Thermal Test Method Research Articles

Методи діагностування дефектів деталей авіаційних двигунів з композиційних матеріалів

The key priority in improving the technical and economic performance of gas turbine engines lays in the use of new composite materials. The use of composites in the components of critical load-carrying structures operating under static and dynamic loads during long service lives determines the need to predict the component lives. Also, in order to increase the safety of engine operation and improve the parts manufacturing process, timely defect detection in such structures is of great importance. This article is devoted to the detection of the composite parts defects and damages that occur at different stages of manufacturing and operation. The aim is to investigate the existing methods of non-destructive testing of composite materials, describe their functional concept, and determine the field of their application. The article considers acoustic, thermal, optical, and radiation testing methods. Among the acoustic methods, the phased array method is selected as the most informative and multipurpose. The acoustic emission method is also selected; it will allow real-time monitoring of defect growth during testing. Out of thermal methods, the vibrothermography method was selected as the most advanced among the thermographic sub-methods. It allows using the phenomenon of local defect resonance and thus ensures effective defect detection. Shearography is selected for investigation out of optical methods. The special aspects of the use of X-ray methods are considered through the example of X-ray computed tomography. It is concluded that the approach combining several methods can significantly increase the efficiency of defect detecting and help to assess their criticality. Active thermal testing is well suited for fast scanning of large-sized parts and searching for areas of defect accumulation. In the following, local methods, such as impedance, vibrothermography, or one of the ultrasonic, should be used. To measure deformations under static load, it is a good practice to use shearography. To identify progressive defects under static load, it makes sense to use the acoustic emission method.

Deep Learning Automated System for Thermal Defectometry of Multilayer Materials

Currently, along with growth in industrial production, the requirements for product quality testing are also increasing. In the tasks of defectoscopy and defectometry of multilayer materials, the use of thermal nondestructive testing method is promising. At the same time, interpretation of thermal testing data is complicated by a number of factors, which makes the use of traditional methods of data processing ineffective. Therefore, an urgent task is to search for new methods of thermal testing that will automate the diagnostic process and increase information content of obtained results. The purpose of article is to use the advances in deep learning for processing results of active thermal testing of products made of multilayer materials and development of an automated system for thermal defectoscopy and defectometry of such products. The proposed system consists of a heating source, an infrared camera for recording sequences of thermograms and a digital information processing unit. Three neural network modules are used for automated data processing, each of which performs one of the tasks: defects detection and classification, determination of the defect depth and thickness. The software algorithms and user interface for interacting with system are programmed in the NI LabVIEW development environment.Experimental studies on samples made of multilayer fiberglass have shown a significant advantage of the developed system over using traditional methods for analyzing thermal testing data. The defect classification (determining the type) error on the test dataset was 15.7 %. Developed system ensured determination of defect depth with a relative error of 3.2 %, as well as the defect thickness with a relative error of 3.5 %.

Experimental analysis of natural wax as phase change material by thermal cycling test using thermoelectric system

The stability of the type of Phase Change Material (PCM) during operation are important factors to know before PCM applied. The purpose of this study is to analyze the characteristics and thermal stability of PCM using the thermal cycle testing. The development of thermal cycle test method to test the thermal stability of PCM has been carried out in this study by using thermoelectric as a heating and cooling media with the number of cycles, namely 500, 1000, 3000 and 5000. The PCM used in this study is consisted of 3 types that derived from natural waxes, namely palm wax, soy wax and paraffin wax. All the natural wax have chemical compositions (C and O) and morphological form are lump layer. The Differential Scanning Calorimetry (DSC) results show that the lowest melting and freezing points are owned by soy wax at 43.92 °C and 38.49 °C, respectively. Thermoelectric as a thermal cycle test device and the addition of the test module to 4 modules can increase the test efficiency. Thermoelectric characterization for 1 h produce 24, 13 and 45 cycles for palm wax, soy wax and paraffin wax, respectively. This thermal cycle tester was capable of testing up to 5000 cycles in each module. Degradation of the thermal properties occured for each wax after 5000 cycles. The highest reduction value of ΔH was observed for soy wax that reaced 60% reduction in ΔH freezing. Overall, based on these degradations of PCM after treated a number of cycles, they can provide data on the time when the PCM should be replaced with new material.

