Transient Thermal Effects Research Articles

Investigation of unsteady Buongiorno nanofluid in a slanted thermally radiated revolving channel under upstream microbial movement in the absence of chemical reaction

Analysis of Buongiorno nanofluid in a thermally radiated channel in the occurrence of microbes is an enrich research motive. Thermal radiations, dissipation energy, transient effects and upstream microbial acceleration potentially alter the performance of Buongiorno nanofluid. This is a two phase nanofluid model which accommodates the thermophoretic and Brownian movement of the particles along with other integrated physical quantities. Hence, the current research aims to conduct the study of Buongiorno nanofluid in a slanted thermally radiated micro channel in the presence of aforementioned physical phenomenon. The outcomes of the model achieved numerically and discussed deeply. It is investigated that the unsteady and channel revolving parameters enhances the nanofluid movement while adjusting the channel at different inclination also favors the velocity. The velocity G(η) upsurges for larger rotation of the channel while it drops for more transient fluid. Further, the thermophoretic and particles deposition boosts the thermal performance of the setup while thermal radiations depreciated the efficiency. The Schmidt effects in the range of 1.0–7.0 highly contributes in the improvement of mass transport. Moreover, density motile of microbes improved for Lewis and transient effects while Peclet effects are examined excellent to control the microbial influence.

Research on transient thermal effects of dynamic rotating complex enclosed optical system

With the Boussinesq approximation of incompressible Navier-Stokes equations, the temperature distribution introduced by natural convection due to buoyancy is analyzed. Then ray optics is applied to calculate the changes of wavefront. For this system, characteristics of the temperature distribution and outlet wavefront are emphatically investigated on different propagation angle. It is found that the wavefront has a change rule of first rising, then decreasing, and then asymptotically converging within 60 s. Furthermore, the buoyancy will seriously affect the temperature distribution, thus affecting the wavefront and propagation at low angles has better output wavefront.

Formation of β-Ti phase during L-PBF processing of martensitic NiTi

Shape memory activations in martensitic NiTi are highly influenced by the processing technique used. Laser Powder Bed Fusion (L-PBF) is a metal additive manufacturing method being investigated for NiTi processing. The rapid transient thermal effects involved in L-PBF processing are found to cause microstructural anomalies which can result in unfavourable mechanical and functional properties. In this paper, anomalous hard protrusions observed in L-PBF processed NiTi microstructure were investigated in detail. The spatial distribution and cause of these protrusions were analysed. Studies were conducted using EDX, BSE, EBSD, TEM, DSC, AFM and nanoindentation, to identify the compositions, crystal structures, thermal characteristics and nanomechanical properties of these protrusions. The protrusions were identified to be hard β – Ti phase.

Thermo-elasticity displacement formulation for constrained articulated mechanical systems

This paper proposes an approach for thermal analysis of articulated systems subject to boundary and motion constraints (BMC). The solution framework is designed to capture large temperature fluctuations, significant change in geometry due to reference configuration and deformations, and geometric nonlinearity due to articulated mechanical systems (AMS) large displacements and spinning motion. Thermal-expansion displacements, which do not contribute to rigid-body translations, are determined from thermal stretch of position-gradient vectors using a new sweeping matrix technique designed to eliminate dependence on translational rigid-body modes. A new quadratic thermal-energy kinetic form is defined and used to formulate a dynamic force vector that accounts for thermal transient and inertia effects. Nodal thermal displacements are used in formulating AMS differential/algebraic equations (DAEs), and consequently, thermal stresses due to BMC equations are automatically accounted for based on integration of thermal analysis and Lagrange-D’Alembert principle, which is the foundation of computational multibody system (MBS) algorithms. The approach used in this study for large-displacement constrained and unconstrained thermal expansions is based on multiplicative decomposition of position-gradient matrix, instead of strain additive decomposition, for solution of thermo-elasticity problems. Four configurations are used to define continuum geometry and displacements: straight configuration, reference configuration, thermal-expansion configuration, and current configuration. The proposed approach allows applying thermal loads during constrained large displacements, does not impose restrictions on the choice of thermal coefficients, captures reference-configuration geometry and change in inertia forces due to temperature fluctuations, accounts for thermal displacement in formulating AMS nonlinear constraint equations, and allows for integration with MBS algorithms for the study of a wide range of thermo-elasticity problems.

