Excellence in Research and Innovation for Humanity

International Science Index

Commenced in January 1999 Frequency: Monthly Edition: International Abstract Count: 42820

Energy and Power Engineering

Flame Spread along Fuel Cylinders in High Pressures
Flame spread over solid fuels in high pressure situations such as nuclear containment shells and hyperbaric oxygen chamber has potential to result in catastrophic disaster, thus requiring best knowledge. This paper reveals experimentally the flame spread behaviors over fuel cylinders in high pressures. The fuel used in this study is polyethylene and polymethyl methacrylate cylinders with 4mm diameter. Ambient gas is fixed as air and total pressures are varied from naturally normal pressure (100kPa) to elevated pressure (400kPa). Flame appearance, burning rate and flame spread were investigated experimentally and theoretically. Results show that high pressure significantly affects the flame appearance, which is as the pressure increases, flame color changes from luminous yellow to orange and the orange part extends down towards the base of flame. Besides, the average flame width and height, and the burning rate are proved to increase with increasing pressure. What is more, flame spread rates become higher as pressure increases due to the enhancement of heat transfer from flame to solid surface in elevated pressure by performing a simplified heat balance analysis.
Fire Characteristic of Commercial Retardant Flame Polycarbonate under Different Oxygen Concentration: Ignition Time and Heat Blockage
The commercial retardant flame polycarbonate samples as the main high speed train interior carriage material with different thicknesses were investigated in Fire Propagation Apparatus with different external heat fluxes under different oxygen concentration from 12% to 40% to study the fire characteristics and quantitatively analyze the ignition time, mass loss rate and heat blockage. The additives of commercial retardant flame polycarbonate were intumescent and maintained a steady height before ignition when heated. The results showed the transformed ignition time (1/t_ig)ⁿ increased linearly with external flux under different oxygen concentration after deducting the heat blockage due to pyrolysis products, the mass loss rate was taken on linearly with external heat fluxes and the slop of the fitting line for mass loss rate and external heat fluxes decreased with the enhanced oxygen concentration and the heat blockage independent on external heat fluxes rose with oxygen concentration increasing. The inquired data as the input of the fire simulation model was the most important to be used to evaluate the fire risk of commercial retardant flame polycarbonate.
Corrosivity of Smoke Generated by Polyvinyl Chloride and Polypropylene with Different Mixing Ratios towards Carbon Steel
Because a relatively small fire could potentially cause damage by smoke corrosion far exceed thermal fire damage, it has been realized that the corrosion of metal exposed to smoke atmospheres is a significant fire hazard, except for toxicity or evacuation considerations. For the burning materials in an actual fire may often be the mixture of combustible matters, a quantitative study on the corrosivity of smoke produced by the combustion of mixture is more conducive to the application of the basic theory to the actual engineering. In this paper, carbon steel samples were exposed to smoke generated by polyvinyl chloride and polypropylene, two common combustibles in industrial plants, with different mixing ratios in high humidity for 120 hours. The separate and combined corrosive effects of smoke were examined subsequently by weight loss measurement, scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. It was found that, although the corrosivity of smoke from polypropylene was much smaller than that of smoke from polyvinyl chloride, smoke from polypropylene enhanced the major corrosive effect of smoke from polyvinyl chloride to carbon steel. Furthermore, the corrosion kinetics of carbon steel under smoke were found to obey the power function. Possible corrosion mechanisms were also proposed. All the analysis helps to provide basic information for the determination of smoke damage and timely rescue after fire.
Passenger Movement Pattern during Ship Evacuation Considering the Combined Effect of Ship Heeling and Trim
Large passenger ship, especially luxury cruise, is one of the most prevalent means of marine transportation and tourism nowadays. In case of an accident, an effective evacuation would be the ultimate way to minimize the consequence. Ship heeling and trim has a considerable influence on passenger walking speed and posture during ship evacuation. To investigate passenger movement pattern under the combined effect of ship heeling and trim, a ship corridor simulator was developed. Both fast and freely individual walking experiments by male and female experimental subjects under heeling and trim conditions were conducted and recorded therein. It is found that routes of experimental subjects would change due to the heeling and trim angles, although they always walk along the right side because of cultural factors. Experimental subjects would also change their posture to adapt the combined heeling and trim conditions, such as leaning forward, adopting larger arm swaying, shorter and more frequent steps. While for individual walking speed, the speed would decrease with the increasing heeling and trim angles. But the maximum individual walking speed is achieved at heeling angle of 0° with trim angle ranging from -15° to -5 °, instead of on level ground, which may be attributable to the effect of the gravitational acceleration. Female is approximately 10% slower than male due to the discrepancy in physical quality. Besides, individual walking speed shows similar trends in both fast and freely walking modes, and the speed value in freely walking mode is about 78% of that in fast walking mode under each experimental condition. Furthermore, to designate the movement pattern of passengers in heeling and trim conditions, a model of the walking speed reduction was proposed. This work would provide guidance on the development of evacuation models and the design of evacuation facilities on board.
