Thermal Loading Conditions Research Articles

Energy Harvesting from a Thermoelectric Zinc Antimonide Thin Film under Steady and Unsteady Operating Conditions.

In practice, there are some considerations to study stability, reliability, and output power optimization of a thermoelectric thin film operating dynamically. In this study stability and performance of a zinc antimonide thin film thermoelectric (TE) specimen is evaluated under transient with thermal and electrical load conditions. Thermoelectric behavior of the specimen and captured energy in each part of a thermal cycle are investigated. Glass is used as the substrate of the thin film, where the heat flow is parallel to the length of the thermoelectric element. In this work, the thermoelectric specimen is fixed between a heat sink exposed to the ambient temperature and a heater block. The specimen is tested under various electrical load cycles during a wide range of thermal cycles. The thermal cycles are provided for five different aimed temperatures at the hot junction, from 160 to 350 °C. The results show that the specimen generates approximately 30% of its total electrical energy during the cooling stage and 70% during the heating stage. The thin film generates maximum power of 8.78, 15.73, 27.81, 42.13, and 60.74 kW per unit volume of the thermoelectric material (kW/m3), excluding the substrate, corresponding to hot side temperature of 160, 200, 250, 300, and 350 °C, respectively. Furthermore, the results indicate that the thin film has high reliability after about one thousand thermal and electrical cycles, whereas there is no performance degradation.

Thermal and mechanical energy harvesting using piezoelectric ceramics

The field of energy harvesting has drawn an increased amount of interest due to the rapid development of wireless sensors and self-powered devices. Currently, there is limited information regarding the impact of coupling both thermal and mechanical excitations in a single material and its energy harvesting capabilities. This paper demonstrates the use of Lead Zirconate Titanate (PZT) as a coupled thermal and mechanical energy harvesting device. PZT ceramic was subjected to different thermal and mechanical loading conditions. Under pure mechanical cycling the sample consistently generated the least power output averaging less than 200 nW. An increase in power output was observed under mechanical cycling and higher temperatures. A peak power of 500 nW was seen under both, thermal cycling, as well as under coupled thermal-mechanical cycling. This study demonstrated the feasibility to harvest different waste energies from a single device.

Investigation and analysis of thermo-mechanical degradation of fingers in a photovoltaic module under thermal cyclic stress conditions

The reliability of current carrying fingers in a photovoltaic (PV) cell is essential to the overall performance of a PV module. The close proximity of the fingers to the solder layer makes it compelling to investigate its reliability under the premise of solder joint degradation, which is susceptible to high temperature transient variations. For the investigation of this particular aspect of finger reliability, a 3-D finite element model (FEM) of a PV module has been simulated under accelerated thermal cycle (TC) and outdoor weather temperature cycles. The FEM has been optimised to reduce computational complexity for accommodation of the small size of fingers in comparison to other components. Experimental TC test has also been performed on PV module batches to support the simulated findings by characterisation of observed finger breakages using illuminated current-voltage (I-V) and electroluminescence (EL) imaging technique. The finger-solder interface was identified to be vulnerable under prevailing thermal loading conditions, from both the simulated and experimental findings. To illustrate a larger spectrum of finger reliability, the influence of variable geometrical design parameters of finger and solder layer have been investigated for its dependence on electrical power loss and thermo-mechanical damage accumulation. It was demonstrated that solder thickness and finger spacing are key to the performance of fingers in a PV module. Under the outdoor weather temperature cycle the finger-solder interface was found to be more vulnerable to damage accumulation during the sunshine hours on a hot day as compared to a cold day. Further, an acceleration factor was estimated to establish a quantitative comparison between the outdoor weather temperature cycle and accelerated TC. This paper highlights the different aspects of thermo-mechanical degradation of fingers in PV modules under transient thermal conditions and is instrumental for optimization of variable design and packaging parameters for its enhanced reliability.

