The Experts below are selected from a list of 26418 Experts worldwide ranked by ideXlab platform
Aldo Steinfeld - One of the best experts on this subject based on the ideXlab platform.
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high temperature thermal storage using a packed bed of rocks Heat Transfer analysis and experimental validation
Applied Thermal Engineering, 2011Co-Authors: Markus Hanchen, Sarah Bruckner, Aldo SteinfeldAbstract:High-temperature thermal storage in a packed bed of rocks is considered for air-based concentrated solar power plants. The unsteady 1D two-phase energy conservation equations are formulated for combined convection and Conduction Heat Transfer, and solved numerically for charging/discharging cycles. Validation is accomplished in a pilot-scale experimental setup with a packed bed of crushed steatite (magnesium silicate rock) at 800 K. A parameter study of the packed bed dimensions, fluid flow rate, particle diameter, and solid phase material was carried out to evaluate the charging/discharging characteristics, daily cyclic operation, overall thermal efficiency and capacity ratio.
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design of a 10 mw particle flow reactor for syngas production by steam gasification of carbonaceous feedstock using concentrated solar energy
Energy & Fuels, 2010Co-Authors: Gilles Maag, Aldo SteinfeldAbstract:Steam-gasification of carbonaceous feedstock is carried out in a solar reactor consisting of a cavity-receiver containing an array of tubular absorbers, through which a two-phase flow of water vapor laden with μm-sized carbonaceous particles reacts to form H2 and CO (syngas). Concentrated solar radiation, entering through the cavity’s aperture, is supplied as the source of high-temperature process Heat to the endothermic reaction. A Heat Transfer model is formulated by coupling radiation/convection/Conduction Heat Transfer to the chemical kinetics for a solid−gas reacting flow. It is solved numerically by Monte Carlo and finite volume techniques. Experimental validation is accomplished for biochar gasification with a 3 kW prototype reactor subjected to high-flux thermal irradiation. The model is applied to analyze the performance of a 10 MW industrial-scale reactor mounted on a solar tower configuration. For an optimized reactor geometry and a desired outlet temperature of 1500 K, a solar-to-chemical energy conversion of 37% is predicted for 1500 suns solar concentration.
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Heat Transfer model of a solar receiver reactor for the thermal dissociation of zno experimental validation at 10 kw and scale up to 1 mw
Chemical Engineering Journal, 2009Co-Authors: Lothar O Schunk, Wojciech Lipinski, Aldo SteinfeldAbstract:A transient Heat Transfer model is developed for analyzing the thermal performance of a thermochemical reactor for the solar-driven dissociation of ZnO in the 1600–2136 K range. The reactor consists of a rotating cavity-receiver lined with ZnO particles that are directly exposed to concentrated solar radiation. The model couples radiation, convection, and Conduction Heat Transfer to the reaction kinetics for a shrinking domain and simulates a transient ablation regime with semi-batch feed cycles of ZnO particles. Validation is accomplished in terms of the numerically calculated and experimentally measured temperature profiles and reaction extents for a 10 kW reactor prototype tested in a high-flux solar simulator and subjected to peak solar concentration ratios exceeding 5000 suns. Scaling-up the reactor technology to 1 MW solar thermal power input has the potential of reaching a solar-to-chemical energy conversion efficiency of 56%.
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transient Heat Transfer in a directly irradiated solar chemical reactor for the thermal dissociation of zno
Applied Thermal Engineering, 2008Co-Authors: Ralph Muller, Wojciech Lipinski, Aldo SteinfeldAbstract:A numerical and experimental investigation is carried out in a solar thermochemical reactor for the thermal dissociation of ZnO at 2000 K using concentrated solar energy. The reactor consists of a cavity-receiver lined with ZnO particles and directly exposed to high-flux irradiation. A transient Heat Transfer model is formulated to link the rate of radiation, convection, and Conduction Heat Transfer to the reaction kinetics. The radiosity and Monte Carlo methods are applied to obtain the distribution of net radiative fluxes at the internal surfaces of the reactor cavity and at the surface of the ZnO bed. Validation is accomplished in terms of the calculated and measured transient temperature profiles and chemical reaction rates.
Fatmir Asllanaj - One of the best experts on this subject based on the ideXlab platform.
