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Numerical simulation of high temperature sodium heat pipe for passive heat removal in nuclear reactors

NUCLEAR ENGINEERING AND DESIGN 2017年 323卷 376-385页

作者： Panda, K. K. Dulera, I. V. Basak, A. Bhabha Atom Res Ctr Reactor Engn Div Engn Hall 7 Mumbai 400085 Maharashtra India

High temperature heat pipes offer an efficient way of heat removal in nuclear reactors under both normal operation and postulated accidental scenarios. Heat pipes with sodium as a working fluid has been proposed to be used in Compact High Temperature Reactor (CHTR), U-233-Thorium fuelled reactor being designed to operate at 1000 degrees C. High temperature heat pipes can also be used for decay heat removal from dump tanks of molten salt breeder reactor and heat removal from first wall of fusion reactors. High temperature heat pipes of special construction can also be used for heat removal from core without use of coolant. Thus, reliable and long term operation of heat pipes is essential for the safe working of the reactor. In this respect, computer codes have been developed for design and simulation of high temperature heat pipes. To assist in the design stages, codes have been developed, which incorporate performance limits based on correlations and having a user friendly GUI. For system level studies, simplified heat transfer model is developed using a FEM model. For a detailed study of the heat pipe, the vapour flow behavior and interface evaporation condensation phenomena using a full CFD analysis is essential. This has been done by using a commercial CFD code by incorporating user defined functions (UDFs) which address the saturated nature of the vapour phase and the vapour wick interface conditions. A three dimensional transient numerical model has been developed to predict the vapour core, wall temperatures, vapour pressure, and vapour velocity in the screen mesh wick of sodium heat pipe. The results have been compared using a sodium heat pipe developed in-house. This paper will give an outline of all the developed models and compared the predicted results against the experimental data. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Sodium heat pipe Vapour-liquid interface CFD Compact High Temperature Reactor user defined functions

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Novel mediator architectures for Grid information systems

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FUTURE GENERATION COMPUTER SYSTEMS-THE INTERNATIONAL JOURNAL OF ESCIENCE 2005年第1期21卷 107-114页

作者： Wöhrer, A Brezany, P Tjoa, AM Univ Vienna Inst Software Sci A-1090 Vienna Austria Vienna Univ Technol Inst Software Technol & Multimedia Syst A-1040 Vienna Austria

Virtualization is one of the key features of the Grid. As data-intensive applications gain on importance, it becomes crucial for the success of the Grid to provide transparent access to distributed/heterogeneous data sources as well. In this paper, we describe our concepts to provide a Virtual Data Source (VDS) - a logically single homogeneous data source - on the Grid. Various data sources like relational/XML databases and comma separated value files can be combined via a Mapping Schema. By allowing to invoke user defined functions during the mediation a flexible way of resolving heterogeneities is provided. To show the feasibility of the developed concepts and elaborate the basis for a dynamic version they have been seamlessly integrated into OGSA-DAI to provide a non-proprietary, centralized and easy to integrate solution. (C) 2004 Elsevier B.V. All rights reserved.

关键词： data integration Grid computing user defined functions mapping schema

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Numerical analysis of a near-room-temperature magnetic cooling system

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INTERNATIONAL JOURNAL OF REFRIGERATION-REVUE INTERNATIONALE DU FROID 2017年 75卷 262-275页

作者： Ezan, Mehmet Akif Ekren, Orhan Metin, Cagri Yilanci, Ahmet Biyik, Emrah Kara, Salih Murat Dokuz Eylul Univ Dept Mech Engn Izmir Turkey Ege Univ Solar Energy Inst TR-35100 Izmir Turkey Yasar Univ Dept Energy Syst Engn Izmir Turkey Izmir Inst Technol Dept Elect & Elect Engn Izmir Turkey