Effect of Porosity on Flexural Vibration of CNT-Reinforced Cylindrical Shells in Thermal Environment Using GDQM

This article investigates the flexural vibration of temperature-dependent and carbon nanotube-reinforced (CNTR) cylindrical shells made of functionally graded (FG) porous materials under various kinds of thermal loadings. The equivalent material properties of the cylindrical shell of concern are estimated using the rule of mixture. Both the cases of uniform distribution (UD) and FG distribution patterns of reinforcements are considered. Thermo-mechanical properties of the cylindrical shell are supposed to vary through the thickness and are estimated using the modified power-law rule, by which the porosities with even and uneven types are approximated. As the porosities occur inside the FG materials during the manufacturing process, it is necessary to consider their impact on the vibration behavior of shells. The present study is featured by consideration of different types of porosities in various CNT reinforcements under various boundary conditions in a single model. The governing equations and boundary conditions are developed using Hamilton's principle and solved by the generalized differential quadrature method. The accuracy of the present results is verified by comparison with existing ones and those by Navier's method. The results show that the length to radius ratio and temperature, as well as CNT reinforcement, porosity, thermal loading, and boundary conditions, play an important role on the natural frequency of the cylindrical shell of concern in thermal environment.

Thermal and mechanical analysis of a sodium-cooled solar receiver operating under a novel heliostat aiming point strategy

The nature in which a solar receiver in a concentrated solar power plant interacts with an accompanying heliostat field plays a significant role in plant performance and economics. An appropriate heat flux distribution should help deliver maximum receiver thermal performance, while minimising mechanical damage – thereby maximising power production and reducing costs. The current work presents an investigation into the thermal performance and mechanical reliability of a sodium-cooled solar receiver operating under heat flux profiles generated by a novel heliostat aiming strategy. A modification of the HFLCAL model is used to generate heat flux profiles for individual heliostats in a representative plant, and simulated annealing optimisation techniques are used to produce a novel heliostat aiming strategy. The importance of giving consideration to receiver limitations under non-uniform thermal boundary conditions in the development of a heliostat aiming strategy is demonstrated in this study, with mathematical optical, thermal, and mechanical models used to complete the analysis. An investigation has been conducted for a point-in-time resulting in maximum thermal loading conditions, with theoretical modelling techniques used to calculate receiver tube temperatures for aiming strategy yielded heat flux profiles, thereby allowing for the determination of heat losses and mechanical reliability through creep-fatigue damage. Results show that the simulated annealing algorithm can significantly improve heat flux homogeneity on the receiver, potentially reducing peak heat flux to less than 10% that of a single aiming point strategy, given an appropriate spillage allowance and aiming point grid size. A satisfactory configuration of spillage allowance and aiming grid size exists so as to supply maximum power to the receiver, while uniformly distributing the incident heat flux in order to meet mechanical reliability requirements. Based on the receiver design and conditions simulated in the analysis, a grid constructed of more than 81 aiming points (receiver area coverage of 32.7%), and an additional spillage allowance of 10% allows the receiver to deliver maximum power output while retaining mechanical durability through a 30 year plant life cycle.

Uncertainty analysis of capacitor reliability prediction due to uneven thermal loading in photovoltaic applications

Because of the high cost of failure, the reliability performance of capacitors is becoming a more and more stringent factor in many energy conversion applications. Since temperature is one of the main stressors that leads to the wear-out of capacitors, it is important to understand the uncertainties introduced by the capacitor thermal modelling within its reliability prediction process. Thus, in this paper, the uncertainties introduced by uneven thermal loading, and their impact on the reliability of a photovoltaic application DC-bank are investigated. Based on a generic model-based reliability assessment procedure, a reliability evaluation tool is initially developed and used in order to quantitatively analyze the impact of these uncertainties. The lifetime evaluation of the individual capacitors/DC-bank is estimated and afterwards benchmarked under even/uneven thermal loading conditions. The outcomes of the uncertainty analysis indicate that the uneven thermal distribution among DC-link capacitors can have a significant impact on both component and system-level reliability performance.