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galerkin method for solving combined radiative and conductive Heat Transfer
International Journal of Thermal Sciences, 2016Co-Authors: Mohamed Ghattassi, Jean Rodolphe Roche, Fatmir Asllanaj, Mohamed BoutayebAbstract:This article deals with a numerical solution for combined radiation and Conduction Heat Transfer in a gray absorbing and emitting medium applied to a two-dimensional domain using triangular meshes. The radiative Transfer equation was solved using the high order Discontinuous Galerkin method with an upwind numerical flux. The energy equation was discretized using a high order finite element method. Stability and error analysis were performed for the Discontinuous Galerkin method to solve radiative Transfer equation. A new algorithm to solve the nonlinear radiative–conductive Heat Transfer systems was introduced and different types of boundary conditions were considered in numerical simulations. The proposed technique's high performance levels in terms of accuracy and stability are discussed in this paper with numerical examples given.
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transient radiation and Conduction Heat Transfer in a gray absorbing emitting medium applied on two dimensional complex shaped domains
Numerical Heat Transfer Part B-fundamentals, 2007Co-Authors: Fatmir Asllanaj, Gilles Parent, G JeandelAbstract:This article is devoted to transient radiation and Conduction Heat Transfer in a gray absorbing-emitting medium in a two-dimensional complex-shaped domain using unstructured triangular meshes. The radiative Transfer equation (RTE) is solved by using a new finite-volume method (FVM) based on a cell vertex scheme and associated to a modified exponential scheme. The PHAML (Parallel Hierarchical Adaptive MultiLevel) code is used to solve the energy balance equation using low- or high-order finite elements. Several benchmark cases including steady and transient states and applied to different geometries are used to validate the developed code. Results show very good agreement.
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transient combined radiation and Conduction Heat Transfer in fibrous media with temperature and flux boundary conditions
International Journal of Thermal Sciences, 2004Co-Authors: Fatmir Asllanaj, Jean Rodolphe Roche, G Jeandel, David LacroixAbstract:Abstract Transient radiative and conductive Heat Transfer in a fibrous medium with anisotropic optical properties is investigated. Two different kinds of boundary conditions are treated: when the temperatures imposed on the boundaries vary with time and when the medium is subject to a radiation source which varies with time. A one dimensional case is considered. The non-linear transient Heat Conduction Equation is solved using the Kirchhoff transformation associated with a P 2 finite elements method using a non-uniform spatial mesh. The Radiative Transfer Equation is solved using a direct method which is analytical in space whereas the spectral scattering and absorption coefficients as well as the phase function are determined using the Mie theory. This procedure is applied on the whole time domain. Finally, a realistic application to a fibrous insulation composed of silica fibers is treated numerically.
Subhransu Roy - One of the best experts on this subject based on the ideXlab platform.
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development of a theoretical process map for laser cladding using a three dimensional Conduction Heat Transfer model
Numerical Heat Transfer Part A-applications, 2009Co-Authors: Amitesh Kumar, Subhransu RoyAbstract:In this article, a three-dimensional Conduction Heat Transfer model is developed to predict the clad geometry (e.g., height, width, and dilution) and microstructure (scale and morphology) of the solidified layer for a laser cladding process. The effect of controllable input process parameters like absorbed laser power, powder deposition rate, and processing speed on the clad characteristics is critically assessed with the help of dimensionless parameters. A process map is developed which enables operators to pick up the proper process parameters for a feasible laser cladding process with desirable characteristics. The present Conduction model is solved using the finite-volume method in a multiblock, nonorthogonal grid system. The effect of melt pool convection is taken care of by introducing an enhanced thermal conductivity factor for the molten pool.
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three dimensional Conduction Heat Transfer model for laser cladding process
Numerical Heat Transfer Part B-fundamentals, 2008Co-Authors: Subrata Kumar, Subhransu Roy, C P Paul, A K NathAbstract:Cladding is the process of depositing a superior built-up layer on a substrate by fusion. In the present study a three-dimensional Conduction Heat Transfer model is developed and solved using the finite-volume method in a nonorthogonal grid system for a blown-powder laser cladding process. Comparisons with experimental data for deposition of copper powder on SS316 stainless steel show that the developed model can predict the geometry of the buildup layer above the substrate within an acceptable range of tolerance. The overall absorption of the CO2 laser radiation is in the range of 14–17%.
