An experimental study on a density driven solar water heating system using supercritical carbon dioxide as working fluid

For supercritical carbon dioxide, a small change in temperature or pressure can result in large change in density, especially close to its critical point. At this pseudocritical region, density decreases rapidly with increase in temperature which aids the thermosyphon flow. Encouraged by this idea, an experimental investigation has been performed to investigate the feasibility and performance of thermosyphon solar water heating (SWH) system using R-744 (CO2) as the working fluid. Experimental results have shown that it is possible to induce the natural convective flow even during solar-adverse conditions. Although during winter this proposed density driven system was not possible to extract any useful heat gain, the system did show some promising results when operated during spring. The time-averaged collector and heat recovery efficiencies for summer were about 58% and 45%, respectively.