Dynamic Process of Single Water Droplet Impacting on a Hot Heptane Surface
Understanding the interaction mechanism between the water droplet and pool fire has an important significance in engineering application of water sprinkle/spray/mist fire suppression. The micro impact process is unclear when the droplet impacts on the burning liquid surface at present. To deepen the understanding of the mechanisms of pool fire suppression with water spray/mist, dynamic processes of single water droplet impinging onto a hot heptane surface are visualized with the aid of a high-speed digital camera at 2000 fps. Each test is repeated 20 times. The water droplet diameter is around 1.98 mm, and the impact Weber number ranges from 30 to 695. The heptane is heated by a hot plate to mimic the burning condition, and the temperature varies from 30 to 90°C. The results show that three typical phenomena, including penetration, crater-jet and surface bubble, are observed, and the pool temperature has a significant influence on the critical condition for the appearance of each phenomenon. A global picture of different phenomena is built according to impact Weber number and pool temperature. In addition, the pool temperature and Weber number have important influences on the characteristic parameters including maximum crater depth, crown height and liquid column height. For a fixed Weber number, the liquid column height increases with pool temperature.
Performance Analysis of Geothermal Energy Using Earth to Air Heat Exchanger in Western Himalayan Region: A Case Study
Energy demand in India is met by non-renewable sources despite the prime geographical location of some states. Geothermal energy is the thermal energy within the earth’s interior. In this paper, an attempt has been made to use the renewable source of energy for sustainable development. The thermal performance of earth to air tunnel heat exchanger for passive winter preheating and summer cooling has been evaluated. The effect of an operating parameter such as pipe/tube material, soil thermal conductivity and air velocity on the thermal performance of earth to air heat exchanger (EATHE) to be used in Western Himalayan region has been analyzed. The results indicate that the exit temperature drops with an increase in underground pipe/tube length during summers and decreases during winters. However, the mean efficiency increases with increase in underground pipe/tube length. Maximum efficiency of 85.6% and 87.7% is achieved during summer and winter respectively at an air velocity of 0.5 m/s for an underground pipe of 60m length. Also, the maximum average cooling potential is 14.81 kWh during summer for earth air tunnel heat exchanger at underground pipe length of 60 m and a velocity of 0.5 m/s. Similarly, the maximum average heating potential is 27.7 kWh during winter for same operating parameters; which is higher as compared to summers. Thus, the results indicate that earth air tunnel heat exchanger is more effective during winter in Western Himalayan Region. The results demonstrate that geothermal energy stored in a western Himalayan region of India can be a driving force for sustainable development.
Renewable Energy Interfaced Shunt Active Filter Using a Virtual Flux Direct Power Control
In this study, we present a control method entitled virtual flux direct power control of a grid connected photovoltaic system associated with an active power filter. The virtual flux direct control of power (VF-DPC) is employed for the calculation of reference current generation. In this technique, the switches states of inverter are selected from a table of switching based on the immediate errors between the active and reactive powers and their reference values. The objectives of this paper are the reduction of Total Harmonic Distortion (THD) of source current, compensating reactive power and injecting the maximum active power available from the PV array into the load and/or grid. MATLAB/SIMULINK simulations are provided to demonstrate the performance of the proposed approach.
Evaluation of Reliability Indices Using Monte Carlo Simulation Accounting Time to Switch
This paper presents the evaluation of reliability indices of an electrical distribution system using Monte Carlo simulation technique accounting Time To Switch (TTS) for each section. In this paper, the distribution system has been assumed by accounting random repair time omission. For simplicity, we have assumed the reliability analysis to be based on exponential law. Each segment has a specified rate of failure (λ) and repair time (r) which will give us the mean up time and mean down time of each section in distribution system. After calculating the modified mean up time (MUT) in years, mean down time (MDT) in hours and Unavailability (U) in h/year, TTS have been added to the time which the system is not available, i.e. MDT. In this paper, we have assumed the TTS to be a random variable with Log-Normal distribution.