Limit load and failure mechanisms of soda lime glass foam

Foamed glass is widely used in the industry as an insulating material. However, its mechanical properties are not well-investigated yet. Foamed glass is produced from glass waste that causes discrepancy in mechanical properties of the final product. This paper shows a way to increase the limit of the load capacity of foamed glass, which is very fragile and sensitive to mechanical and thermal loading conditions. In this paper, three different methods of load application on cellular glass structure (rough contact, resin and flour interfaces) and their influence on failure mechanisms were investigated in detail. The results of numerical analyses, based on finite elements method and compression strength tests using the digital image correlation method, indicate that the overall strength of the material is limited by boundary effects. A careful adjustment of the interface property is the main factor to draw useful conclusions and to extend load limits of cellular glass in engineering applications.

Material Shear Strength Assessment of AU/20SN Interconnection for High Temperature Applications

AbstractWhen a power module is under a continuous electrical load, a temperature effect is induced by the current load in the module configuration. The joint material therefore has long-term temperature and mechanical loadings under supplied power. A long-term temperature load can change the material and mechanical properties, including voiding, cracking, creeping and fracturing. Au/20Sn eutectic alloy, a highly temperature resistant material, is typically used for electric interconnections in high-power modules. The Au/20Sn is converted into AuSn and an Au5Sn intermetallic compound (IMC) by solid liquid inter-diffusion (SLID) bonding to form joints with high melting points. In this study, a test vehicle based on an actual power module was designed and fabricated to investigate and understand the material properties and mechanical behavior of Au/20Sn solder under a temperature load. The joint microstructure exhibited variation under different thermal treatment conditions such as temperature and load durations. The shear strength test was conducted to examine the mechanical strength of the joints under different thermal load conditions. The failure mode of the joint was further determined using fracture morphology after the shear test. Finally, the shear strength of Au/20Sn was identified to investigate the high temperature resistance of joints under different temperatures. The mechanical strengths of joints under different temperature loads are expressions of different mechanical characteristics and can be used to determine reliability at an intended high application temperature.

Application of the finite element method for evaluating the stress distribution in buried damaged polyethylene gas pipes

During the loading process, buried gas pipes can experience severe stresses due to soil- structure interaction, the presence of traffic load, the soil’s column weight, daily and/or seasonal temperature changes and uniform internal pressure. In this research, the finite element method is employed to evaluate the behavior of buried Medium Density Polyethylene (MDPE) pipes which have been subjected to damage at the pipe crown. The modeled pipe damage ranges from a very small circular hole to a large circular hole and elliptic holes with various minor to major diameter ratios, a/b, to simulate circular to crack-shaped defects. The computer simulation and stress analyses were performed using the ANSYS software finite element package. The stress distribution around the defect was determined under the aforementioned mechanical and thermal loading conditions. Then, the maximum values of Von Mises stresses in the damaged buried PE pipes, which were evaluated by finite element solution, were compared with their corresponding reduced strength for safe operation with a life expectancy of fifty years. Based on the results, the maximum Von Mises stress values in the defective buried polyethylene gas pipeline are significantly above the pipe strength limit at 35 °C. The previously mentioned stress values increase with the following factors: temperature increase, increase in circular hole diameter and decrease in elliptic hole diameter ratio (a/b). The maximum stress in the damaged PE pipe is due to the simultaneous loading effects of soil column weight, internal pressure, vehicle wheel load and pipe temperature increase. Additionally, the novel finite element models and stress plots for the buried damaged pipe and the pipe material allowable strength will be used to investigate the correct repair method for the damaged gas pipeline and to choose the best patch arrangement which will assure a safe repair.

An analysis of the reliability and design optimization of aluminium ribbon bonds in power electronics modules using computer simulation method

Ribbon bonding technique has recently been used as an alternative to wire bonding in order to improve the reliability, performance and reduce cost of power modules. In this work, the reliability of aluminium and copper ribbon bonds for an Insulated Gate Bipolar Transistors (IGBT) power module under power cycling is compared with that of wire bonds under power and thermal cycling loading conditions. The results show that a single ribbon with a cross section of 2000 μm × 200 μm can be used to replace three wire bonds of 400 μm in diameter to achieve similar module temperature distribution under the same power loading and ribbon bonds have longer lifetime than wire bonds under cyclic power and thermal cycling conditions. In order to find the optimal ribbon bond design for both power cycling and thermal cycling conditions, multi-objective optimization method has been used and the Pareto optimal solutions have been obtained for trade off analysis.

