IR Camera Measurements Research Articles

Transient behavior of thermocapillary convection in thin liquid film exposed to step laser heating

Temporally developing thermocapillary convection induced by step laser heating of a thin liquid film has been studied numerically. Computations are performed using the commercial software STAR CCM+ version 2022.1. The liquid film of silicone oil (high Prandtl number fluid) is 60 mm in diameter and 3 mm in thickness. Flow characteristics related to surface velocity and surface temperature have been studied. Validation of the computations is achieved for the surface velocity, the velocity along thickness and the surface temperature through comparison with PIV and IR camera measurements. The laser-beam with a carbon dioxide gas laser (10.4 μm in wavelength) is used for heating. It is found that the temporally developing profile of surface velocity shows two local velocity peaks (uS1 and uS2) at two radial locations (rS1 and rS2) respectively. The first peak, uS1, appearing due to the steep temperature gradient generated by laser-beam heating and its radial position, rS1, do not change noticeably with time. On the other hand, the second peak, uS2, travels radially outwards with decreasing magnitude in a self-propelling manner until its radial position, rS2, approaches an asymptotic maximum. Detailed analysis of the coupling among radial temperature gradient, local pressure variation and local convective acceleration near the second peak reveals that hydrothermal mechanisms are responsible for self-propelling travel of uS2. The transient behaviors of both primary and secondary velocity peaks are found to depend on the fluid viscosity and the laser-beam settings

Upconverting thermal history paint for investigations of short thermal events

The main goal of the work was to develop phosphorescent coating for investigations of surface temperature distribution resulted from short duration and high energy thermal events such as small rocket engine testing. For that purpose, we developed thermal history paint with upconverting Gd2O3: Er3+, Yb3+, Mg2+ nanopowder. The developed paint was heated by Joule effect with precise control over temperature and heating time. Photoluminescence signal of cooled samples was excited with 980 nm laser and collected in automatic manner with use of an optical fibre probe connected to photospectrometer. The results show that irreversible changes of paint emission are temperature and heating time specific for calcination temperatures from 700 °C to 1150 °C. Calibration curves were prepared for heating times of 10, 60 and 180 seconds. Finally, 2D surface temperature samples were determined with use of upconverting thermal history paint and compared to IR camera and pyrometric measurements. The results indicate that uncertainty of temperature measurement below 10 °C was achieved for temperatures above 1000 °C. It has been demonstrated that developed thermal history paint allows for measurements of 2D surface temperature distribution with high spatial resolution and good agreement to standard measurements techniques like thermal camera and pyrometer.

Investigation of 3D effects on heat fluxes in performance-optimized island divertor configurations at Wendelstein 7-X

The 3D effects on divertor heat loads have been investigated for performance-optimized island divertor configurations at Wendelstein 7-X with 3D modeling and IR camera measurements. A new high mirror configuration optimized for more stable island divertor operation due to reduced bootstrap currents and a more even heat load distribution between the main divertor targets has been investigated for the first time numerically and experimentally.Transport calculations with EMC3-EIRENE show a strong dependence of the heat flux distributions on the configurations and the details of the 3D island geometry. IR camera measurements confirm the predictions concerning the global heat load distributions for the standard configuration but show more even distributions between the main wetted divertor plates in the high mirror configurations. The local heat load profiles show offsets in their position of up to 5 cm to each other and averaged peak heat fluxes varying between 0.5 MWm−2 and 2.2 MWm−2 depending on the divertor module considered. These heat flux asymmetries complicate the local matching of profiles between experiment and 3D modeling.The 3D equilibrium of a high mirror high-performance scenario predicted by the HINT code has been investigated with EMC3-EIRENE for the first time to anticipate plasma response in higher performance scenarios. The island divertor is preserved for β=3% despite enhanced stochasticity. However, the islands are increased in size while the path lengths for parallel transport are reduced causing a substantial change in the divertor heat flux patterns.

The surface eroding thermocouple for fast heat flux measurement in DIII-D.

A novel type of surface eroding thermocouple (SETC) has been tested and demonstrated in the small angle slot (SAS) divertor of DIII-D for fast local heat flux measurements. The thermojunction of the SETC is formed between two thin (10 μm) ribbons, which are filed over to create microfiber junctions. These thermocouples are able to be exposed directly to the plasma at surface temperatures exceeding 2000 °C and are capable of sub-10 ms time resolution. Before installation in SAS, the SETCs were exposed in the lower DIII-D divertor during L-mode and H-mode discharges, from which results are presented. In preliminary tests, SETCs proved to be a qualified diagnostic to accurately measure both the intra-edge localized mode (ELM) and inter-ELM heat flux during H-mode shots with high frequency ELMs (hundreds of Hz) and to resolve heat flux profiles during strike point sweeps. The heat fluxes measured by using SETCs are consistent with the heat fluxes measured by using IR cameras and Langmuir probes. These new diagnostic capabilities will complement the existing IR camera measurements and will be of particularly significant value to measure surface heat flux in the SAS divertor or other regions where the IR camera lacks line of sight.

