comfort and save energy in buildings, we have developed a closed-loop air conditioning (AC) sensor-controller that predicts occupant thermal sensation from the thermographic measurement of skin temperature distribution, then uses this information to reduce overcooling (cooling-energy overuse that discomforts occupants) by regulating AC output. Taking measures to protect privacy, it combines thermal-infrared (TIR) and color (visible spectrum) cameras with machine vision to measure the skin-surface temperature profile. Since the human thermoregulation system uses skin blood flow to maintain thermoneutrality, the distribution of skin temperature can be used to predict warm, neutral, and cool thermal states. We conducted a series of human-subject thermal-sensation trials in cold-to-hot environments, measuring skin temperatures and recording thermal sensation votes. We then trained random-forest classification machine-learning models (classifiers) to estimate thermal sensation from skin temperatures or skin-temperature differences. The estimated thermal sensation was input to a proportional integral (PI) control algorithm for the AC, targeting a sensation level between neutral and warm. Our sensor-controller includes a sensor assembly, server software, and client software. The server software orients the cameras and transmits images to the client software, which in turn assesses occupant skin temperature distribution, estimates occupant thermal sensation, and controls AC operation. A demonstration conducted in a conference room in an office building near Houston, TX showed that our system reduced overcooling, decreasing AC load by 42% when the room was occupied while improving occupant comfort (fraction of “comfortable” votes) by 15 percentage points.

Operando analysis of in-plane heterogeneity for the PEM electrolyzer cell: Mappings of temperature and current density

The internal multi-physical fields of a proton exchange membrane electrolyzer cell (PEMEC) are affected by various factors, exhibiting an intricate coupling state. During electrolysis process, the complexity manifests as heterogeneous distribution of in-plane temperature and current density, potentially leading to local hot spots and performance degradation. Such challenges pose threats to the lifespan and operational safety of PEMEC. This study developed temperature measurement endplates and segmented printed circuit board (PCB), enabling operando measurement of in-plane temperature and current density distribution inside a 25 cm2 lab-scale PEMEC. The mappings of temperature and current density were plotted, and the in-plane heterogeneity was assessed by the introduced indexes. The results indicate that variations in operational parameters affect the balance among cell heat production, heat dissipation, and heat input in the flow area, leading to temperature distribution heterogeneity. The migration mechanism of high-temperature zone is elucidated. Factors such as water-gas flow and local conduction contribute to the heterogeneity in current density distribution. Additionally, specific operating conditions including cold and warm start-up, and water starvation are taken as cases, and a detailed analysis is conducted on the dynamic behaviors of current and temperature distribution and the heterogeneity evolution. This work not only provides experimental evidence for the electrical-thermal characteristics inside the PEMEC but also offers insights for local performance evaluation and operation fault diagnosis in practical applications.

Investigation of non-uniform temperature distribution in air-cooled proton exchange membrane fuel cells with multizone temperature measurement

ABSTRACT Open-cathode air-cooled proton exchange membrane fuel cell stack relies on air fans both for fuel supply and stack cooling. Inappropriate stack thermal management and non-uniform temperature distribution can lead to compromised stack performance, reduced lifespan, and even thermal runaway. Thus, temperature distribution measurement, investigation and analysis are essential for air-cooled PEMFC’s optimized operation and performance. This study uses a multi-zone temperature measurement approach to investigate the impact of air supply method, airflow, and output current on stack temperature distributions. The experimental results reveal that the highest stack temperature occurs at the cathode channel outlet, while the lowest temperature is near the hydrogen inlet. At a 75A load, the maximum temperature difference between the inlet and outlet is 17°C. Increasing fan speed from 4500 to 8800 r/min reduces temperature non-uniformity in cell 10, the most uneven among the 19 cells, by 11.2%. Comparing blowing and suction air supply modes, blowing enhances stack output performance by 2.1%, with smaller temperature differences. Specifically, cell 10 experiences a 7.5°C lower difference at 4500 r/min and a 3.6°C lower difference at 8800 r/min airflow. Under blowing air supply, temperature non-uniformity decreases by 36.95% at 4500 r/min and 29.2% at 8800 r/min.

Comprehensive analysis method of acquiring wall heat fluxes in rotating detonation combustors

