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Description
Large windows are being evaluated for use in high temperature concentrated solar receivers to reduce radiative and convective losses, maintain a differential pressure, and separate reactants from ambient air for chemical processing. The design of a 1.7 meter diameter quartz dome window is evaluated for its ability to maintain acceptable stresses when exposed to pressure differentials and large heat loads from solar irradiation and re-radiation from the receiver walls. Just as important as the window geometry is the method to mount the window to the receiver. This thesis is a contribution to the design of a window mount prototype for a solar receiver called the Small Particle Heat Exchange Receiver (SPHER) intended to be built and tested at the National Solar Thermal Test Facility at Sandia National Laboratories as part of a DOE Sunshot Award to San Diego State University. The work presented in the following chapters builds upon successful pressurized solar receivers by others, including previous work done by colleagues at SDSU, and discussions with industry partners, Aerojet Rocketdyne and L-3 Brashear, to determine specific design constraints. An evaluation of varying window geometries is preformed and a spherical window with a cap angle of 45 degrees is evaluated using different mounting techniques. Since this is much more than an academic exercise, research is done with commercialization in mind - factors like material procurement, cost, reliability and assembly all need to be heavily considered. Trade studies of materials, gaskets, and conceptual designs are presented along with the methodology of the design process. To first understand the acceptable tensile stresses in the window a Weibull failure probability method is used to arrive at a projected lifetime of the window under a constant state of stress. This approach is used to determine the maximum design tensile stress of 7.25 MPa during operation of the solar receiver under the assumption that is under a constant load. A reduced in duty cycle at the same load will effectively lengthen the lifetime. Remediating the tensile stresses proves to be a challenge and many design concepts are evaluated. Window temperatures from a Monte Carlo Ray Trace (MCRT) method of the National Solar Thermal Test Facility heliostat field and receiver re-radiation are utilized to couple the thermal mechanical effects of the window and its mount. A design concept is developed using Grafoil as the sealing interface at the window edge and a flexure system to accommodate the thermal expansion differences between the window mount and the receiver body. The mapped temperatures within the window, boundary pressure of 5 MPa, along with other mechanical effects become inputs to COMSOL Multiphysics, a Finite Element Analysis (FEA), model where the maximum stresses in the window and surrounding components are evaluated to ensure the failure criterions are met. The design is promising but varying results of the tensile stress based on contact conditions are observed and the resulting analysis is presented.
