Infrared Thermography Technique Research Articles

Experimental gas-fluidized bed drying study on the segregation and mixing dynamics for binary and ternary solids

Fluidized bed drying is an evolving process: The bed hydrodynamics, including the segregation and mixing tendencies, and its interplay with mass and heat transfer change in time. In this study, pseudo-2D fluidized bed experiments are performed using binary (50/50%) and ternary (33.3/33.3/33.3%) solids mixtures. A coupled particle image velocimetry infrared thermography technique provides local solids velocity and temperature fields. Furthermore, a machine learning algorithm is applied to characterize the bed segregation and mixing dynamics. Significant hydrodynamic changes and various segregation and mixing tendencies due to the evaporation of water from the porous γ-Al2O3 material were observed. A competition between size and density-based segregation and mixing dynamics resulted in changing bed configurations, which are correlated to the local solids drying behavior. Besides, it showed that drying of wider size distributions could lead to more complex efficient process operation.

Spectral analysis of laser speckle contrast imaging and infrared thermography to assess skin microvascular reactive hyperemia.

Post-occlusive reactive hyperemia (PORH) test with signal spectral analysis coupled provides potential indicators for the assessment of microvascular functions. The objective of this study is to investigate the variations of skin blood flow and temperature spectra in the PORH test. Furthermore, to quantify the oscillation amplitude response to occlusion within different frequency ranges. Ten healthy volunteers participated in the PORH test and their hand skin temperature and blood flow images were captured by infrared thermography (IRT) and laser speckle contrast imaging (LSCI) system, respectively. Extracted signals from selected areas were then transformed into the time-frequency space by continuous wavelet transform for cross-correlation analysis and oscillation amplitude response comparisons. The LSCI and IRT signals extracted from fingertips showed stronger hyperemia response and larger oscillation amplitude compared with other areas, and their spectral cross-correlations decreased with frequency. According to statistical analysis, their oscillation amplitudes in the PORH stage were obviously larger than the baseline stage within endothelial, neurogenic, and myogenic frequency ranges (p<0.05), and their quantitative indicators of oscillation amplitude response had high linear correlations within endothelial and neurogenic frequency ranges. Comparisons of IRT and LSCI techniques in recording the reaction to the PORH test were made in both temporal and spectral domains. The larger oscillation amplitudes suggested enhanced endothelial, neurogenic, and myogenic activities in the PORH test. We hope this study is also significant for investigations of response to the PORH test by other non-invasive techniques.

Condition and characterization analysis of a twentieth century cultural heritage through non-destructive testing (NDT) methods: the case of the Sivas industry school ironworking atelier in Turkey

Before the conservation and restoration of many types of cultural heritage, it is necessary to perform careful examination. This study aimed to determine the original building state and deterioration by applying non-destructive testing (NDT) methods in the case of a heritage building. Another goal was to determine, via NDT methods, whether the limestones observed in this study of different forms, colours, and textures were truly different. The Sivas Industry School Ironworking Atelier, which constitutes the research object, is one of the important public buildings in the city of Sivas, Turkey. Within the scope of the study, non-destructive infrared thermography (IRT), Schmidt hammer rebound (SHR) tests, and X-ray fluorescence (XRF) spectroscopy were applied. Accordingly, through IRT, deteriorations, anomalies, and material differences were investigated, and via SHR testing, uniaxial compressive strength (UCS) estimates, strength levels and hardness classes of stones were obtained. Moreover, via XRF spectroscopy, characterization analysis of stones was conducted. The data obtained could provide information to establish a basis for subsequent conservation. The innovation of this study is that although the infrared thermography technique is typically used in the investigation of materials, it was revealed that another technique such as XRF analysis is needed to better determine whether stones that seem different based on IRT are actually different. With IRT technique, anomaly and material detorioration can be determined. In addition to these two techniques, SHR tests that are non-destructive methods are needed to think about mechanical features of the material. Therefore, when determining the conditions and for characterization analysis of a cultural heritage before restoration, different techniques should be jointly used to complement each other.