Modifications to the conventional design methods for borehole heat exchangers based on a novel response factor model

For ground source heat pumps with boreholes, the rule-of-thumb and thermal performance test (TPT) methods are commonly adopted for borehole design but suffer from inaccuracy. The response factor model can calculate the time-varying soil heat transfer of boreholes fast and accurately. Based on the response factor model, the characteristic diagrams of borehole heat transfer are summarized to show the influential laws of different factors (borehole inlet temperature, velocity of fluid inside the pipe, initial soil temperature, soil thermophysical properties, and operation time). The characteristic diagrams can be used as a new design method that improves the accuracy of the rule-of-thumb method by considering different influential factors and avoiding the subjective errors of designers. For different soils, the borehole design errors of the new diagram method are −5% to 10%, which are much less than the errors (−15% to 72%) of the conventional rule-of-thumb method. In addition, a modification to the TPT method is also proposed using the response factor model. The borehole design errors of the conventional TPT method (48 h testing) can be reduced by 13%–20% using the derived correction factors. The proposed modification methods contribute to more reasonable borehole design, improved heating reliability as well as increased energy efficiency.

Ways to increase the production efficiency of hardwood blanks

The article presents the main results of experimental studies on the identification of the main grade defects of oak lumber by the thermal non-destructive testing method. Regressional dependences of wood defects temperature display from the main factors for the studied grade defects are proposed. Indicators of infrared radiation (temperature range) of the main visible oak grade defects obtained as a result of experimental studies are presented. A conceptual scheme for the line control methods of identification of the main grade defects in lumber are proposed.

An frequency domain analysis method of thermal parameters unsteady-state detection of building wall

ABSTRACT The in-situ inspection technology of thermal properties of building wall is an important technical guarantee to achieve the goal of building energy conservation. However, there is still a lack of fast, simple, and accurate unsteady-state detection method under natural conditions. This paper focuses on the thermal performance test and analysis method of building wall under natural condition. Two frequency domain analysis methods were developed for the thermal conductivity, as well as volume specific heat and thermal inertia of homogeneous wall along with the harmonic reaction method and the frequency domain analysis theory. The frequency response relationship between the internal and external surface temperature waves and indoor air temperature waves was established, and the relationship contains thermal performance parameters of wall. The thermal conductivity and specific volume heat of wall can be solved by using the response relation. Numerical simulation verification of the method was completed by using ANSYS software and the experimental verification by using wall insulation materials were accomplished in the laboratory. The maximum relative error of numerical simulation results is 1.48%, and that of laboratory experiment results is 8.75%. The implications of these results with respect to the influence on the in-situ inspection technology of building wall are discuss.

Field Test and Numerical Simulation on Heat Transfer Performance of Coaxial Borehole Heat Exchanger

Ground thermal properties are the design basis of ground source heat pumps (GSHP). However, effective ground thermal properties cannot be obtained through the traditional thermal response test (TRT) method when it is used in the coaxial borehole heat exchanger (CBHE). In this paper, an improved TRT (ITRT) method for CBHE is proposed, and the field ITRT, based on the actual project, is carried out. The high accuracy of the new method is verified by laboratory experiments. Based on the results of the ITRT and laboratory experiment, the 3D numerical model for CBHE is established, in which the flow directions, sensitivity analysis of heat transfer characteristics, and optimization of circulation flow rate are studied, respectively. The results show that CBHE should adopt the anulus-in direction under the cooling condition, and the center-in direction under the heating condition. The influence of inlet temperature and flow rate on heat transfer rate is more significant than that of the backfill grout material, thermal conductivity of the inner pipe, and borehole depth. The circulating flow rate of CBHE between 0.3 m/s and 0.4 m/s can lead to better performance for the system.

Thermal quantitative sensory testing in burning mouth syndrome.

Subjects with burning mouth syndrome (BMS) have altered sensitivity and pain thresholds for thermal stimuli compared to a control group. Fourteen women and 6 men (average age = 62.60 years, median = 63.50) with BMS and a control group were tested using the method of thermal quantitative sensory testing (tQST) (tip, right, and left lateral border of the tongue, left thumb) to determine their heat/cold detection threshold (WDT/CDT) and heat/cold pain threshold (HPT/CPT). Only the CPT values at the tip and both lateral border of the tongue show a statistically significant difference: tip of the tongue: sick = 12.0 ± 5.5 °C, median 14.2°C; healthy = 4.5 ± 2.9 °C; median = 6.4 °C; p = 0.000; right lateral border: sick = 8.55 ± 3.34 °C; healthy = 4.46 ± 1.90 °C; median 5.8 °C; p < 0.001; left lateral border: sick = 10.18 ± 3.94 °C¸ healthy = 4.15 ± 2.18 °C; median = 6.0 °C; p < 0.001. BMS may be a combination of a dysfunction of free nociceptive nerve endings in the peripheral nervous system and impaired pain processing in the central nervous system. This preliminary study provides hints to other causes of BMS. This offers the possibility of further therapeutic options.

