Index of content:
Volume 8, Issue 6, November 2016
- Bioenergy and Biofuels
8(2016); http://dx.doi.org/10.1063/1.4966159View Description Hide Description
Calcined copper slag (CCS) catalytic steam reforming of jatropha oil was investigated in a fixed bed tubular reactor for hydrogen. The pyrolysis mechanism of jatropha oil was characterized by high performance liquid chromatograph, thermogravimetric analysis, and infrared spectroscopy. At 300–400 °C the fatty acid glycerides cracked into fatty acid, ketene, and acrolein. However, carboxyl, aldehyde, and ketone groups completely became broken bonds when the reactive temperature was 400–500 °C. Dynamic analysis of jatropha oil's thermogravimetric curves was researched by Coats-Redfern equation, where the jatropha oil pyrolysis process accorded with the Z-L-T equation. The activation energy E was 294.14–349.47 kJ/mol, and the pre-exponential factor A was 7.38 × 1020–3.53 × 1025 min−1. Four catalysts were used for catalytic steam reforming of jatropha oil, the active components of CCS were ferric oxide and other metal oxides, and ferric oxide had a good effect on C=C double bond fracture of jatropha oil.
8(2016); http://dx.doi.org/10.1063/1.4966695View Description Hide Description
This paper presents experimental investigation of pyrolysis process of corn cob from Vojvodina (Republic of Serbia). The influence of temperature, reaction time, particle size, and heating rate on pyrolysis products yields was investigated. Studying of biomass pyrolysis kinetics led to the conclusion that thermogravimetry is an appropriate method for explaining decomposition of different biomass types. Experimental research showed that temperature increase leads to decrease in char yield and volatile yield. Mass yield of pyrolysis oil increased with higher heating rate. Methane volume fraction in pyrolysis gas increased with temperature increase, while the volume fraction of carbon dioxide decreased. Particle size affected the methane yield. It was shown that with the increase in particle size, the volume fraction of methane in pyrolysis gas decreased. Based on the char composition obtained after corn cob pyrolysis process, it was determined that char is rich in carbon (74.80%). Lower heating value of char was 26182.09 kJ/kg. High heating value of char contributes to economic justification for applying corn cob pyrolysis.
8(2016); http://dx.doi.org/10.1063/1.4966696View Description Hide Description
To study the influence of additives on the pyrolysis behavior of microwave-heated biomass, cotton stalk pyrolysis was performed using both a particular microwave pyrolysis reactor and an electric heating system with the addition of acid (H3PO4) and metal salts (NaCl, K2CO3, and MgCl2) at 550 °C. The derived products were evaluated by environmental scanning electron microscopy, gas chromatography with mass spectrometric detection, and temperature adsorption analysis. The results indicated that microwave heating with additives was beneficial to enhance the quality of the pyrolysis products. The addition of H3PO4 was favorable for liquid oil formation with higher furfural and acetic acid contents. The highest yield of oil was achieved with 8% H3PO4, while the maximum char yield and surface area were obtained at 12% H3PO4, as higher percentages caused the formation of more porous solid char. The addition of metal salts promoted the formation of char at the cost of decreasing the liquid oil production. The maximum yields of bio-oil and char were achieved with the addition of MgCl2, while the minimum yields were obtained by adding K2CO3. The addition of MgCl2 (8%) promoted the formation and pore growth of char during the pyrolysis process; moreover, it was helpful for the production of furfural and acetic acid substances as well as a small amount of naphthalene. The addition of K2CO3 (8%) increased the gas production significantly but decreased the specific surface area of char. The addition of NaCl (8%) increased the char yield but decreased the oil and gas yields slightly. The comparative results showed that microwave pyrolysis with H3PO4 and MgCl2 additives were beneficial for the preparation of activated char with a large specific surface area and optimal formation of bio-oil.
8(2016); http://dx.doi.org/10.1063/1.4966160View Description Hide Description
This work presents a simple time-lag model for biogas production from anaerobic digestion of organic wastes (biomass) in a batch digester. The model has the ability of predicting the S-shaped nature of the cumulative biogas yield with retention time that is commonly observed experimentally. The model is calibrated against biogas production data from anaerobic digestion of three types of organic waste: OFMSW (organic fraction of municipal solid waste), FVW (fruit and vegetable waste) and RH (rice husk). For these three wastes, the fit of the model to the experimental data has an average root-mean-square deviation of 9%. The time-lag model leads to the formulation of two measures or indexes of biodegradability of a particular waste. The values of these indexes are much higher for FVW compared to those for OFMSW and RH showing that the susceptibility of FVW to anaerobic digestion far exceeds that of the other two wastes.
