A Receiver-Reactor for the Solar Thermal Dissociation of Zinc Oxide

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
L. O. Schunk ◽  
P. Haeberling ◽  
S. Wepf ◽  
D. Wuillemin ◽  
A. Meier ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Dissociation ◽  
Ceramic Matrix Composite ◽  
Chemical Reactor ◽  
Heat Fluxes ◽  
Solar Simulator ◽  
Rotating Cavity ◽  
Zno Particles ◽  
Concentrated Solar Radiation ◽  
Chemical Reactant

An improved engineering design of a solar chemical reactor for the thermal dissociation of ZnO at above 2000K is presented. It features a rotating cavity receiver lined with ZnO particles that are held by centrifugal force. With this arrangement, ZnO is directly exposed to concentrated solar radiation and serves simultaneously the functions of radiant absorber, chemical reactant, and thermal insulator. The multilayer cylindrical cavity is made of sintered ZnO tiles placed on top of a porous 80%Al2O3–20%SiO2 insulation and reinforced by a 95%Al2O3–5%Y2O3 ceramic matrix composite, providing mechanical, chemical, and thermal stability and a diffusion barrier for product gases. 3D computational fluid dynamics was employed to determine the optimal flow configuration for an aerodynamic protection of the quartz window against condensable Zn(g). Experimentation was carried out at PSI’s high-flux solar simulator with a 10kW reactor prototype subjected to mean radiative heat fluxes over the aperture exceeding 3000suns (peak 5880suns). The reactor was operated in a transient ablation mode with semicontinuous feed cycles of ZnO particles, characterized by a rate of heat transfer—predominantly by radiation—to the layer of ZnO particles undergoing endothermic dissociation that proceeded faster than the rate of heat transfer—predominantly by conduction—through the cavity walls.

A Rotary Receiver-Reactor for the Solar Thermal Dissociation of Zinc Oxide

2007 ◽  
Author(s):  
L. O. Schunk ◽  
P. Haeberling ◽  
S. Wepf ◽  
D. Wuillemin ◽  
A. Meier ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Dissociation ◽  
Ceramic Matrix Composite ◽  
Chemical Reactor ◽  
Heat Fluxes ◽  
Solar Simulator ◽  
Rotating Cavity ◽  
Zno Particles ◽  
Concentrated Solar Radiation ◽  
Chemical Reactant

An improved engineering design of a solar chemical reactor for the thermal dissociation of ZnO at above 2000 K is presented. It features a rotating cavity-receiver lined with ZnO particles that are held by centrifugal force. With this arrangement, ZnO is directly exposed to concentrated solar radiation and serves simultaneously the functions of radiant absorber, chemical reactant, and thermal insulator. The multilayer cavity is made of sintered ZnO tiles placed on top of a porous 80%Al2O3-20%SiO2 insulation and reinforced by a 95%Al2O3-5%Y2O3 ceramic matrix composite, providing mechanical, chemical, and thermal stability and a diffusion barrier for product gases. 3D CFD was employed to determine the optimal flow configuration for an aerodynamic protection of the quartz window against condensable Zn(g). Experimentation was carried out at PSI’s high flux solar simulator with a 10 kW reactor prototype subjected to mean radiative heat fluxes over the aperture exceeding 3000 suns (peak 5880 suns). The reactor was operated in a transient ablation mode with semi-batch feed cycles of ZnO particles, characterized by a rate of heat transfer — predominantly by radiation — to the layer of ZnO particles undergoing endothermic dissociation that proceeded faster than the rate of heat transfer — predominantly by conduction — through the cavity walls.

