Thermal Stress Monitoring Research Articles

Monitoring of thermal stress in metal plates by using bonded shear horizontal wave piezoelectric transducers

Thermal stress is one of the major causes of failure of engineering structures and its measurement has attracted more attention in recent years. The ultrasonic wave method is very promising in stress measurement due to its non-destructive nature and easy manipulation. The traditional ultrasonic wave transducers require a coupling medium which would introduce large repeatability errors in travel time measurement and thus in the measured stress. In this work, a methodology based on bonded shear horizontal (SH) guided wave piezoelectric transducers was developed to monitor thermal stress in metal plates. The adhesive bonding between the transducer and the specimen ensures the repeatability in travel time measurements, and the strain gauges are also employed to monitor the wave path length. The dispersive equation of acoustoelastic SH wave propagating in an isotropic medium under the uniaxial stress is derived. Both the uniaxial tension test and thermal modulation test have been performed in aluminum and steel plates. The results show that the acoustoelastic constants of the SH0 wave are identical to that of the shear bulk wave as predicted by the acoustoelastic theory and the thermal stress measured from −60 °C to 100 °C by the proposed method has a very good repeatability (better than 2 MPa) in both the aluminum and steel plates. Considering the convenience and reliability of the bonded SH0 wave piezoelectric transducer, the proposed method is very promising for monitoring of thermal stress in engineering structures, such as rails, etc.

A Low-Cost Sensor Network for Real-Time Thermal Stress Monitoring and Communication in Occupational Contexts.

The MoBiMet (Mobile Biometeorology System) is a low-cost device for thermal comfort monitoring, designed for long-term deployment in indoor or semi-outdoor occupational contexts. It measures air temperature, humidity, globe temperature, brightness temperature, light intensity, and wind, and is capable of calculating thermal indices (e.g., physiologically equivalent temperature (PET)) on site. It visualizes its data on an integrated display and sends them continuously to a server, where web-based visualizations are available in real-time. Data from many MoBiMets deployed in real occupational settings were used to demonstrate their suitability for large-scale and continued monitoring of thermal comfort in various contexts (industrial, commercial, offices, agricultural). This article describes the design and the performance of the MoBiMet. Alternative methods to determine mean radiant temperature (Tmrt) using a light intensity sensor and a contactless infrared thermopile were tested next to a custom-made black globe thermometer. Performance was assessed by comparing the MoBiMet to an independent mid-cost thermal comfort sensor. It was demonstrated that networked MoBiMets can detect differences of thermal comfort at different workplaces within the same building, and between workplaces in different companies in the same city. The MoBiMets can capture spatial and temporal differences of thermal comfort over the diurnal cycle, as demonstrated in offices with different stories and with different solar irradiances in a single high-rise building. The strongest sustained heat stress was recorded at industrial workplaces with heavy machinery.

Review of Thermal Stress and Condition Monitoring Technologies for Overhead Transmission Lines: Issues and Challenges

The overhead transmission line system is one of the methods of transmitting electrical energy at a high voltage from one point to another, especially over long distances. The demand for electrical energy is increasing due to the increase in the world population, the evolution of transport technology, and economic expansion, thereby resulting in overloading to the overhead line (OHL) system. In building new infrastructure for transmission lines, several issues need to be addressed. Thus, optimizing existing power by increasing the ampacity of power line is a practical solution to meet energy demand issues. During long-term operation, the temperature of OHL conductors may increase beyond their rated temperature, which is typically 75 °C for conventional conductors such as aluminum-conductor steel-reinforced cable. This condition is defined as thermal stress, which results in lower sag vertical clearance, tensile loss, elongation and creep, and reduced life span of the conductors. This condition must be avoided to ensure that the line is not permanently elongated, which can disrupt the vertical ground clearance, and to expand the conductor’s life. Other factors such as lightning, wildfire, aging, and degradation of the conductor can also cause thermal stress on the conductors and have thermal effects on the conductor’s performance. Therefore, unwanted thermal stress needs to be examined and identified by monitoring the thermal effect and behavior of the lines. This paper presents the state of the art in monitoring technologies that can be used to identify thermal stress on OHL conductors, including the issues and challenges in monitoring. At the end of this paper, a few suggestions are included to address the occurrence and assessment of thermal stress in lines. Ultimately, this work may provide complete information to researchers and maintenance engineers to enable them to make better decisions on condition monitoring, operation, and maintenance of the system.