Effect of Fire Retardant Painting Product on Smoke Optical Density of Burning Natural Wood Samples
Natural wood is used in many applications such as furniture, partitions, and cupboards. Smoke produced from combustion of certain samples of natural wood was analyzed in this study. Smoke generated from burning of natural wood is considered as a major cause of the loss of life in the furniture fires. The critical parameter for life safety in fires is available time for escape, so the visual obscuration due to smoke release during fire is taken into a consideration in this work. The effect of smoke produced by burning of wood depends on the amount of smoke released in case of fire; the higher smoke production leads to lower time available for escape. To minimize the loss of life from burning of wood, fire retardant painting products is used in the study. The tested specimens of natural wood include beech, red oak, yellow pine, and white pine wood. A smoke density chamber which is manufactured by fire testing technology has been used to perform measurement of smoke properties. The procedure of test was carried out according to the ISO5659. A vertical heat radiant flux with 25 kW/m² without flame is exposed to 25mm thick of wood samples in a horizontal orientation. The objective of the current study is to present an experimental result on smoke emission for samples of natural woods. Specific optical density, transmittance, thermal conductivity, and mass loss are main measured parameters in the work. Also, a comparison between painted and no painted samples are carried out between the selected samples of woods.
A Review on Control of a Grid Connected Permanent Magnet Synchronous Generator Based Variable Speed Wind Turbine
Among all available wind energy conversion systems (WECS), the direct driven permanent magnet synchronous generator integrated with power electronic interfaces is becoming popular due to its capability of extracting optimal energy capture, reduced mechanical stresses, no need to external excitation current, meaning less losses, and more compact size. Simple structure, low maintenance cost; and its decoupling control performance is much less sensitive to the parameter variations of the generator. This paper attempts to present a review of the control and optimization strategies of WECS based on permanent magnet synchronous generator (PMSG) and overview the most recent research trends in this field. The main aims of this review include; the generalized overall WECS starting from turbines, generators, and control strategies including converters, maximum power point tracking (MPPT), ending with DC-link control. The optimization methods of the controller parameters necessary to guarantee the operation of the system efficiently and safely, especially when connected to the power grid are also presented.
A Simulation-Based Method for Evaluation of Energy System Cooperation between Pulp and Paper Mills and a District Heating System: A Case Study
A step towards reducing greenhouse gases and energy consumption is to collaborate with the energy system between several industries. This work is based on a case study on integration of pulp and paper mills with a district heating system in Sundsvall, Sweden. Present research shows that it is possible to make a significant reduction in the electricity demand in the mechanical pulping process. However, the profitability of the efficiency measures could be an issue, as the excess steam recovered from the refiners decreases with the electricity consumption. A consequence will be that the fuel demand for steam production will increase. If the fuel price is similar to the electricity price it would reduce the profit of such a project. If the paper mill can be integrated with a district heating system, it is possible to upgrade excess heat from a nearby kraft pulp mill to process steam via the district heating system in order to avoid the additional fuel need. The concept is investigated by using a simulation model describing both the mass and energy balance as well as the operating margin. Three scenarios were analyzed: reference, electricity reduction and energy substitution. The simulation show that the total input to the system is lowest in the Energy substitution scenario. Additionally, in the Energy substitution scenario the steam from the incineration boiler covers not only the steam shortage but also a part of the steam produced using the biofuel boiler, the cooling tower connected to the incineration boiler is no longer needed and the excess heat can cover the whole district heating load during the whole year. The study shows a substantial economic advantage if all stakeholders act together as one system. However, costs and benefits are unequally shared between the actors. This means that there is a need for new business models in order to share the system costs and benefits.
Evaluation of Compatibility between Produced and Injected Waters and Identification of the Causes of Well Plugging in a Southern Tunisian Oilfield
Scale deposition during water injection into aquifer of oil reservoirs is a serious problem experienced in the oil production industry. One of the primary causes of scale formation and injection well plugging is mixing two waters which are incompatible. Considered individually, the waters may be quite stable at system conditions and present no scale problems. However, once they are mixed, reactions between ions dissolved in the individual waters may form insoluble products. The purpose of this study is to identify the causes of well plugging in a southern Tunisian oilfield, where fresh water has been injected into the producing wells to counteract the salinity of the formation waters and inhibit the deposition of halite. X-ray diffraction (XRD) mineralogical analysis has been carried out on scale samples collected from the blocked well. Two samples collected from both formation water and injected water were analysed using inductively coupled plasma atomic emission spectroscopy, ion chromatography and other standard laboratory techniques. The results of complete waters analysis were the typical input parameters, to determine scaling tendency. Saturation indices values related to CaCO3, CaSO4, BaSO4 and SrSO4 scales were calculated for the water mixtures at different share, under various conditions of temperature, using a computerized scale prediction model. The compatibility study results showed that mixing the two waters tends to increase the probability of barite deposition. XRD analysis confirmed the compatibility study results, since it proved that the analysed deposits consisted predominantly of barite with minor galena. At the studied temperatures conditions, the tendency for barite scale is significantly increasing with the increase of fresh water share in the mixture. The future scale inhibition and removal strategies to be implemented in the concerned oilfield are being derived in a large part from the results of the present study.