Coupled Fluid/Solid Heat Transfer Computation for Turbine Discs

2001 ◽  
Author(s):  
John A. Verdicchio ◽  
John W. Chew ◽  
Nick J. Hills
Keyword(s):  
Heat Transfer ◽  
Convergence Rates ◽  
Heat Fluxes ◽  
Test Cases ◽  
Transfer Coefficients ◽  
Flow Solver ◽  
Heat Transfer Coefficients ◽  
Rotating Cavity ◽  
Air Temperatures ◽  
Conjugate Solution

This paper considers the coupling of a finite element thermal conduction solver with a steady, finite volume fluid flow solver. Two methods were considered for passing boundary conditions between the two codes — transfer of metal temperatures and either convective heat fluxes or heat transfer coefficients and air temperatures. These methods have been tested on two simple rotating cavity test cases and also on a more complex real engine example. Convergence rates of the two coupling methods were compared. Passing heat transfer coefficients and air temperatures was found to give the quickest convergence. The coupled method gave agreement with the analytic solution and a conjugate solution of the simple free disc problem. The predicted heat transfer results for the real engine example showed some encouraging agreement, although some modelling issues are identified.

Thermal Dissociation of CH4 Using a Particle-Flow Chemical Reactor Exposed to Concentrated Solar Radiation

2008 ◽  
Author(s):  
Gilles Maag ◽  
Francisco Javier Gutierrez ◽  
Wojciech Lipinski ◽  
Aldo Steinfeld
Keyword(s):  
Solar Radiation ◽  
Volume Fraction ◽  
Solid Phase ◽  
Particle Volume Fraction ◽  
Thermal Dissociation ◽  
Chemical Reactor ◽  
Particle Flow ◽  
Carbonaceous Particles ◽  
Phase Volume Fraction ◽  
Concentrated Solar Radiation

The performance of a 5 kW particle-flow chemical reactor for the co-production of H2 and C by thermal decomposition of CH4 is investigated using concentrated solar radiation as the energy source of high-temperature process heat. The solar reactor features a directly-irradiated flow of CH4 laden with carbonaceous particles that serve the functions of radiant absorbers and nucleation sites for the heterogeneous cracking reaction. Main operational parameters are the solar power input, CH4 mass flow rate, and solid phase volume fraction. Their effect on the chemical conversion and solid products’ characteristics are examined for active carbon and carbon black laden particles. Higher particle volume fraction resulted in higher radiative absorption and enhanced kinetics.

EFFECT OF RADIATION ON HEAT TRANSFER INSIDE AEROENGINE COMPRESSOR ROTORS

2021 ◽  
pp. 1-21
Author(s):  
Hui Tang ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Pressure Ratio ◽  
Relative Effect ◽  
Heat Fluxes ◽  
View Factor ◽  
Aircraft Engines ◽  
Rotating Cavity ◽  
Blade Clearance ◽  
Body Heat ◽  
Grey Body

Abstract The blade clearance in aero-engine compressors is mainly controlled by the radial growth of the compressor discs, to which the blades are attached. This growth depends on the radial distribution of the disc temperature, which in turn is determined by the heat transfer inside the internal rotating cavity between adjacent discs. The buoyancy-induced convection inside the cavity is significantly weaker than that associated with the forced convection in the external mainstream flow, and consequently radiation between the cavity surfaces cannot be ignored in the calculation of the disc temperatures. In this paper, both the Monte Carlo Ray-Trace Method and the view factor method are used to calculate the radiative flux when the temperatures of the discs, shroud and inner shaft of the compressor vary radially and axially. Given distributions of surface temperatures, the blackbody and grey body heat fluxes were calculated for the discs, shroud and inner shaft in two experimental compressor rigs and in a simulated compressor stage. For the experimental rigs, although the effect of radiation was relatively small for the case of large Grashof numbers, the relative effect of radiation increases as Gr (and consequently the convective heat transfer) decreases. For the simulated compressor, with a pressure ratio of 50:1 for state-of-art aircraft engines, radiation could have a significant effect on the disc temperature and consequently on the blade clearance; the effect is predicted to be more prominent for next generation of aircraft engines with pressure ratios up to 70:1.