Numerical Simulation and Analysis of Thermal Stress on Restressed Assembly Steel Struts System in Foundation Excavation

When using horizontal internal bracing system in large span deep foundation pit, the influence of temperature effect on bracing system must be considered. Based on the long-term thermal stress monitoring of a project in the west of Hangzhou, this paper studied the influence of Angle brace temperature effect on the foundation pit enclosure structure after excavation to the bottom by using three-dimensional finite element model. When the strut temperature rises, the strut axial force increases. The longer the length is, the higher the axial force rises. The horizontal displacement of the surrounding wall and soil will be in the external direction of the pit, which is conducive to the stability of the surrounding system. The second layer struts are more affected by the temperature effect than the first layer struts, and the combined action of the two struts makes the surrounding wall produce greater displacement. The pouring of the bottom plate makes the strut subject to the temperature effect to generate greater axial force, the second layer struts change more violently, and at the same time reduces the displacement and deformation of the retaining structure. When the temperature drops, the strut axial force decreases and the horizontal displacement of the retaining structure to the pit increases, which is not conducive to the stability of the system. At this time, the reinforcement of the nearby soil body can be considered to reduce the deformation of the soil body and the retaining wall.

Feasibility study of embedded FBG thermal sensing use for monitoring electrical fault‐induced thermal excitation in random wound coils

This paper reports an experimental feasibility study of the potential for using Fibre Bragg Grating (FBG) thermal sensing technology for electrical fault detection in random wound coils. The study is performed on prototype test coils housed in a purpose built steel core section. The FBG thermal sensors are embedded between copper conductors in multiple positions within the coil structure and in close proximity of the known hot spots of interest. The examined coils are designed to enable emulation of hot spots representative of those that would be expected at the outset of winding fault events. A series of experiments were separately conducted in order to characterise the potential of coil internal thermal stress monitoring to provide recognition of a developing winding fault. To this end, winding fault scenarios with different severity levels of inter-turn fault are experimentally examined. The reported findings demonstrate the potential of the proposed in-situ thermal sensing scheme to enable monitoring and recognition of coil internal thermal stress induced at various stages of emulated electrical fault.

Monitoring of transient 3D temperature distribution and thermal stress in pressure elements based on the wall temperature measurement

Two methods for monitoring the thermal stresses in pressure components of thermal power plants are presented. In the first method, the transient temperature distribution in the pressure component is determined by measuring the transient wall temperature at several points located on the outer insulated surface of the component. The transient temperature distribution in the pressure component, including the temperature of the inner surface is determined from the solution of the inverse heat conduction problem (IHCP). In the first method, there is no need to know the temperature of the fluid and the heat transfer coefficient. In the second method, thermal stresses in a pressure component with a complicated shape are computed using the finite element method (FEM) based on experimentally estimated fluid temperature and known heat transfer coefficient. A new thermometer with good dynamic properties has been developed and applied in practice, providing a much more accurate measurement of the temperature of the flowing fluid in comparison with standard thermometers. The heat transfer coefficient on the inner surface of a pressure element can be determined from the empirical relationships available in the literature. A numerical-experimental method of determination of the transient heat transfer coefficient based on the solution of the 3D-inverse heat conduction problem has also been proposed. The heat transfer coefficient on the internal surface of a pressure element is determined based on an experimentally determined local transient temperature distribution on the external surface of the element or the basis of wall temperature measurement at six points located near the internal surface if fluid temperature changes are fast. Examples of determining thermal and pressure stresses in the thick-walled horizontal superheater header and the horizontal header of the steam cooler in a power boiler with the use of real measurement data are presented.