Accurate perception of the combustor thermal environment is crucial for thermal protection design of a rotating detonation combustor (RDC). In this study, a comprehensive analysis method is established to calculate the non-uniform heat flux distribution of the RDC by utilizing the measured temperature distribution of the combustor outer wall obtained by the high-speed infrared thermal imager. Firstly, a physical model based on the geometric characteristics of the RDC is constructed and its thermal conductive process is simulated, given by different heat flux boundary conditions. The analysis results indicate that the method used in current research for computing the heat flux of RDC leads to significant discrepancies, particularly in regions of obvious axial heat flux gradients near the top of the combustor. Then the Levenberg-Marquardt (L-M) method for inversely solving non-uniform heat flux is developed based on the two-dimensional heat conduction equation, and the wall heat fluxes are inversely calculated by the L-M method based on the above numerical data. Results show that the L-M method can obtain more accurate heat flux distribution even in the zones with large heat flux gradients, considering the axial heat conduction within the combustor outer wall caused by the non-uniform heat flux. Finally, the wall heat flux distribution is analyzed coupling the L-M method together with the experimental measurements in kerosene two-phase RDC. The analyses show that the wall heat flux exhibits non-uniform distributions both circumferentially and axially, with axial non-uniformity being particularly pronounced. The highest temperature of combustor outer surface and the highest wall heat flux occurs within the region of 20 mm from the combustor head, which corresponds to nearly 14 % of the combustor length. The heat flux peak and thermal heat rate are positively correlated with the combustor equivalence ratio in the range between 0.44 and 0.64. In this study, the distribution of wall temperature field in the two-phase RDC is obtained for the first time and the wall heat flux is calculated inversely by L-M method. This work provides a more accurate method for calculating heat flux in RDC and offers references for thermal protection designs in RDCs.

Thin-film temperature sensors with grid-type circuits for temperature distribution measurements

Measuring the temperature of satellites is crucial for thermal control. Efficient heat control is possible when the location of the heat source can be quickly identified and the heat transfer area can be measured. Grid-type thin-film temperature sensors have been proposed for this purpose. Grid-type thin-film temperature sensors use electrohydrodynamic (EHD) inkjet printing technology, a next-generation printing technology. Sensors with high sensing resolution can be manufactured using these technologies. However, the EHD inkjet printing technology is sensitive to printing conditions, and determining the optimal conditions is crucial. Therefore, we produce inks for application in EHD inkjet printing technology and conduct experiments to validate their characteristics. In addition, we determine the optimal conditions for printing and manufacturing grid-type thin-film temperature sensors. The heating element is placed at an arbitrary location and the location of heat generation is detected using the manufactured temperature sensors. We have obtained visualization data showing the heat distribution with time. As a result, the production of a grid-type thin film temperature sensor using the printing process was confirmed. This temperature sensor was able to track the heat source and check the distribution process through which heat is transferred. Therefore, it can be expected to be used in fields that require temperature monitoring.

Numerical Study on the Application of Near-Infrared Temperature Distribution Measurement of HIFU

Numerical Study on the Application of Near-Infrared Temperature Distribution Measurement of HIFU

Measurement of Temperature Distributions in a Transparent Germanate Glass-ceramic at the Micron Scale

Measurement of Temperature Distributions in a Transparent Germanate Glass-ceramic at the Micron Scale

Ultrasonic measurement of temperature distributions in extreme environments: Electrical power plants testing in utility-scale steam generators

Thermal heterogeneities within energy conversion and storage, material processing, nuclear processes, aerospace, and military applications are often inaccessible to characterization by insertion sensors. When sensor deployment is possible, conventional pointwise temperature probes quickly degrade when inserted into harsh environments typical of such processes. We developed spatially-resolved ultrasonic thermometry to noninvasively measure the spatial distributions of thermal properties in such applications, even when sizable thermal gradients are present. Our method divides the path of ultrasonic propagation into segments bound by echogenic features, which create echoes in pulse-echo mode, encoding the information about interior temperature distributions. We use the acquired ultrasonic responses to estimate the internal temperature distributions by solving an inverse problem or concatenating segmental estimates. This work describes the implementation and industrial testing of the developed method at a coal-fired electrical power generation plant. We inserted an echogenically segmented Inconel 625 waveguide into the combustion zone of the utility-scale boiler and continuously acquired ultrasonic data while keeping sensitive components away from the damaging combustion environment. The accuracy of the time-dependent temperature distributions reconstructed from the ultrasonic measurements was comparable to that of thermocouples. The resiliency of ultrasonic thermometry to harsh combustion conditions was far superior to conventional insertion sensors. The measurements obtained during plant operation captured daily steam generation cycles in response to changing customer demand and intermittent contributions of renewable power sources to the power grid. These measurements have revealed new insights into the relationship between the dynamic power generation load and the conditions inside the steam generator. The successful industrial testing of spatially-resolved ultrasonic thermometry in solids indicates that the developed technology has matured to become an attractive alternative to conventional sensing in solving challenging problems of long-term thermal characterizations in extreme environments.

Analyzing Temperature Distribution Patterns on the Facing and Backside Surface: Investigating Combustion Performance of Flame-Retardant Particle Boards Using Aluminum Hypophosphite, Intumescent, and Magnesium Hydroxide Flame Retardants.