Life-Based Geometric Design of HVDC Cables—Part 2: Effect of Electrical and Thermal Transients

This study, in two parts, investigates the design of high-voltage direct-current (HVdc) cables depending on electrothermal life modeling of the insulating material. The first part investigated the way in which different parameters affect the design of an HVdc cable in steady-state conditions, i.e., with known nominal voltage and ampacity. This article investigates the effect of electrical (i.e., voltage) transients, such as voltage polarity reversals (VPRs), in addition to thermal transients (such as load cycles of cable current) on the electrothermal life map of HVdc cables, and their influence on cable feasibility. An ad hoc MATLAB code has been developed for this study. The results show a considerable negative effect of electrical transients on the expected life. A more severe effect of electrical transients is noticed for materials with a lower value of the temperature coefficient of conductivity, due to a longer duration of transients. On the contrary, thermal transients associated with load cycles—which mostly imply current values equal to or lower than cable ampacity—imply insulation temperature values always lower than the maximum permissible temperature, and thus, they have a positive effect on the electrothermal life since the thermal stress applied on the cable insulation will be reduced, allowing for smaller cable geometries for a fixed voltage and ampacity rating. It must be noticed that only the electrothermal life is investigated in this article, and other types of stresses (e.g., mechanical stress) may also affect insulation life, but this is out of the scope of this study.

Dynamic analysis and investigation of the thermal transient effects in a CSTR reactor producing biogas

In the field of primary energy saving, biomethane is becoming more and more attractive. The need to manage urban waste, combined with the increasing use of biofuels, makes this resource crucial for sustainability objectives. Therefore, a detailed estimation of biogas production from an anaerobic digester is an important aspect for the related research activity. This work presents a thermal transient model developed in MATLAB® that can accurately predict heat transfer and biological phenomena occurring within the digester. The model developed in this paper can conveniently consider the thermal inertia of the treated biomass during the retention time. This model is subsequently linked to the TRNSYS environment, where the produced biogas is upgraded to biomethane. For this purpose, a membrane permeation model is considered. A concentrating photovoltaic/thermal collector is coupled to the digester to meet the plant electricity and thermal energy demands. In particular, the electricity demand is mainly due to the upgrading process while the thermal energy is necessary for the anaerobic digestion process. The results of the dynamic analysis show that neglecting the thermal inertia of the digester leads to an overestimation of the total biogas production by 20%. Furthermore, the integration of renewables with the anaerobic digestion process shows remarkable results. In this case study, the Primary Energy Saving is roughly 5% and the Simple-Pay Back is less than 10 years, despite the small scale selected for solar collectors.

Thermal lens effect induced in a Cr,Tm,Ho:YAG laser rod: A comparison between under lasing and non-lasing conditions

In this paper, transient thermal lensing effects in a typical flashlamp-pumped CTH:YAG laser crystal under lasing and non-lasing conditions are studied and compared in a low repetition-rate regime. It is shown that in the lasing regime (for pumping energies higher than 90J) the time-resolved behavior and the strength of the three mode thermal lenses of the rod are different from the non-lasing condition. According to this research, it can be referred that higher-order processes such as excited state absorption of both pump and laser radiation and energy transfer up-conversion may have a more significant contribution to the laser dynamics in the lasing regime. The analysis of the results also shows that the energy transfer between different manifolds in Cr3+, Tm3+, and Ho3+ ions may depend on coolant temperature.

Life-Based Geometric Design of HVDC Cables—Part I: Parametric Analysis

This study, in two parts, investigates the cable design of high-voltage direct-current (HVDC) cables depending on life modeling of the insulating material. This article is the first part, in which a parametric analysis is carried out, illustrating the way in which different parameters affect the life-based feasible designs of an HVDC cable with known nominal voltage and ampacity. An <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad hoc</i> MATLAB code has been developed for this study. Results show great sensitivity of the lifetime to insulation geometry, as a slight variation in inner and outer insulation radii leads to a significant variation of cable life due mainly to the related electric field variation. The effect of temperature can be hardly observed in the life map due to the predominant effect of electric field. Increasing the maximum conductor temperature may not necessarily extend the feasible design area, which is also limited by the maximum temperature drop across insulation thickness. The higher the applied voltage, the greater the cable dimensions. This study also emphasizes the need to keep a low enough value of soil thermal resistivity, which considerably reduces the cable dimensions. Temperature coefficient of conductivity shows a nonlinear (mainly drastic) effect on the life. On the contrary, field coefficient of conductivity shows a slight positive effect on the life. Part II of this study will investigate the effect of electrical and thermal transients on the life-based geometric design of HVDC cables.