8(2016); http://dx.doi.org/10.1063/1.4967717View Description Hide Description
The framework of theoretical method is two-fluid model coupled with reaction process. The k-ε model is used for gas phase, and the kinetic theory of granular flow is employed for solid phase. In the simulation, gasification process consists of three parts: pyrolysis, homogenous reaction, and heterogeneous reaction. In the first stage, biomass particles crack into carbon particles and volatile gases upon entering the reactor. Subsequently, the carbon particles and volatile gases react with oxygen, which includes both homogenous reaction and heterogeneous reaction. The effect of equivalence ratio (ER) is studied. It is found that all the products have same tendency with the increase of ER. H2 and CH4 change linearly with ER; CO and CO2 change cubically with ER. This is because the mechanism of formation of CO and CO2 is more complex than that of H2 and CH4. H2 and CH4 are consumed by O2, so they tend to decrease with the increase of ER, whose value corresponds to the amount of O2 fed. For CO and CO2, however, things are more complicated: the extents at which CO and CO2 decrease are converse. CO decreases significantly and then reaches a plateau and finally decreases again, while CO2 decreases moderately at the beginning and then decreases sharply and finally becomes flat. The conclusion is that when oxygen concentration is low, increment of oxygen favors production of CO2, and when oxygen concentration reaches a certain level, increment of oxygen favors production of CO, and when oxygen concentration continually increases, increment of oxygen favors production of CO2 again.
8(2016); http://dx.doi.org/10.1063/1.4971875View Description Hide Description
The wastewater of a petroleum processing facility was used to grow the oleaginous bacterium Rhodococcus opacus PD630 to produce microbial oils. Undiluted wastewater supplemented with molasses (20 g/l) and ammonium chloride (1 g/l) provided a maximum dry biomass concentration of nearly 6 g/l in a 96 h batch culture. The lipid concentration in the bacterial broth exceeded 3 g/l and the lipid content in the dry biomass was nearly 52% by weight. Biomass and oil production were further improved using a 96-h fed-batch fermentation instead of a batch culture. The final biomass concentration exceeded 7.2 g/l and the lipid concentration was nearly 4 g/l. The lipid content of the dry biomass exceeded 54% and the lipid yield on sugars was 0.33 g/g. The lipids were similar to vegetable oils. They contained mainly long chain C16 and C18 fatty acids. Potentially such lipids may be used to replace vegetable oils in production of biodiesel.
- Wind Energy
8(2016); http://dx.doi.org/10.1063/1.4966968View Description Hide Description
This article presents the research findings of an extensive model test investigation of the dynamic response to vortex-induced motions (VIMs) of the OC3 spar-type floating offshore wind turbine (FOWT). Particulars of this research are to investigate the unique and crucial effects of wind load on the spar-type FOWT, which differs considerably from other traditional spar-type floating systems utilized in the gas and oil industry, on the VIMs. The model test was performed with a sequence of current, wind, and irregular wave sea states to analyze the nature of the coupled dynamic response behavior of VIMs. Many unique characteristics were found and analyzed. The lock-in phenomenon of sway in the cross flow (CF) direction was found to occur first, followed by the lock-in phenomenon of surge in the in-line (IL) direction. For the current-only case, the remaining responses, including the other 4-degree-of-freedom motions, mooring tensions, and turbine bearing loads, were found to be coupled by sway/surge VIMs. Moreover, the oscillation amplitudes of all of the responses increased significantly with increasing current velocity, particularly after locking-in. Furthermore, the wind load had a clear suppression effect on the CF and IL VIM responses. The experimental measurements demonstrated that the wave load excites wave-induced oscillations for some CF responses and all IL responses, and it further restrains the VIM oscillation amplitudes on the foundation of the wind suppression effect. In particular, when a wind load is involved, the influence of current or wave is limited to the yaw and IL tower-top bending moment.