UAS IR-Thermograms Processing and Photogrammetry of Thermal Images for the Inspection of Building Envelopes

Infrared thermography techniques (IRT) are increasingly being applied in non-invasive structural defect detection and building inspection, as they provide accurate surface temperature (ST) and ST contrast (Delta-T) information. The common optional or off-the-shelf installation, of both low- and high-resolution thermal cameras, on commercial UAS further facilitates the application of IRT by enabling aerial imaging for building envelope surveys. The software used in photogrammetry is currently accurate and easy to use. The increasing computational capacity of the hardware allows three-dimensional models to be obtained from conventional photography, thermal, or even multispectral imagery with very short processing times, further improving the possibilities of analysing buildings and structures. Therefore, in this study, which is an extension of a previous work, the analysis of the envelope of a wine cellar, using manual thermal cameras, as well as cameras installed on board an Unmanned Aerial System (UAS), will be presented. Since the resolution of thermal images is much lower than that of conventional photography, and their nature does not allow for accurate representation of three-dimensional objects, a new, but simple, digital image pre-processing method will be presented to provide a more detailed 3D model. Then, the three-dimensional reconstruction, based on thermal imagery, of the building envelope will be performed and analysed. The limitations of each technique will be also detailed, together with the anomalies found and the proposed improvements.

A digital and non-destructive integrated methodology for heritage modelling and deterioration mapping. The case study of the Moorish Castle in Sintra

The development of non-destructive, non-contact and autonomous unmanned techniques is extremely important for the preservation of heritage integrity. This paper presents a digital integrated methodology combining Terrestrial Laser Scanning (TLS), Aerial Digital Photogrammetry (ADP) and Infrared Thermography (IRT), which accelerate data collection and facilitate the creation of point clouds, the deterioration mapping and the state of conservation monitoring of historic structures. Both Digital Photogrammetry and Infrared Thermography were coupled with unmanned aerial vehicle (UAV). The proposed methodology was applied to the Moorish Castle in Sintra, Portugal. Manual Infrared Thermography, complemented with other traditional non-destructive techniques, were also applied in a pilot area for comparison purposes. Resultsdemonstrate the high potential of the integration of TLS, ADP and IRT techniques for heritage modelling digitalization, inspection and deterioration mapping with a positive impact on conservation and restoration projects.

Digital Rock Mass Analysis for the Evaluation of Rockfall Magnitude at Poorly Accessible Cliffs

The analysis of a digital rock cliff model, built by airborne photogrammetric data and infrared thermal images, is herein presented as an alternative tool for rock mass study in restricted and poorly accessible areas. Photogrammetric and infrared thermography techniques were combined for the geostructural and morphological characterization of an unstable cliff located in a nature reserve, where the rock mass extension and the environmental preservation rules required the use of minimally invasive surveying solutions. This methodological approach provided quantitative and qualitative data on both the spatial orientation of discontinuities and the location of major structural features, jutting blocks and past rockfall source areas. The digitally derived spatial data were used to carry out a rock mass kinematic analysis, highlighting the most recurring unstable failure patterns. Thermal images were overlapped to the photogrammetric cliff model to exploit the data combination and to analyze the presence of protruding rock mass volumes to be referred to as potential unstable volumes. Based on this activity, rock volumes were quantified on the digital model and the results were used to provide a zonation map of the potential magnitude of future rockfalls threatening the reserve. Digital data were validated by a field surveying campaign, which returned a satisfactory match, proving the usefulness and suitability of the approach, as well as allowing the quick and reliable rock mass characterization in the frame of practical use and risk management purposes.

Experimental and analytical study on local heat transfer distribution between smooth flat plate and free surface impinging jet from a circular straight pipe nozzle