Thermal stress monitoring in thick walled pressure components of steam boilers

Two methods for monitoring the thermal stresses in pressure components of thermal power plants are presented. In the first method, the transient temperature distribution in the pressure component is determined by measuring the transient wall temperature at several points located on the outer insulated surface of the component. The transient temperature distribution in the pressure component, including the temperature of the inner surface is determined from the solution of the inverse heat conduction problem (IHCP). In the first method, there is no need to know the temperature of the fluid and the heat transfer coefficient.In the second method, thermal stresses in a pressure component with a complicated shape are computed using the finite element method (FEM) based on experimentally estimated fluid temperature and known heat transfer coefficient. A new thermometer with good dynamic properties can be used for providing a much more accurate temperature of the flowing fluid in comparison with standard thermometers. A numerical-experimental method of determination of the transient heat transfer coefficient based on the solution of the 3D-inverse heat conduction problem was proposed. The heat transfer coefficient on the internal surface of a pressure element can be estimated based on an experimentally determined local transient temperature distribution on the external surface of the element or on the basis of wall temperature measurement at six points located near the internal surface if fluid temperature changes are fast. Examples of determining thermal and pressure stresses in the thick-walled horizontal steam header with the use of real measurement data are presented.

Monitoring of transient thermal stresses in pressure components of steam boilers using an innovative technique for measuring the fluid temperature

Abstract High thermal loads of the thick-walled components arise during the start-up and shutdown in the thermal power units, both classical and nuclear. The thermal stresses should be determined on-line during start-up of the power unit, to avoid reducing the lifetime of the so-called critical pressure components. It is necessary to know the time variations in fluid temperature, and heat transfer coefficient on the internal surface of the pressure components to determine the transient distribution of temperature and thermal stresses in the critical components of boilers. The thermal stress can only be calculated correctly if the temperature of the flowing fluid is accurately measured. Unfortunately, massive industrial thermometers used in power units are not able to measure the transient temperature of the fluid with sufficient accuracy due to their high thermal inertia. The goal of the paper is to present the use of the new measurement technique to determine the unsteady temperature of the superheated steam. The temperature of superheated steam was measured after the second stage of superheater using the proposed measuring technique and conventional industrial thermometers that are used today. The tests carried out showed very clearly the advantage of the proposed method over conventional thermometers.

Thermal stress monitoring in thick-walled pressure components based on the solutions of the inverse heat conduction problems

Thick-walled components of the thermal power unit limit the maximum heating and cooling rates during startup or shutdown of the unit. A method of monitoring the thermal stresses in thick-walled components of thermal power plants is presented. The time variations of the local heat transfer coefficient on the inner surface of the pressure component are determined based on the measurement of the wall temperature at one or six points, respectively, for one- and three-dimensional unsteady temperature fields in the component. The temperature sensors are located close to the internal surface of the component. A technique for measuring the fast-changing fluid temperature was developed. Thermal stresses in pressure components with complicated shapes can be computed using finite element method (FEM) based on experimentally estimated fluid temperature and heat transfer coefficient.

Monitoring of thermal stresses in pressure components based on the wall temperature measurement

Thick-wall boiler components limit maximum heating and cooling rates during start-up or shut-down of the boiler. First, the allowable heating rates of the critical pressure components of the boiler were determined, and the temperature of the fluid was determined. The rate of change of the wall temperature of the pressure element and the thermal stress on the inner surface are controlled online and compared with the permissible values. Boiler manufacturers designate thermal stresses on the inner surface of the pressure component on the edge of the hole based on the measurement of the wall temperature at two points located inside it. Due to the low accuracy of the method used by boiler manufacturers, a new stress-determination method has been proposed in this paper in which only the internal temperature measurement point is used to determine the stresses on the inner surface of the component. In the method proposed in the paper, first, the internal surface temperature is determined from the inverse heat conduction solution, and then the stresses are calculated. Numerous computational tests were performed for cylindrical and spherical elements. Thermal stresses on the inner surface were also determined based on actual measurement data. Thermal stresses can be monitored at small time intervals. The advantage of the method is its high accuracy even at rapid changes in the fluid temperature.

