Adjusting and Performance assessment of an elliptical dish (scheffler reflector). In case of an installed scheffler coffee roaster at Jimma University.

Abstract

Solar energy is now days one of the most important source of energy due to the scarcity (limited source of fossil fuel) and environmental crisis of carbon release from fossil fuel. It is clean and has no any negative impact on environment and ecology. As its source is a sun, it is renewable and free energy, which mostly used for power generation and heating purposes. Scheffler reflector is one of the various methods of harvesting the solar energy. These concentrators are lateral sections of paraboloids and provide fixed focus away from the path of incident beam radiations throughout the year. This study presents the performance assessment of scheffler reflector that installed at JUCAVM campus, which has a total surface area of 16m2 .The scheffler reflector installed has attempted to roast coffee bean for commercial purposes, but due to the error that is committed during the installation, the reflector could not concentrate the ray coming from the sun. Hence, this study reveals the reason why the solar beam reflected dispersed instead of concentrating since scheffler reflector has a fixed focus throughout the year. Finally, after a successful assessment and corrective measures taken the dish has brought to concentrate the ray at the fixed focus and the required amount of heat for roasting coffee bean have been harnessed. Additionally, collecting solar data at the place of assessment and observing the effect of seasonal change on the reflector performance was also part of the assessment. After series of assessments, the scheffler reflector has concentrated the solar ray at the fixed focus. The other corrective measure has also been done on the absorber (roaster). Since the roaster could not distribute the required heat needed for roasting coffee then the improved absorber with better surface reaction for heat distribution capacity has raised. A temperature of 1520C has been achieved with the help of simulation using COMSOL MULTIPHYSICS software package to show how much heat distribution on the absorber has been achieved. Temperature distribution on the receiver of scheffler reflector has also been compared with the temperature on receiver of parabolic solar dish. During the sunny day, the maximum temperature of above 3000C and 2100C from absorber of scheffler reflector and parabolic solar dish have been observed during the assessment respectively.