Experimental Investigation of Vortex Flow in a Two-Chamber Solar Thermochemical Reactor

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Erik E. Koepf ◽  
Matthew D. Lindemer ◽  
Suresh G. Advani ◽  
Ajay K. Prasad
Keyword(s):  
High Temperature ◽  
Flow Visualization ◽  
Large Scale ◽  
Gas Flow ◽  
Vortex Flow ◽  
Solar Reactor ◽  
Concentrated Solar Energy ◽  
Wide Range ◽  
Reactor Geometry ◽  
Solar Thermochemical

Recent advances in the field of large-scale solar thermochemical processing have given rise to substantial research efforts and demonstration projects. Many applications of high-temperature solar-thermal technology employ an enclosed cavity environment, thus requiring a transparent window through which concentrated solar energy can enter. One configuration employed is a two-cavity reactor connected by a narrow aperture, where solar flux entering through the window is focused at the aperture plane before diverging into the lower chamber, where the chemical reaction occurs. For the Zn/ZnO thermochemical cycle where Zn is solar-thermally reduced from ZnO in a high-temperature cavity environment, effective removal of the product gas stream containing zinc vapor is of paramount importance to prevent fouling by condensation on the reactor window. Two argon-jet configurations, tangential and radial, located around the circumference of the upper chamber are used to control the gas flow within the reactor cavity. First, the tangential jets drive a vortex flow, and second, the radial wall jet travels across the window before converging at the reactor center line and turning downward to create a downward jet. The tangential jet-induced flow creates a rotating vortex, contributing to overall flow stability, and the radial jet-induced downward flow counters the updraft created by the vortex while actively cooling and sweeping clear the inner surface of the window. Flow visualization in a full-scale transparent model of the reactor using smoke and laser illumination is employed to characterize the effectiveness of aerodynamic window clearing and to characterize the processes by which a vortex flow develops and breaks down in a two-chamber solar reactor geometry. Based on a large dataset of flow visualization images, a metric is developed to define vortex stability over a wide range of flow conditions and identify an ideal operating range for which a vortex formation path is established that maintains stable flow patterns and removes product gases while minimizing the use of argon gas. The predominant influence of vortex instability and breakdown is identified and examined for the case of a beam-down, two-chamber solar reactor geometry.

Design of a Lab-Scale Rotary Cavity-Type Solar Reactor for Continuous Thermal Reduction of Volatile Oxides Under Reduced Pressure

2009 ◽  
Author(s):  
Marc Chambon ◽  
Ste´phane Abanades ◽  
Gilles Flamant
Keyword(s):  
High Temperature ◽  
Metal Oxide ◽  
Thermal Reduction ◽  
Reduction Reaction ◽  
High Specific Surface Area ◽  
Reduced Pressure ◽  
Water Steam ◽  
Solar Reactor ◽  
Concentrated Solar Energy ◽  
Solar Thermochemical

The investigated two-step MxOy/ MxOy−1 solar thermochemical cycles consist of two redox reactions. Net result is watersplitting with concentrated solar energy as the source of high temperature process heat: 1)Solarreduction:MxOy→MxOy−1+1/2O2(about1700°Catatmosphericpressure,endothermal)2)Hydrolysis:MxOy−1+H2O→MxOy+H2(about400°C,exothermal) The MxOy−1 species produced in reaction (1) is gaseous in the case of the ZnO/Zn cycle. The oxide (ZnO) is injected in a solar thermochemical reactor and undergoes a thermal reduction reaction (oxygen release). Dilution/quenching with a neutral gas at the reactor exit yields nanoparticles of metal by condensation. The particles have a high specific surface area that leads to a high reactivity in the 2nd step. The reduced species (Zn) can then be fed to another reactor to react with water steam. The reaction produces pure H2 and forms the original metal oxide. A high-temperature lab-scale solar reactor prototype was designed, constructed and operated, allowing continuous metal oxide processing under controlled atmosphere. It is based on a cavity-type rotating receiver absorbing solar radiation. The reactant powder is injected continuously inside the cavity and the produced particles (Zn) are recovered in a downstream filter. The solar reduction of ZnO has been achieved, the reaction yields were quantified, and a first concept of solar reactor was qualified.

