In the current study, Multilayer Perceptron Artificial Neural Network (MLP‐ANN) mode, Radial Basis Function Artificial Neural Network (RBF‐ANN), and Elman Back Propagation Neural Network (Elamn BP‐ANN) are developed to predict the thermal efficiency of a flat‐plate solar collector. TiO₂ (20 nm)/water nanofluids are prepared using two‐step method and used in the designed solar system. All experiments are done in Mashhad city, Iran (Longitude/Latitude: 36.2605°N, 59.6168°E), according to EUROPEAN STANDARD EN 12975‐2 as a quasi‐dynamic test (QDT) method, and the solar collector is exposed to the south with the tilt angle of 55°. Three levels of inlet temperature (ambient air temperature, 52 and 74°C), 3 levels of volumetric flow rate (36, 72, and 108 L/(m².h)), and 4 levels of nanofluid concentrations (0, 0.1, 0.2, and 0.3 wt.%) are considered as the input data, and the thermal efficiency of the solar system is calculated. According to the output results of developed models, the best prediction of thermal performance is obtained by MLP‐ANN model, although other generated models are also able to predict the efficiency of the solar collector with appropriated accuracy.

In this study, a small flat plate solar collector (FPSC) was fabricated and tested for studying the effects of different nano particle concentrations of in water as base fluid. Three flow rates (i.e. 36, 72 and 108 lit/m 2 .hr) and four particles concentration ratios (i.e. 0, 0.1, 0.2 and 0.3 % wt) were investigated. Experimental testing method was selected based on EUROPEAN STANDARD EN 12975-2 as a quasi-dynamic test method (QDT). Adding nano particles to water brought about an improvement of initial efficiency of FPSC between 3.5 and 10.5% and the index of collector total efficiency between 2.6 and 7% relative to base fluid. Also the results indicate that the initial efficiency () for 36, 72 and 108 lit/m 2 .hr flow rates of water as base fluid were 0.4712, 0.4998 and 0.5457, respectively which reveals the increase of 6.1 and 15.8% of it in the two latter cases in comparison with the first case, 36 lit/m 2 .hr flow rate. In addition, the index of collector total efficiency of 72 and 108 lit/m 2 .hr mass flow rates has increased by 6.7 and 15.7%, respectively in comparison with 36 lit/ m 2 .hr mass flow rate.