Allowable Rates of Fluid Temperature Variations and Thermal Stress Monitoring in Pressure Elements of Supercritical Boilers

ABSTRACTAllowable rates of fluid temperature changes in critical elements of supercritical steam boilers were determined assuming a quasi-steady state of temperature distribution in pressure components. A method was proposed for monitoring the thermal stresses in the critical pressure components.

Distiller’s dried grain with solubles (Zea mays L) in the diet of sheep reared in the tropical region of Brazil: ingestive behavior and physiological parameters

This study aimed to evaluate the effects of inclusion of different levels of distiller’s dried grain with solubles (DDGS) in the diet of sheep raised in the tropical region of Brazil on ingestive behavior and physiological parameters. We used four sheep with mean body weight (BW) of 25 ± 2 kg, distributed in a Latin square design, with four periods, and four DDGS inclusion levels (0, 8, 16, and 24%). The sheep were placed in metabolism cages, and received two meals per day. The data on ingestive behavior and physiological parameters of the sheep were analyzed with analysis of variance (ANOVA), and the observed differences were tested using regression equations at 5% probability. The inclusion of DDGS levels in sheep diets did not change the time spent on ingestive behavior, such as dry matter intake (DMI), rumination (RUM), resting (RES), water intake (WAI), and other activities (OAC) expressed in minutes. However, during the night period, there was an increase (p < 0.05) in the time spent ruminating in relation to the daytime period. However, there was a reduction (p < 0.05) in the time spent on the activities of RES and WAI of the sheep. The inclusion of DDGS in sheep rations did not change (p > 0.05) the physiological parameters measured. However, we found that the afternoon period influenced (p < 0.05) the physiological parameters evaluated, such as body temperature of the front (BTF), body temperature of the rear (BTR), rectal temperature (RET), and respiratory frequency (REF), which were higher in relation to the values observed in the morning. Thus, we conclude that the inclusion of up to 24% of dried distillery grains with solubles in the feeding of sheep in the tropical region of Brazil does not alter the ingestive behavior and physiological parameters of sheep. However, sheep raised in confinement in the tropical region of Brazil spent more time ruminating at night. During the day, sheep spent more time on resting activities and water intake. In addition, sheep raised in a tropical environment need to be monitored for thermal stress during the afternoon, due to the increase in rectal temperature and respiratory frequency. In addition, sheep raised in a tropical environment require greater monitoring of thermal stress during the afternoon, due to the elevation of physiological parameters such as rectal temperature and respiratory frequency in this period.

Comparing biomarker responses during thermal acclimation: a lethal vs non-lethal approach in a tropical reef clownfish

Abstract Knowledge of thermal stress biology for most tropical fish species in reef ecosystems under climate change is still quite limited. Thus, the objective of this study was to measure the time-course changes of thermal stress biomarkers in the commercially exploited coral reef fish Amphiprion ocellaris , during a laboratory simulated event of increased temperature. Heat shock protein 70 kDa (Hsp70) and total ubiquitin (Ub) were determined in the muscle (lethal method) and in the fin (non-lethal alternative method) under two temperature treatments (control – 26 °C and elevated temperature – 30 °C) throughout one month with weekly samplings. Results suggest that biomarker basal levels are tissue-specific and influence the degree of response under temperature exposure. Responses were highly inducible in the muscle but not in fin tissue, indicating that the latter is not reliable for monitoring purposes. Thermal stress was observed in the muscle after one week of exposure (both biomarkers increased significantly) and Ub levels then decreased, suggesting the animals were able to acclimate by maintaining high levels of Hsp70 and through an effective protein turnover. In addition, the results show that mortality rates did not differ between treatments. This indicates that A. ocellaris is capable of displaying a plastic response to elevated temperature by adjusting the protein quality control system to protect cell functions, without decreasing survival. Thus, this coral reef fish species presents a significant acclimation potential under ocean warming scenarios of + 4 °C. Monitoring of thermal stress through a non-lethal method, fin-clipping, although desirable proved to be inadequate for this species.