The present study describes the heat transfer characteristics of free surface single-phase circular liquid jet impinging on a thin smooth flat surface subjected to uniform heat flux. The experimental setup is developed to measure the local temperature of a thin stainless steel metal foil using the infrared thermography technique. The effects of nozzle diameter (d = 2.5 to 10.8 mm), nozzle to plate spacing (z/d = 2 to 10), and Reynolds number (Re = 5000 to 24,000) on the local Nusselt number (Nu) distributions are studied. The local Nu is maximum in the stagnation region, and it decreases in the downstream flow following the stagnation region. The nozzle with a larger diameter shows maximum Nu compared to other nozzles. For a given z/d of 2 and a Reynolds number of 15,000, a maximum increment of 67% in local Nu is observed for a 10.8 mm nozzle in comparison to a 2.5 mm nozzle. The local Nu in the viscous boundary layer is found to be a function of the Reynolds number, Prandtl number, dimensionless r/d, and Weber number. The Nu increases with an increase in Reynolds number, however, the effect of the nozzle to plate spacing is negligible. The off-stagnation peak is observed for the 10.8 mm nozzle in the region of 0≤r/d≤0.7. The existing correlations reported in the literature are not able to capture the measured local Nusselt number distribution. Therefore, in the present study, an effort has been made to propose semi-empirical correlations for local Nu in the stagnation and viscous boundary layer region which will incorporate the diameter effect of the nozzle. The proposed correlations are able to predict the local Nusselt number distribution within the maximum deviation of 20%. The comparison between the free surface and submerged jet has been made which suggests that the local Nu for the submerged jet is higher compared to the free surface jet.

Passive infrared thermography technique for concrete structures health investigation: case studies

Passive infrared thermography technique for concrete structures health investigation: case studies

A Feasibility Analysis of the Infrared Thermography Technique in Surface Crack Detection for High‐Speed Rail Slab Track

The surface crack on track slab is the main cause of the service reliability deterioration of the high‐speed rail (HSR) slab track. To realize the rapid and accurate detection of these cracks, infrared thermography (IRT) can be regarded as an effective way in HSR application. However, the performance of IRT can be significantly affected by the testing environment. This study aims to analyze the feasibility of IRT in crack detection for HSR slab track by investigating the key factors affecting the detection accuracy. Firstly, the principle of IRT in detecting surface crack of track slab is given, and the key factors influencing the detection performance are discussed. Considering the difficulty in conducting field tests for slab tracks, this study establishes a finite element (FE) model to simulate the temperature field of track slab with surface cracks. This model is verified by using the field measurement results of track slab temperature. With the FE model, the effects of detection time, ambient temperature, and sensitivity of the thermal imager on the detection accuracy are revealed. The results show that, during the window time for track maintenance (0:00 am–3:00 am), the difference of temperature between crack areas and noncrack areas gradually increases with time, so it is recommended to conduct detection during 2:00–3:00 am; under the condition of no auxiliary heat source, the crack detection is suggested to be arranged in summer with a high incidence of crack; the minimum limit of thermal sensitivity of thermal imager is below 108mk@25°C. The findings in this research can offer guidance for the implementation of IRT‐based crack detection for HSR slab crack.

Data-Augmented Manifold Learning Thermography for Defect Detection and Evaluation of Polymer Composites.

Infrared thermography techniques with thermographic data analysis have been widely applied to non-destructive tests and evaluations of subsurface defects in practical composite materials. However, the performance of these methods is still restricted by limited informative images and difficulties in feature extraction caused by inhomogeneous backgrounds and noise. In this work, a novel generative manifold learning thermography (GMLT) is proposed for defect detection and the evaluation of composites. Specifically, the spectral normalized generative adversarial networks serve as an image augmentation strategy to learn the thermal image distribution, thereby generating virtual images to enrich the dataset. Subsequently, the manifold learning method is employed for the unsupervised dimensionality reduction in all images. Finally, the partial least squares regression is presented to extract the explicit mapping of manifold learning for defect visualization. Moreover, probability density maps and quantitative metrics are proposed to evaluate and explain the obtained defect detection performance. Experimental results on carbon fiber-reinforced polymers demonstrate the superiorities of GMLT, compared with other methods.

Infrared thermography detection of grouting defects in external post-tensioned tendon ducts under construction hydration heat excitation

Most duct grouting defects are caused during the construction period, and its existence will seriously affect the safety performance of the structure. Timely detection and remediation during the construction period will reduce the high inspection and maintenance costs and the probability of structural failure later. This study proposed an approach for detecting grouting defects in external post-tensioned tendon ducts using infrared thermography (IRT) under the hydration heat of duct grouting material. IRT semi real-time detection of four different grouting defect specimens was performed indoors in the first 48 h after grouting completion to validate the proposed approach. Results showed that grouting defects with 0%, 40%, and 70% grouting compactness in high-density polyethylene ducts could be identified simultaneously from 12 h to 21.5 h after grouting completion, while defects in galvanized steel pipes (GSP) could also be identified after improving the emissivity and reflectivity of the pipe surface. Furthermore, grouting compactness could be quantified by the distance between the half maximum contrast, and PCA-based image preprocessing could reduce the quantitative error of grouting compactness detection. In addition, the detection in high temperature environment should be avoided because the rise in ambient temperature would reduce the identification ability of grouting defects. IRT technique could guide the grouting construction of external tendon ducts in actual engineering because of its ability to efficiently identify grouting defects during the hydration heat release stage of grouting material.

