Figure1.2. Schematic solar tower central receiver with quartz window on it. southern Spain couple of year back. And recently BrightSource's IVANPAH which has.
WINDOW AND SEAL DESIGN FOR A SMALL PARTICLE SOLAR RECEIVER
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A Thesis Presented to the Faculty of San Diego State University
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In Partial Fulfillment of the Requirements for the Degree Master of Science in Mechanical Engineering
ABSTRACT OF THE THESIS Window and Seal Design for a Small Particle Solar Receiver by Onkar Kiran Mande Master of Science in Mechanical Engineering San Diego State University, 2011 Central receivers for solar power towers have recently been under intense investigation. They can convert solar radiation into electricity by supplying heat to a thermodynamic cycle. In particular, air-cooled solar central receivers can power gas turbine engines for electrical generation. Solar heating of the compressed air is realized in a pressurized volumetric receiver. A new type of receiver module consists of an insulated pressure vessel, closed by a quartz glass window and a mixture of small particles in air as working medium. The process has so far been investigated mainly in Spain, Israel, Germany and United States with different designs with varying power outputs, all below 400 kW. However, the critical part of the whole assembly is the window which transmits solar flux into the receiver. To overcome the drawbacks of the previously designed windows a new geometry was developed and an appropriate method of building it economically and commercially is suggested. The main focus of this project is to analyze different materials obtainable from the market, Optimize the window design of one large window and Ideal mounting arrangement. A part of this work is carried out by using Finite Element Analysis of quartz glass windows of different shapes using the commercial software Hypermesh and Solidworks. The analysis will be performed taking in to account the load and boundary conditions for the window design. The operating conditions for the receiver will provide a uniform 5bar pressure distribution on the window. The high pressure makes receiver window design difficult, further analysis was done with considering different seal arrangements for window design and a better seal arrangement with reduced stresses on to the window is suggested. Finally a unique morphed geometry of the window was produced and a seal arrangement for it was suggested. Project is been multi-disciplinary in nature with structural analysis followed by modeling and optimization of the different geometries.
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TABLE OF CONTENTS PAGE ABSTRACT...............................................................................................................................v LIST OF TABLES ................................................................................................................... ix LIST OF FIGURES ...................................................................................................................x ACKNOWLEDGEMENTS ................................................................................................... xiii CHAPTER 1
INTRODUCTION .........................................................................................................1 1.1 Small Particle Solar Receiver ............................................................................4 1.2 Requirements for a Windowed Receiver ...........................................................6 1.3 Scope of Work in Thesis ....................................................................................7
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A REVIEW OF WINDOWED SOLAR CENTRAL RECEIVERS ..............................9 2.1 General Description about Solar Tower Receivers ............................................9 2.2 Solar-Hybrid Gas Turbine-based Power Tower Systems (REFOS) ................13 2.2.1 Description of the Test Setup..................................................................13 2.2.3 Elliptical Window of REFOS .................................................................15 2.2.4 Window Sealing ......................................................................................18 2.2.5 Cooling of the Window...........................................................................19 2.3 Solgate..............................................................................................................21 2.4 DIAPR..............................................................................................................22 2.4.1 Description of the Test Setup ..................................................................22 2.4.2 Receiver Design and Main Components.................................................23 2.4.3 A Porcupine Volumetric Absorber .........................................................24 2.4.4 A Frustum like High Pressure Window (FLHIP) ...................................25 2.4.5 Window Sealing ......................................................................................27 2.5 A Multistage Solar Receiver ............................................................................28 2.6 A Bell Shaped Window Receiver Concept ......................................................30 2.7 E-Solar Windowed (LGR) Receiver Concept..................................................32 2.8 SOLUGAS- Project by Abengoa Solar............................................................34
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SPHER WINDOW MATERIAL CONSIDERATION AND MANUFACTURING TECHNIQUES ........................................................................36 3.1 Different Material Considerations ...................................................................36 3.2 Fabrication Technique of a 3m Quartz Window..............................................45 3.2.1 The Sag Method ......................................................................................46 3.2.2 Spin Casting Method...............................................................................49 3.3.3 A Survey of Telescope Mirror Blanks that have been Manufactured so Far ........................................................................................51 3.4 Anti-Reflective Coatings for the Windows......................................................52
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OPTIMIZATION OF A HEMISPHERE .....................................................................54 4.1 To Find an Appropriate Cap Angle by Using Buckling Criterion ...................54 4.2 Minimum Thickness Calculation for Spherical Window Cap .........................59
