Thermal Paint Research Articles

Transient Thermal Mapping Utilizing the Sintering of Glass‐Ceramics

Thermal paints are essential for mapping the surface temperature of gas turbine engine components but can only indicate maximum temperature. A novel transient thermal history sensor that combines the capabilities of a thermocouple with those of a thermal paint is developed here, enabling the retrieval of full thermal history using a “sintering” model. The glassy ceramic thermal paint undergoes a qualitative optical transition due to sintering in response to temperature that is quantified using UV–vis spectroscopy. This provides high‐resolution transient temperature measurement (±6 °C) when maximum temperature is above its glass transition temperature (Tg) of 563 °C and up to 660 °C. The glass‐ceramic coating exhibits strong adhesion to Inconel 718 substrates due to matched coefficients of thermal expansion. By fabricating similar paints with distinct temperature ranges and placing them in proximity, this approach can significantly reduce the number of thermocouples needed for surface temperature mapping, thereby improving the accuracy of measurements required for engine validation.

Analysis of the aerothermal performance of modern commercial high-pressure turbine rotors using different levels of fidelity

In the field of design and optimization of sophisticated geometries such as film-cooled turbine blades of modern jet engines, Computational Fluid Dynamics (CFD) simulation is commonly employed. As the pursuit for higher turbine entry temperatures intensifies, it becomes crucial for computational analyses to offer accurate predictions of metal temperatures and heat transfer coefficients on these critical components. This study investigates the impact of key physical factors that characterize the operation of these components on the accuracy of the computational model. In particular, the effects of including the exchange of thermal energy between the fluid and solid domains, as well as modelling the unsteady interaction between the rotor and stator are studied. The research focuses on a fully featured one-and-a-half stage high-pressure turbine of a commercial jet engine, utilizing proprietary software for conducting 3D Reynolds-Averaged Navier-Stokes flow simulations. To model the fluid-solid thermal interaction, steady-state Conjugate Heat Transfer (CHT) simulations are performed. The CHT results are then compared with experimental data obtained from a thermal paint test, achieving good levels of agreement. Additionally, phase-lag simulations are executed under adiabatic-wall conditions to evaluate the influence of stator-rotor interaction on near-wall gas temperatures. This work shows that, by modelling the periodic unsteadiness at the stator-rotor interface with a phase-lag technique, the maximum near-wall gas temperature prediction is significantly increased, sometimes more than 100K, with respect to the steady-state model one. Findings from this work also suggest that simplified “strip” source terms used to model the presence of film cooling hole rows on the surface of a blade can be used with satisfactory accuracy only for nominal conditions. The mass flows delivered by each source strip should not be linearly scaled based on mainstream quantities for use in different conditions, but they should be recalculated from scratch for the new conditions.

EXPERIMENT TO EVALUATE THE EFFECTIVENESS OF THERMAL REFLECTIVE COATING APPLIED TO CONSTRUCTIONS

Constructions are usually made of materials like reinforced concrete and steel. In hot weather conditions, the reflected thermal radiance in the daytime and the emitted thermal radiance of human activities inside the structure are significantly higher than in the background. Thanks to the temperature difference between them, thermal imaging systems can easily detect or recognize the target. In order to reduce the thermal contrast, it is vital to research and apply the specific coating that can be used to cover the construction and the outside door. On the other hand, there is yet to be a method to evaluate the effectiveness of thermal reflective coating for constructions and mobile targets in Vietnam. Hence, the article has focused on performing the experimental measurement of the thermal difference between two coating materials. The result will also be applied to evaluate and select the effective thermal paint for the protected system.

Application of pulsed laser ablation thermal model in nanosecond pulsed laser removal of the epoxy resin paint film

The effect of laser surface paint removal depends on the mechanism of paint removal. The mechanism of nanosecond laser removal of epoxy resin paint film on aluminum alloy surfaces was studied theoretically and experimentally. Firstly, a laser thermal paint removal model was established based on the heat conduction equation, Hertz-Knudsen equation, and Hooke's law. The adsorption relationship between the paint film and the aluminum alloy substrate molecules and the adsorption force between the paint film and the substrate were analyzed and calculated. A laser thermal paint removal model was solved using COMSOL finite element software. By analyzing the changes in temperature and thermal stress with laser fluence, we obtained the theoretical threshold for laser paint removal. Subsequently, experimental research was conducted on laser paint removal. Through theoretical and experimental studies, it was found that the paint removal threshold of nanosecond pulse laser is 0.47 J/cm2. The primary mechanism of nanosecond laser paint removal is thermal stress stripping. When the laser fluence is low, the nanosecond pulse laser can only ablate the paint on the surface, and the thermal stress between the paint film and the substrate makes it difficult to remove the paint film. As the laser fluence increases, the nanosecond laser will ablate the surface paint film, and the thermal stress between the paint film and the substrate will cause the stripping of the underlying paint film and the substrate. The primary mechanism of laser paint removal is stripping.

