Caracterização e aplicação de uma superfície seletiva para coletores solares térmicos a partir do líquido da casca da castanha de caju

Abstract

Solar energy is one of the most promising sources of energy on the planet, due to its great availability and applicability in thermal processes. However, its use still represents a major technological and economic challenge, as many systems that use this energy still have low efficiency and high cost. Thus, the development of new materials and technologies to increase the efficiency of solar thermal collectors is both a challenge and a necessity. In this context, the objective of this work is to obtain and analyze selective surfaces for thermal solar collectors, using as material the Cashew Nut Shell Liquid (CNSL) - the natural and the technical. For the tests, an experimental bench was constructed to simulate a flat plate solar collector under real operating conditions. Some characterizations will be carried out, such as: scanning electron microscopy (SEM) techniques, infrared analysis and determination of UV-VIS absorbance, as well as graphs with surface temperatures and with radiation during the tests in the sun for all surfaces: 100 % Natural CNSL, 25% Technical CNSL + 75% Natural CNSL, 50% Technical CNSL + 50% Natural CNSL, 75% Technical CNSL + 25% Natural CNSL and MRTiNOX. In the field test, all five surfaces composed of technical CNSL and natural CNSL, presented temperature values close to the values reached with the commercial surface, however, in relation to the absorptivity values, the surfaces with a higher percentage of technical CNSL (100 % technical CNSL and 75% technical CNSL + 25% natural) showed values close to those obtained by MRTiNOX, mainly for the 100% technical CNSL surface, which obtained the value of 0,90. In general, the 100% technical CNSL surface was the closest to the commercial surface in all the analyzed results. Therefore, it can be concluded that the technical CNSL presents itself as a possible alternative material for use in solar thermal collectors, which would represent a decrease in the cost of these collectors, in addition to giving a more adequate destination to the CNSL.