Thermal Numerical Simulation Research Articles

Solar Thermal Energy Storage in Power Generation Using Phase Change Material with Heat Pipes and Fins to Enhance Heat Transfer

Phase change materials absorb or otherwise release heat at close to a constant temperature during its melting and solidification phases. This is a very sought after property in power generation, where a high temperature heat source is required within a narrow temperature range as heat input for the turbine. Solar tower technology provides a high temperature heat source, but unfortunately it is time dependent. A sufficient amount of this heat may be stored in a phase change storage system which can deliver dispatchable heat. In such a storage system the phase change material needs to be exposed to a sufficient heat transfer area to melt or solidify at sufficient rates. In this study this is achieved with heat pipes with metallic fins. The analysis of this design included testing an experimental module during heat absorption and heat removal cycles, as well as a numerical analysis to model the storage module. To determine the parameters for a specific phase change storage system in a high temperature solar tower application the validated numerical thermal response simulation is incorporated. Certain solar input conditions and load cases are applied to the phase change storage system model and the size and geometry of the solar thermal storage system are determined from this analysis.

Evaluation of pulsed laser annealing for flexible multilayer MoS2 transistors

To realize the proper electrical characteristics of field-effect transistors, the quality of the contact and interface must be improved because they can substantially distort the extracted mobility, especially for materials with low densities of states like molybdenum disulfide (MoS2). We show that mechanically flexible MoS2 thin-film transistors (TFTs) with selectively laser annealed source/drain electrodes achieve enhanced device performance without plastic deformation including higher field-effect mobility (from 19.59 to 45.91 cm2 V−1 s−1) in the linear regime, decreased subthreshold swing, and enhanced current saturation. Furthermore, numerical thermal simulations, measured current-voltage characteristics, and contact-free mobility extracted from the Y-function method suggest that the enhanced performance originated from a decrease in the Schottky barrier effect at the contact and an improvement of the channel interface. These results demonstrate that picosecond laser annealing can be a promising technology for building high performance flexible MoS2 TFTs in flexible/stretchable circuitry, which should be processed at low temperatures.

Simulation-based Assessment of the Thermal Performance of High-rise Office Buildings in Ghana

The lack of empirical data and practical advice on thermal performance and efficient use of energy in our buildings are gradually becoming a burden to the country. Amidst the recent development in the usage of curtain walls for office buildings, high utilization of energy and poor thermal comfort issues have become paramount. Given the warm-humid climatic characteristics of Ghana, energy requirements for cooling of office buildings represent a growing burden for the environment and the economy. The current paper explores the implications of alternative design options for the thermal performance of four high-rise office buildings in Accra, Ghana. Multiple design alternatives were considered involving various glazing types, shading and shading schedules, thermal insulation options, lighting, various ventilation options and thermal mass. A numeric thermal simulation application was used to model the performance of these alternatives parametrically. Simulation results were expressed in terms of annual cooling loads (active building operation scenario) and mean overheating (passive building operation scenario). Careful combination of improvement measures (such as efficient glazing, thermal mass, facade insulation, night ventilation, efficient electrical lighting, form and orientation) has a significant potential to reduce buildings' cooling loads Original Research Article Simons et al.; BJAST, 8(2): 165-179, 2015; Article no.BJAST.2015.195 166 (31% – 49%) in the climatic context of Accra. Over-heating tendencies were also reduced from 8.6K to 3.9K depending on the air-change-rate per hour (ACH).

Air change rates driven by the flow around and through a building storey with fully open or tilted windows: An experimental and numerical study

Abstract Air change rates (ACH) through open and tilted windows in rooms of residential buildings driven by atmospheric motions are investigated to evaluate natural ventilation concepts. Model experiments in wind tunnels, numerical flow simulations (CFD) and thermal building simulations are used. Pressure profiles are measured on the facade of a building model for selected wind directions and velocities. A separated sample storey and a sample single room in larger scales were used to measure air transport through window openings under the influence of the external pressure distribution. The ACH was obtained by velocity measurements in the window cross sections and by tracer gas measurements using the decay method. ACH from CFD computations of the wind tunnel environment agreed well with the experimental values. Therefore the numerical simulations were extended to real dimensions. The dependency of the ACH on the position in the external flow field and a scaling law for the ACH are presented. The wind-driven ACH obtained are much larger than the temperature-driven values prescribed in the Austrian standard O-NORM B 8110-3 on the prevention of high room temperatures during summer. A comparison of the impact of temperature-driven with wind-driven ACH, i.e. natural ventilation concepts, in thermal building simulations is presented.