Monitoring of thermal stresses in pressure components using inverse heat conduction methods

PurposeThe purpose of this paper is to present a method for monitoring transient thermal stresses. This paper also presents the analysis of thermal stresses of boiler pressure element heating during the start-up in real conditions. The inverse methods are used to determine the wall temperature, whereas the commercial software ANSYS is used to determine the thermal stresses in the pressure component.Design/methodology/approachThe method is based on the solution of the inverse heat conduction problem. Thermal stresses are determined indirectly taking into account the measured temperature values at selected points on the outer wall of a pressure component. First, the transient temperature distribution in the entire pressure element is calculated, and then, thermal stresses are determined by the finite element method. Measured pressure changes are used to determine the stresses resultant from the internal pressure.FindingsThe obtained stresses and temperature in the thick-walled pipe are illustrated and compared with experimental data. Satisfactory agreement was found between computational and experimental results.Originality/valueThe method can be used in the monitoring of thermal and mechanical stresses during the boiler’s start-up and shut-down. Because the temperature distribution at each time level is determined, it can be applied as a thermal load during the structural analysis.

Comparing biomarker responses during thermal acclimation: A lethal vs non-lethal approach in a tropical reef clownfish

Knowledge of thermal stress biology for most tropical fish species in reef ecosystems under climate change is still quite limited. Thus, the objective of this study was to measure the time-course changes of thermal stress biomarkers in the commercially exploited coral reef fish Amphiprion ocellaris, during a laboratory simulated event of increased temperature. Heat shock protein 70kDa (Hsp70) and total ubiquitin (Ub) were determined in the muscle (lethal method) and in the fin (non-lethal alternative method) under two temperature treatments (control – 26°C and elevated temperature – 30°C) throughout one month with weekly samplings. Results suggest that biomarker basal levels are tissue-specific and influence the degree of response under temperature exposure. Responses were highly inducible in the muscle but not in fin tissue, indicating that the latter is not reliable for monitoring purposes. Thermal stress was observed in the muscle after one week of exposure (both biomarkers increased significantly) and Ub levels then decreased, suggesting the animals were able to acclimate by maintaining high levels of Hsp70 and through an effective protein turnover. In addition, the results show that mortality rates did not differ between treatments. This indicates that A. ocellaris is capable of displaying a plastic response to elevated temperature by adjusting the protein quality control system to protect cell functions, without decreasing survival. Thus, this coral reef fish species presents a significant acclimation potential under ocean warming scenarios of +4°C. Monitoring of thermal stress through a non-lethal method, fin-clipping, although desirable proved to be inadequate for this species.

Improved First-Order Approximate Models of Temperature and Thermal Stresses for Online Fatigue Monitoring

Online monitoring of temperature and thermal stresses is an important way to ensure the safety of power plants considering fatigue and creep damages. The effect of online monitoring is determined by the accuracy and calculating time of monitoring models. In this paper, the improved first-order analytical models of temperature and thermal stresses considering temperature-dependent material properties have been derived by using homotopy analysis method (HAM) and superposition principle. The optimal convergence control parameters are obtained by calculating the mean-square residual errors. The validity and accuracy of the proposed models were proved by results comparisons with finite element method (FEM) and artificial parameter method.

Simple method for monitoring transient thermal stresses in pipelines

ABSTRACTThis paper presents a seminumerical method for solving inverse heat conduction problems (IHCP) encountered in the monitoring of thermal stresses in pressurized thick-walled elements of steam boilers. The objective is to give a simple and quick method of determining transient temperature histories in thick-walled components based on temperature measurements on the outer thermally insulated surface. The method is suitable for solving one-dimensional problems. However, it can be extended to multidimensional temperature fields. The IHCP will be solved using the control volume approach. The accuracy of the method is demonstrated by comparing computational and experimental results. Gram orthogonal polynomials are used to smooth the measured time-dependent temperature and for evaluating time derivatives of noisy data with high accuracy. Due to the simplicity of the final formulations, the developed method is very useful for estimating the thermal stresses and controlling the fatigue damage of boiler components.