Achieving High Renewable Energy Penetration in Western Australia Using Data Digitisation and Machine Learning
The energy industry is undergoing significant disruption. This research outlines that, whilst challenging; this disruption is also an emerging opportunity for electricity utilities. One such opportunity is leveraging the developments in data analytics and machine learning. As the uptake of renewable energy technologies and complimentary control systems increases, electricity grids will likely transform towards dense microgrids with high penetration of renewable generation sources, rich in network and customer data, and linked through intelligent, wireless communications. Data digitisation and analytics have already impacted numerous industries, and its influence on the energy sector is growing, as computational capabilities increase to manage big data, and as machines develop algorithms to solve the energy challenges of the future. The objective of this paper is to address how far the uptake of renewable technologies can go given the constraints of existing grid infrastructure and provides a qualitative assessment of how higher levels of renewable energy penetration can be facilitated by incorporating even broader technological advances in the fields of data analytics and machine learning. Western Australia is used as a contextualised case study, given its abundance and diverse renewable resources (solar, wind, biomass, and wave) and isolated networks, making a high penetration of renewables a feasible target for policy makers over coming decades.
Comparative Study on Subcritical and Supercritical Organic Rankine Cycle Applications for Exhaust Waste Heat Recovery
Waste heat recovery by means of Organic Rankine Cycle is a promising technology for the recovery of engine exhaust heat. However, it is complex to find out the optimum cycle conditions with appropriate working fluids to match exhaust gas waste heat due to its high temperature. Hence, this paper focuses on comparing subcritical and supercritical ORC conditions with eight working fluids on a combined diesel engine-ORC system. The model employs two ORC designs, Regenerative-ORC and Pre-Heating-Regenerative-ORC respectively. The thermodynamic calculations rely on the first and second law of thermodynamics, thermal efficiency and exergy destruction factors are the fundamental parameters evaluated. Additionally, in this study, environmental and safety, GWP (Global Warming Potential) and ODP (Ozone Depletion Potential), characteristic of the refrigerants are taken into consideration as evaluation criteria to define the optimal ORC configuration and conditions. Consequently, the study’s outcomes reveal that supercritical ORCs with alkane and siloxane are more suitable for high-temperature exhaust waste heat recovery in contrast to subcritical conditions.
Role of SiOx Interlayer on Lead Oxide Electrodeposited on Stainless Steel for Promoting Electrochemical Treatment of Wastewater Containing Textile Dye
The main objective of this work is to investigate the efficiency of depollution power related to PbO₂ layer deposited onto a stainless steel (SS) substrate with SiOx as interlayer. The elaborated electrode was used as anode for anodic oxidation of wastewater containing Amaranth dye, as recalcitrant organic pollutant model. SiOx interlayer was performed using Plasma Enhanced Chemical Vapor Deposition ‘PECVD’ in plasma fed with argon, oxygen, and tetraethoxysilane (TEOS, Si precursor) in different ratios, onto the SS substrate. PbO₂ layer was produced by pulsed electrodeposition on SS/SiOx. The morphological of different surfaces are depicted with Field Emission Scanning Electron Microscope (FESEM) and the composition of the lead oxide layer was investigated by X-Ray Diffractometry (XRD). The results showed that the SiOx interlayer with more rich oxygen content improved better the nucleation of β-PbO₂ form. Electrochemical Impedance Spectroscopy (EIS) measurements undertaken on different interfaces (at optimized conditions) revealed a decrease of Rfilm while CPE film increases for SiOx interlayer, characterized by a more inorganic nature and deposited in a plasma fed by higher O2-to-TEOS ratios. Quantitative determinations of the Amaranth dye degradation rate were performed in terms of colour and COD removals, reaching a 95% and an 80% respectively removal at pH = 2 in 300 min. Results proved the improvement of the degradation wastewater containing the amaranth dye. During the electrolysis, the Amaranth dye solution was sampled at 30 min intervals and analyzed by ‘High-performance Liquid Chromatography’ HPLC. The gradual degradation of the Amaranth dye confirmed by the decrease in UV absorption using the SS/SiOx(20:20:1)/PbO₂ anode, the reaction exhibited an apparent first-order kinetic for electrolysis time of 5 hours, with an initial rate constant of about 0.02 min⁻¹.
