Thermal Loading Conditions Research Articles

Assessment of thermo-mechanical fatigue in a nickel-based single-crystal superalloy CMSX-4 accounting for temperature gradient effects

Turbine blades are working under complex thermal gradient mechanical loading conditions. In the present study, a nickel-based single-crystal superalloy CMSX-4 is experimentally and computationally investigated under the thermo-mechanical fatigue (TMF) and thermal gradient mechanical fatigue (TGMF) loading conditions of the in-phase and out-of-phase thermal-mechanical angel. The fatigue life of TGMF with and without the thermal barrier coating was studied. It was confirmed that the lifetime of TGMF is affected by the temperature gradient significantly and substantially differs from conventional isothermal high temperature fatigue and thermo-mechanical fatigue. Since conventional fatigue models fail to characterize the TGMF, a modified model considers temperature gradient effects and thermal-mechanical phase angle and can describe the TGMF lifetime of the single-crystal superalloy reasonably.

Fiber Bragg Sensors Embedded in Cast Aluminum Parts: Axial Strain and Temperature Response.

In this study, the response of fiber Bragg gratings (FBGs) embedded in cast aluminum parts under thermal and mechanical load were investigated. Several types of FBGs in different types of fibers were used in order to verify general applicability. To monitor a temperature-induced strain, an embedded regenerated FBG (RFBG) in a cast part was placed in a climatic chamber and heated up to 120 within several cycles. The results show good agreement with a theoretical model, which consists of a shrink-fit model and temperature-dependent material parameters. Several cast parts with different types of FBGs were machined into tensile test specimens and tensile tests were executed. For the tensile tests, a cyclic procedure was chosen, which allowed us to distinguish between the elastic and plastic deformation of the specimen. An analytical model, which described the elastic part of the tensile test, was introduced and showed good agreement with the measurements. Embedded FBGs - integrated during the casting process - showed under all mechanical and thermal load conditions no hysteresis, a reproducible sensor response, and a high reliable operation, which is very important to create metallic smart structures and packaged fiber optic sensors for harsh environments.

Low load performance of tangentially-fired boiler with annularly combined multiple airflows

A novel burner arrangement scheme with annularly combined multiple airflows (ACMA) was previously proposed for wall-tangentially fired boiler (WTFB), and its superiority over traditional WTFB had been proved. However, coal-fired boilers are often required to play the role of peak-shaving. To this, low load performances of ACMA boiler were investigated in this work to test whether ACMA can still work well under low boiler thermal load (BTL) conditions. Results show that ACMA boiler performance is still better than that of traditional WTFB under low BTL condition, with smaller airflow deflection, improved coal combustion behavior and alleviated thermal deviation on suspended heating surfaces. Besides, NOx emission characteristic of ACMA boiler under low BTL is more desirable. Furthermore, the location of non-service burners has significant effects on coal combustion and heat transfer processes under 440 MW load conditions, and closing the upper burner group is the optimal choice in terms of the comprehensive boiler performance. These findings deepen the understanding of ACMA boiler and provide theoretical and practical guidance in its application in power plants.

Thermal stability enhancement of ultrathin Ag film electrodes by incorporating atomic oxygen

The structural deformation of a continuous thin film to discrete nanoscopic particles due to solid-state thermal dewetting has been considered an inevitable consequence of using ultrathin Ag films under severe thermal and electrical loading conditions. Thermal dewetting diminishes the electrical and optical performance of Ag film electrodes. Herein, a highly smooth, less defective, completely continuous ultrathin Ag film was used to prove the effectiveness of the atomic O-mediated Ag growth mode in suppressing thermal dewetting. The strong O interference at the outermost surfaces of the Ag nanoscopic geometries provided morphological perfection and chemical modification that contributed to the suppression of the migration of thermally activated Ag atoms. The alleviation of thermal dewetting could be attributed to the reduction in free energies because of the incorporation of the minimal amount of oxygen atoms into interstitial Ag lattice sites without forming oxide phases. The ultrathin (4.5 nm) Ag films sandwiched between thin ZnO films maintained a strong structural integrity and high electrical endurance by successfully circumventing thermal dewetting after exposure to high annealing temperatures up to 673 K and under heavy voltage loading conditions. This facilitated the integration of the heat generating and saving functions, while maintaining optical transparency.