Finite element simulation of self-heated pavement under different mechanical and thermal loading conditions

Aiming to overcome the hazards associated with icy roads, a new technique to de-ice pavement surfaces is proposed in this paper. The idea of this technique is to bury small-diameter heat exchange loops in the pavement’s base layer, which will be heated using geothermal or solar energy via a circulating fluid. The fluid will be circulated using a pump that will be powered by a solar system. In order to optimise the design of pavement loops, i.e. geometry and material, to ensure acceptable thermal and mechanical performance, finite element analyses were conducted. The simulation results show that the loop geometry and material have a limited effect on the mechanical performance of pavement due to their small diameter-to-length ratio. From the thermal performance standpoint, the material of the loop affects the temperature distribution in the pavement significantly; the higher the thermal conductivity of the loops, the hotter the pavement section. Moreover, the pavement surface temperature remains ice-free when warm water at 23°C is circulated in aluminium loops spaced at 300 mm and placed at depth 25 mm below the bottom of the asphalt, indicating that sufficient amount of thermal energy can be provided to the pavement via the presented technique to keep its surface ice-free.

Criterial equations for describing boundary conditions of thermal loading during tests of models of gas turbine engine blades in gas flows

The paper describes the method of obtaining the equation for spatial-temporal dependence of the heat transfer intensity of model samples under standardized thermo-fatigue damage studies of gas turbine blades in gas flow of variable parameters. Methods of the theory of the similarity of thermal processes underlie in the equation’s structure. The described numerical analysis uses results of complex bench tests of models under different regimes of non-stationary gas overflow. The obtained equation in criteria form allows describing conditions of samples’ heat exchange under thermal loading on the gas-dynamic test bench under a wide range of sizes and regimes.

Development, validation and analysis of an efficient micro-scale representative volume element for unidirectional composites

In the present work, a simple procedure to build periodic representative volume elements (RVE) is developed for UD composite laminae. The procedure is based on the alteration of an initially regular fibre distribution, and includes the possibility to start from different fibre configurations, to use of non-uniform fibre diameter, and for fibres to cross the RVE edges.The obtained RVEs were found to differ from a theoretical hard-core process in terms of Voronoi equivalent radius distribution and nearest neighbour distribution, for which a novel analytical method is proposed. The fibre distributions were instead in good agreement with real microstructures in terms of both short- and long-range morphological indexes, especially when the actual fibre diameter distribution is used. A novel short-range index, called neighbour distance diagram, is also proposed to represent the distances of all the fibre neighbours.The RVEs were then compared to real microstructures in terms of stress distributions. The Cumulative Distribution Function (CDF) of Local Maximum Principal Stress (LMPS) and the Local Hydrostatic Stress (LHS) in the matrix are calculated under transverse, shear and longitudinal stresses and under a temperature gradient, validating the RVE also under a mechanical point of view. Using uniform fibre diameter was found not to have a significant influence on the stress distributions.Eventually, a parametric analysis was carried out to analyse the influence of the fibre volume fraction on LMPS and LHS CDF, under both mechanical and thermal loading conditions.

Modelling and analysis of radial thermal stresses and temperature field in diesel engine valves with and without air cavity

A theoretical investigation has been undertaken to study operating temperatures, heat fluxes and radial thermal stresses in the valves of a modern diesel engine with and without air-cavity. Temperatures, heat fluxes and radial thermal stresses were measured theoretically for both cases under all four thermal loading conditions. By creating an air cavity inside the valves stem, it acts as an insulating medium and prevents the heat flow, hence the need of providing insulation coating on valves is minimized. The main motive of this is to reduce the weight of engine and cost associated with thermal coating. Results observed in the engine valves revealed that after creating an optimized air cavity in the valve, thermal stresses and temperatures at all nodal points decreases slightly. The weight of the valve decreased up to 11% without losing its strength. In addition to heat transferred by convection and radiation from combustion gases, the temperature and heat flux distributions are considerably affected by heat conduction from valve seat. The temperature field, heat transfer rate and thermal stresses were investigated with numerical simulation models using FORTRAN FE (finite element) software.Keywords: combustion chamber, temperatures field, diesel engine valve, finite elements