Simulation and Experimental Study on Continuous Wave Fiber Laser Removal of Epoxy Resin Paint Film on the Surface of 6061 Aluminum Alloy

Paint removal is an essential process in the industrial field. Laser technology provides an effective method of paint removal to replace traditional mechanical and chemical methods. This paper establishes a continuous wave (CW) laser thermal paint removal model based on heat conduction theory and Arrhenius’ law. The paint stripping process of epoxy paint film on the surface of 6061 aluminum alloy via CW laser was studied through simulation and experiment. We found that the carbonization of the paint film during the CW laser paint removal process will inhibit the laser paint removal process. Therefore, the paint removal efficiency of the CW laser is limited. The depth of CW laser paint removal increases linearly with the CW laser power density. However, during the CW laser paint removal process, due to the pyrolysis of the paint film and the reflection of the laser by the substrate, the surface temperature of the material first increases and then decreases. In addition, after laser paint removal, the surface roughness of the material after paint removal is reduced due to the melting of the base material. The model established in this article can provide a theoretical reference for studying the CW laser paint removal process.

Advanced Simulation Technologies and Testing Methodologies Applied in the Design and Development of Aero Gas Turbine Engines

An overview of Gas Turbine Engine Development, KAVERI, the power plant for the Light Combat Aircraft (Tejas) and a description of the validated numerical tools, aerothermodynamic and mechanical test facilities of the Gas Turbine Research Establishment (GTRE) are presented. The KAVERI engine compressor, combustion system, turbine, analytical tools, blade heat transfer, exhaust system, Integrated Nozzle Actuation System (INAS), Non-intrusive Stress Measurement System (NSMS) and thermal paint tests are described in detail.

An optical technique based on silicate glass sintering for temperature mapping

AbstractThermal paints have been used for decades by the gas turbine engine community to map surface temperature with low resolution. A novel thermal paint based on the sintering of a lead‐silicate glass powder was developed that can map maximum temperature with high resolution (±5°C) over a 60°C range beginning at the glass transition temperature (). The paint exhibited excellent adhesion to nickel‐based superalloy components due to similar coefficients of thermal expansion between the superalloy and glassy ceramic coating. An optical transition was qualitatively and quantitatively observed using scanning electron microscopy, ultraviolet‐visible (UV‐VIS) reflectance spectroscopy, and visual inspection. UV‐VIS reflectance spectroscopy was used to confirm the optical transition observed by the naked eye and quantitatively assess the transition of the thermal paint with high resolution. This technique for obtaining high resolution experimental temperature maps can aid the performance, efficiency, and reliability of gas turbine engines.

High-Resolution Thermal Profiling of a Combustor in a Non-Dedicated Test Using Thermal History Coatings

Abstract The requirement for reduced emissions and the growing demand for gas turbine efficiency are in part met through increasing firing temperatures. However, development budgets leave only limited time for dedicated thermal testing. Consequently, manufacturers are seeking novel temperature measurement technologies to validate new engine designs. This paper will demonstrate how a new temperature mapping technology can be utilized for non-dedicated (multi-cycling) testing while still delivering high-resolution temperature data in a non-dedicated test on a combustor of an industrial gas turbine. Typically, thermocouples are used to monitor the temperature during tests, but they only provide one data point. Color-changing thermal paints are used to deliver measurements over complete surfaces, but they require dedicated testing with short-duration exposure, necessitating dismantling and re-assembling the engine for further testing. Thermal History Coatings (THC) present an alternative solution to providing high-density temperature information. This coating permanently changes consistent with the maximum temperature of exposure during the test. A laser-based instrumentation technique is then used to obtain temperatures. The maximum temperature profile of the surface can be determined through a customized calibration. Given the complex cooling system of a combustor, the high temperatures, and the long-time exposure, this case offers a unique possibility for the testing of the coating under real engine conditions. The coated region covered the external surface of the can. Highly significant is the number of measurement points above 7000 (2 × 2 mm resolution), which enables advanced analysis. This provides insight into the impact of local features, e.g., the region adjacent to a cooling hole. The temperature profile is compared to a computational fluid dynamics-conjugate heat transfer model and thermocouple measurements for the calibration of cooling pre-design methods.

