Caracterização de novas superfícies seletivas, à base de óxido de titânio, de óxido de cromo e de pó de granito, para coletores solares

Abstract

The depletion of fossil fuel reserves and climate change caused by atmospheric pollution have led the human being to seek alternatives that are less harmful to the environment. The concern and the awareness of the population open space for the study of renewable energies to be deepened, among them the best use of solar energy. The use of alternative materials to replace selective surfaces is a natural trend, since improvements in surface efficiency are usually sought while attempting to reduce costs. Composite substances have already been used to obtain some selective surfaces, and, as a result, the search for better processes awakens research on more appropriate and lower cost materials, which represents a great scientific potential in the evolution of these technologies. Thus, the present work consisted in obtaining and studying selective surfaces for applications in low-cost flat plate solar collectors, using residues from the granite industry, titanium oxide and chromium oxide. Different selective surfaces were produced, consisting of the use of the following materials, varying the percentage by weight: 100% granite powder, 100% chromium oxide, 100% titanium oxide, granite powder + chromium oxide (75% - 25%, 50-50% and 25% -75%) and granite powder + titanium oxide (also 75% -25%, 50%-50% and 25% -75%). For the tests, an experimental wooden bench was built, and it was possible to simulate the conditions of a flat plate solar collector. Thus, the selective surfaces were simultaneously tested. The efficiency of the surfaces was determined by the ratio of the absorptivity through the emissivity, as well as the trademark MRTiNOX. An efficiency of 23.58 was obtained for this, while for the 50% granite - 50% titanium surface the value of 23.30 (closest to the trade mark) was calculated. Therefore, replacing the traditional components of selective surfaces with granite proved to be a satisfactory solution, contributing to the reduction of costs with work involving solar energy.