In this study, for a near-room-temperature magnetic cooling system, a decoupled multiphysics numerical approach (Magnetism, Fluid Flow, and Heat Transfer) is developed using a commercial CFD solver, ANSYS-FLUENT, as a design tool. user defined functions are incorporated into the software in order to take into account the magnetocaloric effect. Magnetic flux density is assumed to be linear during the magnetization and demagnetization processes. Furthermore, the minimum and maximum magnetic flux densities (B-min and B-max) are defined as 0.27 and 0.98, respectively. Two different sets of analyses are conducted by assuming an insulated cold heat exchanger (CHEX) and by defining an artificial cooling load in the CHEX. As a validation case, experimental work from the literature is reproduced numerically, and the results show that the current methodology is fairly accurate. Moreover, parametric analyses are conducted to investigate the effect of the velocity of heat transfer fluid (HTF) and types of HTF on the performance of the magnetic cooling system. Also, the performance metrics of the magnetic cooling system are investigated with regards to the temperature span of the magnetic cooling unit, and the cooling load. It is concluded that reducing the cycle duration ensures reaching lower temperature values. Similarly, reducing the velocity of the HTF allows reducing the outlet temperature of the HTF. In the current system, the highest temperature spans are obtained numerically as around 6 K, 5.2 K and 4.1 K for the cycle durations of 4.2 s, 6.2 s and 8.2 s, respectively. (C) 2016 Elsevier Ltd and IIR. All rights reserved.

关键词： Magnetic cooling Computational fluid dynamics ANSYS-FLUENT user defined functions

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Energy storage efficiency analyses of CO₂ reforming of methane in metal foam solar thermochemical reactor

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APPLIED THERMAL ENGINEERING 2017年 111卷 1091-1100页

作者： Wang Fuqiang Cheng Ziming Tan Jianyu Zhang Jiaqi Leng Yu Liu Linhua Harbin Inst Technol Weihai Sch Automobile Engn 2 West Wenhua Rd Weihai 264209 Peoples R China Harbin Inst Technol Dept Phys 92 West Dazhi St Harbin 150001 Peoples R China Univ Tulsa Dept Mech Engn 800 South Tucker Rd Tulsa OK 74104 USA

Solar driven CO2 reforming of methane can store extra 20% concentrated solar energy to chemically bonded energy. With the aim to evaluate key operational parameters on energy storage efficiency, a finite volume method (FVM) coupled with thermochemical kinetics was developed to analyze the solar driven CO2 methane reforming performance in a metallic foam thermochemical reactor. The LH kinetic model of CO2 reforming of methane was compiled by user defined functions (UDFs) to exactly predict the temperature distribution and mole fractions of gas species. The numerical results were validated with experimental results which were tested in Niigata University to guarantee the accuracy of the developed model. Effects of gas mixture inlet velocity, porosity of metal foam reactor, CH4/CO2 ratio and heat flux distribution on energy storage efficiency were analyzed for providing theoretical guideline to the application of solar driven CO2 methane reforming. The numerical results indicated that maximum energy storage efficiency of CO2 reforming of methane was found when the CH4/CO2 ratio is 0.67. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Solar energy Thermochemical reaction Methane reforming Energy storage efficiency user defined functions Methane reforming

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Improved numerical approaches to predict hydrodynamics in a pilot-scale bubbling fluidized bed biomass reactor: A numerical study with experimental validation

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ENERGY CONVERSION AND MANAGEMENT 2018年 156卷 53-67页

作者： Cardoso, J. Silva, V. Eusebio, D. Brito, P. Tarelho, L. Polytech Inst Portalegre Interdisciplinary Ctr Res & Innovat C3i Portalegre Portugal Univ Aveiro Dept Environm & Planning Ctr Environm & Marine Studies Aveiro Portugal

A computational 2-D Eulerian-Eulerian approach was developed to simulate the hydrodynamics and heat transfer of a biomass gasification process in a pilot-scale bubbling fluidized bed reactor. The mathematical model was validated under experimental results collected from fluidization curves gathered at different temperatures in a pilot-scale reactor (75 kWth). Own user defined functions (UDFs) were developed in C programming and included to improve drag and heat transfer phenomena, as well to minimize deviations between experimental and numerical data found in previous works. Mesh selection was achieved by comparing solid fraction and pressure drop contours with grids comprised of different number of cells. A comparative study for particle diameter and inlet gas velocity was conducted for three different biomass feedstocks' and their impact in the mixing and segregation index was studied. Mixing and segregation index were measured by implementing the standard deviation concept. Results indicated that UDFs significantly improved the mathematical model predictions on the reactor's fluidization curves. Biomass and sand particles size and density showed direct influence on the solids distribution along the bed height. Smaller biomass particles revealed faster heat conduction and improved mixing properties.