Effects of Brass (Cu3Zn2) as High Thermal Expansion Material on Shrink Disc Performance During High Thermal Loading

This research work is focused on shrink disc operation at high temperature. Geometrical and material design selections have been done by taking into consideration the existing shrink disc operating at high temperature condition. The existing shrink disc confronted slip between shaft and shaft sleeve during thermal loading condition. The assessment has been obtained through virtual experiment by using Finite Element Analysis (FEA) -Thermal Transient Stress for 900 seconds with 300 °C of thermal loading. This investigation consists of the current and improved version of shrink disc, where identical geometries and material properties were utilized. High Thermal Expansion (HTE) material has been introduced to overcome the current design of the shrink disc. Brass (Cu3Zn2) has been selected as the HTE material in the improved shrink disc design due to its high thermal expansion properties. The HTE has shown a significant improvement on the total contact area and contact pressure on the shaft and the shaft sleeve. The improved shrink disc embedded with HTE during thermal loading exhibit a minimum of 1244.1 mm2 of the total area on shaft and shaft sleeve which uninfluenced the total contact area at normal condition which is 1254.3 mm2. Meanwhile, the total pressure of improved shrink disc had an increment of 108.1 MPa while existing shrink disc total pressure has lost 17.2 MPa during thermal loading.

Uncertainty-based life-cycle analysis of near-zero energy buildings for performance improvements

Near-zero energy buildings (nZEBs) are considered as an effective solution to mitigating CO2 emissions and reducing the energy usage in the building sector. A proper sizing of the nZEB systems (e.g. HVAC systems, energy supply systems, energy storage systems, etc.) is essential for achieving the desired annual energy balance, thermal comfort, and grid independence. Two significant factors affecting the sizing of nZEB systems are the uncertainties confronted by the building usage condition and weather condition, and the degradation effects in nZEB system components. The former factor has been studied by many researchers; however, the impact of degradation is still neglected in most studies. Degradation is prevalent in energy components of nZEB and inevitably leads to the deterioration of nZEB life-cycle performance. As a result, neglecting the degradation effects may lead to a system design which can only achieve the desired performance at the beginning several years. This paper, therefore, proposes a life-cycle performance analysis (LCPA) method for investigating the impact of degradation on the longitudinal performance of the nZEBs. The method not only integrates the uncertainties in predicting building thermal load and weather condition, but also considers the degradation in the nZEB systems. Based on the proposed LCPA method, a two-stage method is proposed to improve the sizing of the nZEB systems. The study can improve the designers’ understanding of the components’ degradation impacts and the proposed method is effective in the life-cycle performance analysis and improvements of nZEBs. It is the first time that the impacts of degradation and uncertainties on nZEB LCP are analysed. Case studies show that an nZEB might not fulfil its definition at all after some years due to component degradation, while the proposed two-stage design method can effectively alleviate this problem.

HYGIENIC EVALUATION OF THE IMPACT OF WORKING CONDITIONS ON THE HEALTH OF WORKERS OF THE COMPLEX FOR PRODUCTION OF PHTHALIC ANHYDRIDE AND FUMARIC ACID

