Obtenção e estudo de uma superfície seletiva para coletores solares térmicos a partir de resíduos de granito

Abstract

The using of alternatives materials to replace selective surfaces is a natural trend, because it usually looks for improvements on efficiency of surfaces at the same time that it tries to reduce costs. Composites are already used on obtainment of some selective surfaces, however, if the possibility to use residue that would be discarded was associated to these characteristics, providing an added-value, it would brings some benefits like a possible reduction of manufacturing costs. Thus, this thesis proposes the obtainment and study of selective surfaces for flat plate solar collectors for low cost by using residue from granite industry. Three different surfaces was studied, two of them of obtained on the laboratory, one is granite powder made and the other is a surface composed by a mixture of granite powder and CRFO (Cr0,75Fe1,25O3); the third surface is a commercial one, known as TiNOX. To perform the tests of the surfaces it was built an experimental stand, it allows simulating a solar collector conditions. The tests was performed in a stagnation condition, in other words, there wasn’t any water flow inside tubes. Through this experimental apparatus it was possible to test the three surfaces simultaneously. The field tests showed that the highest temperatures were reached by granite powder surface, which reached an average temperature of 119 °C, while the granite powder and CRFO mixture surface reached an average of 96 °C. The TiNOX achieve an average temperature of 101 °C. The three surfaces was compared each other through an equation that gives a global heat loss coefficient. The granite powder surface was the one which achieved the lowest global heat loss coefficient