8(2016); http://dx.doi.org/10.1063/1.4966706View Description Hide Description
The Savonius rotor has been attracting more and more attention in recent years owing to its appealing features, such as simplicity of the fabrication, cost-effectiveness in low wind speed areas and low noise levels. It can be used for lighting, ventilation, hydropower generation and irrigation. As a traditional single-stage two-blade Savonius rotor has two defects, researchers proposed the multi-stage two-blade Savonius rotor to overcome them. However, most of the previous studies on the multi-stage Savonius rotors focused on the comparison between one- and two-stage rotors or the effect of the aspect ratios. This paper is different from previous researches and focuses on the comparison between two-stage rotors through the wind tunnel test. It also studies the effect of the gap ratio (GR) and phase shift angle (PSA) on the performance of the two-stage rotors at different wind speeds. Results showed that the negative azimuth angle range was narrowed and the torque coefficient (CT) values were improved as GR and PSA increased. Hence, the two-stage rotor with larger GR and PSA can overcome the two defects of the single-stage rotor. In terms of the power coefficient (CP), the optimized performance was determined by the GRs, PSAs, and wind speeds. When the wind speed increased, the difference among CP curves of one tested rotor was reduced. Generally speaking, the rotors with GR = 1/6 exhibited the optimized performance compared with those with other GRs when the PSA = 0° and PSA = 45°. While keeping the PSA = 90°, the rotor with GR = 0 had a superior performance to the others when PSA = 90° at wind speed of 4 m/s. The rotor with GR = 1/3 gave the highest CP value of 0.303 in the vicinity of the tip speed ratio 0.9 at wind speed of 6 m/s. And the rotor with GR = 1/6 attained the best CP when the wind speeds were 8 m/s and 10 m/s.
Aerodynamic optimal blade design and performance analysis of 3 MW wind turbine blade with AEP enhancement for low-wind-speed-sites8(2016); http://dx.doi.org/10.1063/1.4967971View Description Hide Description
The annual average wind speed in more than 80% of the global area that can potentially be employed for onshore wind farm development is lower than 7 m/s. Onshore wind farm development has been accomplished in most regions with excellent wind resource. Based on the increasing need for onshore wind farm development in low-wind-speed sites owing to the effect of environmental factors, commercial demand of IEC-Class III wind turbine has significantly increased among the world's leading developers and wind turbine manufacturers of the wind power industry. Thus, aerodynamic design of a 3 MW wind turbine blade for low-wind-speed sites was performed in this study. The geometry was optimized to improve AEP (Annual Energy Production) and minimize the increasing rate of thrust. The performance analysis result by Blade Element Momentum method showed that the increase in thrust was limited to less than 5% and AEP was enhanced by 20% at annual average wind speed of 7 m/s compared to the reference blade. To verify the final aerodynamic design result, CFD simulation was performed. It was confirmed that AEP was increased by 15%, and the increasing rate of thrust was found to be 5.1% at the same annual average wind speed.
A simulation exploration on the grounding characteristic of monopile foundation offshore wind turbines8(2016); http://dx.doi.org/10.1063/1.4968242View Description Hide Description
An exploration on the grounding characteristic of monopile foundation offshore wind turbines (WTs) is carried out in this paper by using the Grounding System Safe Analysis Software (GSSAS). A basic description is given for the structural feature of the monopile foundation. The discretization model is built for the monopile foundation by subdividing its continuous shell body into a discrete multiconductor system. The simulation computation is performed for analyzing the actual factors influencing the grounding resistance, including the seawater depth, thickness of clay layer, and resistivity of gravel layer. It is found from the simulation computation that the grounding resistance is mainly influenced by the seawater depth. Then, the result obtained from the software GSSAS is also compared with that from the software current distribution, electromagnetic fields, grounding and soil structure analysis for checking the validity of the GSSAS simulation in the exploration of grounding characteristic of offshore WTs.
8(2016); http://dx.doi.org/10.1063/1.4968600View Description Hide Description
The main objective of this research is to investigate the degree to which variations in mechanical properties of constitutive composite materials can influence the aeroelastic behavior of a wind turbine blade. First, structural behavior of a full-scale wind turbine blade is evaluated from different aspects of bending, torsional and axial rigidities. For this purpose, simplified model of the blade is constructed and it is validated with experimental data of the full-scale blade. Then, a parametric study is performed to determine the most dominant mechanical properties which have a severe impact on the structural behavior of the blade. Identified dominant properties are varied randomly and independently. Thus, stochastic analysis is performed to investigate the variations in natural frequencies of the blade as the governing parameter in defining aeroelastic behavior. Finally, susceptibility of the blade to dynamics instability is also examined. Aeroelastic effects are found to have a stronger effect on the blade with lower material properties that lead to more power reduction.