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development of theoretical process maps to study the role of powder preHeating in laser cladding
Computational Materials Science, 2006Co-Authors: Subrata Kumar, Subhransu RoyAbstract:Cladding is the process of depositing a superior built-up layer by fusion on a substrate. In blown powder laser cladding process, the powder travels across the laser path, gets Heated up by absorbing laser energy, and finally melts on the substrate under the intense laser beam; as the substrate moves away this melt pool solidifies to form a continuous built-up layer. The laser energy is partly absorbed by the solid powder during its flight path (termed preHeating) and partly by the top surface of the melt pool. In the present study a two-dimensional Conduction Heat Transfer equation has been solved using finite-volume method to model the cladding process. It is observed that preHeating allows higher scanning speed resulting in thin clad layer with low dilution. PreHeating also permits high powder feed rate resulting in thick cladding with low dilution.
Wonpyo Chang - One of the best experts on this subject based on the ideXlab platform.
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experimental study of critical Heat flux enhancement during forced convective flow boiling of nanofluid on a short Heated surface
International Journal of Multiphase Flow, 2010Co-Authors: Hangjin Jo, Soonho Kang, Wonpyo ChangAbstract:Enhancements of nucleate boiling critical Heat flux (CHF) using nanofluids in a pool boiling are well-known. Considering importance of flow boiling Heat Transfer in various practical applications, an experimental study on CHF enhancements of nanofluids under convective flow conditions was performed. A rectangular flow channel with 10-mm width and 5-mm height was used. A 10 mm-diameter disk-type copper surface, Heated by Conduction Heat Transfer, was placed at the bottom surface of the flow channel as a test Heater. Aqueous nanofluids with alumina nanoparticles at the concentration of 0.01% by volume were investigated. The experimental results showed that the nanofluid flow boiling CHF was distinctly enhanced under the forced convective flow conditions compared to that in pure water. Subsequent to the boiling experiments, the Heater surfaces were examined with scanning electron microscope and by measuring contact angle. The surface characterization results suggested that the flow boiling CHF enhancement in nanofluids is mostly caused by the nanoparticles deposition of the Heater surface during vigorous boiling of nanofluids and the subsequent wettability enhancements.
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experimental study of critical Heat flux enhancement during forced convective flow boiling of nanofluid on a short Heated surface
International Journal of Multiphase Flow, 2010Co-Authors: Ho Seon Ahn, Soonho Kang, Wonpyo Chang, Hyungdae Kim, Moo Hwan KimAbstract:Enhancements of nucleate boiling critical Heat flux (CHF) using nanofluids in a pool boiling are well-known. Considering importance of flow boiling Heat Transfer in various practical applications, an experimental study on CHF enhancements of nanofluids under convective flow conditions was performed. A rectangular flow channel with 10-mm width and 5-mm height was used. A 10 mm-diameter disk-type copper surface, Heated by Conduction Heat Transfer, was placed at the bottom surface of the flow channel as a test Heater. Aqueous nanofluids with alumina nanoparticles at the concentration of 0.01% by volume were investigated. The experimental results showed that the nanofluid flow boiling CHF was distinctly enhanced under the forced convective flow conditions compared to that in pure water. Subsequent to the boiling experiments, the Heater surfaces were examined with scanning electron microscope and by measuring contact angle. The surface characterization results suggested that the flow boiling CHF enhancement in nanofluids is mostly caused by the nanoparticles deposition of the Heater surface during vigorous boiling of nanofluids and the subsequent wettability enhancements.
Xinxin Zhang - One of the best experts on this subject based on the ideXlab platform.
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discontinuous finite element method for combined radiation Conduction Heat Transfer in participating media
International Communications in Heat and Mass Transfer, 2019Co-Authors: Cunhai Wang, Yanyan Feng, Kai Yue, Xinxin ZhangAbstract:Abstract A discontinuous finite element method (DFEM) is extended to combined radiation-Conduction Heat Transfer in gray and isotropically scattering media. The computational domain is discretized into finite elements and the shape functions are constructed on each discrete element. The forced inner-boundary continuity in the continuous finite element method (FEM) is released and the DFEM elements are connected by a simulated numerical flux across the inner-element boundaries, this makes the DFEM numerical stable and flexible in dealing with irregular geometry with curve boundaries. The accuracy of the DFEM algorithm for combined Heat Transfer is verified by comparing the DFEM results with other benchmark solutions. Combined Heat Transfer in two-dimensional media with irregular geometries is further solved by using the DFEM. Results show that the DFEM demands little on unstructured mesh quality and is highly accurate for solving coupled radiation-Conduction Heat Transfer in participating medium with complex configurations.