Thermal-fluid Simulation Research Articles

FSW Numerical Simulation of Aluminium Plates by Sysweld - Part I

Abstract Friction Stir Welding (FSW) is one of the most effective solid state joining processes and it has numerous potential applications in many industries. The simulation process can provide the evolution of physical quantities such as temperature, metallurgical phase proportions, stress and strain which can be easily measured during welding. The numerical modelling requires the modelling of a complex interaction between thermal, metallurgical and mechanical phenomena. The aim of this paper is to describe the thermal-fluid simulation of FSW using the finite element method. In the theoretical part of the paper heating is provided by the material flow and contact condition between the tool and the welded material. The thermal-fluid results from the numerical simulation for aluminium alloy using SYSWELD are also presented in this paper.

Full through Process Simulation for Low Pressure Die Casting – From Casting to Design

To achieve a required product quality during Low Pressure Die Casting (LPDC) process, it is necessary to identify and also control the main input parameters affecting the casting defects to arrive at the desired output quality. In industrial scale LPDC, where the issues of part quality, cost, and cast speed are the main driving forces for the industries, the cast process optimization to have minimum defects is quite essential. The LPDC process of light weight metals is defined as a casting process where the die is filled relatively slowly at low pressure. The melt flow regime has low turbulence, and filling process can be defined as relatively smooth filling. In recent years, in order to limit the component defects, the through process simulation has widely been used. In an interactive simulation environment, a full multi-phase casting process simulation (thermal-fluid simulation using multi-physical domain) along with its material and mechanical simulations are carried out in a single environment. One of the main contributions of this paper is to show the advantages of using full through process simulation of LPDC to limit the defect in the component. An experimental program along with a comprehensive process simulation has been setup to optimize the casting process and the results were presented for real world case studies.

Cooling Systems Design in Hot Stamping Tools by a Thermal-Fluid-Mechanical Coupled Approach

Hot stamping tools with cooling systems are the key facilities for hot stamping process of Ultrahigh strength steels (UHSS) in automotive industry. Hot stamping tools have significant influence on the final microstructure and properties of the hot stamped parts. In serials production, the tools should be rapidly cooled by cooling water. Hence, design of hot stamping tools with cooling systems is important not only for workpieces of good quality but also for the tools with good cooling performance and long life. In this paper, a new multifield simulation method was proposed for the design of hot stamping tools with cooling system. The deformation of the tools was also analyzed by this method. Based on MpCCI (Mesh-based parallel Code Coupling Interface), thermal-fluid simulation and thermal-fluid-mechanical coupled simulation were performed. Subsequently, the geometrical parameters of the cooling system are investigated for the design. The results show that, both the distance between the ducts and the distance between the ducts and the tools loaded contour have significant influence on the quenching effect. And better quenching effect can be achieved with the shorter distance from the tool surface and with smaller distance between ducts. It is also shown that, thermal expansion is the main reason for deformation of the hot forming tools, which causes the distortion of the cooling ducts, and the stress concentration at corner of the ducts.

Separate effects tests to determine the thermal dispersion in structured pebble beds in the PBMR HPTU test facility

Thermal-fluid simulations are used extensively to predict the maximum fuel temperatures, flows, pressure drops and thermal capacitance of pebble bed gas cooled reactors in support of the reactor safety case. The PBMR company developed the HTTF test facility in cooperation with M-Tech Industrial (Pty) Ltd. and the North-West University in South Africa to conduct comprehensive separate effects tests as well as integrated effects tests to study the different thermal-fluid phenomena. This paper describes the separate effects tests that were conducted to determine the effect of the porous structure on the fluid effective thermal conductivity due to the thermal dispersion. It also presents the methodology applied in the data analysis to derive the resultant values of the effective thermal conductivity and its associated uncertainty.

Separate effects tests to determine the effective thermal conductivity in the PBMR HTTU test facility

Thermal-fluid simulations are used extensively to predict the maximum fuel temperatures, flows, pressure drops and thermal capacitance of pebble bed gas cooled reactors in support of the reactor safety case. The PBMR company developed the HTTU non-nuclear test facility in cooperation with M-Tech Industrial (Pty) Ltd. and the North-West University in South Africa to conduct comprehensive separate effects tests as well as integrated effects tests to study the different thermal-fluid phenomena. This paper describes the separate effects tests that were conducted to determine the effective thermal conductivity through the pebble bed under near-vacuum conditions and temperatures up to 1200°C. It also presents the measured temperature distributions and the methodology applied in the data analysis to derive the resultant values of effective thermal conductivity and its associated uncertainty.