scholarly journals Persistent magnetic vortex flow at a supergranular vertex

2018 ◽  
Vol 610 ◽  
pp. A84 ◽  
Author(s):  
Iker S. Requerey ◽  
Basilio Ruiz Cobo ◽  
Milan Gošić ◽  
Luis R. Bellot Rubio
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Vortex Flow ◽  
Spatial Scales ◽  
Magnetic Vortex ◽  
Magnetic Feature ◽  
Magnetic Element ◽  
Flow Maps ◽  
Wide Range ◽  
Intensity Images

Context. Photospheric vortex flows are thought to play a key role in the evolution of magnetic fields. Recent studies show that these swirling motions are ubiquitous in the solar surface convection and occur in a wide range of temporal and spatial scales. Their interplay with magnetic fields is poorly characterized, however. Aims. We study the relation between a persistent photospheric vortex flow and the evolution of a network magnetic element at a supergranular vertex. Methods. We used long-duration sequences of continuum intensity images acquired with Hinode and the local correlation-tracking method to derive the horizontal photospheric flows. Supergranular cells are detected as large-scale divergence structures in the flow maps. At their vertices, and cospatial with network magnetic elements, the velocity flows converge on a central point. Results. One of these converging flows is observed as a vortex during the whole 24 h time series. It consists of three consecutive vortices that appear nearly at the same location. At their core, a network magnetic element is also detected. Its evolution is strongly correlated to that of the vortices. The magnetic feature is concentrated and evacuated when it is caught by the vortices and is weakened and fragmented after the whirls disappear. Conclusions. This evolutionary behavior supports the picture presented previously, where a small flux tube becomes stable when it is surrounded by a vortex flow.

Design of HTS Magnetically Controlled Saturable Reactor

2013 ◽  
Vol 380-384 ◽  
pp. 2982-2985
Author(s):  
Hong Da Dong
Keyword(s):  
High Temperature ◽  
High Voltage ◽  
Large Scale ◽  
Reactive Power ◽  
Magnetic Circuit ◽  
Reactive Power Compensation ◽  
Model Design ◽  
Power Capacity ◽  
Wide Range ◽  
Small Capacity

There are many problems for traditional reactive power compensation devices to be applied in the grid, such as discontinuous adjustment, small capacity, complex control and harmonics. This paper aims to study a high temperature superconducting magnetically controlled saturable reactor (HTS MCSR), which has a wide range of stepless adjustment. It has a good application prospect in large scale reactive power compensation devices. Based on research of theory and core structure, a shaped-cylinder core is proposed. By means of calculation of saturable reactor and analysis of algebraic and magnetic circuit model, design of 220V HTS MCSR is finished. Results of normal conductive reactor prototype and simulations verify that the range of inductance adjustment is very wide. Furthermore, conceptual design of 35kV HTS MCSR confirms its reactive power capacity is so large, therefore, it is suitable for high voltage power system.

Model Combustor to Assess the Oxidation Behavior of Ceramic Materials Under Real Engine Conditions

1999 ◽  
Author(s):  
D. Filsinger ◽  
A. Schulz ◽  
S. Wittig ◽  
C. Taut ◽  
H. Klemm ◽  
...  
Keyword(s):  
High Temperature ◽  
International Development ◽  
Gas Turbines ◽  
Gas Flow ◽  
Oxidation Behavior ◽  
Elevated Temperatures ◽  
Ceramic Materials ◽  
Test Rig ◽  
Combustion Gas ◽  
Wide Range

A further increase of thermal efficiency and a reduction of the exhaust emissions of ground based gas turbines can be achieved by introducing new high temperature resistant materials. Therfore, ceramics are under international development. They offer excellent strengths at room and elevated temperatures. For gas turbine combustor applications, however, these materials have to maintain their advantageous properties under hostile environment. For the assessment and comparison of the oxidation behavior of different nonoxide ceramic materials a test rig was developed at the Institute for Thermal Turbomachinery (ITS), University of Karlsruhe, Germany. The test rig was integrated into the high temperature/ high pressure laboratory. A ceramic model combustion chamber was designed which allowed the exposure of standard four-point flexure specimens to the hot combustion gas flow. Gas temperatures and pressures could be varied in a wide range. Additionally, the partial steam pressure could be adjusted to real combustor conditions. The present paper gives a detailed description of the test rig and presents results of 100 hours endurance tests of ceramic materials at 1400°C. The initial strengths and the strengths after oxidation tests are compared. In addition to this, photographs illustrating the changes of the material’s microstructure are presented.