Particle boards are manufactured through a hot pressing process using wood materials (natural polymer materials) and adhesive, which find common usage in indoor decorative finishing materials. Flame-retardant particleboard, crucial for fire safety in such applications, undergoes performance analysis that includes assessing temperature distribution across its facing surface and temperature increase on the backside surface during facade combustion, yielding critical insights into fire scenario development. In this study, a compact flame spread apparatus is utilized to examine the flame retardancy and combustion behavior of particle boards, with a specific emphasis on the application of cost-effective flame retardants, encompassing aluminum hypophosphite (ALHP), an intumescent flame retardant (IFR) comprising ammonium polyphosphate (APP), melamine (MEL), and Dipentaerythritol (DPE), alongside magnesium hydroxide (MDH), and their associated combustion characteristics. The D300°C values, representing the vertical distance from the ignition point (IP) to P300°C (the temperature point at 300 °C farthest from IP), are measured using a compact temperature distribution measurement platform. For MDH/PB, APP + MEL + DPE/PB, and ALHP/PB samples, the respective D300°C values of 145.79 mm, 117.81 mm, and 118.57 mm indicate reductions of 11.11%, 28.17%, and 27.71%, compared to the untreated sample's value of 164.02 mm. The particle boards treated with ALHP, IFR, and MDH demonstrated distinct flame-retardant mechanisms. MDH/PB relied on the thermal decomposition of MDH to produce MgO and H2O for flame retardancy, while APP + MEL + DPE/PB achieved flame retardancy through a cross-linked structure with char expansion, polyphosphate, and pyrophosphate during combustion. On the other hand, ALHP/PB attained flame retardancy by reacting with wood materials and adhesives, forming a stable condensed P-N-C structure. This study serves as a performance reference for the production of cost-effective flame-resistant particleboards and offers a practical method for assessing its fire-resistant properties when used as a decorative finishing material on facades in real fire situations.

Infrared-thermography measurement of temperature distribution in carbon fiber–reinforced polypropylene during ultrasonic welding

Herein, the temperature distribution during ultrasonic welding of carbon fiber–reinforced polypropylene (CF/PP) was investigated. The temperature distribution was assessed using a thermographic camera that specifically targeted the lateral aspect of the welded section of the adherend in the lap joint. In addition, single lap shear tests were performed on the resulting welded joints. The welding experiments confirmed that the amplitude of the sonotrode impacts both the temperature distribution during welding and the quality of the joint, eventually affecting the mode of failure. By applying the half-width method to the measured temperature distribution in the thickness direction of the adherend, we assessed the spread of the high-temperature region centered on the welding interface. In this study, at a small amplitude (36 μm), the half-width of the maximum temperature showed approximately twice higher slope than at other amplitudes, indicating a wider high-temperature range even at the same interface temperature.

Measurement of reaction temperature distribution inside of methanol steam reforming microreactor using infrared thermography

Methanol steam reforming is a promising method for in-situ hydrogen production and greatly affected by the reaction temperature inside the microreactor, while the inside reaction temperature distribution is quite difficult to be measured. Here, we developed a visible methanol steam reforming microreactor using optical crystal as observation window and using infrared thermography to measure the real-time reaction temperatures. The method of using infrared thermography to measure the distribution of reaction temperature was presented and characterized with the accuracy of 98.4 % in the range of 300.0–575.0 K. Then, temperature heating and hydrogen production tests were conducted, and results showed that the lower oxygen to carbon (O/C) ratio leads to higher heating rate of 18.0 K/min during microreactor heating stage. The measured temperature distribution on the copper foam increases with a stable gradient of 0.91 K/mm along the reactant flow direction and the temperature difference in vertical direction is less than 10.0 K. The maximum methanol conversion is 98.0 % at the gas hourly space velocity (GHSV) of 3600 mL/(g·h) and maximum reformate flow rate is 100.8 mL/min at the GHSV of 6000 mL/(g·h). The obtained results demonstrated that the visible methanol steam reforming microreactor and reaction temperature measurement method would be beneficial for future microreactor’s design.

Noninvasive measurement of body temperature distribution during radiofrequency hyperthermia for cancer treatment

Noninvasive measurement of body temperature distribution during radiofrequency hyperthermia for cancer treatment

Heat dissipation promotion of LED chips by c-BN film

The light-emitting diodes (LEDs) are now the most important lighting devices due to their excellent wall-plug efficiency (WPE). However, their unique structure means that heat dissipation from the chip can only be achieved by conduction. The insulating thermal conductivity layer becomes a bottleneck in the heat transfer of the chip, seriously affecting its lifetime and reliability. Cubic boron nitride (c-BN) has good thermal stability, electrical insulation and high thermal conductivity, making it a potential insulating and heat dissipating material. In this study, we investigate the application of c-BN films to promote heat dissipation in LEDs based on c-BN films grown by physical vapor deposition (PVD) sputtering. In our study, we highlighted the performance variations between c-BN and Si substrates under different driving powers, ranging from 9 W to 12 W. By incorporating the c-BN film onto the Si substrate, we observed a distinct improvement in the temperature distribution of the LED array. Specifically, with a driving power of 9 W, the temperature was reduced by approximately 4.1 °C, and with 12 W, the reduction reached 16.8 °C. This enhanced thermal management not only augments the stability and lifespan of the components but also boosts the optical output power of the LED chip array, with an increase ranging from 21.3% to 27.9%. We find that c-BN films can effectively enhance chip heat dissipation, significantly improve WPE, and suppress light decay, as demonstrated by temperature distribution and luminescence power measurements. The experimental and simulation results demonstrate that c-BN films can reduce the temperature of LED beads by approximately 5–17 °C compared to Si substrates. This c-BN thin film substrate shows promise for use in commercial device heat dissipation structures.