Small wind turbines operating in low wind speed regions have not had any significant success. In addition, small wind speed regions occupy a large area of the world, so they represent a potential area for installing small wind turbines in the future. In this paper, a method to design an efficient airfoil for small wind turbines in low wind speed conditions using XFLR5 and CFD simulations is implemented. Because the impact of the airflow on the blade surface under low Re number conditions can change suddenly for small geometries, designing the airfoil shape to optimize the aerodynamic performance is essential. The tuning of the key geometric parameters using inversion techniques for better aerodynamic performance is presented in this study. A two-dimensional model was used to consider the airflow on the airfoil surface with differences in the angle of attack. The original S1010 airfoil was used to design a new airfoil for increasing the aerodynamic efficiency by using V6.57 XFLR5 software. Subsequently, the new VAST-EPU-S1010 airfoil model was adjusted to the maximum thickness and the maximum thickness position. It was simulated in low wind speed conditions of 4–6 m/s by a computational fluid dynamics simulation. The lift coefficient, drag coefficient, and C_L/C_D coefficient ratio were evaluated under the effect of the angle of attack and the maximum thickness by using the k-ε model. The simulation results show that the VAST-EPU-S1010 airfoil achieved the greatest aerodynamic efficiency at an angle of attack of 3°, a maximum thickness of 8%, and a maximum thickness position of 20.32%. The maximum value of C_L/C_D of the new airfoil at 6 m/s was higher than at 4 m/s by about 6.25%.

This research addresses the urgent need for sustainable bioenergy alternatives, specifically evaluating betel nutshells as potential replacements for conventional biomass materials like coconut and palm fibers. The objective of the study was to gauge the inherent bioenergy potential of betel nutshells through an investigation of torrefaction under varying conditions, specifically temperatures ranging from 200-300 °C and residence times between 20-60 minutes in an inert environment. In this study, proximate analyses were utilized to investigate essential characteristics including moisture content, volatile matter, ash content, and fixed carbon, while a bomb calorimeter was used to determine their higher heating values. Initial results indicated that untreated betel nutshells had higher heating values and compositional similarities to coconut and palm fibers, highlighting their potential as a bioenergy source. Advanced torrefaction processes, involving increased temperatures and extended residence times, raised the fixed carbon content and reduced moisture in betel nutshells, thereby optimizing their higher heating value. This improvement is attributed to the decomposition of covalent bonds in the biomass structures, leading to the release of volatile compounds and consequent reductions in both oxygen-to-carbon and hydrogen-to-carbon ratios. Remarkably, at an operating temperature of 300 °C and a residence time of 60 minutes, torrefied betel nutshells reached a higher heating value of 25.20 MJ/kg, marking a substantial 31.39 % increase compared to untreated specimens. This study conclusively positions betel nutshells, typically considered agricultural waste, as competitive alternatives to traditional biomass resources in the biofuel industry.

In the present research, an investigational study on thermal performance of a mixed asphalt conical solar water heater (MACSWH) was analyzed under field conditions. The key target of the present research is to evaluate the dynamics of heat and performance of a conical solar collector with an attached mixed asphalt as an absorber plate. In the current experimental test setup, the mixed asphalt as an absorber plate with a diameter of 0.20 m and thickness of 0.05 m was set in the middle of the focal area for accumulating the solar radiation, reflecting from a polished zinc conical reflector. The aperture diameter of the MACSWH was 0.45 m with a concentration ratio of 2.20. The copper pipe had a total length of 2 m, and the inclination angle of the conical was fixed at 15 deg. The experimental results provide evidence that the mixed asphalt set as an absorber plate at the center of the focal area was an effective practical approach to improve the performance of a conical solar collector. This method raises the maximum percentage difference between inlet water temperature and outlet water temperature by approximately 47.27%, while the maximum temperatures of absorber plate, copper pipe, and efficacy are at 82 °C, 62 °C, and 72%, respectively.