关键词： Hydrodynamics Heat transfer Mixing and segregation index Pilot-scale bubbling fluidized bed gasifier user defined functions Biomass gasification

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Numerical simulation of a thermal energy storage system using sunrise and sunset transient temperature models

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RENEWABLE ENERGY 2024年 227卷

作者： Ikeleji, Raymond O. Bello-Ochende, Tunde Univ Cape Town Dept Mech Engn Private Bag X3 ZA-7701 Rondebosch South Africa

The temperature of the sun was modeled in this study using two transient solar temperature equations for sunrise and sunset that were developed for designing a latent heat thermal energy storage (LHTES) system for a concentrated solar power (CSP) plant. The derivation of the equations was based on the existing solar hour angle and the fundamental periodic function equations. Ansys' computational fluid dynamics code was used to investigate numerically the transient response of the conjugate melting and solidification of a phase change material (PCM) in a cylindrical shell and helical heat pipe (HHP) thermal system. The models for both equations were applied as user-defined functions (UDFs). The heat transfer medium was air. The predicted liquid and solid fractions provide quantitative data on the temperature and the stored solar energy. The effectiveness of both models in enhancing heat transfer and their suitability as real-time transient solar temperature models in heat transfer engineering is demonstrated by comparisons between their outputs. With high agreement, experimental data from the open literature was used to validate the numerical model's predictions. The solar temperature models aim to contribute to heat transfer enhancement for a reduced PCM energy storage time in designing a high-temperature solar thermal storage that is adequate to maintain a steady supply of electricity and energy for domestic and commercial applications and to accelerate the global transition to low-carbon energy.

关键词： Concentrated solar power Computational fluid dynamics user defined functions Phase change material Helical heat pipe Latent heat thermal energy storage Sunrise and sunset temperature equations

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Numerical analysis of hydrogen production via methane steam reforming in porous media solar thermochemical reactor using concentrated solar irradiation as heat source

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ENERGY CONVERSION AND MANAGEMENT 2014年 87卷 956-964页

作者： Wang, Fuqiang Tan, Jianyu Shuai, Yong Gong, Liang Tan, Heping Harbin Inst Technol Weihai Sch Automobile Engn Weihai 264209 Peoples R China Harbin Inst Technol Sch Energy Sci & Engn Harbin 150001 Peoples R China China Univ Petr Huadong Coll Pipeline & Civil Engn Qingdao 266580 Peoples R China

The calorific value of syngas can be greatly upgraded during the methane steam reforming process by using concentrated solar energy as heat source. In this study, the Monte Carlo Ray Tracing (MCRT) and Finite Volume Method (FVM) coupling method is developed to investigate the hydrogen production performance via methane steam reforming in porous media solar thermochemical reactor which includes the mass, momentum, energy and irradiative transfer equations as well as chemical reaction kinetics. The local thermal non-equilibrium (LTNE) model is used to provide more temperature information. The modified P1 approximation is adopted for solving the irradiative heat transfer equation. The MCRT method is used to calculate the sunlight concentration and transmission problems. The fluid phase energy equation and transport equations are solved by Fluent software. The solid phase energy equation, irradiative transfer equation and chemical reaction kinetics are programmed by user defined functions (UDFs). The numerical results indicate that concentrated solar irradiation on the fluid entrance surface of solar chemical reactor is highly uneven, and temperature distribution has significant influence on hydrogen production. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Hydrogen production Methane steam reforming Solar thermochemical reactor Porous medium user defined functions Monte Carlo

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Next-generation heartbeat classification with a column-store DBMS and UDFs

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JOURNAL OF INTELLIGENT INFORMATION SYSTEMS 2020年第2期54卷 363-390页

作者： Castro-Lopez, Oscar Lopez-Barron, Daniel E. Vega-Lopez, Ines F. Univ Autonoma Sinaloa Fac Informat Culiacan Sinaloa Mexico Univ Missouri Comp Sci & Elect Engn Kansas City MO 64110 USA Univ Autonoma Sinaloa Parque Innovac Tecnol Culiacan Sinaloa Mexico

