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Abstract In this study, photoelectrochemical performance of reduced graphene oxide (RGO)-CdxZn1-xS composites, which were synthesized through a novel two-steps thermal sulfurization process by using elemental sulfur, was reported. This is the first time that the two-step thermal sulfurization process with elemental sulfur for the preparation of photoanode based on RGO-CdxZn1-xS. The electrodes exhibited high photostability and photocurrent response in the presence of visible light. The presence of RGO in CdxZn1-xS as electron collector and transporter increased the photocurrents approximately 40%. Among the RGO-CdxZn1-xS composites, RGO-CdS photoanode yielded an extremely high photocurrent density of 6.5 mAcm−2 with the rate of hydrogen production rate of 551.1 μ m o l h − 1 c m − 2 . This value of photocurrent density is almost 89% of its theoretical value. This is the maximum attained photocurrent density with superior stability in comparison with related literature.

Abstract Gold nanoparticles (Au-NPs) seeded plasmonic nanofluids (PNFs) have shown promising results in overall performance enhancement of direct absorption solar collector (DASC) due to localized surface plasmon resonance (LSPR) effect. For the work presented here, Au-NPs were synthesized by the wet chemical method and were utilized to prepare plasmonic nanofluid. The surface plasmon resonance peak of Au-NPs was observed at 531 nm using UV–Visible spectrophotometer study. The testing for performance enhancement of gold plasmonic nanofluid (GPNF) laden DASC so far is limited to laboratory scale setups or simulation studies. Considering the dearth of outdoor experimental studies, an attempt has been made in the present study to evaluate the thermal performance of Au-NPs (∼40 nm) based nanofluid (∼0.0002 wt%) in full scale DASC. The experiments have been performed at different flow rates under clear sky outdoor conditions in winter season at Jalandhar, India. The maximum collector outlet temperature was measured to be 55 °C with GPNF which is about 7 °C higher than the maximum outlet temperature obtained with de-ionized water as working fluid. Thermal efficiency with GPNF is about 33% higher than de-ionized water at the optimal flow rate of 0.030 kg/s.

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 Individual pitch control and trailing edge flaps have been shown to be capable of reducing flapwise fatigue loads on wind turbine blades, with research to date focusing on controller development and performance assessment. This work covers development of a blade optimisation process which integrates synthesis of individual pitch and trailing edge flap controllers to evaluate their impact on the levelised cost of energy. The optimisation process selects blade chord, twist and material distributions, along with the spar cap width, and integrates a turbine cost and mass model with existing simulation codes. Constraints based on ultimate stresses, fatigue damage, blade deflection, resonant frequency, and rotor thrust are considered. Using the NREL 5 MW reference turbine as an initial point, reductions in the levelised cost of energy of 1.05% are obtained with collective pitch control only, while the addition of individual pitch control increases this reduction to 1.17%. The use of trailing edge flaps on top of individual pitch control increases the reduction in the levelised cost of energy to 1.27%. Blade mass and material cost reductions from 13.6 to 16.4% and 18.1–21.5% respectively are also obtained. Optimised blade designs are driven by blade deflection, rotor thrust and ultimate stresses in the spar cap.

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.