EER or Fcsp: A performance analysis of fixed and variable air conditioning at different cooling thermal conditions

This study explores a performance analysis of variable and fixed types of air conditioning equipment at different thermal load conditions using the cooling seasonal performance factor (FCSP) evaluation method (ISO 16358-1:2013), and the energy efficiency ratio (EER) evaluation method (ISO 5151:2017) which are applied to tropical climates. There are currently several types of energy efficiency evaluation methods available. The EER evaluates one functioning mode of the equipment at full load. While the FCSP takes into account the behavior of the equipment during seasonal periods and the outdoor temperature variations at different cooling load thermal conditions. Currently, it is not clear whether the application of the FCSP is better than the EER for tropical climates. This paper provides a comprehensive revision of the standard conditions, testing procedures, and the test results comparison of two types of air conditioning equipment tested at cooling mode operation. The results were obtained by conducting a comparative analysis of both methods using a balanced ambient room — type calorimeter. The tests were performed in an accredited laboratory that complies with the international standards ISO 17025: 2017, ISO 5151: 2017, and ISO 16358-1:2013. At real operating conditions the results show that the EER evaluation method seems to be less approximate when compared to the FCSP.since the FCSP takes into account how the system behaves when the outdoor temperature varies. These findings could be useful for better technical planning as well as to improve public policies for designing and developing better energy efficiency programs.

Thermal conductivity of a thick 3D textile composite using an RVE model with specialized thermal periodic boundary conditions

Finite element analysis is performed to virtually measure homogenized thermal conductivity of a thick 3D woven textile composite (T3DWC). Temperature-dependent thermal and mechanical properties of constituents are considered for the measurements over a wide range of temperature. A two-step homogenization approach is adopted here to simplify the analysis at the microscopic level without losing heterogeneity of the material at the macroscopic scale. First-step homogenization is carried out at a tow level using an analytical homogenization scheme. Fiber tows are homogenized and assigned with effective elastic and thermal properties. The solid tows are then implemented into a representative volume element considering the unique in-plane periodic fiber architecture of the thick composite material. Due to the unique in-plane periodicity, conventional periodic boundary conditions for thermal and mechanical loading conditions are reformulated. Anisotropic thermal conductivity of T3DWC is obtained from the second-step homogenization based on virtual thermal tests performed at ambient to elevated temperatures.

Thermoelastic Structural Topology Optimization Based on Moving Morphable Components Framework

This study investigates structural topology optimization of thermoelastic structures considering two kinds of objectives of minimum structural compliance and elastic strain energy with a specified available volume constraint. To explicitly express the configuration evolution in the structural topology optimization under combination of mechanical and thermal load conditions, the moving morphable components (MMC) framework is adopted. Based on the characteristics of the MMC framework, the number of design variables can be reduced substantially. Corresponding optimization formulation in the MMC topology optimization framework and numerical solution procedures are developed for several numerical examples. Different optimization results are obtained with structural compliance and elastic strain energy as objectives, respectively, for thermoelastic problems. The effectiveness of the proposed optimization formulation is validated by the numerical examples. It is revealed that for the optimization design of the thermoelastic structural strength, the objective function with the minimum structural strain energy can achieve a better performance than that from structural compliance design.

Steady State Heat Conduction Structural Thermal Analysis of Boiler Tubes and its Design Attributed Failure

One of the important parts of the thermal power plants are tubes carrying steam generally called as boiler tubes. Any leakages in these tubes cannot be identified easily with human senses and also boiler operating condition it is impossible to investigate these tubes or leak. In order to do inspection it require shut down of the plant involving production losses. Though we do inspection with human abilities there is possibility of occurrence of error. Frequent shut downs for inspection leads to huge production loss. In recent days boiler explosions and its impact have become regular news. The intent of this paper is to identify design related failure of the boiler tubes under the thermal loading conditions. A single boiler tube is designed and its behaviour under thermal load operating conditions has been studied with the help of Ansys R15 student release simulation software. This paper gives the detailed study of the more vulnerable regions of boiler tube in design aspect.