Shrink connection modelling of the steam turbine rotor

The paper analyzes the causes of improper operation of the interference connection between two members of the 34MW turbine rotor. Diagnostic signals, especially in the form of vibrations arising at some operation stages of the machine, pointed to a possible malfunction of the interference connection. After dismantling, a visual inspection and material testing confirmed these predictions. Numerical thermal and strength simulations of the rotor operation showed a loss of the capacity to transfer load on part of the interference connection between the rotor components in some phases of the turbine start-up. The repair involved an increase in values of interference stress and an additional protection in the form of a circumferential weld between the linked parts of the rotor, which removed the problem and ensured a further safe and reliable operation of the turbine under analysis.

Probabilistic Forecasting and Model Validation for the First-Eocene Large-Scale Pilot Steamflood, Partitioned Zone, Saudi Arabia and Kuwait

Summary The First-Eocene heavy-oil reservoir (1E) in the Wafra field is a candidate for steamflooding because of its world-class resource base and low-estimated primary recovery. However, industry has little experience in steamflooding carbonate reservoirs, which has prompted the staging of several 1E steamflooding tests, the latest of which is the large-scale pilot (LSP) started in 2009. To assist in facilities design, to help understand expected performance in a very heterogeneous reservoir, and to provide input to early-decision analyses, numerical thermal simulation was used to generate probabilistic forecasts. When adequate pilot history was available, the model was validated with probabilistic methods. The LSP model contained 1.5 million cells, which allowed the maintenance of adequate resolution and proper boundary conditions in the pilot area. Parallel computation enabled a probabilistic workflow to be implemented with this large thermal model. In this paper, we highlight the methodologies and inputs used to generate the probabilistic forecasts and validate the model. Major results of this work include the following: In contrast to many greenfield forecasts, the LSP forecasts were conservative, likely because of the unique aspects of the forecasting methodology, proper selection of uncertainty ranges, and the relatively high density of input data for model construction; wide variations in production metrics were forecast, indicative of a highly heterogeneous reservoir; results indicated that the validated model adequately captured the global or statistical pilot heterogeneity, enabling proper capture of steamflood flow/drainage mechanisms; and despite this heterogeneity, forecast oil-recovery levels were comparable with those observed in steamfloods in sandstone reservoirs.

Forging penetration efficiency of steel H13 stepped shaft radial forging with GFM forging machine

The numerical thermal mechanical simulation of radial forging process of steel H13 stepped shaft with GFM (Gesellschaft fur Fertigungstechnik und Maschinenbau) forging machine was carried out by three-dimensional finite element code DEFORM 3D. According to the effective plastic strain, the mean stress and the mean plastic strain distribution of the radial forging, the forging penetration efficiency (FPE) was studied throughout each operation. The results show that the effective plastic strain in the center of the forging is always greater than zero for the desirable larger axial drawing velocity. The mean stress in the center of the workpiece is proposed to describe hydrostatic pressure in this paper. There is compressive strain layer beneath the surface of the workpiece to be found, while there is tensile strain core in the center of the workpiece. These results could be a valuable reference for designing the similar forging operations.

Three-dimensional Numerical Simulation of Thermal and Solutal Marangoni Convection in a Liquid Bridge under Zero-gravity Field

Three-dimensional Numerical Simulation of Thermal and Solutal Marangoni Convection in a Liquid Bridge under Zero-gravity Field

Coaxial Slot Antenna Design for Microwave Hyperthermia using Finite- Difference Time-Domain and Finite Element Method

Hyperthermia also called thermal therapy or thermotherapy is a type of cancer treatment in which body tissue is exposed to high temperatures. Research has shown that high temperatures can damage and kill cancer cells, usually with minimal injury to normal tissues. Otherwise, ablation or high temperature hyperthermia, including lasers and the use of radiofrequency, microwaves, and high-intensity focused ultrasound, are gaining attention as an alternative to standard sur- gical therapies. The electromagnetic microwave irradiation applied to the tumor tissue causes water molecules to vibrate and rotate, resulting in tissue heating and subsequently cell death via thermal-induced protein denaturation. The effective- ness of this technique is related to the temperature achieved during the therapy, as well as the length time of treatment and cell and tissue characteristics. Numerical electromagnetic and thermal simulations are used to optimize the antenna design and predict heating patterns. A computer modeling of a double slot antenna for interstitial hyperthermia was designed us- ing two different numerical methods, the Finite Element Method and a Finite-Difference Time-Domain. The aim of this work is to analyze both numerical methods and finally experiments results are compared to the simulated results generated by a thermal model. Our results show that normalized SAR patterns using FEM and FDTD look broadly similar. Further- more, the computed 60 °C isotherm using FEM and the measured lesion diameter in ex vivo tissue results agree very well.