Glycerol /Phthalic Anhydride Novel Nano Composite for Microwave Absorbing Applications

High-efficiency radar wave absorbing material was prepared utilizing nanoparticles poly (glycerol /phthalic anhydride), and the effect of using these nanocomposites with thermal paint on the properties of electromagnetic absorbing was analyzed and investigated. Results show that when the percentage of nano polymers is increased from 1% to 3%, with the presence of 2.5% of iron oxide, the reflectivity loss value rises dramatically. For the reflectivity up to 27.2dB at a frequency of 8.3 GH and a bandwidth of (8.1-8.2GH), there is a clear attenuation of the radar waves, which is confined within a bandwidth of GH (9-9.3GH). This material can be utilized as a high- efficiency radar wave absorbing applications.

Experimental evaluation of thermal stress on the surface of butterfly specimen through irreversible colour change of thermal paint

Gas Turbines have been used effectively and extensively in jet propulsion and the sectors of electricity production. The flame produced due to combustion of air & fuel propagates through the gas turbine’s parts. As the hot combustible gases flow through these components, high thermal stresses are imposed on these components. The material life of the individual elements of the gas turbine system depends on its operating temperature and thermal stress. To achieve higher efficiency, the operating temperature may be increased to a certain level. Temperature (or) thermal profiling of the engine components is mandatory to make the engine design reliable. Thermal paint used for temperature profiling of hot surfaces is estimated to be the structured method even after removing the heat source. The present research concentrates on the investigations on the evaluation of thermal stress induced on a hot specimen through the application of thermal paint. A butterfly specimen made of Mild Steel has been fabricated and used for the present experimental investigations. The current work also concentrates on the variation in the surface temperature of the specimen based on the heat input using the butterfly specimen. The colour change on the surface of the specimen has been related to temperature using the RGB values of colour through MATLAB’s fuzzy logic. The results of the experimental investigation prove that the usage of thermal paint reveals the exact deal of stress developed thermally on the surface of the specimen based on the colour change.

A review on modern heat-insulating materials for improving the energy efficiency of buildings and life-support utilities

The main heat engineering characteristics of modern traditional and innovative heat-insulating materials, their advantages, and application fields are considered. Particular attention is paid to liquidceramic heat-insulating materials - thermal paints, which are now actively used for thermal insulation of facades of capital and completed construction projects, engineering and technical life support systems, installations, and separate elements. Interest in the study of this group of building materials is explained by the widespread use of heaters to improve the energy efficiency of civil and industrial buildings, as well as engineering life support systems for various purposes.

PRELIMINARY STUDY OF A IMAGE ANALYSIS SETUP APPROACH OF THERMAL TRACING JET ENGINE PARTS USING THERMAL PAINTS

Reduced engine performance comes with a higher operating temperature, and that limit is imposed by component material life. It is critical to have an accurate, full-field evaluation of the metal temperature of the hot section components for engine designers to develop dependable and lasting engines. Using conventional thermometry isn't recommended since it fails to generate heat gradients and results in problems when transferring data from measurement sites to the readout unit. It has recently been discovered that the thermal transfer condition has changed, and as a result, the actual temperature of the components cannot be measured. A paint will permanently change color if it is exposed to heat, this kind of paint is known as a temperature signaling paint. The traditional method is to test the thermal coatings personally. A manual process of interpretation results in mistakes because there is no accurate detection of isothermal limits that impact human eyesight. A systematic methodology for automated interpretation of thermal paints is detailed in this paper. A technique for orderly picture capture, image segmentation, and image processing, which employs a correct algorithm for surface temperature interpretation, has been addressed.

Thermal history analysis on a hot surface using temperature indicating paints

Temperature-sensitive paint (or) Temperature indicating paint (or) Thermal paint is a kind of coating to measure the temperature distribution (or) profile through its colour change. Thermal paint is considered to be one of the most efficient ways for temperature measurement. The analysis of these paints can be done through the observation of irreversible colour change with temperature. This paper describes the investigations done on the chemistry and behaviour of thermal paints with respect to temperature and time. The study also focuses on the calibration of thermal paints in both experimental and computational methods. In the experimental methods, the results hold in good agreement with K-type thermocouples as well as the computational results of ANSYS also provide similar results. The experimental thermal map of a butterfly specimen has been observed through the continuous exposure of thermal paint MC 350-8 to the continuous flame.