SolarReceiver2D: a Modelica Package for Dynamic Thermal Modelling of Central Receiver Systems

This paper describes the Modelica Package SolarReceiver2D which has been developed for the dynamic thermal analysis of central receiver systems. The package includes all the components necessary for the dynamic simulation of the solar receiver operation and it enables consideration of different receiver geometries, materials, HTFs, and operating conditions (e.g., HTF mass flow rate control strategies, heat flux, ambient conditions). Some of the package components are taken from existing Modelica libraries originally developed to model water and gas flows, while other are implemented as new components. The SolarReceiver2D package allows assessment of the receiver thermal efficiency and the temperature distributions experienced by the tubes and the HTF during its operation. The tubes temperature field is modelled in the axial, circumferential, and radial directions, and this makes the package suited for a thermo-mechanical analysis of the receiver. Moreover, the receiver response to passing clouds is dynamically simulated accounting for the effect of thermal transients. The SolarReceiver2D represents a useful tool for the design and optimization of solar tower receivers.

Evaluation of the Environmental Fatigue at a Long Radius Elbow of a Piping System under Transient Thermo Mechanical Stresses

Thermal fatigue widely takes place in light water reactor (LWR) piping systems. It is an important aging mechanism of a nuclear reactor. Thermal transient effects occur at the startup and shutdown of a nuclear power plant. During the thermal transients, local and global cyclic stresses are induced in the piping systems. They are exacerbated by local geometric imperfections and environmental factors, which may lead to crack initiation. The elbows of such piping systems are subject to various combinations of loads (internal pressure, bending, and torsion, as well as thermal fluctuations) during their service life. As can be seen, high-stress concentrations are developed in these piping elements. Therefore, it is important to make a failure evaluation. In this paper, a 12” pipe system segment, which was made with SA 106 Gr C steel, has been considered. It was composed by two straight sections joined by a long radius elbow. Typical start-up and shutdown transient effects of a BWR-5 were considered. A computer-aided thermo-mechanical analysis was carried out using the finite element method. The linearization of the stresses was considered, based on the ASME B &amp; PVC Code Section III, subsection NB. Under these conditions, environmental fatigue was analyzed after 40-and 60-years operation.

The effects of fusion reactor thermal transients on the microstructure of Eurofer-97 steel

Plasma-wall interactions in a commercial-scale fusion power station may exert high transient thermal loads on plasma-facing surfaces, repeatedly subjecting underlying structural materials to high temperatures for short durations. Specimens of the reduced activation ferritic-martensitic steel Eurofer-97 were continuously aged at constant temperature in the range of 550°C to 950°C for up to 168 hours in a furnace to investigate the microstructural effects of short-term high temperature exposure. A CO2 laser was also used to repeatedly heat another specimen from 400°C to 850°C a total of 1,480 times over a period of 41 hours to explore transient heating effects. Microstructural changes were studied via scanning electron and focused ion beam microscopy and include (i) the coarsening of Cr-rich secondary phase precipitates when continuously heated above 750°C, (ii) an increase in average grain size above 800°C and (iii) the evolution of a new lath martensite microstructure above 850°C. Conversely, transient heating via a laser was found to result in the decomposition of the as-received lath martensite structure into ferrite and Cr-rich carbide precipitates, accompanied by a significant increase in average grain size from 0.1-2 µm to 5-40 µm. Experimental analysis was supported by thermodynamic simulation of the equilibrium phase behaviour of Eurofer-97 in MatCalc and thermal finite element modelling of plasma-wall interaction heating on the water-cooled lithium-lead tritium breeding blanket concept in Comsol Multiphysics. Simulated thermal transients were found to significantly alter the microstructure of Eurofer-97 and the implications of this are discussed.

Reduced order modeling of selective laser melting: from calibration to parametric part distortion

Additive manufacturing is an appealing solution to produce geometrically complex parts, difficult to manufacture using traditional technologies. The extreme process conditions, in particular the high temperature, complex interactions and couplings, and rich metallurgical transformations that this process entails, are at the origin of numerous process defects. Therefore, the numerical simulation of the process is gaining the interest of both the scientific and the industrial communities. However, simulating that process demands impressive computational resources, limiting high resolution simulations to the microscopic and mesoscopic scales. This paper proposes a thermo-mechanical modeling framework at the process scale as well as its associated reduced order simulation counterpart, enabling the parametric evaluation of the part distortion. It deeply addresses the process calibration using a high-resolution computational procedure based on the use of an in-plane-out-of-plane separated representation at the heart of the so-called Proper Generalized Decomposition (PGD), as well as the analysis of the transient thermal effects, defining the conditions in which the thermal and mechanical analyses can be decoupled.