Development and Validation of a Numerical Thermal Simulation Model for Compressed Hydrogen Gas Storage Tanks

Development and Validation of a Numerical Thermal Simulation Model for Compressed Hydrogen Gas Storage Tanks

The Forging Penetration Efficiency of C45 Steel Stepped Shaft Radial Forging with GFM Forging Machine

The numerical thermal mechanical simulation of radial forging process of C45 steel stepped shaft with GFM forging machine was carried out by three dimensional finite element method DEFORM 3D. According to effective plastic strain, mean stress and mean plastic strain distribution of the radial forging process, the forging penetration efficiency (FPE) was studied throughout. The results show that: effective plastic strain in the center of the forging is never be zero; The mean stress in the center of the workpiece is proposed to describe hydrostatic pressure in this paper. There is compressive strain layer beneath the surface of the workpiece, while there is tensile strain layer in the center of the forging. These studied results could be a valuable reference for designing the similar forging operations.

Investigation of smart power DMOS devices under repetitive stress conditions using transient thermal mapping and numerical simulation

Temperature distribution in diced and packaged DMOS devices subjected to repetitive stress is analyzed using transient interferometric mapping (TIM) technique combined with measurements on diode built-in temperature sensors. The effect of DMOS device position on dice, duty cycle and chip ambient temperature on thermal distribution is studied. The TIM experiments and transient temperature measurements are in good agreement with numerical 3D thermal simulations. Failure analysis data after long term pulse stress testing indicate electromigration degradation of the top metal.

Numerical Simulation of Thermal and Flow Fields in Induction Skull Melting Process

The electromagnetic, thermal and fluid fields during ISM (Induction Skull Melting)of TiAl alloy are simulated. The effects of ampere-turn, frequency and relative position between crucible and coil on the distribution of thermal and flow fields are numerically studied. The simulation model is verified by experiments and the simulation results are discussed in detail.

USING SIMULATION TO EVALUATE AND IMPROVE THE THERMAL PERFORMANCE OF COURTYARD OFFICE BUILDINGS IN CAIRO

This paper explores the implications of alternative design options for the thermal performance of office buildings in Cairo, Egypt. Typical courtyard office floor plan was selected for the investigation. Multiple design alternatives were considered involving various glazing and shading types, shading schedules, thermal insulation options, orientations, and ventilation scenarios. A numeric thermal simulation application was used to model the performance of these alternatives parametrically*1. The results show the significant degree to which design measures could reduce cooling requirements of (and overheating tendencies in) courtyard office buildings in Cairo.

Numerical thermal simulation of graphite electrode in EAF during normal operation

Working temperature has a crucial effect on the consumption of graphite electrodes in electric arc furnaces (EAFs). In this work, temperature distribution within the EAF electrodes during normal operation was simulated using the finite element method in both 2D and 3D scales. The contributions of electrical current passing the electrode, thermal effects of the furnace sidewall refractory, slag layer, a titanium based coating as a protective layer, and the process parameters such as water spraying at the end of the electrodes were investigated. The proximity effect of the graphite electrodes in EAF was analysed using a 3D thermal model. The numerical model was validated against experimental measurements of temperature distribution over the electrode surface as well as the published results in literature. The results showed a relatively deep temperature gradient at the electrode tip. Among the environmental and processing parameters affecting the temperature distribution of the electrode, the heat transfer coefficient in the water cooling zone was found to be more important for predicting the accurate thermal field of the electrode. The value 8500 W m−2 K−1 was proposed for the investigated electrode based on the validated 3D numerical results. The results also indicated the importance of the proximity effect on temperature distribution not being ignored.

Dynamic thermal modelling of a power integrated circuit with the application of structure functions

This paper presents dynamic thermal analyses of a power integrated circuit with a cooling assembly. The investigations are based on the examination of the cumulative and differential structure functions obtained from the circuit cooling curves recorded during transient circuit temperature measurements. The experiments carried out and the comprehensive study of the computed structure functions rendered possible determination of the interface contact resistance and the heat transfer coefficient values necessary for numerical thermal simulations illustrating the influence of these thermal model parameters on circuit temperature.

Dynamic Heating in Micron- and Submicron-Patterned TbFe Films

The dynamic heating of micron- and submicron-patterned TbFe films using current pulses for the thermally assisted writing scheme has been investigated. The evolution of the required power/energy density with pulse width has been studied using experimental measurements and numerical thermal simulations. Two heating regimes (adiabatic and diffusive regimes) are revealed by simulation in the investigated range of the current pulse widths (0.01 ns–1 µs). The energy density required for writing is almost independent of the pulse width and element size, and about 13 pJ/µm2 at the very short pulse width associated with the adiabatic regime. Two distinct zones are also observed in the diffusion regime, and the dependence of the heating power density on the pulse width variation (Δt) shows a 1-exp (-Δt/t1) phenomenological variation in each zone. The power/energy densities required for the writing of four patterned TbFe films with different sizes are measured in the range of the pulse width from 10 up to 1000 ns, and the experimental results are well explained by the simulation. The required power density for the writing of 0.74 µm2 patterned films using the pulse duration of 10 ns is experimentally estimated to be around P = 2 mW/µm2, which corresponds to the energy density of E = 20 pJ/µm2.