P-172: Temperature Distribution in WRGB AMOLED Displays

This paper explains how a non-uniform temperature distribution arises across an OLED display and how it is influenced by the image content. IR camera measurements on a sample 55” WRGB OLED display and a thermal model that allows simulating the temperature distribution across an OLED display are presented. It has been shown before that temperature has a direct impact on the picture quality of an OLED display. Therefore, a good understanding of the thermal behavior of an OLED display is important. The presented thermal model can be a useful tool in the design phase of an OLED display.

Modeling of Plasticating Injection Molding – Experimental Assessment

Abstract A computational model for the description of polymer flow during the plasticating phase of the injection molding process is proposed. The polymer behavior is determined during the dynamic and static phases of the process. The model takes into account the backwards movement of the screw, the presence of a non-return valve and the conduction of heat during the idle times. Results for the dynamic and static phases of the plasticization are presented. The model is also used to study the influence of some important operative process parameters, such as, screw speed, backpressure, barrel temperatures and injection chamber length. The assessment of the computational results is made experimentally by comparing the average temperature calculated with measurements made in front of the screw nozzle using both, an IR camera and an IR thermometer. The differences between the computational and the IR camera measurements are below 5%.

Effect of Meniscus Recession on the Effective Pore Radius and Capillary Pumping of Copper Metal Foams

An experimental study is performed to characterize the effect of meniscus recession on the effective pore radius and capillary pumping of copper metal foams which are to be used as wicks in heat pipes for electronic cooling. Knowledge of the effective pore radius is critical in defining the capillary pumping of a wicking material but is rarely measured under operating conditions. It is known that the meniscus of a liquid recedes when evaporating from a porous media, which could impact the effective pore radius and therefore the capillary pumping capabilities of the foam. To elucidate this impact, the evaporation rate is measured from foam strips wicking ethanol from a reservoir while applying heat fluxes to the foam. Using thermocouple and IR camera measurements, the measured evaporation rates are corrected to account for different thermal losses, including natural convection, direct thermal conduction to the liquid, and evaporation from the container. An analytical model is then developed to relate the evaporated mass to the maximum capillary pressure (minimum effective pore radius) provided by the foam. It is shown for the first time, that just before the onset of dryout, the recessed meniscus will lead to 15%, 28%, and 52% decrease in effective pore radius for samples with 68%, 75%, and 82% porosities, respectively. The capillary pumping therefore increases during evaporation. This can have significant impact on the prediction of the capillary limits in two phase capillary driven devices.

Relationships Between Surface Thermal Gradients and Disc Distortion During Stop-Braking with High Energy Dissipation

This paper focuses on the study of the relationships between brake disc surface temperatures and disc distortion for various high-energy stop-braking conditions. An original thermal metrology method combining an infrared camera and a fibre-optic two-colour pyrometer was used to record the spatial and temporal variation in disc surface temperature during braking. Disc distortion was investigated in situ by means of a high-frequency displacement sensor. In addition, an optical trigger kept track of disc revolutions and enabled the synchronization of the IR camera, two-colour pyrometer and displacement sensor measurements. This experimental set-up was successfully used to determine the surface temperature and investigate thermal localization and waviness distortion during braking. The results were correlated with each other in relation to the level of energy dissipation. It was shown that the highest temperature was reached in the hot spot regions at an early stage of stop-braking. By contrast, the greatest disc distortion appeared much later, during the last stage of stop-braking.

Characterization of transient particle loads during lithium experiments on the National Spherical Torus Experiment

Transient events such as Edge Localized Modes (ELMs) or disruptions can lead to large particle and power loads on the divertor plates of tokamak experiments. These events can cause significant erosion and are detrimental to the lifetime of the plasma facing components. Understanding the impact of ELMs remains a complex problem and a major challenge. In this study, an effort is made to characterize these ELMs and other transients based on their characteristics using a particle flux probe and surface temperature measurements from a dual-band IR camera. Typically, the temporal evolution of an ELM from the particle flux probe is characterized by a steep rise and a gradual decrease of current signal. This burst like structure is seen by the Langmuir probes as a rise in the ion saturation current with a width of a few milliseconds. This study entails gathering statistics of typical ELM-like events for various shots in order to assess the typical loading of ELMs on the Liquid Lithium Divertor (LLD) that was installed in the FY10 run campaign. Later, the power deposition profiles during ELMs are also characterized from IR camera measurements for certain discharges to find that only 15% of the energy flux arrives at the divertor target before the surface temperature reached its maximum value. Finally, a correlation was found between the particle flux from the probes during the ELMs and the neutral particle flux from Dα signal indicating the utility of the particle flux probe as a means to characterize ELMs.

