Investigation of concentrating and nonconcentrating evacuated tube solar water heaters using 2D particle imaging velocimetry

Under transient climatic conditions, solar water heaters using heat pipes are more effective at capturing incident solar radiation than other equivalent sized solar water heaters. The cost must be reduced to improve uptake of such systems. To investigate two methods were considered by this study: thermosyphon fluid flow and reflective concentrators. A physical reconfigurable laboratory model of the manifold and associated condensers of a heat-pipe-evacuated tube system were fabricated; fluid circulation was via thermosyphonic action, particle imaging velocimetry derived velocity maps and the use of concentrators was simulated. When condenser spacing was doubled, the Nusselt number increased by 43%, the velocity by 55% but the heat transfer efficiency of the model manifold decreased by 9%. Potential annual energy savings of 10 207 GWh could be realized if such systems could be successfully fabricated.