有明海の干潟における底泥の熱環境特性とモデル化に関する研究

It is difficult to clarify the environmental condition in tidal flat because of the complicated interaction of atmosphere, sea water, land and creature. The thermal environment is an important factor in water quality closed relationship phytoplankton growth and activated biological. The objective of this study is the characteristic grasp of thermal and the attempted to calculate the numerical thermal model simulation in the bottom mud at tidal flat. The thermal water or bottom was observed at three sites that were different in the ground level and the meteorological variables was observed using an weather station deployed in the inter-tidal zone near Kumamoto Port As a result, the thermal water and air temperature influenced not only just bottom surface but also the interior bottom at tidal flat and the use of seepage flow in the numerical thermal model improved the accuracy of the model.

Field Study on Characteristic of Thermal in Bottom Mud at Tidal Flat

It is difficult to clarify the environmental condition in tidal flat because of the complicated interaction of atmosphere, sea water, land and creature. The thermal environment is an important factor in water quality closed relationship phytoplankton growth and activated biological. The objective of this study is to grasp the characteristic thermal from field observation and calculate the numerical thermal model simulation in the bottom mud at tidal flat. The thermal water or bottom was observed at four sites that were different in the ground level and the meteorological variables in the inter-tidal zone near Kumamoto Port. As a result, the thermal in bottom was depended on tide change and the numerical thermal model improved the accuracy with a scheme thermal diffusion.

The Origin, Prediction and Impact of Oil Viscosity Heterogeneity on the Production Characteristics of Tar Sand and Heavy Oil Reservoirs

Abstract A defining characteristic of heavy and super heavy oilfields is the large spatial variation in fluid properties, such as oil viscosity, commonly seen within the reservoirs. Traditional heavy oil and tar sand exploration and production strategies rely significantly on the characterization of key reservoir heterogeneities and assessment of fluid saturations. While it is important to understand how these properties vary, the spatial distribution of fluid properties can often dominate production behaviour but surprisingly, are usually ignored! Heavy oil and tar sands are formed by microbial degradation of conventional crude oils over geological timescales. Constraints such as oil charge mixing, reservoir-temperature dependant biodegradation rate and supply of water and nutrients to the organismsultimately dictate the final distribution of API gravity and viscosity found in heavy oil fields. Large-scale lateral and smallscale vertical variations in fluid properties due to interaction of biodegradation and charge mixing are common, with up to orders of magnitude variation in viscosity over the thickness of a reservoir. These variations are often predictable and can be integrated into reservoir simulation models in a manner similar to specifying geological heterogeneity. In this work, we describe and illustrate quantitative geological controls on fluid property variations and show how petroleum geochemistry can be used to rapidly produce high resolution fluid property images of tar sand and heavy oil reservoirs. The impact of viscosity variations in a heavy oil reservoir on production depends on recovery method. Numerical thermal reservoir simulations reveal that oil viscosity heterogeneity (i.e. a vertical viscosity profile in the reservoir) lowers the oil production volumes from steam assisted gravity drainage (SAGD) in geologically realistic reservoirs compared to results from equivalent models run with uniform average viscosity profiles. Similar results are found for the cyclic steam stimulation (CSS) process. In cases with viscosity profiles, the relatively high viscosity at the base of the reservoir slows the growth of the steam chambers relative to that in uniform viscosity reservoirs. We also describe how the chemical fluid heterogeneities can be used to predict oil viscosity from well cuttings and/or core or to de-mix produced oils into zonal contributions from different parts of the production well. Introduction There are over six trillion barrels of heavy oil and tar reserves on Earth, but average recoveries remain tantalizingly low (5 to 15% for cold heavy oil production and 40 to 85% for steam assisted gravity drainage operations)(1). We consider that a defining characteristic of heavy and super heavy oilfields is the large spatial variation in fluid properties, such as oil viscosity, commonly seen within the reservoirs. Traditional heavy oil and tar sand exploration and production strategies rely significantly on characterization of key reservoir heterogeneities and distributions of porosity and permeability and assessments of fluid saturations. While these reservoir characteristics are important controlling factors, variations in fluid properties can often dominate production behaviour, but are usually ignored. According to Darcy's law, reservoir permeability and fluid viscosity contribute equally to controlling the net flowrate of oil during production under a given fluid potential gradient.