Prediction of 3D Unsteady Flow and Heat Transfer in Rotating Cavity by Discontinuous Galerkin Method and Transition Model

2014 ◽  
Author(s):  
Qinxue Tan ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
High Order ◽  
Heat Fluxes ◽  
High Order Accuracy ◽  
Model Errors ◽  
Order Accuracy ◽  
Flow And Heat Transfer ◽  
Rotating Cavity ◽  
Dg Method ◽  
3D Unsteady Flow

Rotating cavities with axial throughflow are found inside the compressor rotors of turbo-machines. The flow pattern and heat transfer in the cavities are known as sophisticated problems. Because of the numerical errors and model errors, as well as the stiffness introduced by low-Ma number, prediction of 3D unsteady flow and heat transfer in rotating cavity is still a challenge for modern CFD technology. An in-house 3D unsteady CFD code was developed in this study. The discontinuous galerkin method, which can fulfill any high-order accuracy on the unstructured grid, was applied to reduce the discretization errors. The SST-γ-Reθ transition model proposed by Menter was applied to reduce the model errors. To overcome the stiffness and achieve good convergence characteristics and solution quality, the preconditioning matrix technique combined with DG method was introduced for low-Ma number viscous flow. First, natural convection of air in a square cavity was studied to test the code. The feasibility and credibility, of applying the DG method and the preconditioned matrix technique for buoyancy–induced Rayleigh-Bénard like flow, were further verified. Second, the 3D compressible flow field in a rotating cavity was investigated numerically using the FV method, DG method and laminar/SA/SST-transition turbulence model. It is demonstrated that the whole flow structure of all calculated cases was similar after comparing the calculated results with the available experimental data. But, the transition turbulence model fitted the experimental data better. On the other hand, the performance of high-order method was much better for both the rotating cavity flow and natural convection, in terms of heat transfer. To better understand this phenomenon, an accuracy analysis of heat flux using DG method and FV method was performed. It showed the DG method could realize arbitrary precision of viscous stress and heat fluxes on irregular unstructured grids, while the FV method could only realize the first-order accuracy of the heat fluxes at the boundary faces and may exhibit erroneous behaviors. It also demonstrated that the high-order accuracy of gradients was needed to decrease errors of heat fluxes and viscous stresses, and that DG method was a promising method.

Improvement Of Free Convection From Three horizontal Finned Cylinders Fixed Between Two Walls

2018 ◽  
Vol 6 (2) ◽  
pp. 98-114 ◽  
Author(s):  
Hassan K. Abdullah ◽  
Haneen H. Rahman
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Prandtl Number ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Head Orientation ◽  
Outer Diameter ◽  
Gravitational Acceleration ◽  
Convection Heat

Improvement of  free convection heat transfer from three finned cylinders arranged at a triangle shape fixed between two walls has been investigated in this study. Three mild steel finned cylinders fixed between two walls from Pyrex glass have been used as a test rig. It has been changed the spacing between the cylinders (X/D=1,2,3 & S/D=2,4,6) and the head orientation of a triangle to the top under constant heat flux values (38, 254, 660, 1268) W/m2 and compare with case of three finned cylinders arranged in vertical array in line fixed between two wall. The experiments are carried for Rayleigh number (Ra) from (15x103 to 14 x104 ) and Prandtl  number from (0.706-0.714 ). The results indicated an increase in Nu with increasing Ra for all cylinders. Furthermore,hx and Nu increased proportionally with the increasing of cylinder spacings for all heat fluxes. Also the experimental results show the case of triangle arrangement is improvement the heat transfer more than case of vertical arrangement. Heat transfer dimensionless correlating equation is also proposed.              Nomeclature: Ax: surface area(m2), T∞: surrounding temperature(k), D: the outer diameter of fin (m), Kf: the thermal conductivity for air at film temperature(W/m.k), hx: Local convection heat transfer(W/m2.k),  Gravitational acceleration(m/s2), I: Electric current (Amp), Nu: Nusselt number, Pr: Prandtl number

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