Validation of Reef-Scale Thermal Stress Satellite Products for Coral Bleaching Monitoring

Satellite monitoring of thermal stress on coral reefs has become an essential component of reef management practice around the world. A recent development by the U.S. National Oceanic and Atmospheric Administration’s Coral Reef Watch (NOAA CRW) program provides daily global monitoring at 5 km resolution—at or near the scale of most coral reefs. In this paper, we introduce two new monitoring products in the CRW Decision Support System for coral reef management: Regional Virtual Stations, a regional synthesis of thermal stress conditions, and Seven-day Sea Surface Temperature (SST) Trend, describing recent changes in temperature at each location. We describe how these products provided information in support of management activities prior to, during and after the 2014 thermal stress event in the Commonwealth of the Northern Mariana Islands (CNMI). Using in situ survey data from this event, we undertake the first quantitative comparison between 5 km satellite monitoring products and coral bleaching observations. Analysis of coral community characteristics, historical temperature conditions and thermal stress revealed a strong influence of coral biodiversity in the patterns of observed bleaching. This resulted in a model based on thermal stress and generic richness that explained 97% of the variance in observed bleaching. These findings illustrate the importance of using local benthic characteristics to interpret the level of impact from thermal stress exposure. In an era of continuing climate change, accurate monitoring of thermal stress and prediction of coral bleaching are essential for stakeholders to direct resources to the most effective management actions to conserve coral reefs.

On-line monitoring and control of thermal stresses in steam turbine rotors

The requirement of high operational flexibility of utility power plants creates a need of using on-line systems for monitoring and control of damage of critical components, e.g. steam turbine rotors. Such systems make use of different measurements and mathematical models enabling calculation of thermal stresses and their continuous control. The paper presents key elements of the proposed system and discusses their use from the point of view of thermodynamics, heat transfer and solid mechanics. Thermodynamic relationships, well proven in design calculations, are applied to calculate on-line the steam temperature at critical locations using standard turbine measurements as input signals. The model predictions are compared with operational data from a real power plant during a warm start-up and show reasonably good accuracy. The effect of variable heat transfer coefficient and material properties on thermal stresses is investigated numerically by finite element method (FEM) on a cylinder model, and a concept of equivalent Green's function is introduced to account for this variability in thermal stress model based on Duhamel's integral. This approach was shown to produce accurate results for more complicated geometries by comparing thermal stresses at rotor blade groove computed using FEM and Duhamel's integral. Finally, the applicability of Neuber's and the Glinka–Molski rule with ideal elastic and bilinear material model to estimating elasto-plastic strains at the rotor groove was investigated by FEM. For the considered groove geometry, Neuber's rule with bilinear material model resulted in most accurate strain predictions.

Rotor thermal stress monitoring in steam turbines

One of the issues of steam turbines diagnostics is monitoring of rotor thermal stress that arises from nonuniform temperature field. The effort of steam turbine operator is to operate steam turbine in such conditions, that rotor thermal stress doesn't exceed the specified limits. If rotor thermal stress limits are exceeded for a long time during machine operation, the rotor fatigue life is shortened and this may lead to unexpected machine failure. Thermal stress plays important role during turbine cold startup, when occur the most significant differences of temperatures through rotor cross section. The temperature field can't be measured directly in the entire rotor cross section and standardly the temperature is measured by thermocouple mounted in stator part. From this reason method for numerical solution of partial differential equation of heat propagation through rotor cross section must be combined with method for calculation of temperature on rotor surface. In the first part of this article, the application of finite volume method for calculation of rotor thermal stress is described. The second part of article deals with optimal trend generation of thermal flux, that could be used for optimal machine loading.