Thermal matching using Gaussian process regression

Thermal matching is a key stage of the development process for a gas turbine engine where component models are verified to ensure the correct metal temperature distribution has been used in life calculations. The thermal match involves adjusting parameters of a thermal model in order to match an experimental temperature distribution, usually obtained from a thermal paint test. Current methodologies involve manually adjusting parameters, which is both time consuming and leads to variation in the matches achieved. This paper presents a new method to conduct thermal matching, where Gaussian process regression is utilised to obtain a surrogate model from which optimal parameters for matching are obtained. This standardised procedure removes subjectivity from the match and gives faster and more consistent matches. The method is introduced and demonstrated for a number of cases involving a leading edge impingement system that has been isolated from a high pressure turbine blade.

Study on Temperature Recognition of Thermal Paint Based on Color Camera

As a temperature-sensing material, the thermal paint will show different colors at different temperatures, so the temperature of the thermal paint can be judged by observing the color. It is an efficient way to identify the color of the thermal paint by the color image, so the calibration of the color camera is very important. The main work of this paper is to calibrate a color industrial camera and compare our proposed method with several commonly used methods. Finally, it is concluded that the proposed method combining BP neural network and maximum entropy estimation works best.

Thermal performance of thermal paint and surface coatings in buildings in heating dominated climates

A purported approach to reducing heating energy in solid wall “hard to heat” housing is the simple application of a thin layer (<1 mm) of thermal paint containing insulating additives. The objective of this study was to test the energy saving claims by a systematic study of the material characteristics and thermal performance of internal coatings using accepted international standard test methods. The coatings have been compared with conventional internal coverings such as emulsion paint, wallpapers and expanded polystyrene liner. A dynamic model of the Energy House research facility has been used to evaluate energy savings, costs, and payback times.The thermal resistance of the thermal paint coatings was generally found to be not much better than that of conventional vinyl textured wallpapers with a lining paper. When all building heat losses are considered, modelling predictions for thermal paint coatings indicate an unfavourable payback period of several hundred years, and energy savings of between 0.4% and 2.9% depending on coating thickness and type. The evidence from the results and models, as well as scanning electron microscopy, do not support the claims that the additive powder particles are effectively nano-porous, evacuated, or that the coatings have low emissivity surfaces.

Scientific and Practical Bases of a Method of Reception of Thin-Layer Heat-Insulating Coverings

The paper presents a brief overview of the thin-layer thermal insulation paints used now and their characteristics. A new composition of thin-layer heat-insulation coating is proposed. The introduction of solid phases of non-autoclaved foam concrete with the average density D150 with high values of the standard entropy of formation in it is scientifically substantiated from the point of view of increasing the thermal protection properties. It is shown that such phases have an advantage in comparison with the solid phases of the glass and ceramic microspheres used now. It is also proved that the presence of thin-layer thermal insulation coating of nanoscale particles in the form of silica in the composition favours the reflection of the incident heat flux due to the Tindal effect and provides an increase in the polydispersity of the composition. The calculation of the resulting composition by the Van Vleсk formula used in the classical science is given.

The potential for implementation of liquid thermal insulation in organizational and technological solutions

Nowadays, the consumer is provided with an extensive selection of various thermal insulation materials. Particularly interesting is the possibility of using liquid insulation in the construction of new facilities, as well as overhaul and renovation programs. This article is devoted to the introduction of relatively new building material on the market - thermal paint (liquid insulation). It features the key characteristics of the product and provides a set of conclusions about its applicability and safety in comparison with other insulation materials according to the results of research and testing. The necessary steps for a massive project introduction of the material into the industry are given, taking into account the development of organizational and technological solutions, depending on the conditions of using this material.

Heat transfer measurements using thermal sensitive paint

Paper discussed the measurements of steady state heat transfer during jet impingement cooling. Particular attention was given to the thermal sensitive paint calibration process. Obtained results were briefly described and compared to available test data. Authors recommends the thermal sensitive paint measuring technique as credible and accurate method for heat transfer research.

Characteristics of Thermal Control Plasma Electrolytic Coatings on Aluminum Alloy

The structure and properties of thermal control white and black coatings for space applications on AMg3 aluminum alloy, obtained by plasma electrolytic oxidation in silicate–alkaline electrolytes, are studied experimentally. The composition and structure of the coatings are studied using scanning electron microscopy, energy-dispersive microanalysis, and X-ray diffraction analysis. It is found that aluminosilicates dominate in the porous structure of the white slightly conductive coatings, while vanadium is present in the black coatings. The solar absorbance As and thermal emissivity e are measured: As = 0.28, e = 0.93 for the white coatings and As = 0.95, e = 0.88 for the black coatings. These values correspond to the characteristics of EKOM thermal control paint coatings produced by Kompozit (Russia). The effect of atomic oxygen flux on the coatings under investigation leads to insignificant erosion of their surface, as compared to other materials.