Theory of fast particle generation in front of LH grills

During tokamak operation with lower hybrid (LH) power a few per cent of the launched power is absorbed by the scrape-off layer plasma in magnetic flux tubes in front of the LH grill. At strike points of these flux tubes, intense plasma–wall interaction is seen in visible and infrared wavelengths, and local wall damage can occur. The parallel power flux within these ‘hot spots’ is estimated to be up to about 10 MW m−2 by infrared imagery. Recent experimental results from retarding field analyzer measurements on Tore Supra as well as JET IR camera measurements have shown the existence of fast electrons as far as a few centimeters from the grill mouth. This finding cannot be explained by the standard theory. We present therefore in this paper a novel theory explaining the fast electron generation in a several cm wide layer in front of the LH grill by taking into account LH wave propagation features closely connected with the blob character of edge turbulence. We demonstrate that the computed power-flows then essentially agree with data from infrared diagnostics. An alternative theoretical explanation considers plasma density modulations due to ponderomotive force effects in front of the LH grill.

SOLPS5 modelling of the type III ELMing H-mode on TCV

Although ohmic H-modes have long been produced on TCV and the effects of ELMs at the divertor target studied in some detail, no attempt has yet been made to model the scrape-off layer (SOL) in these plasmas. This paper describes details of the first such efforts in which simulations of the inter-ELM phases using the coupled fluid-Monte Carlo SOLPS5 code (without drifts) are constrained by careful upstream Thomson scattering and Langmuir probe profiles. Simulated divertor profiles are compared with Langmuir probes and fast IR camera measurements at the targets. To account for the very differing transport rates in the edge pedestal and main SOL regions, radial variation of edge transport coefficients has been introduced in the simulations. Similarly, it is found that transport in the main chamber and divertor regions must be separately adjusted to provide an acceptable code-experiment match.

Disruption heat loads on the JET MkIIGB divertor

Combined analysis of divertor thermocouple and IR camera measurements during JET disruptions can provide valuable information on the distribution of the energy loads, even if the stored energy of the JET plasmas is small compared to that foreseen for the next-generation tokamaks. Typically the energy collected at the divertor represents a small fraction of the pre-disruption plasma energy; this is consistent with the high level of radiation observed and with part of the magnetic energy being transferred to the plasma-coupled conductors. The data for this paper are taken from the whole set of disruptive plasmas of JET operation in the years 2000 and 2001. In most of the MkIIGB disruptions, the plasma displaces upwards (away from the divertor); therefore, only a small number of downward events are available for analysis. However, divertor heat loads seem to be more strongly correlated to the delay of the loss of the X-point with respect to the thermal quench than the direction of the plasma displacement.When the plasma thermal energy is lost with the plasma still in X-point configuration, the septum and the tiles wetted by the strike-points, often more than one tile per strike-point, experience a sharp increase in temperature, equivalent to up to 1 MJ m-2. When the thermal quench occurs at the same time as, or after, the loss of plasma vertical control, no significant divertor tile temperature \ obreak increase can be observed for both upwards and downwards events. Most of the disruptions purposely made to produce runaway electrons went towards the divertor and, although not systematically, lead to local (mostly at the septum) temperature increase equivalent to a load up to 2 MJ m-2, often toroidally asymmetric.

RFX first wall thermal power handling: 3D numerical models and experimental validations

One of the emerging issues for future thermonuclear devices is the non-uniform power deposition on the first wall or divertor surfaces. The localized peaks of power are detrimental both for the lifetime of the plasma facing components and for plasma heating and confinement. The thermal monitoring of the first wall can be done with temperature measurements acquired during the experiments by means of thermocouples and/or infrared camera images. If the measurement system is integrated with analytical or numerical models, it is possible to estimate the applied thermal loads and to obtain a thorough knowledge of the thermal behaviour of the first wall and vacuum vessel system. The numerical model developed for the RFX machine is hereby described and validated by means of comparisons with IR camera and thermocouple temperature measurements.