Coupled Concentrating Optics, Heat Transfer, and Thermochemical Modeling of a 100-kWth High-Temperature Solar Reactor for the Thermal Dissociation of ZnO

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
W. Villasmil ◽  
T. Cooper ◽  
E. Koepf ◽  
A. Meier ◽  
A. Steinfeld
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Energy Conversion ◽  
Solar Flux ◽  
Solar Furnace ◽  
Solar Irradiation ◽  
Radiation Boundary Condition ◽  
Solar Reactor ◽  
Concentrated Solar Energy ◽  
Conversion Efficiencies

This work reports a numerical investigation of the transient operation of a 100-kWth solar reactor for performing the high-temperature step of the Zn/ZnO thermochemical cycle. This two-step redox cycle comprises (1) the endothermal dissociation of ZnO to Zn and O2 above 2000 K using concentrated solar energy, and (2) the subsequent oxidation of Zn with H2O/CO2 to produce H2/CO. The performance of the 100-kWth solar reactor is investigated using a dynamic numerical model consisting of two coupled submodels. The first is a Monte Carlo (MC) ray-tracing model applied to compute the spatial distribution maps of incident solar flux absorbed on the reactor surfaces when subjected to concentrated solar irradiation delivered by the PROMES-CNRS MegaWatt Solar Furnace (MWSF). The second is a heat transfer and thermochemical model that uses the computed maps of absorbed solar flux as radiation boundary condition to simulate the coupled processes of chemical reaction and heat transfer by radiation, convection, and conduction. Experimental validation of the solar reactor model is accomplished by comparing solar radiative power input, temperatures, and ZnO dissociation rates with measured data acquired with the 100-kWth solar reactor at the MWSF. Experimentally obtained solar-to-chemical energy conversion efficiencies are reported and the various energy flows are quantified. The model shows the prominent influence of reaction kinetics on the attainable energy conversion efficiencies, revealing the potential of achieving ηsolar-to-chemical = 16% provided the mass transport limitations on the ZnO reaction interface were overcome.

Rapid High Temperature Solar Thermal Biomass Gasification in a Prototype Cavity Reactor

2010 ◽  
Vol 132 (1) ◽  
Author(s):  
Paul Lichty ◽  
Christopher Perkins ◽  
Bryan Woodruff ◽  
Carl Bingham ◽  
Alan Weimer
Keyword(s):  
High Temperature ◽  
Solar Energy ◽  
Gas Flow ◽  
Biomass Conversion ◽  
Biomass Gasification ◽  
Solar Furnace ◽  
Concentrated Solar Energy ◽  
Product Stream ◽  
Tar Reduction ◽  
Composition Ratios

High temperature biomass gasification has been performed in a prototype concentrated solar reactor. Gasification of biomass at high temperatures has many advantages compared with historical methods of producing fuels. Enhancements in overall conversion, product composition ratios, and tar reduction are achievable at temperatures greater than 1000°C. Furthermore, the utilization of concentrated solar energy to drive these reactions eliminates the need to consume a portion of the product stream for heating and some of the solar energy is stored as chemical energy in the product stream. Experiments to determine the effects of temperature, gas flow rate, and feed type were conducted at the high flux solar furnace at the National Renewable Energy Laboratory, Golden, CO. These experiments were conducted in a reflective cavity multitube prototype reactor. Biomass type was found to be the only significant factor within a 95% confidence interval. Biomass conversion as high as 68% was achieved on sun. Construction and design considerations of the prototype reactor are discussed as well as initial performance results.

scholarly journals Turbulence in Large-Scale Two-Dimensional Balanced Hard Sphere Gas Flow

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1520
Author(s):  
Rafail V. Abramov
Keyword(s):  
Turbulent Flows ◽  
Hard Sphere ◽  
Large Scale ◽  
Gas Flow ◽  
Spatial Scales ◽  
Mean Field ◽  
Current Work ◽  
Two Dimensional ◽  
Dynamical Mechanism ◽  
Wide Range

