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Abstract Designing a high-performance hydrofoil is a fundamental challenge for the current turbine blade designers. In this paper, the performance of S1210 hydrofoil, commonly used in the tidal current turbine blades, in presence of (i) Vortex Generators (VGs), and (ii) modified trailing edge is numerically studied. The results show that attaching counter-rotating VGs near the trailing edge of the foil can increase the lift coefficient by 17% and delay the stall angle from 10° to 12°. Constructing a rounded and thicker trailing edge can help to improve the hydrodynamic performance by increasing the lift coefficient by 13.5%. The combination of VGs (located near the trailing edge) and rounded trailing edge can increase the glide ratio significantly. These observations have been explained by plotting the pressure coefficients and velocity profiles at different locations on the foil surface. The findings will be useful to manufacture a stronger blade profile and extract more power from the current turbines that operate at wide current speed variation.

Abstract Many countries produced biodiesel from crude vegetable oil. However, current vegetable oil feedstock to produce biodiesel slow the growth of biodiesel blend implementation due to the high cost of feedstock production. As a result, waste cooking oil (WCO) is claimed to be economic and readily available without cultivation and highly potential feedstock for high yield biodiesel. In this study, Fe-exchanged montmorillonite K10 (Fe-MMT K10) was employed as a catalyst in converting WCO to biodiesel. In comparison, Fe-MMT K10 was able to produce 95.26% biodiesel, which is higher than biodiesel produced using unmodified MMT K10 as catalyst and reaction without catalyst (38.39% and 29.50%, respectively). The full process of biodiesel production was carried out by response surface methodology (RSM) in conjunction with the central composite design (CCD) for statistically optimization and modelling. From the ANOVA, it was found that the production of biodiesel achieved an optimum level of 92.74% biodiesel at 134.07 °C, under a specific optimized condition of 6.32 h reaction time, 4.68 wt% of catalyst and 11.77:1 methanol to oil ratio.

It is sometimes assumed that renewable technologies which emit carbon dioxide (CO 2 ) in their operation do not offset CO 2 emissions as much as technologies such as wind energy, PV or hydro. Firstly this paper examines the CO 2 savings achieved by electricity generated from renewables as a result of their being substituted for fossil fuel-fired generation. These savings are then balanced against the CO 2 emissions arising from the manufacture of the power plant and, in the case of some technologies, the CO 2 produced in operation. The end result for all technologies is a net CO 2 saving. Some renewable energy technologies also reduce methane emissions. These methane emission savings are converted into CO 2 equivalents to give a measure of the net global warming reduction effect of generating electricity from these sources.

Abstract γ-Valerolactone (GVL)/water/acid has been developed as a mild solvent system to pretreat biomass. In this study, Eucalyptus was pretreated with 80/20 GVL/water with the addition of H2SO4 (20–100 mM) at 120 °C for 30–60 min, and the resulting cellulose-enriched residual fractions were further enzymatically hydrolyzed. Results showed that the pretreatment of Eucalyptus with GVL/water/acid system led to a significant decrease in the contents of lignin and hemicelluloses, and the enzymatic hydrolysis efficiency of the pretreated sample was significantly improved. Meanwhile, the removal of lignin and hemicelluloses from the cell walls during the pretreatment process was monitored by the confocal Raman spectra. Under the optimum conditions (50 mM H2SO4 and 60 min), the delignification rate was up to 90.7% and the cellulose content in the residue was reached to 86.1%. The high cellulose content led to a high cellulose conversion rate and the glucose yield was 6.1-fold higher than that of the raw material without pretreatment. In short, this process provided an efficient approach to remove hemicelluloses and lignin from Eucalyptus to enhance enzymatic hydrolysis for bioethanol production.

Renewable energy has become more popular since it is cost-effective and more efficient than conventional energy sources. Biomass-based renewable energy is primarily used in emerging economies to ensure environmental sustainability. This study examines the asymmetric correlation between biomass energy consumption and CO2 emissions in the top-10 biomass energy consumer countries (Brazil, Canada, Thailand, China, Italy, India, Germany, USA, UK, and Japan). A new approach "Quantile-onQuantile (QQ)" is employed by utilizing the data from 1991 to 2018. Biomass energy consumption, with the exception of Thailand, significantly mitigates CO2 emissions at various quantiles in selected countries. As a robustness check, we used the quantile regression test, whose findings are consistent with the outcomes from the quantile-on-quantile method. However, the degree of asymmetry in the biomass energy-CO2 nexus varies by country, necessitating extra attention and government vigilance when developing biomass energy and environmental policies.