We live in a digital world where data is being generated at an always increasing rate. This creates the need to develop new technology not only for storing these vast amounts of data, but also for manipulating and analyzing it. It is through this data analysis that we can make decisions and generate knowledge. The medical field is no exception and healthcare and biomedical data must be stored and analyzed to gain insights that help in disease prevention and diagnostics. An example of this kind of data are electrocardiograms (ECG), whose careful analysis has proven to be of significant help to diagnose cardiovascular abnormalities. ECG recording devices can produce a very large amount of data in a short period of time. Usually abstracted as unstructured data, ECG digital signals have traditionally been stored and analyzed using file-based solutions for storage, and ad-hoc programs for data processing. We favor the idea that ECG signals can be abstracted as sets of tuples and stored in database relations. In this paper we present a proposal to store, manage, and analyze ECG data in a column-store database management system (DBMS). We provide extensive empirical evidence showing that incorporating complex analytical tasks such as ECG transformation and classification into a DBMS is not only feasible but also efficient and scalable. For this, we rely on the Structured Query Language provided by relational DBMSs, and the implementation of user defined functions.

关键词： user defined functions Machine learning deployment Data management Signal database

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Performance simulation of a Stirling cryocooler using CFD 16

Performance simulation of a Stirling cryocooler using CFD

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16th International Bhurban Conference on Applied Sciences and Technology (IBCAST)

作者： Ahmed, Luqman Masud, Jehanzeb Toor, Zakria NUST Coll Aeronaut Engn Dept Aerosp Engn Risalpur Pakistan Air Univ IAA Dept Mech & Aerosp Engn Islamabad Pakistan

ISBN: (纸本)9781538677292

Small Stirling cryocoolers, with refrigeration capacities in the range of 0.5W to 5W, at cooling temperatures as low as 60K have found their way into the fields of aerospace, medical and energy. The present work is aimed at performance simulation of a gamma type, split -Stirling cryocooler using CFD. Simulation of the reciprocating flow inside a 2-D model of the cryocooler has been accomplished using the dynamic mesh technique in ANSYS Fluent. For this purpose, two separate user defined functions (UDFs) have been compiled for the movement of piston and displacer. In order to operate the cryocooler based on the Stirling cycle an appropriate phase difference has been maintained between the piston and displacer movement. Linearly elastic solid model of the dynamic mesh technique has been adopted for mesh motion inside the displacer. This model is time intensive but proves to be appropriate for cyclic simulations. The mesh inside the working spaces is compressed and expanded proportionally avoiding the negative volume error that is often encountered in moving mesh problems. Temperature -dependent properties of the working fluid and matrix material have been incorporated by using appropriate coefficients of polynomial functions as a function of temperature. Area weighted temperature and pressure inside the compression and expansion spaces have been reported for the ANSYS Fluent simulations. It is shown that the modelled cryocooler can achieve a refrigeration temperature of 60K with a heat load of 0.75W. The results thus obtained have been compared with the experimental result and found to be in close conformance. The methodology adopted in the current work can be utilized to simulate the performance of a cryocooler and can be helpful in finding the optimum values of its operational parameters.

关键词： Stirling cryocoolers reciprocating flow user defined functions dynamic mesh refrigeration

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Transient Heat Transfer Analysis of Thermo-Electric Cooler Thermal Tools 17

Transient Heat Transfer Analysis of Thermo-Electric Cooler T...

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17th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)

作者： Sanchez, Jaime A. Intel Corp 2111 NE 25th Ave Hillsboro OR 97124 USA

ISBN: (纸本)9781538612729

With increasing complexity of semiconductor devices, testing of integrated circuit packages is an integral part of the manufacturing process. A key component of testing is the temperature control of the junction temperature of the silicon for the purposes of binning and debug. For this reason, efficient and cost-effective tools used across the industry rely on the use of thermo-electric coolers. These devices are based on the Peltier effect to induce a temperature change when power is applied to them. Active thermal control of the silicon junction is thus achieved by changing the magnitude of the applied voltage to the Peltier device as well as modulating its polarity. The result is the dynamic response of the thermal tool when trying to control the temperature of the device under test. In this paper, the dynamic performance of these tools is characterized. A highly accurate numerical model is developed to evaluate the response of the thermal tool under different testing conditions. Various test cases and sensitivity studies are presented to address the optimization of the response of the Peltier device under simulated power profiles, considering the thermal control goals and the reliability of the thermal tool itself.

关键词： Thermo-electric coolers transient heat transfer analysis closed loop control numerical models user defined functions test of microprocessors transient thermal characterization PID controller

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