In recent works, we developed a model of balanced gas flow, where the momentum equation possesses an additional mean field forcing term, which originates from the hard sphere interaction potential between the gas particles. We demonstrated that, in our model, a turbulent gas flow with a Kolmogorov kinetic energy spectrum develops from an otherwise laminar initial jet. In the current work, we investigate the possibility of a similar turbulent flow developing in a large-scale two-dimensional setting, where a strong external acceleration compresses the gas into a relatively thin slab along the third dimension. The main motivation behind the current work is the following. According to observations, horizontal turbulent motions in the Earth atmosphere manifest in a wide range of spatial scales, from hundreds of meters to thousands of kilometers. However, the air density rapidly decays with altitude, roughly by an order of magnitude each 15–20 km. This naturally raises the question as to whether or not there exists a dynamical mechanism which can produce large-scale turbulence within a purely two-dimensional gas flow. To our surprise, we discover that our model indeed produces turbulent flows and the corresponding Kolmogorov energy spectra in such a two-dimensional setting.

scholarly journals Heat, Mass and Fluid Flow in a Solar Reactor for Fullerene Synthesis

2001 ◽  
Author(s):  
Tony Guillard ◽  
Gilles Flamant ◽  
Daniel Laplaze
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Large Scale ◽  
Solar Furnace ◽  
Variable Pressure ◽  
Cooling Zone ◽  
Solar Reactor ◽  
Wide Range ◽  
Vaporization Process ◽  
Temperature And Pressure

Abstract A 2 kW solar furnace was used to vaporize a graphite target for fullerene synthesis. Tests were performed in a wide range of vaporization rates (0.1–4 g/h), under variable pressure and argon flow rate. Experimental results are interpreted with numerical simulation to define key parameters for large-scale synthesis of fullerenes with solar energy. We demonstrate that the vaporization process is controlled by diffusion in the temperature and pressure ranges 3000–3700 K and 70–250 hPa respectively. Experimental data and numerical simulation suggest that in the solar reactor, fullerene yield is governed by the dilution of carbon vapor in argon and by the temperature gradient in the cooling zone. Criteria for both parameters are suggested. Consequently, these data, combined with the numerical model accounting for heat, mass and fluid flow inside the reactor, may be used for the design of large-scale solar process.

Heat, Mass, and Fluid Flow in a Solar Reactor for Fullerene Synthesis

2001 ◽  
Vol 123 (2) ◽  
pp. 153-159 ◽  
Author(s):  
T. Guillard ◽  
G. Flamant ◽  
D. Laplaze
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Solar Furnace ◽  
Variable Pressure ◽  
Cooling Zone ◽  
Carbon Vapor ◽  
Solar Reactor ◽  
Wide Range ◽  
Vaporization Process ◽  
Temperature And Pressure

Experimental results with a 2 kW solar furnace, in a wide range of vaporization rates (0.1–4 g/h), under variable pressure and flow rate of argon, are used with numerical simulation to define key parameters for large scale synthesis of fullerenes with solar energy. The vaporization process is controlled by diffusion in the temperature and pressure ranges 3000-3700 K and 70-250 hPa respectively. In the solar reactor, fullerene yield is governed by the dilution of carbon vapor in argon and the temperature gradient in the cooling zone. Criteria for both parameters are suggested. Consequently, these data, combined with a validated numerical model of the reactor, may be used for the design of large-scale solar process.

Experimental Investigation of Microscale Effects in Perforated Plate Aerodynamics

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Ryszard Szwaba ◽  
Tomasz Ochrymiuk ◽  
Tomasz Lewandowski ◽  
Justyna Czerwinska
Keyword(s):  
Experimental Investigation ◽  
Compressible Flows ◽  
Large Scale ◽  
Gas Flow ◽  
Perforated Plate ◽  
Quadratic Function ◽  
Accommodation Coefficient ◽  
Turbulence Transition ◽  
Wide Range ◽  
Strong Relation

This paper contains an extensive analysis of the flow in microholes based on an experimental investigation. Experiments of the gas flow past a perforated plate with microholes (110μm) were carried out. A wide range of pressure differences between the inlet and the outlet were investigated for that purpose. Two distinguishable flow regimes were obtained: the laminar flow with the slip effects and the turbulence transition regime for a very low Reynolds number. The results are in good agreement with the theory, simulations, experiments for large scale perforated plates, and compressible flows in microtubes. The relation between the mass flow rate and the Knudsen, Reynolds, and Mach numbers for the laminar and transitional regime was obtained. It is a quadratic function of the Reynolds and Knudsen numbers (ReKn) based on the hole's diameter. The value of the first order tangential momentum accommodation coefficient was estimated. It shows a strong relation to the inlet Knudsen number.

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