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SEAL DESIGN OF SMALL PARTICLE SOLAR RECIVER WINDOW ................67 5.1 Working Stresses .............................................................................................70 5.1.1 Window ...................................................................................................70 5.1.2 Metallic Hatch Ring ................................................................................71 5.1.3 Graphite Ring ..........................................................................................73 5.2 Selection of Dimensions ..................................................................................75 5.3 New Seal Design ..............................................................................................77 5.4 Development of the FEA Model ......................................................................79 5.4 Stress Analysis on Modified Model .................................................................84 5.5 Compressive Stresses Inside Grafoil for all Seal Assemblies .........................85
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FREE SHAPE OPTIMIZATION TO REDUCE STRESSES .....................................88 6.1 Comparison of Bending Stress in Ellipse ........................................................89 6.2 Free Shape Optimization using Optistruct .......................................................92 6.2.1 Deciding on Optimization Solver and Type of Optimization .................92 6.2.2 Optimization Model in OptiStruct ..........................................................93 6.2.3 Optimization Model in OptiStruct ..........................................................94 6.2.4 Element Shape Consideration and Type of Elements .............................96 6.2.3 Defining the Control Cards and the Criteria for the Free Shape Optimization ....................................................................................................97 6.3 Optimization Results : Shape Change and 1st Principle Stress Optimized.............................................................................................................100
viii 6.4 Comparison of New Geometry with an Ideal Ellipse ....................................104 7
FINDINGS AND CONCLUSION ............................................................................106
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FUTURE WORK .......................................................................................................108
LIST OF TABLES PAGE Table 2.1. Summary of Previously Build Windowed Solar Receivers ....................................12 Table 2.2. General Description of the REFOS Receiver .........................................................14 Table 2.3. General Description of the DIAPR Receiver ..........................................................23 Table 2.4. General Description of the Multi-Stage Receiver...................................................30 Table 3.1. Comparison of Different Materials .........................................................................39 Table 3.2. Refractive Index for Different Wavelength for Infrasil 302 ...................................41 Table 3.3. Different Grades of the Infrasil ...............................................................................44 Table 3.4. Different Telescopic Mirror Blanks Made Out of Quartz ......................................52 Table 4.1. Comparison of Two FEA Models with Analytical Solution ..................................64 Table 5.1. Different Material Properties of Fused Silica .........................................................72 Table 5.2 Different Material Properties of Grafoil ..................................................................73 Table 5.3. Different Material Properties of Kovar ...................................................................74 Table 5.4. Change in Young's Modulus for Different Surface Pressures ................................74 Table 5.5. Analysis Results for the Seal Design ......................................................................83 Table 5.6. Analysis of the New Modified Design ...................................................................86 Table 6.1. Optimization Model Description ............................................................................98 Table 6.2. Results of the Optimization Model .......................................................................100
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LIST OF FIGURES PAGE Figure 1.1. Different CSP technologies. ....................................................................................2 Figure1.2. Schematic solar tower central receiver with quartz window on it............................4 Figure 1.3. Cross section of the small particle solar receiver. ...................................................6 Figure 2.1. Tubular type solar receiver (solar one). .................................................................10 Figure 2.2. Schematic of a DLR volumetric receiver. .............................................................14 Figure 2.3. Design of the elliptical window (REFOS).............................................................16 Figure 2.4. Different foot designs for the DLR window..........................................................18 Figure 2.5. Basic seal concept of the DLR window. ...............................................................19 Figure 2.6. Different cooling arrangements of the DLR window using nozzels. ....................20 Figure 2.7. SOLGATE receiver concept having 3 DLR receivers in series. ...........................21 Figure 2.8. Directly irradiated pressurized air receiver (DIAPR). ...........................................23 Figure 2.9. Design of the frustrum-like high pressure window (DIAPR). ..............................26 Figure 2.10. The frustum-like high-pressure window, for the 50kW receiver that was tested. ...........................................................................................................................28 Figure 2.11. Assembly of the concentrator array and pre-heaters over the central stage CPC ..............................................................................................................................29 Figure 2.12. A bell shaped window receiver concept. .............................................................31 Figure 2.13. Light guided receiver concept by eSolar. ............................................................33 Figure 2.14. Quartz rods in an absorber tubes. ........................................................................33 Figure 2.15. SOLUGAS proposed tubular receiver. ................................................................35 Figure 3.1. Transmittance chart for various materials at different wavelengths. ....................39 Figure 3.2. Calculation of the refractive index n for different wavelengths (Infrasil 302). .............................................................................................................................42 Figure 3.3. Spectral absorptance of Infrasil 302. .....................................................................43 Figure 3.4. Stacked boules-stacked and sealed. .......................................................................46 Figure 3.5. Fused silica mirror blank fabrication by using sag method. ..................................47 Figure 3.6. Cooling rate curve for a fused silica (annealing)...................................................48 Figure 3.7. Spin casting method. .............................................................................................49
