SnO₂ aerogel/reduced graphene oxide (rGO) nanocomposites were synthesized using the sol–gel method. A homogeneous dispersion of graphene oxide (GO) flakes in a tin precursor solution was captured in a three-dimensional network SnO₂ aerogel matrix and successively underwent supercritical alcohol drying followed by the in situ thermal reduction of GO, resulting in SnO₂ aerogel/rGO nanocomposites. The chemical interaction between aerogel matrix and GO functional groups was confirmed by a peak shift in the Fourier transform infrared spectra and a change in the optical bandgap of the diffuse reflectance spectra. The role of rGO in 3D aerogel structure was studied in terms of photocatalytic activity with detailed mechanism of the enhancement such as electron transfer between the GO and SnO₂. In addition, the photocatalytic activity of these nanocomposites in the methyl orange degradation varied depending on the amount of rGO loading in the SnO₂ aerogel matrix; an appropriate amount of rGO was required for the highest enhancement in the photocatalytic activity of the SnO₂ aerogel. The proposed nanocomposites could be a useful solution against water pollutants.

The goal of this paper is to study and optimize the conical chimney angle (α) of a divergent solar chimney power plant (DSCPP) by using CFD technique. The local airflow characteristics were analyzed in four configurations with different conical angles α = 0°, α = 3°, α = 6° and α = 9°. The first design is validated experimentally by using a pilot prototype build at the National School of Engineers of Sfax, Tunisia. In addition, some experimental results of the temperature, the velocity and the power output were presented during a typical day. A novel mathematical correlation was developed to prove the effect of the conical angle and the DSCPP scale on the power output. In fact, the relationship between the optimum conical angle and the system scale was performed based on both quadratic and cubic regressions. The computational results ensure that the conical chimney angle presents a parabolic tendency with the turbulence airflow characteristics and the power output. The performance of the DSCCP was degraded since the conical angle is greater than α = 3°. Furthermore, the optimum angle decreases with an increasing system scale. A commercial solar chimney with a conical angle around α = 1° presents an efficient system.

This study focuses on improving the thermal performance of a solar air heater (SAH) using a single-pass spiral-shaped ducts. The SAH is designed and tested under prevailing weather conditions of Gabes, Tunisia (33°52.8876′ N,10°5.892′ E). The experimental measurements are carried out over 4 days. Similarly, a computational fluid dynamics (CFD) model was developed to study the fluid flow and the heat transfer inside the SAH using the commercial software ansys fluent 2021 R1”. The discrete ordinate (DO) radiation model and the k-ω shear stress transport (SST) turbulence model are used to study the radiative heat transfer and the turbulent flow in the SAH, respectively. The numerical model is validated against experimental data, and the average error does not exceed 3.6%. To improve the heat transfer phenomena, the ratio of horizontal baffle spacing “d” to vertical baffle spacing “p” (d/p) is numerically investigated. Moreover, the highest air outlet temperature during the test days reached 81.1 °C under a mass flowrate of 0.0077 kg/s. The maximum efficiencies are 57%, 54%, 49%, and 46% for the configurations d/p = 1.5, d/p = 2, d/p = 1, and d/p = 0.5 under a mass flowrate of 0.02 kg/s, respectively. The SAH design with d/p = 1.5 is about 4–10% more efficient than the standard design with d/p = 1 under a mass flowrate ranging from 0.0077 kg/s to 0.025 kg/s.