Thermoregulation mechanisms and perspectives for validating thermal windows in pigs with hypothermia and hyperthermia: An overview.

Specific anatomical characteristics make the porcine species especially sensitive to extreme temperature changes, predisposing them to pathologies and even death due to thermal stress. Interest in improving animal welfare and porcine productivity has led to the development of various lines of research that seek to understand the effect of certain environmental conditions on productivity and the impact of implementing strategies designed to mitigate adverse effects. The non-invasive infrared thermography technique is one of the tools most widely used to carry out these studies, based on detecting changes in microcirculation. However, evaluations using this tool require reliable thermal windows; this can be challenging because several factors can affect the sensitivity and specificity of the regions selected. This review discusses the thermal windows used with domestic pigs and the association of thermal changes in these regions with the thermoregulatory capacity of piglets and hogs.

Infrared thermographic evaluation of thermal release phenomena in polycarbonate during plastic deformation

To investigate the applicability of infrared thermography technique as a method for obtaining dynamic plastic deformation in polycarbonate, an infrared thermography experiment has been performed under four different loading rates. Three-point bending tests of polycarbonate have been conducted to evaluate thermal evolution obtained via infrared thermography in order to detect capabilities of plastic deformation. And photoelastic tests under the same experimental conditions were carried out to verify the reliable of experimental results of infrared thermography. The stability of the plastification region demonstrated the validity of infrared thermography as an approach for describing the dynamic plastic deformation when used on complex structures. Meanwhile, the conversion coefficient β of plastic work to heat at different loading rates have been investigated, and the results shown the β increases in 0.2–0.7 with plastic deformation. The photoelastic fringe patterns further verified the generation and propagation of plastification region. This research based on two basic tests, providing a useful suggestions for complex structure materials to evaluate the plastic deformation where middle wave infrared thermography was applied.

Application of infrared thermography technique to assist peroneal artery perforator flap in the repair of oral and maxillofacial defects

To explore the application value of infrared thermography (IRT) technique assisted peroneal artery perforator flap in repairing oral and maxillofacial defects. The clinical data of 20 patients with oral and maxillofacial malignant tumors treated with peroneal artery perforator flap between October 2020 and December 2021 were retrospectively analysed. There were 13 males and 7 females, with an average age of 56.5 years (range, 32-76 years). There were 8 cases of tongue cancer, 5 cases of parotid gland cancer, 4 cases of buccal cancer, and 3 cases of mandibular gingival cancer; and 12 cases of squamous cell carcinoma, 3 cases of adenoid cystic carcinoma, and 5 cases of mucoepidermoid carcinoma. Color Doppler ultrasound (CDU) and IRT technique were performed before operation to locate the peroneal artery perforator and assist in the design of the flap. The sensitivity, specificity, positive predictive value, and negative predictive value of CDU and IRT technique were compared with the actual exploration during operation. The accuracy of CDU and IRT technique in detecting the number of peroneal artery perforator and the most viable perforating points was compared. The patients were followed up regularly to observe the recovery of donor and recipient sites, the occurrence of complications, and the recurrence and metastasis of tumors. The sensitivity, specificity, positive predictive value, and negative predictive value of peroneal artery perforators detected by IRT technique before operation were 72.22%, 50.00%, 92.86%, and 16.67% respectively, which were higher than those by CDU (64.17%, 33.33%, 84.62%, and 14.29% respectively). Forty-five peroneal artery perforators were found by CDU before operation, and 35 were confirmed during operation, with an accuracy rate of 77.8%; 43 "hot spots" were found by IRT technique, and 32 peroneal artery perforators were confirmed within the "hot spots" range during operation, with an accuracy rate of 74.4%; there was no significant difference between the two methods ( χ²=0.096, P=0.757). The accuracy rates of the most viable perforating points found by CDU and IRT technique were 80.95% (17/21) and 94.74% (18/19), respectively, and there was no significant difference between them ( χ²=0.115, P=0.734). The localization errors of CDU and IRT technique were (5.12±2.10) and (4.23±1.87) mm, respectively, and there was no significant difference between them ( t=1.416, P=0.165). All the perforator flaps survived, and the incisions of donor and recipient sites healed by first intention. All patients were followed up 5-18 months, with an average of 11 months. The skin flap was soft and had good blood supply, and the lower limb scar was concealed and the lower limb had good function. No lower limb swelling, pain, numbness, ankle instability, or other complications occurred, and no tumor recurrence and metastasis were found during the follow-up. Compared with the CDU, using the IRT technique to assist the preoperative peroneal artery perforator flap design to repair the oral and maxillofacial defects has a high clinical application value.