Focused-based multifractal analysis of the wake in a wind turbine array utilizing proper orthogonal decomposition8(2016); http://dx.doi.org/10.1063/1.4968032View Description Hide Description
Hot-wire anemometry measurements have been performed in a 3 × 3 wind turbine array to study the multifractality of the turbulent kinetic energy dissipation. A multifractal spectrum and Hurst exponents are determined at nine locations downstream of the hub height, bottom and top tips. Higher multifractality is found at 0.5D and 1D downstream of the bottom tip and hub height. The second order of the Hurst exponent and combination factor shows the ability to predict the flow state in terms of its development. Snapshot proper orthogonal decomposition (POD) is used to identify the coherent and incoherent structures and to reconstruct the stochastic velocity signal using a specific number of the POD eigenfunctions. The accumulation of the turbulence kinetic energy in the top tip location exhibits fast convergence compared with the bottom tip and hub height. The dissipation of the large and small scales is determined using the reconstructed stochastic velocities. The higher multifractality is shown in the dissipation of the large scale compared with small scale dissipation showing consistency with the behavior of the original signals. Multifractality of turbulent kinetic energy dissipation in the wind farm is examined and the effect of the reconstructed flow field via proper orthogonal decomposition on the multifractality behavior is investigated. Findings are relevant in wind energy as multifractal parameters identify the variation between the near- and far-wake regions.
- Photovoltaic Energy
8(2016); http://dx.doi.org/10.1063/1.4967261View Description Hide Description
This paper proposes a model for coordinated transmission expansion planning-reactive expansion planning (TEP-RPP) that incorporates the costs related to the operation of large-scale photovoltaic units (LPU). The model is based on the dynamic evaluation of LPU generation and the effect of it on TEP-RPP problem. In a system with the presence of LPU and conventional units, the network expansion project has been dependent on two important environmental factors, solar irradiation and ambient temperature. The TEP-RPP issue has been systematized in a multi-purpose form based on investment and operation cost, voltage deviation, and stability criterion. A multi-objective gravitational search method is implemented to extract the Pareto-archive curve of the presented multi-purpose issue. Algorithm of similarity to ideal solution is used to trade-off different points of Pareto curve. The proposed mythology has been evaluated on two different modified systems, Azarbaijan regional power system of Iran and IEEE 30 bus test system. It is indicated that the presented model can be used effectively to study the intermittent impact of LPU on the solution of the TEP-RPP problem.
Study on the mutual influence between enterprises: A complex network perspective of China's PV enterprises8(2016); http://dx.doi.org/10.1063/1.4971452View Description Hide Description
With the economic integration of the world, the correlation between enterprises does not only include their cooperative and competitive relationships but also involves their mutual relationship in the market. In this paper, a new index, with considering cooperative, competitive as well as market relationships, is proposed to quantify the mutual influence between any two enterprises. Then, the influence index threshold network is built from a new perspective of complex network theory. Focusing on the empirical research by taking China's photovoltaic (PV) industry as an example, the leading enterprises are identified by their -shell decomposition analysis in conjunction with their nodal degree. In addition, the reasons for some belong to the leading enterprises are explained using random matrix theory. The results show that leading enterprises with core technologies producing basic products, having complete industrial chain, and owning brand products are likely to have prominent positions during the fierce competition. Finally, some suggestions are made to promote the sustainable development of China's PV market.
- Solar Energy
Fabrication of high aspect ratio broadband antireflection porous nano-network on glass using candle soot as a sacrificial layer for solar energy utilization8(2016); http://dx.doi.org/10.1063/1.4967973View Description Hide Description
In this paper, we report the fabrication of broadband antireflection porous nano-network on the glass substrate using the combination of candle soot and HF-based vapor phase etching method. Candle soot layer plays a key role to control the pore size during the etching process. Field emission electron microscopy results showed that the pores have the tapering profile, and the pores size was restricted to the sub-wavelength dimension. Therefore, an excellent broadband antireflection with an enhancement of ∼7% in the maximum total transmittance as compared to plain glass has been achieved. Moreover, reflectance from the etched surface remains quite low (<4%) over a broad range of incident angles up to 58°. The broadband antireflection property was further examined by finite difference time domain simulation. Further, we demonstrate a relative improvement of ∼6% in the Jsc (ΔJsc/Jsc) of solar cell covered with the etched glass.
