Design and Performance of Evacuated Solar Collector Microchannel Plates

摘要

Solar thermal collectors for buildings have traditionally used either a flat panel or evacuated tube design. Arnhigh vacuum (<1 Pa) can eliminate heat loss via gas conduction effects, thereby increasing efficiency in coldrnclimates or in applications requiring elevated delivery temperatures e.g. for process heat. Combining therntwo established technologies, an evacuated flat panel design would be more architecturally elegant thanrntubular collectors and have a better fill factor, yet be thinner and more efficient than conventional flat panels.rnBeyond the efficiency gains from vacuum insulation, the collector design aims to limit temperature nonuniformityrn(with its increased radiative losses) by achieving homogeneous flow across micro-channels withinrnthe plate. A design methodology has been adopted that optimises the channel hydraulic diameter in terms ofrnplate-to-fluid temperature difference and power required to pump the fluid. Two collectors (aluminium,rnstainless steel) have been designed and fabricated, with machined plates and laser-welded joints.