Research On Spectral Emissivity Measurement Technologies Of Solar Selective Absorbing Coating

The solar thermal power technology has been paid more attention by countriesall over the world with the energy crisis and environmental pollution. In the solarpower generation, selective absorbing coatings are the key components of thesolar-thermal energy conversion. Spectral radiance characteristic of the coatings isthe underlying technology indicator to determine the absorption efficiency and keyfator influencing on the efficiency of the solar thermal power generation system.Emissivity measurements have an important scientific value for coatings to enhancethe absorption of solar energy and reduce its thermal radiation losses at hightemperature by improving the design and preparation of coatings, and a far-reachingsignificance for solving the problem of energy crisis and environmental pollution bypromoting the development of solar thermal power generation technology.The multi-spectral emissivity measurement method based on the assumingmodel has its limitations for in-situ measurement. It is important to solve theproblem of emissivity model for multilayer materials in order to achieve in-situemissivity measurement of collector coatings. Without the uniform referencestandard, emissivity measurement technology based on integrating spherereflectometer is impossible to solve problems arised from the emssivity quantitytransmission. It has an important theoretical significance to achieve the emissivityquantity transmission without the utilization of reference standard. For the oxidationof remarkable selectivity coatings and significant change of its spectral emissivity, itis the key technology problem solved in this paper to develop the spectral emissivitymeasurement system for solar selective absorbing coating. According to theproblems above, the main research contents are as follows:An in-situ multi-spectral emissivity measurement method of collector tubecoatings is proposed. For the multi-layer structure of coatings, electromagnetic wavepenetration depth and reflective characteristics of metal films are analysised. Therelations between optical constants of absorbing film and metal-doped volumenumber, and the influence of the absorption film thickness on the reflectivity of thecomposite membrane are studied. The emissivity model of metal-ceramic coatingfilm structure parameters is established. The method to achieve emissivity modelparameters in adaptive simulated annealing is proposed with the constraint equationsbetween measurement values of spectral radiance and calculated values withemissivity model. Using the spectral radiance values measured by the fouriertransform infrared spectrometer, the consistency of values measured by multi-spectral emissivity measurement method based on the structural parametersmodel of coatings and values measured by energy method is better than two existingassume models.A new quantity transmission method of spectral emissivity measurement basedon integrating sphere reflectometer is proposed. Based on the radiation powercalibration, the incident radiation power of the sample is derived by a function of themeasured voltage of detector and solid angle relationship formula between theprojection area of the sample and the sensitive area of detector. The reflectedradiation power of the sample is derived by a function of the measured outputvoltage of integrating sphere and steradian formula of its output hole. Thetransimissin model of spectral emissivity is established by determining the transfercoefficient between measured voltages and spectral emissivities.A spectral emissivity measurement system for the solar selective absorbingcoating is developed. The high vacuum equipment with10-3Pa is developed to avoidthe oxidation of coatings being measured at high temperature. A silica glassintegrating sphere vacuum-plated with Al on its internal surface is developed tosolve the spectral emissivity measurement problems in the infared region. Thedifficult problem of temperature overshooting control in the heating process underhigh vacuum is solved with dynamic heating algorithm of target temperature value.The emissivity measurement system in the range0.4-10μm and in the temperaturefrom300K to over900K is built.Based on the emissivity measurement system for the solar selective absorbingcoating, the transfer coefficient between measured voltages and spectral emissivitiesis calibrated. Measurement experiments of the high and low emissivity materialshow that the transfered values of emssivity is consistent with literature values. Theemissivity of the Mo-SiO2coating sample is measured, its measurement curve isconsistent with literature data. The uncertainty is analyzed and estimated emissivitymeasurement standard uncertainty is0.029.