Horizontal and Vertical Illuminance Correlations in a Case Study for Shaded South Facing Surfaces
Daylight utilization is a key factor in achieving visual and thermal comfort, and energy savings in the integrated building design. However, lack of measured data in this topic has become a major challenge with the increasing need for integrating lighting concepts and simulations at the early stages of design procedures. The current manuscript deals with values of daylight illuminance on horizontal and south facing vertical surfaces. The data are estimated using IESNA model and measured values of the horizontal and vertical illuminance, and a regression model with an acceptable linear correlation is obtained. The resultant illuminance frequency curves are useful for estimating daylight availability on south facing surfaces in Tehran. In addition, the relationship between indirect vertical illuminance and the corresponding global horizontal illuminance is analyzed. A simple parametric equation is proposed in order to predict the vertical illumination on a shaded south facing surface. The equation correlates the ratio between the vertical and horizontal illuminance to the solar altitude and is used with another relationship for prediction of the vertical illuminance. Both of these equations show a good agreement which allows for the calculation of indirect vertical illuminance on a south facing surface at any time through the year.
Clean and Energy Efficient Application of Fuel Cell Using Photovoltaic Generated Hydrogen in DC Microgrid
Renewable energy technology based generators such as Photovoltaic (PV) and Fuel cell (FC) are well suited for creating a microgrid system because of simpler on-site power generation using either/both of the generators, high power quality and reduced overall harmful environmental effects. Ministry of New and Renewable Energy (MNRE) India has started a programme for DC microgrid application for electrifying the rural areas in the country for different voltage levels such as 24 V, 48 V, 72 V and 110 V. Different voltage (24 V and 48 V) DC microgrids using the PV and FC as power generators have been developed in the Photovoltais Lab. The hydrogen requirement for FC operation is met using the excess PV electricity for operating an alkaline electrolyzer and then storing the generated hydrogen in a metal hydride cylinder. In order to create a stable DC voltage at the DC bus interconnecting the DC generators and the DC loads, DC-DC converters have been designed using buck-boost methodology having efficiency ≈ 85%. The DC-DC converter can be conveniently used for 24 V / 48 V DC bus by using suitable inductor value. The DC-DC converter has been used with roof mounted PV modules to study the performance under actual operating conditions throughout the day. It is found that the DC voltage remains stable even when the PV modules voltage varies from 20 V to 58 V. A similar study with FC has also established the suitability of the converter for the variable FC output under different loads. Thus, the DC microgrid design providing suitable voltage for given DC loads has been established to operate different loads like LED lamps, fans etc. The configuration used for the DC microgrid comprises PV generator (5 kWP), FC generator (1 kW), electrolyzer (600 W) and MH storage (5000 NL), these system components were originally designed for grid interactive PV-FC hybrid system with hydrogen storage and now are being used for the DC microgrid study. This has resulted in operating the generators for lower power generation to meet the DC load demand of 250 W, for which the two DC-DC converters have been designed. The study of the DC microgrid using PV and FC generator has proven the suitability of the system component design and can be expanded to include more DC power sources including batteries. The stable operation of the microgrid under simulated day and night conditions has proven that the microgrid combining different generators located in a distributed manner can be established for an efficient utilization of the DC electricity to meet different types of DC loads which can also be distributed. Such a system will find suitable applications in rural as well as urban areas in the country to promote clean energy technologies.
Declining Costs of Renewable Energy Systems: An Opportunity for Increasing Electricity Access in Sub-Saharan Africa
Traditionally, electric networks in Africa are dominated by centralized fossil base grids, relying on gas, coal and hydropower plants for generation. Analysis of the energy market in sub-Saharan Africa (SSA) have consistently displayed a stunted growth. Previous reports have argued that increasing electricity access through expansion of the existing grid is no longer sufficient due to costs and environmental concern. Other arguments are based on the existence of Islands and mountainous locations not immediately accessible to the utility grid. This situation has lent credence to the argument in support of renewable energy systems. The current decline in the cost of renewable energy technology provides an opportunity to explore this market. However, the assessment of energy climate in SSA suggests that a lot needs to be done in order to avail these opportunities. This paper investigates the technical challenges, policy issues and financing barriers inhibiting the penetration of green energy in SSA. The study shows that upscaling electricity access requires building of strong institutions to guide against policy inconsistencies. Electrification programs should incorporate capacity building with technology transfer from the outset. Also, it identifies capital expenditure (CAPEX) and operational expenditure (OPEX) phases of projects as the two key failure points in this region.