Methodological bases for using express and implied expert knowledge when evaluating the state of difficult objects

Purpose. Currently, in the process of solving a wide range of problems in various subject areas, methods for assessing the state of complex objects (SLO) are actively used, among which expert knowledge (EK) occupies a special place. The article proposes a methodological approach to the use of explicit and implicit EK in assessing and predicting the state of the SL. Materials and methods. The article proposes an original fuzzy-feasibility approach to extracting, representing and formalizing the EK in the form of analytical models for assessing the state of the SL. Results. The article describes the essence of solving problems of extraction, formalization, processing and use of explicit and implicit expert knowledge for assessing the state of an SLO at a meaningful level. An example of solving the problem of predicting the level of damage to structural elements and equipment of launch complexes under conditions of intense thermal loading is given. Conclusions. The proposed methodological approach to formalization of explicit and implicit EZ in the form of fuzzy-possibility models has great prospects, since relies on fundamental and applied results obtained so far in theory and practice of application in various subject areas.

Stress Calculation and Analysis of a 600MW Supercritical Boiler’s Steam-water Separator

The steam-water separator of a 600MW boiler has been chosen as the research object. By theoretical analysis’s method and finite element analysis, the stress and secure research has been carried out in the steam-water separator as the thick-walled pressure vessel. For its start-up and normal operation of the working process and features and considering the internal pressure load and thermal stress loading conditions, the initiation of separation stress and security analysis have been carried out about the steam-water separator. The primary stress at the continuum of the cylinder structure can be calculated by the formula, and the calculated results are basically in agreement with the simulated graphic results. And the research work provides a theoretical basis for on-line stress monitoring and life assessment.

Theoretical Minimum Thermal Load in Buildings

Summary Building cooling and heating accounts for a large portion of total global energy use and requires commensurate amounts of resources, which contribute significantly to global warming. Traditionally, addressing this issue has meant improving the efficiency of equipment supplying the thermal energy, reducing envelope heat transfer, and reducing air infiltration. However, this approach is already reaching practical limits. In this perspective, we explore (1) how to reduce thermal load in buildings theoretically and (2) how to achieve that reduction and dramatically lower the energy required to support building loads practically. First, we discuss our framework developed for calculating the theoretical minimum thermal load (TMTL) in buildings. Our analysis shows that current thermal loads in buildings are more than an order of magnitude higher than the TMTL. We also introduce an approximate formula to calculate energy savings from zonal control of thermal load, which shows that the majority of zonal control benefits can be achieved with fewer than 10 zones. Then, we discuss pros and cons of various approaches and strategies to achieve the TMTL. We conclude our perspective with some longer-term R&D ideas, such as thermally adaptive clothing and thermal storage to help approach the TMTL, while providing the additional benefit of interacting with the renewable grid of the future.

Effect of hybrid thermal cycling shocks on the mechanicalproperties of structural composites

In the present research, tensile and flexural mechanical properties of glass epoxy structural composites under simultaneous thermal cycling loading and thermal shocks called hybrid thermal cycling shocks, have been studied. A series of tensile and flexural tests under static and hybrid thermal loading conditions (15 and 30 thermal cycles with -70oC (Degrees Celsius) and +100oC (Degrees Celsius) thermal shocks), were applied on the structural composite specimens and the obtained results are fully compared and investigated. It was found that shocks have a more effective role in changing stiffness in comparison to cycles but the tensile strength of glass/epoxy composites was influenced by the hybrid thermal loads more sensible. For instance, tensile strength was reduced by 12.1% under 30 cycles and thermal shocks. In addition, the flexural bending strength and stiffness were decreased in comparison to static loading conditions. The flexural bending strength and stiffness under hybrid thermal loadings were changed and reduced by 27.64% and 7.2% under 30 cycles under thermal shocks respectively.

Influence of thermomechanical fatigue loading conditions on the nanostructure of secondary hardening steels

Abstract Dual hardening steels reach their well-balanced mechanical properties in terms of strength and toughness through the combination of secondary hardening carbide and intermetallic particle precipitation. This characteristic profile makes them well suited for hot-work applications. In this study, out-of-phase thermomechanical fatigue tests, recreating operating conditions present during hot-work applications, were performed on a dual hardening steel and a 5% Cr martensitic hot-work tool steel. Via high resolution analysis utilizing atom probe tomography and transmission electron microscopy, the behaviour of the different precipitate populations under combined thermal and mechanical loading conditions were compared. Coarsening of the different precipitates and partial dissolution of the intermetallic compounds was observed. It could be shown that with rising maximum fatigue test temperature, the dual hardening steel reaches an increased lifetime caused by its higher tempering resistance.

