Direct absorption solar collector: Use of nanofluids and biodegradable colloids

In this paper, an experimental and numerical analysis was performed on both carbon black nanofluids and a biodegradable fluid in a novel pump-free direct absorption solar collector (DASC). In the experiments, the nanofluid consisted of carbon black nanoparticles in water with concentrations ranging from 0.005 to 0.020 wt%, while the biodegradable fluid was coffee colloid. The overall findings indicated a concurrence: the nanofluids exhibited the best thermal performance when compared to pure water. The optimum nanoparticle concentration of 0.010 wt% carbon black yielded a 102% thermal enhancement compared to the base fluid. Furthermore, a numerical analysis using computational fluid dynamics (CFD) software was performed to study the experimental rig. According to these simulations, the optimal nanofluid concentration showed a 76.6 - 90.9% increase compared to the base fluid. The biodegradable fluids did not show a significant enhancement in the experiments, which differs from what has been reported in the scientific literature. Nevertheless, from the computer simulations, the biodegradable fluids also slightly outperformed the case when the pure water was used.