Effect of solar heat flux and thermal loading on the flow distribution within the riser pipes of a closed-loop solar thermo-syphon hot water system

Solar energy is one of the main sources of renewable energy that is abundantly available throughout the world. Solar energy can be used for useful purposes through a number of mechanical artefacts. One such artefact is known as Thermo-syphon, which typically contains water as its working fluid. One of the major applications of Thermo-syphon is within the residential and industrial units, where a constant supply of hot water is required. The use of Computational Fluid Dynamics (CFD) based solvers has recently been proven capable of predicting the flow behaviour within thermo-syphons with reasonable accuracy. Hence, the present study focuses on using a commercial CFD based solver to predict the flow behaviour within the riser pipes of a thermo-syphon with varying solar heat flux and thermal loading conditions. In order to qualitatively and quantitatively analyse the flow structure within the riser pipes of the thermo-syphon, velocity magnitude and static temperature distributions within these pipes is analysed in detail. The results depict that the solar heat flux has a significant impact on the velocity magnitude and static temperature profiles within the riser pipes. Furthermore, it has been observed that the thermal loading has negligible effects on the velocity magnitude and static temperature profiles within the riser pipes. The data has also been used to develop novel design correlations.