Sustainability of Mini-Grid Electrification Programs in Sub-Saharan Africa: The Nexus for Challenges and Enablers
Empirical evidence and field performance assessment of rural electrification programs in developing countries indicates low level of developmental impacts on rural dwellers. Numerous scholarly reports have recommended the use of mini-grid electricity as a panacea for jumpstarting development in rural settlements, due to the low power capacity of solar home system (SHS) alternative. However, lessons from implemented systems shows that issues related to low energy demand density, unavailable technical supports for after sales service, insufficient revenue, and poor logistics for feedstock replacement, high electricity production cost and lack of local buy-in into the introduced novel technology, often limit long-term viability of electrification programs. This paper calls into question the use of electrification programs as the starting point for rural development, and reports on the requisite issues to be addressed as a precondition for the establishment of mini-grid in order to ensure sustainability of the electrification programs in developing countries. The finding shows that incentivization of potential and existing businesses, and provision of accessible roads for local produce prior to the introduction of mini-grid electricity could lead to long-term viability of projects. Availability of infrastructures and local industries close to source of raw materials could lead to densification of the mini-grid.
Investigation of Net Metering as a Tool for Increasing Electricity Access in Developing Countries
Uncertainties associated with implementation of small scale energy projects in emerging markets limited the entrance for independent power producers (IPP) in their energy market. Due to the dismal performance of most utility grids largely owned and operated by governments, integration of IPPs in the energy mainstream is instructive. Net metering is one of the policy instruments used in developed countries to attract private electricity generators in power networks. It has been argued that its success is attributable to the large scale energy market, for this reason, success in developing countries is uncertain. Other policy instruments like renewable energy feed-in-tariff have been used to this end in South Africa, but failed due its lack of compliance with her public procurement laws. As a result, renewable energy independent power producer procurement (REIPPP) program is used instead. The use of net metering as an incentive to encourage private electricity generators has been blithely ignored by most governments in this region. This paper investigates the use of net metering policy as a means of improving electricity access in emerging economies. Our finding shows that it could improve power reliability, reduce economy, limit over dependence on monopolistic utility grid, and relief congestion in power networks.
Optimization Design of Single Phase Inverter Connected to the Grid
In grid-connected photovoltaic systems, significant improvements can be carried out in the design and implementation of inverters: reduction of harmonic distortion, elimination of the DC component injected into the grid and the proposed control. This paper proposes a control strategy based on PWM switching patterns for an inverter for the photovoltaic system connected to the grid in order to control the injected current. The current injected must be sinusoidal with reduced harmonic distortion. An additional filter is designed to reduce high-order harmonics on the output side. This strategy exhibits the advantages: Simplicity, reduction of harmonics, the size of the line filter, reduction of the memory requirements and power calculation for the control.
Control Technique for Single Phase Bipolar H-Bridge Inverter Connected to the Grid
In photovoltaic system connected to the grid, the main goal is to control the power that the inverter injects into the grid from the energy provided by the photovoltaic generator. In this paper is proposed, a control technique for a photovoltaic system connected to the grid based on the digital pulse-width modulation (DPWM) which can synchronise a sinusoidal current output with a grid voltage and generate power at unity power factor. This control is based on H-Bridge inverter controlled by bipolar PWM Switching. The functional structure of this system is presented and simulated. Detailed analysis, Simulations results of the output voltage and current waveform demonstrate the contribution of this approach to determinate the suitable control of the system. A digital design of a generator PWM using VHDL is proposed and implemented on a Xilinx FPGA.
Soft-Template Mediated Hollow Gold Nanoparticles Formation via Galvanic Replacement Reaction of As(0) and Its Catalytic Application for 4-Nitrophenol Reduction
Galvanic replacement reaction (GRR) is a widely used powerful synthesis technique to produce different hollow nanoparticles. In the present work, As(0) nanoparticles of two different size ranges (e.g. 50 ± 7 and 70 ± 10 nm) are synthesized by sodium borohydride reduction of arsenite under controlled pH, and subsequently they are used as templates for GRR reaction to produce two different sized hollow gold nanoparticles (HGNPs), which are designated as AuNP1 and AuNP2, with average diameter 55 ± 7 and 72 ± 7 nm, respectively. The unique feature of the reduction of arsenite to As(0) and not to AsH3, is the control of medium pH at 7-9. The use of AuNP1 and AuNP2 in homogeneous phase is restricting them to recollect and reuse properly. Here, a soft solid template, surfactant-modified silica (SMS) (having positive charge in the surface) is taken to attach AuNP1 and AuNP2. The ionic attraction between negatively charged surface of AuNP1 and AuNP2 which arises due to the stabilization of in situ H₂AsO₄⁻ helps to attach properly in the surface of SMS. Now the two catalysts can be reused. The catalytic reduction of 4-nitrophenol (4-NP), which is a toxic compound used in many industries, to 4-aminophenol (4-AP), an industrially important compound is a well-studied model reaction. The size dependent catalytic activities of the as-prepared HGNPs have been examined on the reduction of 4-NP to 4-AP in the presence of sodium borohydride. While both the nanoparticles exhibit excellent catalytic activity, the smaller particles (SMS-Au1) are observed to be more effective. The reaction is carried out with various catalyst doses and initial 4-NP concentrations, and the reaction follows first order kinetics in all cases. The turn over frequency (TOF) for the catalytic reaction using SMS-Au1 and SMS-Au2 suggests that SMS-Au1 bears ~2 times higher catalytic activity compared to that of SMS-Au2. The reusability of both the catalysts SMS-Au1 and SMS-Au2 have also been checked.
