Evaluation of Cellular Glasses for Solar Mirror Panel Applications

摘要

An analytic technique is developed to compare the structural and environmental performance of various materials considered for backing of second surface glass solar mirrors. Metals, ceramics, dense molded plastics, foamed plastics, forest products and plastic laminates are surveyed. Cellular glass is determined to be a prime candidate due to its low cost, high stiffness-to-weight ratio, thermal expansion match to mirror glass, evident minimal environmental impact and chemical and dimensional stability under conditions of use. While applications could employ this material as a foam core or compressive member of a composite material system, the present analysis addresses the bulk material only, allowing a basis for simple extrapolations.nThe current state of the art and anticipated developments in cellular glass technology are discussed. Material properties are corre¬lated to design requirements using a Weibull weakest link statistical method appropriate for describing the behavior of such brittle materials. A mathematical model is presented which suggests a design approach which allows minimization of life cycle cost;given adequate information for a specific application, this would permit high confidence estimates of the cost/performance factor.nA mechanical and environmental testing program is outlined, designed to provide a material property basis for development of cellular glass hardware, together with methodology for collecting lifetime predic¬tive data required by the mathematical treatment provided herein.nPreliminary material property data from measurements is given. Microstructure of several cellular materials is shown, and sensitivity of cellular glass to freeze-thaw degradation and to slow crack growth is discussed. The effect of surface coating is addressed. Conventional manufacturing refinements are considered which, while not generally applied as yet to cellular glass, nevertheless lend themselves readily to this material. They are tentatively seen as promising to answer design needs even using present cellular glass chemistry, for a high performance, low environmental impact, medium cost solar mirror system.