Transient simulation of coolant peak temperature due to prolonged fan and/or water pump operation after the vehicle is keyed-off

Automotive designers should design a robust engine cooling system which works well in both normal and severe driving conditions. When vehicles are keyed-off suddenly after some distance of hill-climbing driving, the coolant temperature tends to increase drastically. This is because heat soak in the engine could not be transferred away in a timely manner, as both the water pump and cooling fan stop working after the vehicle is keyed-off. In this research, we aimed to visualize the coolant temperature trend over time before and after the vehicles were keyed-off. In order to prevent coolant temperature from exceeding its boiling point and jeopardizing engine life, a numerical model was further tested with prolonged fan and/or water pump operation after keying-off. One dimensional thermal-fluid simulation was exploited to model the vehicle’s cooling system. The behaviour of engine heat, air flow, and coolant flow over time were varied to observe the corresponding transient coolant temperatures. The robustness of this model was proven by validation with industry field test data. The numerical results provided sensible insights into the proposed solution. In short, prolonging fan operation for 500 s and prolonging both fan and water pump operation for 300 s could reduce coolant peak temperature efficiently. The physical implementation plan and benefits yielded from implementation of the electrical fan and electrical water pump are discussed.

State space model extraction of thermohydraulic systems – Part I: A linear graph approach

Thermohydraulic simulation codes are increasingly making use of graphical design interfaces. The user can quickly and easily design a thermohydraulic system by placing symbols on the screen resembling system components. These components can then be connected to form a system representation. Such system models may then be used to obtain detailed simulations of the physical system. Usually this kind of simulation models are too complex and not ideal for control system design. Therefore, a need exists for automated techniques to extract lumped parameter models useful for control system design. The goal of this first paper, in a two part series, is to propose a method that utilises a graphical representation of a thermohydraulic system, and a lumped parameter modelling approach, to extract state space models. In this methodology each physical domain of the thermohydraulic system is represented by a linear graph. These linear graphs capture the interaction between all components within and across energy domains – hydraulic, thermal and mechanical. These linear graphs are analysed using a graph-theoretic approach to derive reduced order state space models. These models capture the dominant dynamics of the thermohydraulic system and are ideal for control system design purposes. The proposed state space model extraction method is demonstrated by considering a U-tube system. A non-linear state space model is extracted representing both the hydraulic and thermal domain dynamics of the system. The simulated state space model is compared with a Flownex® model of the U-tube. Flownex® is a validated systems thermal-fluid simulation software package.

A new technology of 3D scaled physical simulation for high-pressure and high-temperature steam injection recovery

Abstract In order to solve the problems of existing physical simulation experiment device for thermal recovery, such as great heat loss, low precision in internal pressure control of physical model and insufficient process monitoring, a new experiment device for high-pressure and high-temperature (HPHT) 3D scaled physical simulation is developed independently, and the relevant experiment technical route is presented. By using thermal fluid simulation, PID auto-control and 3D graphics, the following problems are solved: (1) the heat loss scaled simulation technology is applied for HPHT thermal recovery model, to control the heat dissipating capacity of the model top and bottom and realize the continuous growth of the steam chamber; (2) HPHT 3D formation temperature/pressure simulation technology is applied to keep the model pressure and temperature stable, ensuring temperature difference at each point in high-pressure chamber less than ± 2 °C; (3) 3D data field on-line monitoring and visual analysis technology is applied to monitor and control the reservoir performance at real time. By using this experiment device, 3D scaled physical simulation experiment is performed for commingled thermal recovery of extremely heavy oil by horizontal/vertical wells as well as SAGD of super heavy oil by dual horizontal wells. The evolution of steam chamber is depicted and the knowledge on SAGD mechanism by dual horizontal wells and the production performance is deeply studied.

Concept, Manufacture and Results of the Microtubular Solid Oxide Fuel Cell

This paper summarized concept, manufacture and results of the micro-tubular solid oxide fuel cells (SOFCs). The cells were fabricated by co-sintering of extruded micro-tubular anode support and electrolyte coating layer, and then additional cathode coating. The cells showed quick voltage rising within 1 minute, and the electrochemical performances were closely related to the balance of fuel utilization and performance loss. And a thermal-fluid simulation model was also reported in combination with the electrochemical evaluation results on the GDC-based micro-tubular SOFCs.

Validation of a transient thermal-fluid systems CFD model for a packed bed high temperature gas-cooled nuclear reactor

This paper provides an overview of the theoretical basis for a new thermal-fluid systems CFD simulation model for high temperature gas-cooled reactors, contained in the Flownex software code. Flownex provides for detailed steady-state and transient thermal-fluid simulations of the complete power plant, fully integrated with core neutronics and controller algorithms. The reactor model is founded on a fundamental approach for the conservation of mass, momentum and energy for the compressible fluid flowing through a fixed bed, as well as the heat transfer in the pebbles and core structures. The time-wise integration of the resulting differential equations is based on an implicit pressure correction algorithm. This allows for the use of rather large time steps making it very suitable for simulating the slow transients that can be expected to follow incidents like reactor shutdowns. The paper also compares the Flownex results for four transient tests with the measured results from the SANA test facility as well as to the results of simulations with the Thermix/DIREKT code that were done at the Research Centre, Jülich. The Flownex results compare well with the Thermix/DIREKT results for all the cases presented here. Good comparison was also obtained between the simulated and measured results, except at two points within the pebble bed near the inner wall. The fact that quick computer simulation times were obtained indicates that the new model indeed achieves a fine balance between accuracy and simplicity. However, the discrepancies obtained at the two points near the inner wall, together with the fact that additional uncertainty was introduced in the original SANA test set-up by not being able to control the temperature of the outer wall, highlight the need for additional systematic tests to be performed in order to better validate the new model.

