Measurement Of Temperature Distribution Research Articles

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.

The identification of delamination in CFRP laminates by temperature distribution measurement using Rayleigh scattering distribution sensors

The identification of delamination in CFRP laminates by temperature distribution measurement using Rayleigh scattering distribution sensors

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.

Two-colour thermography for measurement of temperature distribution in laser beam welding

Solidification cracking is a frequently observed phenomenon in laser beam welding of austenitic stainless steels and other metallic alloys. Characterisation of cracking susceptibility requires knowledge of the precise and spatially resolved temperature distribution near the solidification front in the welding process. Thermography is a standard tool that provides a qualitative estimate of the 2D temperature field. The general disadvantage of this method is its dependence on the emission characteristics of the measured object. For welding applications, these can vary significantly in the temperature range above and below the melting temperature. For this purpose, we have developed a thermography-based measurement technique using a SWIR camera system in combination with two narrow bandpass filters that use the principle of two-wavelength pyrometry to estimate absolute temperature values. This technique was used to determine the temperature distributions and gradients near the solidification front of laser-welded austenitic steel. The results were validated by other measurements.

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

Accurate temperature distribution measurement during high-intensity focused ultrasound (HIFU) treatment is crucial for avoiding damage to sensitive tissues and organ systems. To surpass the constraints of conventional thermocouple temperature measurement approaches, near-infrared temperature measurement, as a non-invasive imaging method, is proposed. Using infrared glass as a temperature observation window allows for studying the temperature distribution on the surface of biological tissues under ultrasound exposure. The temperature rise in the tissues near the infrared glass under ultrasound exposure was investigated through numerical simulations. Moreover, the effects of the shear waves and thermal viscosity induced by the infrared glass were also analyzed. The results indicate that the shear wave in the glass weakens the intensity of the ultrasound pressure in the focal region while enhancing the efficiency of the acoustic thermal conversion. Thermal viscosity increases the acoustic pressure and temperature in the focal zone. Furthermore, oblique incidence facilitates the transformation of the acoustic thermal effect, caused by shear waves and thermal viscosity, resulting in an expanded temperature rise range on the tissue surface. The non-linear effects in the ultrasound field further enhance the acoustic thermal effect. Significant errors occur in the near-infrared method when utilizing infrared glass for temperature measurement, with the shear waves exerting the most substantial impact on the temperature distribution. These research findings carry substantial implications for optimizing treatment plans, enhancing treatment safety and efficacy, and offering potential application value for temperature control in HIFU treatment.

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.

Acoustic probe for temperature measurement suitable for operation with audio interfaces having random input/output delays

Measuring temperature distribution is an important technique in the fields of meteorology, agriculture, and architecture. The acoustic probe emits sound waves from a speaker and measures the time it takes for the waves to reach a microphone, enabling the measurement of the average temperature between the speaker and the microphone. Additionally, by placing multiple acoustic probes around the measurement area, it becomes possible to measure the temperature distribution using fewer sensors compared to point-type sensors. However, acoustic probes can have higher costs due to the requirement for externally controllable setups or interfaces with minimal audio input/output (I/O) delays. To address this issue, we propose an acoustic probe that achieves accurate measurements even with a low-cost audio interface featuring random I/O delays. The proposed acoustic probe measures the delay time from the recording start to the playback start. This design cancels the error of sound wave propagation time caused by random delays in the audio interface. Through temperature measurement experiments using the proposed acoustic probe, it was revealed that precise measurements (the error of the proposed probe was 0.34°C, while the error of the existing probe was 4.88°C) could be achieved by canceling the random delays in the audio interface.

Temperature Measurement of Trapped, Thermally Sensitive Single Particles in an Optical Trap Using Raman Spectroscopy.

Single particles trapped in an optical trap may experience temperature elevation, yet direct measurement of temperature and its distribution inside the optical trap of several to hundreds of microns in size remains a big challenge. We introduce a method that can measure the temperature inside a universal optical trap (UOT) using Raman spectroscopy of single trapped particles of high thermal conductivity. We measured temperature and temperature distributions inside the UOT using Raman shifts of single-walled carbon nanotubes (SWCNTs) and micron-sized diamonds (MSDs), which are heated by trapping laser beams directly or indirectly, depending on the location of the particle in the trap. We show that the temperature at the center of the UOT is much lower than the temperature along the hollow beams that form a hollow, cage-shaped UOT. In the range of the trapping laser power of 200-2950 mW, the surface temperature of particles trapped at the center of a UOT changes from 322 K to 830 K, correspondingly. This result gives a heating rate as a high thermal-absorbing particle trapped in the center of the UOT with 18.3 ± 0.4 °C/100 mW. In addition, the temperature gradient outside the UOT was also characterized by trapping SWCNT particles outside the UOT. Results show that when a light-absorbing particle is trapped for the study of material property, phase transitions, surface equilibrium process, chemical reactions, etc., this method can be used to measure temperature distribution and its variations in the trap and its surroundings.

Verification and validation of multi-physics numerical analysis of thermomechanical fatigue test conditions under induction heating and forced convection

This paper presents the validation and verification of thermomechanical fatigue multi-physics numerical analysis. To determine the local thermomechanical stress–strain state and displacement fields, an algorithm for the multi-physics numerical calculations is developed and implemented incorporating the Maxwell 3D, Fluent, and Transient Structural modules of ANSYS 2021R1. Single-edge-notch tension specimen heating is modelled using a rectangular induction coil. The temperature distribution in the specimen under forced and natural convection is considered. The nonlinear solid mechanics are analysed considering the temperature nonuniformity under in-phase and out-of-phase loading cycles with a triangular waveform and temperature range of 400–650 °C. Sensitivity analysis is performed to explore the effects of the mesh density. To complement the multi-physics computations, crack-opening displacement and infrared thermography temperature distribution measurements are employed for the thermomechanical fatigue test control in a single-edge-notch tension specimen produced from a nickel-based alloy XH73M. Based on the interconnected verification and validation of coupled numerical analysis, recommended ranges of numerical model parameters have been found to provide a stable solution.