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ABSTRACT:The room-temperature mechanical properties of a closed-cell, polyurethane encapsulant foam were measured as a function of foam density. Over the range of densities examined, the modulus could be described by a power-law relationship with respect to density. This power-law relationship was the same for both tension and compression testing. The basis for this power-law relationship is explained in terms of the elastic compliance of the cellular structure of the foam using a simple geometric model put forth by Gibson and Ashby. The elastic collapse stress, a property relevant to compression testing, also is found to exhibit a power-law relationship with respect to density. The density dependence of this property is also found in the work of Gibson and Ashby and is explained in terms of the Euler buckling of the struts that comprise the cellular structure. Energy absorption during deformation is also reported for both tension and compression testing.

Quasi-static compression tests have been performed on polyurethane foam specimens. The modulus of the foam exhibited a power-law dependence with respect to density of the form: E* ϰ (*) n , where n ϭ 1.7. The modulus data are described well by a simple geometric model (based on the work of Gibson and Ashby) for a closed-cell foam in which the stiffness of the foam is governed by the flexure of the cell struts and cell walls. The compressive strength of the foam is also found to follow a power-law behavior with respect to foam density. In this instance, Euler buckling is used to explain the density dependence. The modulus of the foam was modified by addition of gas-atomized, spherical, aluminum powder. Additions of 30 and 50 wt % Al measurably increased the foam modulus, but without a change in the density dependence. However, there was no observable increase in modulus with 5 and 10 wt % additions of the metal powder. Strength was also increased at high loading fractions of powder. The increase in modulus and strength could be predicted by combining the Gibson-Ashby model, referred to above, with a well-known model describing the effect on modulus of a rigid dispersoid in a compliant matrix.

Solar Two was a collaborative, cost-shared project between 11 U. S. industry and utility partners and the U. S. Department of Energy to validate molten-salt power tower technology. The Solar Two plant, located east of Barstow, CA, comprised 1926 heliostats, a receiver, a thermal storage system, a steam generation system, and steam-turbine power block. Molten nitrate salt was used as the heat transfer fluid and storage media. The steam generator powered a 10-MWe (megawatt electric), conventional Rankine cycle turbine. Solar Two operated from June 1996 to April 1999. The major objective of the test and evaluation phase of the project was to validate the technical characteristics of a molten salt power tower. This report describes the significant results from the test and evaluation activities, the operating experience of each major system, and overall plant performance. Tests were conducted to measure the power output (MW) of the each major system, the efficiencies of the heliostat, receiver, thermal storage, and electric power generation systems and the daily energy collected, daily thermal-to-electric conversion, and daily parasitic energy consumption. Also included are detailed test and evaluation reports.

The isothermal corrosion behavior of two stainless steels and carbon steel in mixtures of NaNO3 and KNO3 has been evaluated to determine if the impurities found in commodity grades of alkali nitrates aggravate corrosivity as applicable to an advanced solar thermal energy system. Corrosion tests were conducted for approximately 7000 hours with Types 304 and 316 stainless steels at 570°C and A36 carbon steel at 316°C in seven mixtures of NaNO3 and KNO3 containing variations in impurity concentrations. Corrosion tests were also conducted in a ternary mixture of NaNO3, KNO3, and Ca(NO3)2. Corrosion rates were determined by descaled weight losses while oxidation products were examined by scanning electron microscopy, electron microprobe analysis, and X-ray diffraction. The nitrate mixtures were periodically analyzed for changes in impurity concentrations and for soluble corrosion products.