Development of a design methodology for heat-loaded dimensionally stable elements of carbon plastic construction for a remote sensing of the Earth space equipment

One of the most important tasks of the Federal Space Program of Russia for the period until 2025 is the creation of spacecraft for remote sensing of the Earth. An integral part of the design of this class spacecraft is the determination of the parameters of the orbits that are most effective from the standpoint of information content, energy supply and the duration of active existence. In orbital flight, the temperature state of spacecraft in a complex way varies in time and space. The inhomogeneous temperature field of the structural elements of spacecraft can cause shape distortion, which adversely affects the performance of targets. A technique for a comprehensive analysis and determination of the platform composite design parameters, which is part of the spacecraft for remote sensing of the Earth is proposed. The conditions of thermal loading for flight in a sun-synchronous orbit are considered and mathematical modeling of the operating conditions that ensure the effective operation of such spacecraft is performed. The results of modeling the thermal regime of options for composite platform designs are presented. The technique will be useful in determining the complex of orbital characteristics of the Earth remote sensing satellite at the stage of technical proposals.

Mathematical Modelling and Operational Analysis of Combined Vertical–Horizontal Heat Exchanger for Shallow Geothermal Energy Application in Cooling Mode

Geothermal heat exchangers (GHEs) represent a buried pipe system, which can be utilised to harness renewable thermal energy stored in the ground to improve the efficiency of heating and cooling systems. Two basic arrangements of GHEs have been widely used: vertical and horizontal. Vertical GHEs generally have a better performance in comparison with the horizontal arrangement, and these systems are particularly suitable for confined spaces. Nevertheless, the main technical challenge associated with GHEs, for either the vertical or the horizontal arrangement, is the performance deterioration associated with an increase in the operation times during summer or winter seasons. In this paper, a combined horizontal-vertical GHE arrangement is proposed to address the current challenges. The combined GHE arrangement can be operated in five different modes, corresponding to different thermal loading conditions. These five operation modes of the combined GHE are analysed based on the transient finite difference models previously developed for the horizontal and vertical arrangements. The simulation results reveal that for the single operation mode (horizontal or vertical only), the vertical GHE performs better than the horizontal GHE due to relatively stable ground temperature deep down. While, for the combined operation mode, the series operations (horizontal to vertical or vertical to horizontal) of the GHE are superior to the split mode. It is found that the effect of the fluid mass flow rate ratio is trivial on the heat dissipation of the split mode GHE. The highest heat transfer rate in the split flow operational mode is rendered by the ratio of the mass flow rate of 40% horizontal and 60% vertical. In addition, the climate condition has more effect on GHE’s performance and the increase of the fluid flow rate it can enhance the amount of energy released by the GHE.

Progressive collapse behavior of reinforced concrete frame exposed to high temperature

Purpose Technological innovations in the construction field correspond to a wider revolution in metropolitan life and in structural design. With the demand for advanced concrete technology, the introduction of new reinforced materials in concrete, namely, iron, steel and other reinforcing elements. Reinforcement in concrete is developed in the centuries back and several advancements are being stirred to improvise the properties of the concrete through reinforcements. On the basis of this finding from the earlier research studies, a reinforcement methodology is practiced on the current study to investigate the deflection of the M30 mix concrete frame under thermal load conditions. Design/methodology/approach For the examination, corner and the middle frame are considered with the reinforcement provided on four zones with 16-mm diameter for compression and 8-mm diameter is used for the stirrup at 150 mm c/c spacing. The load is applied to the column with live and wall load of 3.5 kN/m and 14.7KN/m. The experimentation is carried out by the finite element analysis strategy in ABAQUS simulation software with five test conditions with the bare frame at single, two and three-bay infill. The model of the frame is developed and meshed with the meshing type of C3D8T under 8-node thermally coupled brick mesh type for the mesh size of 25 mm. Findings From the simulation outcome, the effect of thermal gradient on the reinforced concrete is analyzed and its structural properties are plotted as performance graphs in the result section. Originality/value Under the thermal load condition, the model is simulated for 180 min for five different cases and analyzed the deflection parameters such as deformation, stress and failure rate.