Assessment of Trace Metals Contamination in Surficial and Core Sediments from Ghannouch- Gabes Coastline, Impact of Phosphogypsum Discharge, Southeastern of Tunisia, Mediterranean Sea: Geochemical and Mineralogical Approaches
The purpose of the present study is to assess the level and the distribution of CaO, SO3, Cd, Cu, Pb and Zn incore sediments of Ghannouch-Gabes coast, Gulf of Gabes, Tunisian Mediterranean coast. The XRD analyses indicate that the sediments of Ghannouch-Gabes coast are mainly composed of quartz, calcite, gypsum and fluorine reflecting the impact of the phosphate fertilizer industrial waste. The vertical distribution of surface sediments shows for all the elements analyzed, that the area located between the commercial and the fishing port of Gabes, is the most polluted zone, where the two harbors acted as barriers and limited the dispersion of phosphogypsum discharge. The abundance order of metals was found to be Zn > Cd > Cu >Pb and that the highest levels of heavy metals were found in the uppermost segment of the sediment core compared to lower depth subsurface due to a continuous input of PG release and showed that the area between the two harbor suffered from several types of pollutants compared to reference core C1, collected from non-industrialized area. The level of pollution was evaluated using contamination factor (Cf), pollution load index (PLI) and the geoaccumulation index (Igeo). The obtained results of Igeo allowed us to distinguish that the area between the commercial harbor of Ghannouch and the fishing harbor of Gabes is the most polluted where sediments are strongly contaminated for Pb, Cu and Cd. The pollution load index (PLI) of all sediments collected classified them as "polluted". According to contamination factor (Cf), the sediments can be considered as ‘considerable’ to ‘very high’ contaminated for Pb, ‘very high to moderate’ for Cd, ‘ moderate’ for Zn, between ‘moderate’ and ‘considerable’ for Cu. Statistical analyses show that heavy metals, fluoride, calcium and sulphate are resulting from the same anthropogenic origin. The metallic pollution status of sediments of Ghanouch -Gabes coast is worrying and requires a serious intervention.
Generalized Mathematical Description and Simulation of Grid-Tied Thyristor Converters
Thyristor rectifiers, inverters grid-tied and AC voltage regulators are widely used in industry and on electrified transport have a lot in common both in the power circuit and in the control system. They have a common mathematical structure and switching processes. At the same time, the rectifier, but the inverter units and thyristor regulators of alternating voltage are considered separately both theoretically and practically. They are written about in different books as completely different devices, the aim of this work is to combine them into one class based on the unity of the equations describing electromagnetic processes, and then show this unity on the mathematical model and experimental setup. Based on research from mathematics to the product, a conclusion made about the methodology for the rapid conduct of research and experimental design work, preparation for production and serial production of converters with a unified bundle. In recent years, there has been a transition from thyristor circuits and transistor in modular design. Showing the example of thyristor rectifiers and AC voltage regulators, we can conclude that there is a unity of mathematical structures and grid-tied thyristor converters.
A Physically-Based Analytical Model for REduced SURface Field Laterally Double Diffused MOSFETs
In this paper, a methodology for physically modeling the intrinsic MOS part and the drift region of the n-channel Laterally Double-diffused MOSFET (LDMOS) is presented. The effects of velocity saturation, mobility reduction and nonuniform impurity concentration in the channel are all considered. The analytical model is implemented using MATLAB. A comparison of the TCAD and the proposed analytical model simulations, at room temperature, shows a satisfactory accuracy which is less than 5% for the whole voltage domain.
