Thermal power measurement of the novel evacuated tube solar collector and conventional solar collector during simultaneous operation

• Two types of evacuated tube solar collectors were compared.
• Experimental measuring apparatus was designed and manufactured.
• Modified quasi dynamic outdoor test method was used.
• Solar collectors were compared by thermal power per collector area unit.
• Modified solar collector with metal foam element demonstrated increase of power.

The paper deals with a description of the measurement method and evaluation of the thermal power of evacuated tube solar collectors (ETSC) during their simultaneous operation at the Centre of Renewable Energy Sources, Technical University of Košice, Slovakia. Evaluation was performed during various climatic and solar irradiance conditions on experimental measuring apparatus, that was designed and manufactured by authors. Key feature of measuring apparatus is its ability to ensure simultaneous operation of both evaluated collectors. This method of operation was selected in order to ensure identical conditions for both evaluated solar collectors during all performed measurements. Within the evaluation were investigated two types of ETSC – one with a conventional manifold header, and the other with a parallel flow manifold header with metal foam structural element that was proposed by authors and it is under patent protection. The main objective of the comparison was to evaluate the effect of used metal foam structure and changes in inner configuration on the overall thermal power of the proposed solar collector through outdoor quasi dynamic test. Part of measurement was also devoted to pressure drop analysis of proposed prototype of manifold header. Within the presented measurements, ETSC with parallel flow manifold header with metal foam structural element demonstrated significant thermal power increase ranging from 85.2 to 201.8 W per 1 m2 of collector area (depending on used flow rates of heat transfer medium) and increase of performance enhancement factor in range from 1.14 to 3.20.

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