Most of the solar collectors experiments are carried out under clear-sky conditions to evaluate the maximum performance of collectors, even though this condition is not critical for some uses, such as cooking. The optical and thermal performance of a solar oven heated by Scheffler concentrator is here analyzed in more adverse weather conditions. The receiver for conversion and heat transfer of the concentrated solar energy is coupled to an oven specially developed for this work. The Scheffler concentrator geometry is a lateral cut angled 43.23° of a paraboloid matrix, and it works in a two-axis tracking system, to always maintain its focal image at the stationary receiver with the progression of the Earth rotation and solar declination movements. A model for distributing the daily radiation over the hours is used to compare the results. The time-constant experimental method is considered. The heating and cooling tests were carried out at the official local time. The maximum temperature achieved by the absorber was 328°C, and the maximum average temperature in the oven was 150°C. The results for heat loss factor were evaluated, and the trends for thermal efficiency and optical efficiency factor were analyzed for the system considered.

Our purpose is to help projects of receivers for Scheffler concentrators in order to avoid losses of energy at the entrance of thermal radiation absorbers. The Scheffler concentrator is a paraboloidal solar concentrator that works in a two axes track system and, thus, maintains the focal image fixed in its stopped absorber with the variation of the solar declination and azimuth. The image formed by Scheffler concentrator is presented. The reflector geometry is defined by a lateral section of a paraboloid and its reflector has elliptical profile. At equinox, these rim angles are approximately 49.6 and 109.6 degrees from the paraboloid axis. However the tracking system for adjusting to the variation in solar declination causes a change in these rim angles. An analysis of the effect of these variations over the image of the focus, the aperture area to the Sun, and the concentration ratio is performed. The effect of the variations of rim angles was found to cause variations in the size of the focal image ofScheffler reflectors in two axes, and these variations differ among these axes. Were also found that the aperture area can vary twice, and, the concentration ratio, once during the year.

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As máximas 'Buscai e achareis' é análoga à 'Ajuda-te, e o céu te ajudará'. É o princípio da lei do trabalho, e, por conseguinte, da lei do progresso, porque o progresso é filho do trabalho, e o trabalho coloca em ação as forças da inteligência." Allan Kardec. AGRADECIMENTOSAgradeço a Deus pela oportunidade, força e condições para a realização deste trabalho.À minha esposa Tatiana e filhas Valentina e Victoria, pelo amor, paciência, compreensão e esperança depositado em mim durante este período.Aos meus pais, pelo amor incondicional direcionado a mim, em forma de educação e ensino dos valores de família e missões de vida.Aos meus avós, que me ensinaram o precioso valor da família e instalaram em minha memória preciosos conselhos: "o estudo é a luz da vida".À minha irmã, Gabriela, que ajudou a viabilizar a bancada deste trabalho.Ao professor Flávio Augusto Sanzovo Fiorelli pelo acolhimento e pela orientação bem direcionada com o objetivo no progresso deste trabalho.Ao professor Raul Gonzalez Lima, pela orientação em momentos críticos apoiando a continuidade deste projeto.Aos professores Guenther Carlos Krieger Filho e Sílvio de Oliveira Júnior pela ótima arguição na banca de qualificação deste trabalho.Ao professor Cláudio Roberto de Freitas Pacheco pelas horas de sábias orientações, não somente de engenharia solar, mas também de vida, pelo seu exemplo.A Isabel Kodama, pelo grande auxílio nos trabalhos experimentais e ajustes no texto da tese.Ao Gustavo Moreira Dias, pela grande ajuda nos trabalhos experimentais durante a pandemia.