- Energy Storage
8(2016); http://dx.doi.org/10.1063/1.4967974View Description Hide Description
Mitochondria were deposited via dip coating on different substrates, namely, commercial glass, copper plate (Cu), aluminum plate (Al), and poly (methylmethacrylate). Mitochondria are organelles that are found in live cells. Mitochondria produce most of the ATP via oxidative phosphorylation. First, mitochondria were extracted for the thin film, as described in the literature. Capacitance properties of thin films were measured with Agilent LCR meter. SEM analysis was used for the surface analysis. The structure of mitochondrion was characterized with FTIR, whose spectrum was measured using a Perkin Elmer Spectrum 400 spectrometer. The stretching vibration of the P-O bond was observed at 1236 cm−1 in FTIR spectrum of the thin film. The capacitance and dielectric permittivity were first measured and calculated for the substrates, and then for mitochondria plated substrates. The properties, such as dielectric permittivity, capacitance, energy density, and power density of some substrates have been changed when their surface has been coated with mitochondria.
8(2016); http://dx.doi.org/10.1063/1.4968851View Description Hide Description
A three-dimensional steady state model of internal reaction and mass transfer has been established for a better understanding of electrochemical performance of zinc-nickel single flow battery (ZNB). Combining with a global kinetic, the model is based on a comprehensive description of mass, momentum, charge for reactions considering the flow between anode and cathode, species transport, and electrochemical reaction between electrodes and electrolyte. This paper emphasizes an internal ion concentration and electrode current density distribution of the ZNB. The effect of channel width and electrolyte flow rate on the electrochemical performance is also studied in the simulation. In addition, the verification of the mathematical model is illustrated by the agreement between the numerical and experimental I–V curves.
- Marine and Hydroelectric Energy
8(2016); http://dx.doi.org/10.1063/1.4971817View Description Hide Description
An experimental station for marine current power has been installed in a river. The station comprises a vertical axis turbine with a direct-driven permanent magnet synchronous generator. In measurements of steady-state operation in varying flow conditions, performance comparable to that of turbines designed for significantly higher flow speeds is achieved, demonstrating the viability of electricity generation in low speed (below 1.5 m/s) marine currents.
- Energy Conversion
Generation characteristics of piezoelectric vibrator driven by groove cam: Simulation and experimental analysis8(2016); http://dx.doi.org/10.1063/1.4966969View Description Hide Description
In this paper, a structure for a piezoelectric beam vibrator driven by a groove cam is analysed. The vibrator takes the simplified form of a piezoelectric beam model, where one end of the beam is clamped and the other end is simply supported, and is thus named the clamped/simply supported piezoelectric beam model (CSPBM). Mathematical models of the damped forced vibration and electromechanical energy conversion processes of the CSPBM are established based on the harmonic displacement excitation of the simply supported end. Factors that affect the energy generated by the CSPBM are analyzed theoretically and are simulated separately using both the MATLAB software and ANSYS software. Theoretical analysis results indicate that there is an optimal value of the ratio of the base plate thickness to the beam thickness (α) at which the energy generated by the CSPBM is maximum. In addition, the optimal α value of a unimorph beam is about 0.3 and is irrelevant to the material parameters of the beam. The voltage and energy generated by the CSPBM are measured on an experimental bench and the results show that the maximum generated voltage increases with increasing the first natural frequency when the α value of piezoelectric beam and the amplitude of displacement excitation are constant. In addition, the theoretical results of the generated voltage are coincident with experimental results, which confirms the validity of the theoretical model. The vibrator driven by a groove cam provides a practical form of the piezoelectric beam excited by the displacement.
8(2016); http://dx.doi.org/10.1063/1.4967706View Description Hide Description
To investigate the correlation between the physicochemical and hygroscopic properties of biochar and soil, the moisture sorption properties of typical biochars and soils were observed inside a thermostatically controlled incubator at a temperature of 30 °C and humidity of 70%. Results showed that the equilibrium moisture content (EMC) of tobacco stem biochar, rice husk biochar, Hubei paddy soil, and Jiangxi red soil were 7.66%, 6.40%, 3.34%, and 2.92%, respectively. There was a synergistic interaction between biochar and soil, resulting in a higher EMC of biochar-soil mixtures with increases ranging from 0.16% to 2.52%. The porosity of tobacco stem biochar, rice husk biochar, Hubei paddy soil, and Jiangxi red soil were 82.58%, 65.05%, 59.02%, and 56.71%, respectively. Additionally, according to our findings, the biochar had higher carbon content, C/N ratio, and carbonyl groups, and lower bulk density, oxygen content, O/C ratio, and carboxyl groups than the soil. The linear correlation analysis indicated that there was a positive correlation between EMC and the physicochemical properties of biochar and soil, including porosity, carbon content, nitrogen content, and carboxyl groups. Consideration of the physicochemical properties of biochar and soil will significantly improve the overall properties of biochar used for soil amendment.