xi Figure 3.8. Hexagonal stacks of glass laid down to make a complete circle. ..........................50 Figure 4.1. Different types of buckling domes. .......................................................................55 Figure 4.2. Truncated spherical cap defined by angle ф. .........................................................56 Figure 4.3. Minimum thicknesses for different ф angle at critical buckling pressures. ..........57 Figure 4.4. Weight of the window for different ф angles. .......................................................58 Figure 4.5. Buckling stress x 1/10 for spherical window cap as a function of pressure and edge angle..............................................................................................................59 Figure 4.6. Diagrams showing the membrane forces and bending forces on a axisymmetrically loaded shell. .........................................................................................61 Figure 4.7. Analytical distribution of the principle stresses along different ф angle for an clamped edge. ..........................................................................................................62 Figure 4.8. Value of the first principle stress for different thicknesses for a 3m diameter window. .........................................................................................................63 Figure 4.9. Computational results of distribution of principle stresses along different ф angle (COSMOS). ....................................................................................................64 Figure 4.10. Distribution of maximum tensile stress for different ф angles. ...........................66 Figure 5.1. Window seal design using epoxy/adhesive. ..........................................................69 Figure 5.2. Seal design by bolting the window to the metal plate. ..........................................70 Figure 5.3. f Stress limits of fused silica. .................................................................................72 Figure 5.4. Window seal design similar to that of the DLR concept. ......................................77 Figure 5.5. First principle stresses on to the window and the metallic plate. ..........................78 Figure 5.6. Exploded view of the new window seal design.....................................................79 Figure 5.7. Schematic showing the dimensions of the window seal design similar to that of the submersible window. ..................................................................................79 Figure 5.8. High density mesh of the seal design. ...................................................................81 Figure 5.9. Figure showing the loads and BC on the seal design. ...........................................81 Figure 5.10. First principle stress distribution on to the window and the seal assembly.........83 Figure 5.11. Stress distribution on different phi angles of the window for a new seal design. ..........................................................................................................................83 Figure 5.12. Modified new seal design. ...................................................................................84 Figure 5.13. Distribution of first principle stresses of modified seal design. ..........................85 Figure 5.14. Stress distribution on different phi angles of the window for modified design. ..........................................................................................................................86 Figure 5.15. Maximum compressive stresses in grafoil for different seal designs. .................87
xii Figure 6.1. Morphing of the window to a better geometry. .....................................................90 Figure 6.2. 1st principle distribution of the window with a new shape. ..................................91 Figure 6.3. Stress distribution on different phi angles of the window with a new shape. ...........................................................................................................................91 Figure 6.4. OptiStruct iterative solution. .................................................................................93 Figure 6.5. Free shape optimization model cross-section view and set up. .............................95 Figure 6.6. Mesh distribution and flow of elements. ...............................................................97 Figure 6.7. Assigning the move factor the above nodes. .........................................................99 Figure 6.8. Contour plots for the shape change and different geometries at different iterations.....................................................................................................................102 Figure 6.9. Contour stress plots for the initial and new geometry. ........................................103 Figure 6.10. New shape of the window at iteration 9. ...........................................................104 Figure 6.11. Comparison of all the three window geometries. ..............................................104 Figure 6.12. Stress distributions on different phi angles of the window for an ellipse. ........105
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ACKNOWLEDGEMENTS This dissertation was made possible by the continual supervision and the support of more than a few individuals who in one way or another subsidized and extended their much appreciated assistance in my research for this study. Foremost, I would like to thank my advisor, Professor Fletcher Miller, for his insight and encouragement throughout the time I spent working on this thesis. My co-advisor, Dr. Arlon Hunt, was also there to share his experience from many years of research in the solar energy field. It was a pleasure working alongside both Professor Miller and Dr. Hunt. I also would like to thank Professor Samuel K. Kassagne and Professor Satchi Venkatarman for accommodating my rushed schedule in the weeks leading up to my thesis defense. I would like to thank my friends in the Combustion and Solar Energy Laboratory for all their help and also my family in India who have been there for me through thick and thin. Lastly, I would like to thank Google.org for supporting my thesis research under grant agreement #32-2008 as part of their RE