Experimental investigation of monodisperse solids drying in a gas-fluidized bed

Fluidized bed drying is an unsteady process where particle and gas properties evolve in time. The bed hydrodynamics and its interplay with mass and heat transfer changes in time. In this study, experiments in a pseudo-2D fluidized bed setup are performed to obtain insight in this complex behavior. A coupled particle image velocimetry infrared thermography technique provides solids velocity and temperature fields in the bed. Significant hydrodynamic changes due to the evaporation of water from the porous γ-Al2O3 material for three superficial velocities were observed. The 1.25 umf case resulted in an fixed bed state, but after drying for 580 s a bed inversion took place. The 1.50 and 1.75 umf experiments showed an increase in bed expansion over time. Furthermore, clear asymmetrical solids volume fluxes were observed for the wet material that became more symmetrical over time when the material dried.

Experimental Study on the Thermal Performance of 3D-Printed Enclosing Structures

Three-dimensional printing, or additive manufacturing, is one of the modern techniques emerging in the construction industry. Three-Dimensional Printed Concrete (3DPC) technology is currently evolving with high demand amongst researchers, and the integration of modular building systems with this technology would provide a sustainable solution to modern construction challenges. This work investigates and develops energy-efficient 3D-printable walls that can be implemented worldwide through energy efficiency and sustainability criteria. Numerical research and experimental investigations, bench tests with software packages, and high-precision modern equipment have been used to investigate the thermal performance of 3DPC envelopes with different types of configurations, arrangements of materials, and types of insulation. The research findings showed that an innovative energy-efficient ventilated 3DPC envelope with a low thermal conductivity coefficient was developed following the climatic zone. The annual costs of heat energy consumed for heating and carbon footprint were determined in the software package Revit Insight to assess the energy efficiency of the 3D-printed building. The thermal properties of the main wall body of the tested 3D-printed walls were calculated with on-site monitoring data. The infrared thermography technique detected heterogeneous and non-uniform temperature distributions on the exterior wall surface of the 3DPC tested envelopes.

Effects of mainstream cross-flow and wall contouring on film cooling effectiveness of cylindrical-holes embedded in elliptical craters

The combined effects of the dominated flow parameters at contoured end-wall and the geometrical parameters of elliptical-crater on the cratered-hole film cooling performances and flow mechanisms were investigated experimentally and numerically. Seven cratered-holes were designed to demonstrate the individual and combined influences of the position and size of crater. The original cylindrical-hole was selected as the baseline model. Three test passages were built up to simulate the flat-plate environment, the mainstream cross-flow environment and the environment with mainstream cross-flow coupled by wall contouring, respectively. Under blowing ratio (BR) from 0.25 to 2.0, the surface film effectiveness was measured using infrared thermography technique, and the in-plane scalar transport characteristics were captured by the concentration visualizations, as well as the flow interactions were displayed by the numerical simulations. The comparisons of results revealed that the benefit of crater on the film effectiveness enhancement depends on the contradictory of the crater configuration requirements, bringing to the huge challenge of fine design. The mainstream cross-flow causes the new mechanisms for the cratered-hole film cooling, presenting a new requirement for the design of crater-configuration. Compared to the flat-plate environment, the cratered-hole can improve 20% in film effectiveness under the solo mainstream cross-flow effect. Further adding the wall contouring can improve the uniformity of film coverage and weaken the sensitivity to crater-configuration, while reduce by 40% in the benefit of crater on film effectiveness improvement. The local cooling deterioration under the low flowrates of cooling air results in the combined application of cratered film cooling and end-wall contouring being undesired.