In a priori assessment, the professional risk for workers in the production of phthalic anhydride is characterized by an average (class of labor conditions - 3.2), the main harmful chemical production factors: phthalic anhydride, fumaric acid, maleic aldehyde, dimethylbenzene (MPC for single dose (MPCsd) - up to 5.9). These factors are identified as priority ones in the development of adverse effects from the side of the hepatobiliary system. The impact of chemicals is intermittent in character during the shift, which requires control of the content of chemicals in the air in the working area in the form of average shift concentrations. In workers of the complex for the production of phthalic anhydride and fumaric acid, there is an accumulation of o-xylene, phthalic and fumaric acid, whose concentrations are significantly higher (p = 0.0001 - 0.03) if compared with the reference parameters of the comparison group (the excess multiplicity up to 7 times). Among the workers of the phthalic anhydride and fumaric acid production complex, there were no established statistically significant differences in the blood content of o-xylene, phthalic acid and fumaric acids when performing work under conditions of thermal loading of the environment and under conditions with acceptable microclimate parameters. The development of disorders of the hepatobiliary system was shown to begin with the intensification of free radical damage to cell membranes (manifested by an increase in the MDA content of blood relative to the age physiological norm and relative to the index of workers in the comparison group). With a work experience of up to 5 years, the accumulation of secondary products of lipid peroxidation (LPO) in workers is hampered by the activation of antioxidant protection processes. At the experience of more than 5 years, the development of adverse effects from the side of the liver has been established: significantly higher levels of aspartate aminotransferase (AST) (p = 0.027), in cases with an experience of more than 10 years - the level of total and direct bilirubin in blood serum is elevated by 1.4-1.5 times, p = 0.0001 - 0.002). There was found the statistically significant cause-and-effect relationship of the elevated total blood bilirubin content with labor conditions (RR = 2.86, 95% CI = 1.03-7.98, etiological proportion 65.08%)

Experimental studies on changes in mechanical properties of polymer composites under impact of thermal load determined based on compression testing

The objective of the study was to carry out an analysis of changes in mechanical properties of polymer composites in conditions of thermal load. Such an analysis may allow an initial verification of possibilities of deploying new composites in production of fire helmet shells. The reference material chosen for testing was the Ultramid composite, which is currently used for the production of fire helmet shells. In addition three different materials were selected that contained reinforcement by glass fibres bearing the trade name of Tarnamid, which are not used in manufacturing of shells. Testing was conducted in conditions of quasi-static load, during which compressive tests were performed. Mechanical loads were applied at different levels of thermal exposure, which was to simulate presence in fire conditions. Results of tests indicated that the Tarnamid composites are characterised by better compressive strength and rigidity determined on the basis of the Young module value than Ultramid PA66 GF25 used in the production of head protective shells. It has also been proven that thermal loads contribute to significant degradation in strength and rigidity of tested materials, which affects adversely protective properties of the helmet.

Three Dimensional Finite Element Analysis of Thin Hybrid FRP Skew Laminates for Thermo Elastic Behaviour of Different Materials

The present paper deals with the prediction of thermo elastic behavior of the thin four-layered Angle- ply Hybrid Fibre Reinforced Plastic (FRP) skew laminated composite plate with circular cut out by considering two composite materials Graphite-Epoxy and Boron-Epoxy materials which are subjected to uniform pressure load and thermal loading. The problem is modeled in ANSYS software based on the Classical Lamination Theory (CLT) which is suitable for the analysis of thin laminates with circular cut-out. The effect of size of the circular cut out and skew angle on the stresses are shown for Angle-ply laminates. The principle stresses and shear stresses are evaluated for different cross sections. The present analysis is useful for the safe and effective desi gn of the skew laminates with circular cut out under uniform pressure load and thermal load conditions

Crack growth simulation with Adapcrack3D in 3D structures under the influence of temperature

Lifetime of components or structures that are under cyclic loading rely upon the growth rate and the path of cracks that are developed during its operation. Thus the prediction of fatigue crack growth reduces the adverse effects which can be caused because of its behavior. Many simulation programs are available to foresee the crack growth and growth rate in structures, thereby determining their lifetime. Adapcrack3D is an automatic crack growth simulation program which uses the finite element method to simulate crack growth behavior in structures. FE-Simulations are performed in 3D models of structures to determine the stresses that are developed due to the given loading situations. Thereafter, the software performs fracture mechanical evaluation to determine crack path and the lifetime of components that are under mixed-mode loading. Adapcrack3D is generally used for simulating mechanically loaded components. In addition to the stresses that are caused because of mechanical loading, stresses developed due to the change in temperature in components can also have influence on the crack growth behavior. This paper is an attempt to introduce temperature as a new boundary condition in the software in addition to the mechanical loading conditions that are already available. 3D models of structures are separately created with mechanical and thermal loading conditions. Simulations are conducted to understand the crack growth in models that have only mechanical loading and those having both the mechanical and temperature boundary conditions. The results obtained from both the simulations are evaluated to understand the influence of applying temperature as an additional boundary condition.