Verification and validation of the HTGR systems CFD code Flownex

Regulatory requirements prescribe extensive verification and validation (V&V) of computer codes that are used in the design and analysis of accident conditions in nuclear plants. Flownex is a dynamic systems CFD code used as the primary thermal-fluid simulation code by the Pebble Bed Modular Reactor Company (PBMR). Stringent quality assurance processes have been implemented to ensure that the code conforms to the set standards. These processes include the comparison of Flownex with analytical results as well as with experimental data. The results of this process are summarized in this paper. Analytical solutions are used to verify Flownex's element models so as to ensure that the basic theory is correctly implemented in the computer code. As part of the analytical V&V effort various well-defined problems are solved using numerical methods implemented in independent computer codes. Comparison with experimental and plant data is a very important feature of the V&V program to validate that the chosen theory is fit for purpose. For this, validation data from the pebble bed micro model (PBMM) is used. In addition to the PBMM experimental data Flownex is compared to a number of small thermal-fluid experiments in which certain specific component phenomena is validated. These experiments were developed in collaboration with North-West University (previously Potchefstroom University).

Evaluation of the Light Output Properties of White Massed-LEDs Light Sources and the Verification of Their Heat Radiation Effects by Thermal Fluid Analysis

We investigated light output properties of white massed-LEDs light sources and their characteristics of temperature rise effects. In the white massed-LEDs light sources with heat radiation countermeasures, we found that the decrease of light output under the high forward current condition was alleviated. The thermal fluid simulation analysis of heat radiation effects of white massed-LEDs light sources indicated that the attaching heat sink to light source board material was effective in not only aluminum board but also glass-epoxy board. And it was confirmed that the LED element temperatures were held less than 60°C in the rated lighting condition for both of them.

白色LED集積光源の光出力特性評価と熱流体シミュレーション解析による放熱効果の検証

白色LED集積光源の光出力特性評価と熱流体シミュレーション解析による放熱効果の検証

An Integrated Design Evaluation System Supporting Thermal-Structural Iterations

In the design of high temperature components, design evaluation often requires an iterative procedure between thermal fluid and thermal structural simulations An integrated computer system providing an iterative environment for the multidisciplinary simulations re quired has been developed. The system supports iterations between thermal fluid and thermal structural simulations using two different commercial simulation packages. Traditionally, fluid and structural analysis have been simulated separately and analysis of coupled prob lems has required special, multidisciplinary simulation packages which are seldom used in early stages of design. Improving the infrastruc ture for data exchange between separate computer applications is one way to significantly reduce the lead time for design iterations. This reduction in lead-time allows multidisciplinary effects to be accounted for in early stages of design. The design system is demonstrated on an exhaust manifold, where the thermal interaction between fluid and structure is of significant importance. The commercial simulation tools have been integrated to demonstrate the effect of automised data flow on design methodology, i.e , de sign iterations. This integration method makes use of existing features in the simulation packages and uses an export file format as the neu tral exchange format. In this way, the integrated system is simple and fast to develop which is preferred in small prototype systems and de velopment project Database integration supports a tighter integration, but requires more development effort. For design systems, where several design tools need to communicate, standardised information management procedures are preferable, following the ideas of the STEP framework.

Kinetic Modeling of the Gas Phase Decomposition of Germane by Computational Chemistry Techniques

Very limited experimental data are available on thermal decomposition of germane in the gas phase. Recent developments in theoretical quantum chemistry techniques such as ab initio Hartree-Fock and density functional methods have made accurate determination of molecular properties possible. Systematic development of a detailed gas-phase decomposition mechanism for germane using ab initio molecular orbital calculations is described in this work. A decomposition pathway for germane and higher germanes is proposed and the relevant reaction rates are calculated using transition state theory combined with unimolecular and chemical activation treatments. The decomposition model is implemented into a realistic thermal-fluid simulation.

Vacuum conditions and their attainment in the laboratory: J H Makkink,Rep ESRO-TM-48, Nov 1966 ( European Space Technology Center, Noordwijk, Netherlands).

Thermal-fluid simulations are used extensively to predict the maximum fuel temperatures, flows, pressure drops and thermal capacitance of pebble bed gas cooled reactors in support of the reactor safety case. The PBMR company developed the HTTU non-nuclear test facility in cooperation with M-Tech Industrial (Pty) Ltd. and the North-West University in South Africa to conduct comprehensive separate effects tests as well as integrated effects tests to study the different thermal-fluid phenomena. This paper describes the separate effects tests that were conducted to determine the effective thermal conductivity through the pebble bed under near-vacuum conditions and temperatures up to 1200 °C. It also presents the measured temperature distributions and the methodology applied in the data analysis to derive the resultant values of effective thermal conductivity and its associated uncertainty.