Two-port network modeling for bio-heat transfers in lungs

Abstract In open-heart surgery, temperature changes may severely damage organ tissues, therefore a better knowledge of thermal transient effects is required to improve temperature control. Heat transfer in a biological context is usually treated by means of empirical relationships or simple resistance models. In some cases, fairly simplified models only involving thermal resistance R and a heat capacity C are used. More advanced models which may be accurate enough tend to rely on heavy finite element computations. An intermediate model is sought to more accurately describe transient effects. By combining the well-known Pennes’ bio-heat equation combined to a thermal two-port network, a circuit model is proposed to take into account thermal transients in a perfused tissue. A larger frequency band can be taken into account for such an approach. The proposed models may also consider the effect of blood perfusion on the temperature transients, as well as blood temperature fluctuations (as in extracorporeal circulation, for example) and metabolic heat generation. For a simple 1D scenario, sensitivities to different heat or temperature inputs are compared. The obtained impedance expressions are also analyzed for different branch levels of the lung.

Modeling of an Integrated Thermoelectric Generation–Cooling System for Thermoelectric Cooler Waste Heat Recovery

This paper focuses on the problem of thermoelectric cooler waste heat recovery and utilization, and proposes taking the waste heat together with the original heat source as the input heat source of the integrated thermoelectric generation–cooling system. By establishing an analytic model of this integrated thermoelectric generation–cooling system, the steady-state and transient thermal effects of this system are analyzed. The steady-state analysis results show that the thermoelectric generator’s actual heat source is about 20% larger than the intrinsic heat source. The transient analysis results prove that the current of thermoelectric power generation and the cold end temperature of the system show a nonlinear change rate with time. The cold end temperature of the system has a maximum value. Under different intrinsic heat sources, this maximum value can be reached between 1 s and 2.5 s.

Lamé curve approximation for the assessment of the 3D temperature distribution in keyhole mode welding processes

A novel approach for the reconstruction of an equivalent volumetric heat source from a known weld pool shape is proposed. It is based on previously obtained weld pool geometries from a steady-state thermo-fluid dynamics simulation. Hereby, the weld pool dimensions are obtained under consideration of the most crucial physical phenomena, such as phase transformations, thermo-capillary convection, natural convection, and temperature-dependent material properties. The algorithm provides a time and calibration efficient way for the reproduction of the weld pool shape by local Lamé curves. By adjusting their parameters, the identification of the finite elements located within the weld pool is enabled. The heat input due to the equivalent heat source is assured by replacing the detected nodes' temperature by the melting temperature. The model offers variable parameters making it flexible and adaptable for a wide range of workpiece thicknesses and materials and allows for the investigation of transient thermal effects, e.g., the cooling stage of the workpiece. The calculation times remain acceptably short especially when compared to a fully coupled process simulation. The computational results are in good agreement with performed complete-penetration laser beam welding experiments.

Testing emplacement models for the Rustenburg Layered Suite of the Bushveld Complex with numerical heat flow models and plagioclase geospeedometry

Conventional models of the genesis of the Rustenburg Layered Suite (RLS) of the Bushveld Complex postulate that it is the product of a single multiply-replenished magma chamber that cooled as a single massive unit, i.e., a monolithic magma chamber. This concept has been challenged by alternative hypotheses involving out-of-sequence emplacement of some of its major layers as sills. Both scenarios have partial support from high-precision U-Pb geochronological data. To test these contradictory hypotheses, new zircon geothermometric data and compositional data for plagioclase from the Upper Critical Zone are presented and the available geochronological data are tested against the predictions of the thermal evolution of the entire RLS for both emplacement and cooling scenarios. Crystallization temperatures of zircon within units of the Upper Critical Zone were estimated using Ti-in-zircon thermometry and range between 799±45°C and 865±64°C. The data are used in conjunction with a detailed numerical model of heat flow in the Bushveld Complex that is used to approximate the duration and extent of thermal perturbations felt throughout the system and delimit the time intervals during which zircon crystals could have grown at the measured crystallization temperatures. The results show that prolonged cooling histories (>1 Myr), that would be experienced near the centre of a large, slowly cooled, plutonic magma chamber, would erase signs of plagioclase zoning at 4 kbar and moderate fH2O; however, plagioclase crystals with zoning profiles spanning at least 10 mole% An are common in the Upper Critical Zone. In contrast, emplacement of the major units of the RLS at widely separated intervals, as recorded by the existing high-precision U-Pb dataset, would impose transient thermal effects on the system against a backdrop of generally much lower ambient temperatures throughout its evolution. In this scenario, apparent ages of zircon crystals would record the time of cooling through temperatures near the water-saturated biotite granite solidus, corresponding to the final intercumulus mineral assemblage in both mafic and ultramafic macrolayers. Subsequent reheating of these rocks would be unable to reset primary zircon crystallization dates but might, in some examples, result in some amount of remelting or regrowth of zircon. Comparison of the evolving temperature fields of the two types of emplacement and cooling histories shows that the existing geochronological data and preservation of plagioclase zoning are consistent with out-of-sequence emplacement and rapid cooling of individual ultramafic sills into previously solidified lithologies of the RLS but not with the conventional view of a single monolithic magma body.