Fatigue damage and life evaluation of thick bi‐material double strap joints for use in marine applications

AbstractThe present‐day interest in the use of composite‐steel joints in primary marine structures requires an in‐depth knowledge of the fatigue performance of thick adhesive joints. This paper reports on experimental tests performed on compliant (i.e., thick and ductile) adhesive joints based on a two‐component methyl‐methacrylate adhesive in unaged and aged conditions. Bi‐material double strap joint with thick adhesive bondlines is subjected to quasi‐static and fatigue loading, during which the specimens are monitored by digital mage correlation and infrared thermography techniques to evaluate the types and extent of damage that occur in the joint during fatigue loading. The S‐N curve of the aged joint is evaluated along with its fatigue limit. It is found that the unaged specimens fail due to cohesive damage, hackles, and disbond at the adhesive‐adherend interface and the aged specimens fail due to delamination within the composite. The specimens that survived fatigue loading showed similar residual strength as specimens that were not fatigue loaded.

Thermomechanical Topology Optimization of Three-Dimensional Heat Guiding Structures for Electronics Packaging

Abstract Heterogeneous and complex electronic packages may require unique thermomechanical structures to provide optimal heat guiding. In particular, when a heat source and a heat sink are not aligned and do not allow a direct path, conventional thermal management methods providing uniform heat dissipation may not be appropriate. Here we present a topology optimization method to find thermally conductive and mechanically stable structures for optimal heat guiding under various heat source-sink arrangements. To exploit the capabilities, we consider complex heat guiding scenarios and three-dimensional (3D) serpentine structures to carry the heat with corner angles ranging from 30 deg to 90 deg. While the thermal objective function is defined to minimize the temperature gradient, the mechanical objective function is defined to maximize the stiffness with a volume constraint. Our simulations show that the optimized structures can have a thermal resistance of less than 32% and stiffness greater than 43% compared to reference structures with no topology optimization at an identical volume fraction. The significant difference in thermal resistance is attributed to a thermally dead volume near the sharp corners. As a proof-of-concept experiment, we have created 3D heat guiding structures using a selective laser melting technique and characterized their thermal properties using an infrared thermography technique. The experiment shows the thermal resistance of the thermally optimized structure is 29% less than that of the reference structure. These results present the unique capabilities of topology optimization and 3D manufacturing in enabling optimal heat guiding for heterogeneous systems and advancing the state-of-the-art in electronics packaging.

Thick elastomeric coating removal using tailored infrared- and infrared-sonication hybrid technology

We report an innovative, cost-effective, and eco-friendly coating removal technology that removes thick polyurethane-based elastomeric coatings without damaging the underlying metal or glass-polymer composite substrates. The developed technology eliminates the need for chemical- or media-based treatments, thus reducing environmental problems such as releasing toxic gases or suspended solid particles in the air. This was achieved using tailored infrared and infrared-ultrasonication treatments of the coated substrates that caused bond failure at the surface coat-substrate interface by selective absorption of IR and/or impinging of the topcoat with the ultrasonication technique. The degraded interfacial adhesion strength then allowed easy removal of the specialty coating with the application of a pull at a certain angle to the substrate-coating interface. The effect of different operating parameters such as time of irradiation, surface temperature, sonication power/intensity was investigated to determine the optimal conditions for coating removal. The treated and untreated coated samples were characterized by DSC, SEM, FTIR, peel-tester, embedded thermocouple/LABVIEW, and infrared thermography techniques. The energy analysis revealed that the fracture energy component was 4× lower on the treated sample than the untreated sample indicating reduced bond strength, which can be explained based on residual thermal stress generated due to the thermal coefficient mismatch and the interfacial cell dislocation. Also, coating from the treated sample could be removed 1.75× faster than from the untreated sample. Based on the cost analysis, the operation cost for this technology is meager compared to conventional and energy-intensive technologies such as laser ablation.