Browsing by Subject "Solar radiation"
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Item A theoretical analysis of solar collector/storage panels(Texas Tech University, 1977-12) Fender, David AllenA theoretical model for the evaluation of the transient performance of combination solar energy collection and heat storage panels is derived and analyzed. Beginning with the MIT II House (1947) and including several houses built in the 1960's by the CRNS Solar Energy Laboratory in Odeillo, France, published experimental studies of CS systems have shown considerable variance in determined operating effectiveness. Economic advantages have led to commercial exploitation of these systems, although design criteria are absent from the literature. Use is made of an analytical method for determining fully developed natural convection in a vertical, symmetrically heated channel derived by Ostrach (1952), further developed by Bodoia and Osterle (1962), and modified and empirically verified for simple, uniform, asymmetrically heated boundary conditions by Aung (1972). This method is then further expanded for use with numerically implicit boundary conditions involving glazing wall heat conduction. A simulation program is used to establish CS panel operating characteristics and design criteria for performance optimization. Results indicate that solar thermal efficiencies of up to approximately five percent are obtainable during mild weather with useful heat being recoverable up to about 50 percent of the time, depending on ambient temperature, selected design criteria, and incident solar energy. In cooler weather, excessive heat loss out of the cover glazing prevents any useful heat gain from being obtained.Item Protection against UVB-induced damage to keratinocytes by antioxidant nutrients(Texas Tech University, 1996-05) Stewart, MarjoryThe ultraviolet component of sunlight causes increases in reactive oxygen species, and to the extent that these species exceed the ability of antioxidant defenses to remove them, oxidative damage occurs. Antioxidant systems have evolved to protect organisms from endogenous and exogenous reactive oxygen species — in humans these systems are enzymatic and non-enzymatic, and the non-enzymatic systems include certain nutrients. Evidence from biological and epidemiological studies suggests that vitamins C, E, B-carotene and selenium have useful roles in chemoprevention. 8-OHdG is an oxidative DNA lesion that can be sensitively measured as an index of oxidative stress in cells, using HPLC coupled with ultraviolet and electrochemical detection. These lesions can lead to transversion mutations and can therefore potentially contribute to skin cancer. Using Balb/c MK-2 cells the level of 8-OHdG residues, normalized to normal dG residues, was measured following UVB exposure for keratmocytes grown in several nutrient-specific media. UVB doses from 4-500 mJ/cm increased the level of adducts for cells grown m EMEM, but with supplementation of 5 pg/mL selenite, 0.8 pg/mL ascorbate, or 20 pg/mL trolox (a vitamin E analog), the level of adducts was reduced to the level seen in unirradiated controls. Within 24 hours of a 500 mJ/cm^2 UVB insult, the activity of antioxidant enzymes superoxide dismutase and catalase increased; the level of induction or activity increase was greatest for cells grown with the lowest levels of antioxidant nutrients. This suggests some complementarity for enzymatic and non-enzymatic defenses. Cell culture medium contains little or no selenium, and glutathione peroxidase is consequently very low unless cells are supplemented. With supplementation there is an increase in glutathione peroxidase, but the level of this enzyme is unchanged by increasing Se to concentrations five times greater. P53 constitutively arrests the cell cycle to allow repair of damaged DNA. Immunoblots of protem from cells pre-incubated with supplemental nutrients showed little difference across treatment. Immunoblotting for bcl-2, a protein that inhibits apoptosis, showed a greater that 5x stronger band for Se-treated cells than for the negative control. Collectively these data show that the ultraviolet component of sunlight causes damage that is free-radical mediated, and that some of this damage can be reduced by antioxidant nutrients.Item The anisotropy of diffuse solar radiation(Texas Tech University, 1969-12) Morris, Charles Wayne,Not availableItem The effects of surface roughness on convection with external flow(Texas Tech University, 1982-12) Luttrell, Jeffrey PaulThe receiver external heat transfer geometry for a fixed-mirror, distributed-focus solar power station was simulated with a 3-inch diameter, 12-inch long coil of 0.375-inch diameter stainless steel tubing. The coil was heated electrically and the heat transfer equated to electrical power. Free convection tests were made with the coil axis varied in steps from horizontal to vertical. Forced convection tests were made at four orientations of the coil axis relative to the flow direction: perpendicular, 60, 45 and 30 degrees. Reynolds numbers ranged from 3,000 to 80,000 for the forced convection tests. Temperature differences ranged from 300 to 950 F. Free convection results showed a greater increase of convection with increasing-temperature difference than a smooth cylinder. Forced convection results were similar to those for a smooth cylinder in cross-flow correlations. Contrary to experience with smooth cylinders, convection was increased when the flow had a component along the coil axis and the Reynolds number was greater than 6000.Item The thermal behavior of spherically curved solar collector mirror panels exposed to concentrated solar radiation(Texas Tech University, 1980-12) Agarwal, Vijay KumarUnder certain conditions the mirror panels in 'Fixed Mirror Distributed Focus’ (FMDF) type of solar collectors are subject to a moving heat source (hot spot) formed by concentrated solar radiation. A two-dimensional finite difference scheme was devised to predict the temperature distribution in the panels under these conditions. The predicted results were compared with experimental data and, show good agreement. The prediction model is therefore considered adequate for use in design and selection of materials for the panels. Some parametric studies based on the above model show that severity of the problem can be reduced by choosing mirror materials having higher thermal capacity and lower absorptivity.