Design Analysis of Solar Energy Panels for Tropical Nigeria
More than ever human activity relating to uncontrolled greenhouse gas (GHG) and its effects on the earth is gaining greater attention in the global academic and policy discussions. Activities of man have greatly influenced climate change over the years as a result of a consistent increase in the use of fossil fuel energy. Scientists and researchers globally are making significant and devoted efforts towards the development and implementation of renewable energy technologies that are harmless to the environment. One of such energy is solar energy with its source from the sun. There are currently two primary ways of harvesting this energy from the sun: through photovoltaic (PV) panels and through thermal collectors. This work discusses solar energy as the abundant renewable energy in the tropical Nigeria, processes of harvesting the energy and recommends solar energy as an alternative means of electric power generation in a time the demand for power in Nigeria supersedes supply.
Geochemistry of Nutrients in the South Lagoon of Tunis, Northeast of Tunisia, Using Multivariable Methods
Understanding ecosystem response to the restoration project is essential to assess its rehabilitation. Indeed, the time elapsed after restoration is a critical indicator to shows the real of the restoration success. In this order, the south lagoon of Tunis, a shallow Mediterranean coastal area, has witnessed several pollutions. To resolve this environmental problem, a large restoration project of the lagoon was undertaken. In this restoration works, the main changes are the decrease of the residence time of the lagoon water and the nutrient concentrations. In this paper, we attempt to evaluate the trophic state of lagoon water for evaluating the risk of eutrophication after almost 16 years of its restoration. To attend this objectives water quality monitoring was untaken. In order to identify and to analyze the natural and anthropogenic factor governing the nutrients concentrations of lagoon water geochemical methods and multivariate statistical tools were used. Results show that nutrients have duel sources due to the discharge of municipal wastewater of Megrine City in the south side of the lagoon. The Carlson index shows that the South lagoon of Tunis Lagoon Tunis is eutrophic, and may show limited summer anoxia.
Laboratory Scale Experimental Studies on CO₂ Based Underground Coal Gasification in Context of Clean Coal Technology
Coal is the largest fossil fuel. In India, around 37 % of coal resources found at a depth of more than 300 meters. In India, more than 70% of electricity production depends on coal. Coal on combustion produces greenhouse and pollutant gases such as CO₂, SOₓ, NOₓ, and H₂S etc. Underground coal gasification (UCG) technology is an efficient and an economic in-situ clean coal technology, which converts these unmineable coals into valuable calorific gases. The UCG syngas (mainly H₂, CO, CH₄ and some lighter hydrocarbons) which can utilized for the production of electricity and manufacturing of various useful chemical feedstock. It is an inherent clean coal technology as it avoids ash disposal, mining, transportation and storage problems. Gasification of underground coal using steam as a gasifying medium is not an easy process because sending superheated steam to deep underground coal leads to major transportation difficulties and cost effective. Therefore, for reducing this problem, we have used CO₂ as a gasifying medium, which is a major greenhouse gas. This paper focus laboratory scale underground coal gasification experiment on a coal block by using CO₂ as a gasifying medium. In the present experiment, first, we inject oxygen for combustion for 1 hour and when the temperature of the zones reached to more than 1000 ºC, and then we started supplying of CO₂ as a gasifying medium. The gasification experiment was performed at an atmospheric pressure of CO₂, and it was found that the amount of CO produced due to Boudouard reaction (C+CO₂  2CO) is around 35%. The experiment conducted to almost 5 hours. The maximum gas composition observed, 35% CO, 22 % H₂, and 11% CH4 with LHV 248.1 kJ/mol at CO₂/O₂ ratio 0.4 by volume.
Physicochemical Characterization of Waste from Vegetal Extracts Industry for Use as Briquettes
Wastes from vegetal extracts industry (cocoa, oak, Guarana and mate) were characterized by particle size, proximate and ultimate analysis, lignocellulosic fractions, high heating value, thermal analysis (Thermogravimetric Analysis– TGA, and Differential Thermal Analysis- DTA) and energy density to evaluate their potential as biomass in the form of briquettes for power generation. All wastes presented adequate particle sizes to briquettes production. The wastes showed high moisture content, requiring previous drying for use as briquettes. Cocoa and oak wastes had the highest volatile matter contents with maximum mass loss at 310ºC and 450ºC, respectively. The solvents used in the aroma extraction process influenced in the moisture content of the wastes, which was higher for mate due to water has been used as a solvent. All wastes showed an insignificant loss mass after 565°C, hence resulting in low ash content. High carbon and hydrogen contents and low sulfur and nitrogen contents were observed ensuring a low generation of sulfur and nitrous oxides. Mate and cocoa exhibited the highest carbon and lignin content, and high heating value. The dried wastes had high heating value, from 17.1 to 20.8 MJ/kg. The results indicate the energy potential of wastes for use as fuel in power generation.