Advanced Online Moisture Measurements in Transformer Insulation Using Optical Sensors

The reliable moisture determination in a power transformer is still a challenge for utilities and large power transformer operators. The presence of high moisture can cause serious problems, such as severely reducing the remaining useful life and the operational capability of a transformer. The large insulation structure and slow dynamic moisture migration between cellulose and insulating fluid make it difficult to determine the true moisture level. Fiber optics based sensors offer superior sensing characteristics as compared with other techniques. A key advantage of using fiber optic sensors is their ability to be inserted into the winding structure. However, this is a relatively new technology and so extensive research and testing is required to understand how their measurement is affected by the operation of a transformer, and in particular by any sudden changes during a stepped load. In this work, the application of optical fiber Bragg grating based sensors is investigated under the influence of step cyclic thermal loading condition. The test is similar to the test performed by CIGRE WG D1.52 for evaluating different capacitive water activity probes. The tested optical sensors, coated with polyimide material for moisture sensing, are found to be suitable in comparison with commercial sensors and can be effectively used for moisture measurements in different insulated transformers.

Coupled thermal-structural modelling and experimental validation of spiral mandrel die

The conventional theoretical method to calculate deformations and stress states is only limited to a few cases of simple extrusion dies due to a number of assumptions and simplifications. A coupled thermal-structural modelling framework incorporating finite element method is thus developed and implemented to determine the mechanical performances of the complicated spiral mandrel die, which has a complex geometrical feature of spiral grooves and is exposed to severe conditions of thermal load and high pressure. The steady-state thermal analysis is carried out by mapping the temperature load on the flow channel from previously simulated flow characteristics of polymer melt. The structural analysis takes inputs from both thermal analysis and previously simulated pressure on polymer melt. Both the temperature and pressure loads on flow channel are transferred via the Smart Bucket Surface mapping algorithm. The mechanical properties of the spiral mandrel die are evaluated by analysing the deformation and stress distribution. The experimental validation is conducted to demonstrate the effectiveness of the numerical model. The effects of both structure parameters of the spiral mandrel and processing parameters upon the maximum stress in the die body and the maximum pressure induced deformation at the die orifice are investigated.

Effective Solder for Improved Thermo-Mechanical Reliability of Solder Joints in a Ball Grid Array (BGA) Soldered on Printed Circuit Board (PCB)

Ball grid array (BGA) packages have increasing applications in mobile phones, disk drives, LC displays and automotive engine controllers. However, the thermo-mechanical reliability of the BGA solder joints challenges the device functionality amidst component and system miniaturisation as well as wider adoption of lead-free solders. This investigation determines the effective BGA solders for improved thermo-mechanical reliability of the devices. It utilised a conducted study on creep response of a lead-based eutectic Sn63Pb37 and four lead-free Tin–Silver–Copper (SnAgCu) [SAC305, SAC387, SAC396 and SAC405] solders subjected to thermal cycling loadings and isothermal ageing. The solders form the joints between the BGAs and printed circuit boards (PCBs). ANSYS R19.0 package is used to simulate isothermal ageing of some of the assemblies at − 40°C, 25°C, 75°C and 150°C for 45 days and model the thermal cycling history of the other assemblies from 22°C ambient temperature for six cycles. The response of the solders is simulated using the Garofalo-Arrhenius creep model. Under thermal ageing, SAC396 solder joints demonstrate possession of least strain energy density, deformation and von Mises stress in comparison to the other solders. Under thermal cycle loading conditions, SAC405 acquired the lowest amount of the damage parameters in comparison. Lead-free SAC405 and SAC387 joints accumulated the lowest and highest energy dissipation per cycle, respectively. It is concluded that SAC405 and SAC396 are the most effective solders for BGA in devices experiencing isothermal ageing and temperature cycling during operation, respectively. They are proposed as the suitable replacement of eutectic Sn63Pb37 solder for the various conditions.

A rapid life-prediction approach for solder joints based on modified Engelmaier fatigue model

Accelerated life test (ALT) is widely used to predict life of solder joints nowadays, and how to shorten the test time and improve the precise of evaluation is one of the most important issues. Based on statistical results of field failure for solder joints, improved ALT under combined thermal cycling and vibration loading conditions was designed and carried out. This paper presents a modified Engelmaier fatigue model to predict life of solder joints, by taking into account field failure data and ALT testing data. The results show that test time of improved ALT is more shorter than conventional one, and the result of remaining life prediction based on modified Engelmaier fatigue model becomes more precise due to improving life model and increasing information.