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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 Enhancing microalgae biomass productivity through different abiotic and environmental factors optimization is crucial. Design of experimental (DOE) methodology using Taguchi orthogonal array (OA) was studied to evaluate the specific influence of eight important factors (light, pH, temperature, carbon concentration, nitrates, phosphates, magnesium ion concentration and carbon source) on the biomass production using three levels of factor (2 1 × 3 7 ) variation with experimental matrix [L 18 -18 experimental trails]. All the factors were assigned with three levels except light illumination (2 1 ). Substantial influence on biomass productivity is observed with carbon concentration contributing 16.8%, followed by nitrates 12.8% and light 9.3%. Experimental setup eight (Light, pH-8.5, Temperature 25°C, Carbon concentration 10 g/l, nitrates 1.5 g/l, phosphates 0 g/l, magnesium 150 mg/l, Carbon source (glucose)) showed maximum biomass growth (5.26 g/l) and good substrate degradation (63%, COD removal efficiency) contributing to carbohydrate production (257 mg/g biomass) which is further converted to lipids (20% Total lipid and 10% Neutral lipids). Chlorophyll ( a , b ), carbohydrates composition, FAME analysis for lipid percentage were monitored during process operation. Elemental analysis reveals that the carbon to hydrogen and oxygen ratio present in dried algal biomass can be hydrothermally liquefied (HTL) to produce biocrude.

Abstract In this research, photovoltaic thermal integrated thermoelectric cooler (PVT-TEC) collector has been analyzed, considering three different types of PV modules, namely opaque, semitransparent and Aluminium base. The analysis is based on two models namely, thermal model and artificial neural network (ANN) model. The advantage of ANN model is that it does not require several parameters and complex calculations, unlike thermal model. The performance of opaque PVT-TEC collector [Case 1] has been studied by considering air [Case 1a] and water [Case 1b] as working fluids. The overall electrical efficiency and thermal efficiency of [Case 1b] is greater than [Case 1a] by 1.9–2.8% and 20.8–21.8%, respectively. Also, the impact of base cover material of PV module has been discussed by evaluating and comparing the performances of [Case 1b] opaque PVT-TEC water collector, [Case 2] semitransparent PVT-TEC water collector and [Case 3] Aluminium base PVT-TEC water collector. The results demonstrate that the daily overall electrical energy gain, daily rate of thermal energy gain and daily overall exergy gain is the highest for [Case 3] Aluminium base PVT-TEC water collector. Further, the results calculated from thermal model have been compared with ANN model and a fair agreement has been achieved.

Abstract A floating wave energy converter (FWEC) with central buoy (CB), circumferentially connected by a set of four, smoothly-finished tubular floats is proposed. The central buoy and floats are connected rigidly at one end while the other end is hinged, enabling a relative motion. The rotation of floats about the CB represents the energy extraction mode of the device. Float shapes of five different configurations, including a newly-proposed ‘bean float,’ are investigated to estimate their power outputs with linear PTO. FWEC remains afloat and re-centered using taut-moored tethers. The frequency-domain model is utilized to determine the hydrodynamic coefficients of the device, assuming a Potential Wave Theory (PWT). The research evaluates the impact of the obtained hydrodynamic coefficients on the average power absorbed by the FWEC. The influence of a linear power take-off (PTO) system on the average power output of FWEC is studied by optimization of the damping coefficients for the encountered regular waves. Further, time-domain analysis is carried out on the ‘bean float’ - FWEC configuration using an open-source computer-aided engineering tool called WEC-Sim (Wave Energy Converter Simulator), and MATLAB® - Simulink® implementing nonlinear buoyancy and Froude-Krylov forces.

Abstract Daylight has a significant role for energy conservation in buildings. Luminous efficacy models have been applied by many researchers to estimate the illuminance level from available irradiance data. In the present study, the characteristics of global (Kg) and diffuse (Kd) luminous efficacies are reported based on measured data for the humid sub-tropical region of New Delhi, India. Four existing efficacy models have been compared based on the measured irradiance and illuminance data. Statistical analysis indicates that the existing models performed poorly for the selected location. The performance of the models was significantly improved when the optimized coefficients were adopted using the measured data. Global and diffuse efficacy under clear, intermediate, overcast and all sky conditions, using existing and developed efficacy models were computed and compared. A good agreement has been exhibited for variation of efficacies with the measured values for different sky conditions from cloud to clear skies. Variation of global and diffuse efficacy for sky (clear, intermediate and overcast) w.r.t. solar altitude angle and sky clearness index has been presented. Finally, mean monthly global (Lg) and diffuse (Ld) illuminance were also estimated using the original and optimized version of efficacy models to provide impression of deviation of the models.

Abstract The conversion of renewable lignocellulosic biomass to alternative fuels seems a promising solution to the problem of depleting fossil fuels, global warming. In this work, hydrolysis of biomass-derived cellulose was investigated using SO3H functionalized imidazole based ionic liquids (ILs) with different aliphatic or aromatic linkers and anionic functionalities. These multifunctional ILs were synthesized in the laboratory and characterized using NMR, TGA, FTIR, and UV–Vis spectroscopy. ILs consisting of an aliphatic linker and triflate anion exhibited highest catalytic activity in cellulose hydrolysis with Total Reducing Sugar (TRS) yield of 93% at 100 °C and 90 min reaction time. Density Functional Theory (DFT) was used to calculate the acidity trends of the prepared catalysts and validated experimentally using FTIR and UV–Vis spectroscopy. ILs with aliphatic linker attached SO3H group showed better catalytic performance as compared to aromatic or directly attached SO3H group despite being less acidic. This was confirmed by TG analysis which showed the presence of water molecules in the aromatic and directly attached SO3H (IL1 & 3). Overall this report illustrates significant improvement over the prior art in terms of economic prospects with remarkable TRS production efficiency from renewable feedstock.

Abstract In case of photovoltaic (PV) most of the solar energy gets dissipated in the form of heat into the PV module. In the current context, efforts are made to improve the efficiency by utilizing this dissipated heat. One of the ways is to use low temperature thermoelectric (TE), based on the Seebeck effect, along with the PV cell. The mathematical model studied for performance evaluation, using ANSYS software, was based on cascaded hybrid Photovoltaic-Thermoelectric-Direct Evaporative Cooling System (PV-TE-EC) combinations, i.e. PV-EC (without TE), PV-TE-EC, PV-2TE-EC (two cascaded layers of TE sandwiched between PV and EC) and PV-3TE-EC (module with three cascaded TE layers) modules. Also, the effect of solar concentration ratio, temperature coefficient and wind speed was investigated. At concentration ratio 7, the resultant efficiencies of PV-TE-EC, PV-2TE-EC and PV-3TE-EC were higher than PV (15.71%) by 2.15, 4.87 and 6.54% respectively. It has been proposed that this efficiency can be further increased by using low temperature coefficient PV (0.34–0.38%/⁰C), radiation focusing unit with concentration ratio 3 to 7 and keeping the complete PV-3TE-EC setup at the lower wind speed location (≤1 m/s). This combination of parameters will allow the PV-3TE-EC hybrid system to demonstrate nearly constant efficiency throughout the day.