A study on heat transfer performance of recycled aggregate thermal insulation concrete

Recycled aggregate thermal insulation concrete can achieve the recycling of resources, meanwhile enhancing energy saving effect for buildings. This functional concrete is a heterogeneous material that has complex internal components. Traditional thermal conductivity prediction models can hard characterize the heat transfer performance exhibited by recycled aggregate thermal insulation concrete. This paper proposes a new thermal resistance testing method to study the effects that the volume fraction of recycled coarse aggregates and glazed hollow beads have on the heat transfer performance of recycled aggregate thermal insulation concrete. Also, a thermal resistance prediction model suitable for recycled aggregate thermal insulation concrete through experimental and simulation analysis is established. Results show that recycled aggregate thermal insulation concrete thermal resistance increases with an increase in volume fraction of recycled coarse aggregate and glazed hollow beads. The deviation between the test results and the results of the random aggregate model is 0.96%. The thermal resistance model can be used to accurately predict recycled aggregate thermal insulation concrete thermal resistance. This research method has a certain theoretical value for research on the heat transfer performance of materials that have high porosity and multiple components inside them.

Similarity analysis of thermal-fluid flow for thermal testing using scaled-down model of spent fuel storage cask

The weight of spent nuclear fuel concrete storage casks usually exceeds 100 tons. Therefore, thermal testing of prototype casks is expensive and time consuming. In this study, thermal testing method using a scaled-down model of a storage cask was developed to perform the thermal testing of large-scale storage casks efficiently. Scaling analyses were performed to derive scale ratios between a prototype cask and the scaled-down model. Additionally, thermal analyses were performed on the prototype cask and half-scale model using the obtained scale ratios. The analysis results showed that scale ratios between the prototype cask and half-scale model were conserved well. Thermal tests were performed on the prototype cask and half-scale model. The analysis and test results were in good agreement. The thermal test results confirmed the thermal-fluid flow similarity between the prototype cask and half-scale model.

Critical analysis and innovation propositions to the heat and thermal shock test method of the Brazilian Standard NBR 15575 (2013)

The tests of Brazilian Standard NBR 15575: 2013 are part of the knowledge of the civil construction industry, but the heat and thermal shock test is innovative and does not have a consolidated history. The research objective is to analyze the testing critically and present proposals based on data meta-analysis. Results showed that the test is very inaccurate in describing the procedure and equipment. This study proposed adjustments and innovations in the test to provide more reliable results, but it does not make propositions regarding visual inspection and the number of cycles. The study concluded that the lack of information on the testing has direct responsibility for the results and that the suggested proposals have the potential to be incorporated.

Thermal Oxidation Mechanism and Test Method of Lubricating Oil

Thermal Oxidation Process Mechanism of lubricating oil is described, at the same time, the thermal oxidation test methods of lubricating oil-infrared spectrum, rotating oxygen bomb, Cyclic voltammetry and sludge content are introduced and compared. The correlation and difference between them were compared by experiments.

Synthesizing Data of Active Infrared Thermography under Optical and Ultrasonic Stimulation of Products Made of Complex-Shaped CFRP

We propose a combined method for thermal nondestructive testing using optical and ultrasonic stimulation by means of combining individual thermograms obtained at the corresponding time points. The resulting sequences of infrared thermograms provide more efficient identification of defects of various types and can also be processed using well-known algorithms, for example, thermographic signal reconstruction, principal component analysis, etc. We obtained experimental results on a composite CFRP sample imitating aircraft ribs using a robotic manipulator.

Fault-tolerant nondestructive control of the stress-strain state of the load-bearing elements of pantograph lifts

This paper proposes a method of fault-tolerant nondestructive control of the stress-strain state of the load-bearing elements of lift and transportation machines, considered on the example of a prototype of pantograph-type lifts. The basic requirements for the load-bearing elements of lift and transportation machines are analyzed. An experimental research technique has been developed including tensometric and thermal nondestructive testing methods. A full-scale experiment of a prototype pantograph-type lifts is shown.

Radiowave Methods of Polymer Composite Defect Diagnostics under Nonsteady Temperatures

The paper deals with the issues of the combined radio wave and thermal test methods for nondestructive testing of polymer composite materials (PCM) in laboratory and factory conditions.

Data analysis and discussion of thermal response test under a power outage and variable heating power

In this research, a comprehensive study of power outage and variable heating power were conducted during an in-situ thermal response test (TRT) with a 261-m deep double U-tube borehole heat exchanger. The TRT data obtained during a power outage were measured using the indirect, superposition, equivalent time, and separation methods to obtain the thermal properties of rock-soil. The thermal conductivity of rock-soil, volumetric heat capacity, and thermal resistance were 1.21 W/(m·°C), 2413 kJ/(m3·°C), and 0.41 m2·°C/W, respectively. In the analysis of the test data of the variable heating power conditions, the additional heating as a result of the pump power cannot be ignored, and heat generated by the circulating water pump was stable. The heat transfer rate and average fluid temperature gradually stabilized as the test progressed, and the relationship between them is linear. The trends in the heat exchange rate and average fluid temperature after changing the heating power were expressed using a formula. A thermal response test method with variable heating power was proposed for this test, and the thermal conductivity and initial ground temperature of rock-soil were obtained using this method.

