False color images can be created based on the Raman spectrum – these show the distribution of individual chemical components, and variation in other effects such as phase, polymorphism, stress/strain, and crystallinity. Motorized mapping stages allow Raman spectral images to be generated, which contain many thousands of Raman spectra acquired from different positions on the sample. It can even be used for the analysis of different layers in a multilayered sample (e.g., polymer coatings), and of contaminants and features beneath the surface of a transparent sample (e.g., impurities within glass, and fluid/gas inclusions in minerals). Raman micro-analysis is easy: simply place the sample under the microscope, focus, and make a measurement.Ī true confocal Raman microscope can be used for the analysis of micron size particles or volumes. Such analysis is possible using a Raman microscope.Ī Raman microscope couples a Raman spectrometer to a standard optical microscope, allowing high magnification visualization of a sample and Raman analysis with a microscopic laser spot. Raman spectroscopy can be used for microscopic analysis, with a spatial resolution in the order of 0.5-1 µm. Each peak corresponds to a specific molecular bond vibration, including individual bonds such as C-C, C=C, N-O, C-H etc., and groups of bonds such as benzene ring breathing mode, polymer chain vibrations, lattice modes, etc. However a small amount of light (typically 0.0000001%) is scattered at different wavelengths (or colors), which depend on the chemical structure of the analyte – this is called Raman Scatter.Ī Raman spectrum features a number of peaks, showing the intensity and wavelength position of the Raman scattered light. Most of the scattered light is at the same wavelength (or color) as the laser source and does not provide useful information – this is called Rayleigh Scatter. Raman is a light scattering technique, whereby a molecule scatters incident light from a high intensity laser light source. It is based upon the interaction of light with the chemical bonds within a material. Suspension temperatures of up to 750 ☌ are expected for metallic tubes, thus opening new opportunities for high efficiency thermodynamic cycles such as supercritical steam and supercritical carbon dioxide.Raman Spectroscopy is a non-destructive chemical analysis technique which provides detailed information about chemical structure, phase and polymorphy, crystallinity and molecular interactions. The suspension has a heat capacity similar to a liquid heat transfer fluid, with no temperature limitation but the working temperature limit of the receiver tube. A higher heat transfer coefficient may be expected at high temperatures because the wall-to-suspension heat transfer coefficient increases drastically with temperature. Heat transfer coefficients ranging from 140 W/m 2 K to 500 W/m 2 K have been obtained, thus corresponding to a 400 W/m 2 K mean value for standard operating conditions (high solid fraction) at low temperature. It is very sensitive to the particle volume fraction of the suspension, which was varied from 26 to 35%, and to the mean particle velocity. The mean wall-to-suspension heat transfer coefficient was calculated from experimental data. A single-tube solar receiver was tested with 64 µm mean diameter silicon carbide particles for solar flux densities in the range 200–250 kW/m 2, resulting in a solid particle temperature increase ranging between 50 ☌ and 150 ☌. Contrary to a circulating fluidized bed, the dense suspension of particles’ flows operates at low gas velocity and large solid fraction. This paper demonstrates the capacity of dense suspensions of solid particles to transfer concentrated solar power from a tubular receiver to an energy conversion process by acting as a heat transfer fluid.
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