Development and validation of a full-time-scale semi-analytical model for the short- and long-term simulation of vertical geothermal bore fields

This paper presents the development and validation of a full-time-scale semi-analytical bore field simulation model. The model allows for the simulation of bore fields comprised of arbitrarily positioned boreholes while accounting for both short-term transient thermal effects within the boreholes and long-term thermal interactions in the bore field. The g-function of the bore field, obtained from the finite line source solution, is corrected to account for the cylindrical geometry of the boreholes and coupled to a thermal resistances and capacitances model of the borehole interior, thereby extending the scope of g-functions to short time scales. Additionally, an improved load aggregation scheme for ground thermal response calculations allows the model to be used with variable simulation time steps. The complete model is validated using a combination of analytical, experimental and field monitored data to verify both its short-term and long-term behaviour. The model is implemented using the Modelica language as part of an implementation in the open-source buildings simulation library IBPSA.

Theoretical and experimental study on the thermally dependent transient response of the high power continuous wave Yb-doped fiber laser.

In this paper, transient thermal effects of the Yb-doped fiber and the laser diode (LD) in high power Yb-doped fiber lasers (YDFLs) are studied theoretically to analyze the transient response of the fiber laser. Based on the transient heat conduction equation, we simulated the temperature variation of the YDF and LD. It is found that the transient response of the laser is mainly affected by the thermally induced wavelength shifting of LDs. We modified the rate equations of the fiber laser according to the temperature variation of the LD. To improve the transient response speed of the fiber laser, we present three methods: (a) raising the cooling temperature, (b) increasing the length of gain fiber, and (c) using the YDF with high doping. Finally, experiments were carried out to verify the theory, and the results are in good agreement.

Extraction of Boundary Condition Independent Dynamic Compact Thermal Models of LEDs—A Delphi4LED Methodology

Multi-domain electro-thermal-optical models of LEDs are required so that their thermal and optical behavior may be predicted during a luminaire design process. Today, no standardized approach exists for the extraction of such models. Therefore, models are not readily provided by LED suppliers to end-users. This results in designers of LED-based luminaires wasting time on LED characterization and ad hoc model extraction themselves. The Delphi4LED project aims to address these deficiencies by identifying standardizable methodologies to extract both electro-optical and thermal compact models of LEDs that together can be used in a multi-domain simulation context. This article describes a methodology to extract compact thermal models of LEDs that are dynamic, in that they accommodate transient thermal effects, and are boundary condition-independent, in that their accuracy is independent of their thermal operating environment. Such models are achieved by first proposing an equivalent thermal nodal network topology. The thermal resistances and capacitances of that network are identified by means of optimization so that the transient thermal response of the network matches that of either an equivalent calibrated 3D thermal model or a transient thermal measurement of a physical sample. The accuracy of the thermal network is then verified by comparing the thermal compact model with a 3D detailed model, which predicts thermal responses within a 3D system-level model.

Transient Thermal Effects in Sedimentary Basins with Normal Faults and Magmatic Sill Intrusions—A Sensitivity Study

Magmatic intrusions affect the basin temperature in their vicinity. Faulting and physical properties of the basin may influence the magnitudes of their thermal effects and the potential source rock maturation. We present results from a sensitivity study of the most important factors affecting the thermal history in structurally complex sedimentary basins with magmatic sill intrusions. These factors are related to faulting, physical properties, and restoration methods: (1) fault displacement, (2) time span of faulting and deposition, (3) fault angle, (4) thermal conductivity and specific heat capacity, (5) basal heat flow and (6) restoration method. All modeling is performed on the same constructed clastic sedimentary profile containing one normal listric fault with one faulting event. Sills are modeled to intrude into either side of the fault zone with a temperature of 1000 °C. The results show that transient thermal effects may last up to several million years after fault slip. Thermal differences up to 40 °C could occur for sills intruding at time of fault slip, to sills intruding 10 million years later. We have shown that omitting the transient thermal effects of structural development in basins with magmatic intrusions may lead to over- or underestimation of the thermal effects of magmatic intrusions and ultimately the estimated maturation.