Linear Fresnel Collector Receiver: Heat Loss and Temperatures

For design and component specification of a Linear Fresnel Collector (LFC) cavity receiver, the prediction of temperature distribution and heat loss is of great importance. In this paper we present a sensitivity analysis for a range of geometry and material parameters. For the LFC receiver analysis we use two models developed at Fraunhofer ISE. One is a detailed model, combining the spatial distribution of reflected radiation via ray tracing with detailed convective simulations through computational fluid dynamics. The second one is a fast algorithm based on a thermal resistance model. It is applying a similar methodology as the well-known model for vacuum absorber, enhancing an absorber tube model by parameters describing the influence of the secondary mirror and cover glass. The thermal resistance model is described in detail. Obtained results indicate a significant effect of the secondary mirror temperature on heat loss for specific geometries

Extended Heat Loss and Temperature Analysis of Three Linear Fresnel Receiver Designs

Heat loss prediction models for parabolic trough receivers do not consider the thermal effect of a secondary mirror. As an extension a Thermal Resistance Model (TRM) has been developed at Fraunhofer ISE for the prediction of the heat loss of three different Linear Fresnel Collector (LFC) receiver configurations. In previous investigations we have found the energy balance of a LFC receiver to be strongly influenced by the amount of solar radiation absorbed by the secondary mirror. This absorption provokes an increase of temperature of the secondary mirror and hence a decrease in the total amount of heat loss of a LFC. The size of this effect depends on the receiver geometry and diverse ambient parameters. Investigated parameters are wind velocity, ambient temperature and Direct Normal Irradiance (DNI). This dependency and its effect on heat loss and secondary mirror temperatures are analyzed for three different LFC receiver configurations. As the radiation absorbed by the secondary mirror is affected by the aperture area of the LFC, studies are performed for small-scale and for large-scale collectors

Enhanced equivalent model algorithm for solar mirrors

The SolarPACES Reflectance Guideline provides an essential tool to obtain comparable reflectance measurements, but because of the lack of adequate commercial instrumentation, till now the exhaustive characterization of reflectance behaviour versus incidence ¿i and (half) acceptance angle ¿ is unachieved. An expert group in Task III has been working to outline some practicable solutions. The Equivalent Model Algorithm (EMA) was found quite promising: with few input data, EMA allows to predict any reflectance feature by computation. The recent availability of reliable reflectance measurements at oblique incidence made possible the refinement of EMA by analysing a representative set of commercial solar mirrors. This paper describes the new EMA for solar mirror, named EMA4SM, and reports its validation

Transient channel incision along Bolinas Ridge, California: Evidence for differential rock uplift adjacent to the San Andreas fault

The rates and spatial distribution of active deformation provide critical constraints on the geodynamics of deforming lithosphere, yet such data are often difficult to acquire in eroding landscapes where poor preservation of geomorphic or stratigraphic markers hinders strain reconstruction. Recent advances in understanding of the relationship between bedrock channel profile form and erosion rate have led to their use as an index of rock uplift rate in steady state landscapes. Here we extend this analysis to landscapes experiencing a transient increase in erosion rate using an example from the Marin County region of northern California. We characterize channel and hillslope gradients in a series of small watersheds along a monolithologic portion of the Franciscan terrane in Marin County. Channel steepness indices vary strongly from north to south along the ridge and correspond with the progressive development of relief on threshold hillslopes along valley walls. These patterns argue that recent channel incision has engendered a transient adjustment of hillslope gradient, as incision outpaces soil production rates. These differences in landscape form and inferred incision rate are explained by differential rock uplift within the region east of the San Andreas fault. Relationships between channel gradient and incision rate suggest a threefold to fivefold difference in incision rate across the region and place a minimum bound on differential rock uplift rates. Our study highlights how landscape analysis can place bounds on the distribution of Earth deformation in both space and time and thus lends insight into the processes driving that deformation

Qualifying parabolic mirrors with deflectometry

Phase-measuring deflectometry is a full-field gradient technique that lends itself very well to testing reflective optical surfaces. In the past, the industry’s interest has been focussed mainly on the detection of defects and ripples, since it is easy to achieve sensitivity in the nm range. On the other hand, attempts to reconstruct the absolute surface shape from the gradient map have been plagued by systematic errors that accumulate to unacceptable uncertainties during data integration. Recently, thanks to improved measurement and evaluation techniques, the state of the art in absolute surface measurement has reached a level of maturity that allows its practical usage in precision optical manufacturing and qualification systems. We demonstrate the techniques, and the progress, by way of results from mirrors for telescopes, solar concentrators, and precision laboratory assemblies

The 10 Meter South Pole Telescope

The South Pole Telescope (SPT) is a 10 m diameter, wide-field, offset Gregorian telescope with a 966-pixel, multi-color, millimeter-wave, bolometer camera. It is located at the Amundsen-Scott South Pole station in Antarctica. The design of the SPT emphasizes careful control of spillover and scattering, to minimize noise and false signals due to ground pickup. The key initial project is a large-area survey at wavelengths of 3, 2 and 1.3 mm, to detect clusters of galaxies via the Sunyaev-Zeldovich effect and to measure the small-scale angular power spectrum of the cosmic microwave background (CMB). The data will be used to characterize the primordial matter power spectrum and to place constraints on the equation of state of dark energy. A second-generation camera will measure the polarization of the CMB, potentially leading to constraints on the neutrino mass and the energy scale of inflation.Comment: 47 pages, 14 figures, updated to match version to be published in PASP 123 903 (May, 2011

Efficient transplacental IgG transfer in women infected with Zika virus during pregnancy

Zika virus (ZIKV) is a newly-identified infectious cause of congenital disease. Transplacental transfer of maternal IgG to the fetus plays an important role in preventing many neonatal infections. However, antibody transfer may also have negative consequences, such as mediating enhancement of flavivirus infections in early life, or trafficking of virus immune complexes to the fetal compartment. ZIKV infection produces placental pathology which could lead to impaired IgG transfer efficiency as occurs in other maternal infections, such as HIV-1 and malaria. In this study, we asked whether ZIKV infection during pregnancy impairs transplacental transfer of IgG. We enrolled pregnant women with fever or rash in a prospective cohort in Vitoria, Brazil during the recent ZIKV epidemic. ZIKV and dengue virus (DENV)-specific IgG, ZIKV and DENV neutralizing antibodies, and routine vaccine antigenspecific IgG were measured in maternal samples collected around delivery and 20 paired cord blood samples. We concluded that 8 of these mothers were infected with ZIKV during pregnancy and 12 were ZIKV-uninfected. The magnitude of flavivirus-specific IgG, neutralizing antibody, and vaccine-elicited IgG were highly correlated between maternal plasma and infant cord blood in both ZIKV-infected and -uninfected mother-infant pairs. Moreover, there was no difference in the magnitude of plasma flavivirus-specific IgG levels between mothers and infants regardless of ZIKV infection status. Our data suggests that maternal ZIKV infection during pregnancy does not impair the efficiency of placental transfer of flavivirus-specific, functional, and vaccine-elicited IgG. These findings have implications for the neonatal outomes of maternal ZIKV infection and optimal administration of antibody-based ZIKV vaccines and therapeutics