Thermal conduction characteristics of DTS when detecting the integrity of cast-in-place piles considering their environment

Based on the thermal integrity testing method of foundation pile, distributed optical fiber temperature sensing (DTS) technology was applied to testing the integrity of a cast-in-place pile. A theoretical model was established for the heat transfer and temperature characteristics in consideration of the physical properties of piles and the surrounding media. By establishing a model of a pile with and without covering soil, the thermal conduction of piles could be studied effectively. The results showed that, at the same heating power, the temperature rise of each layer optical fiber in the pile was basically the same when the ambient temperature around the pile did not change by more than 7.0 °C and the soil temperature around the pile did not change by more than 3.1 °C. At the same soil temperature, the temperature rise of each layer optical fiber in the pile increased with an increase in heating power. Further, we studied the heat conduction characteristics of the pile after the soil was compacted. The results showed that the experimental temperature rise in layers F1–F6 was basically consistent with that of the theoretical temperature rise. After the soil around the model pile was compacted, the thermal conductivity of soil was increased, the further contact between the pile and soil interface was enhanced, which accelerated the thermal diffusion of the pile.

Stratified thermal response test measurement and analysis

An improved thermal response test method called the stratified thermal response test (STRT) was proposed and a corresponding system was developed in this study. The difference between the STRT and other methods is that the temperature was measured by sensors placed inside the borehole heat exchangers (BHEs) at different depths to obtain the virtual thermal conductivity in each stratum. The method was validated based on the measurements and determination of the thermal conductivities for two different sedimentary geological conditions using three approaches and was applied to determine the key heat transfer layer and the optimum buried depth of the vertical BHEs. The discrepancies between the thermal conductivities obtained by STRT and the conventional thermal response test were 2.5% and 2.7% respectively, which validates the reliability of the STRT. The positions of the key heat transfer layers of the two boreholes were 50–60 m and 60–80 m respectively; the location of the key heat transfer layer was affected by the intense groundwater activities. At the optimum buried depths of 80 m and 90 m for the two boreholes, the highest heat transfer rate per meter was obtained at the minimum cost. It is expected that the proposed STRT method and system will become increasingly useful for optimizing the depths of BHEs installed in heterogeneous strata because the installation cost can be minimized.

Improved cell nucleating effect of partially melted crystal structure to enhance the microcellular foaming and impact properties of isotactic polypropylene

The effects of a partially melted crystal structure (PMCS) on enhancing the cell nucleating behavior, as well as on the related foaming behavior of isotactic polypropylene (iPP), were investigated. The incorporation of PMCS and the corresponding effects were characterized by rheological, thermal and X-ray testing methods. The microcellular foaming results revealed that the addition of PMCS could dramatically increase the melt strength and the cell nucleating sites of the matrix. The synergistic effects of the PMCS and high melt strength polypropylene (HMSPP) could decrease the average cell size to approximately 2 μm and increase the cell density to 1.49×1011 cells/cm3. Additionally, the gradual melting of the PMCS could also prove its enhancing effect on the melt strength and cell nucleating ability. The uniform microcellular cells obtained could positively affect the notched impact strength of the foamed iPP-HMSPP blends.

Ultrathin-wall mesoporous surface carbon foam stabilized stearic acid as a desirable phase change material for thermal energy storage

A fluffy ultrathin-wall mesoporous surface carbon foam (UMSCF) with high thermal conductivity was prepared via carbon-thermal reduction reaction between a carbon foam and aluminium nitrate, and then used as a supporting material for stearic acid (SA) to form shape-stabilized composite phase change materials (PCMs). The UMSCF and the as-prepared SA/UMSCF composite PCMs were characterized by SEM, TEM, XRD, Raman, BET, FTIR, wettability test, compression test, TG, DSC, thermal cycling test and laser flash method, respectively. Results shows that the carbon-thermal reduction temperature greatly influences the microstructures of the UMSCF, and the UMSCF prepared at 1600°C (UMSCF-1600) possesses good lipophilicity, high thermal conductivity and superior mechanical properties. The prepared UMSCF as supporting matrix simultaneously improves thermal conductivity and shape-stabilization of PCMs, as well as retains relative high phase change enthalpy. The melting and freezing enthalpy for SA/UMSCF-1600 composite was measured as 149.3 and 151.2J/g, respectively. The thermal conductivity of the composite PCMs is as high as 1.725W/mK, which increases by about 6.791-fold compared with pristine SA. Meanwhile, the composites display good thermal reliability and chemical stability, suggesting their promising characteristics for thermal management applications.