We derived an equation for saturation in carbonate reservoirs based on the electrical efficiency model in the case of lacking core data. Owing to the complex pore structure and strong heterogeneity in carbonate reserv...We derived an equation for saturation in carbonate reservoirs based on the electrical efficiency model in the case of lacking core data. Owing to the complex pore structure and strong heterogeneity in carbonate reservoirs, the relation between electrical efficiency and water porosity is either complex or linear. We proposed an electrical efficiency equation that accounts for the relation between electrical efficiency and water porosity. We also proposed a power-law relation between electrical efficiency and deep-formation resistivity and analyzed the factors controlling the error in the water saturation computations. We concluded that the calculation accuracy of the electrical efficiency is critical to the application of the saturation equation. The saturation equation was applied to the carbonate reservoirs of three wells in Iraq and Indonesia. For relative rock electrical efficiency error below 0.1, the water saturation absolute error is also below 0.1. Therefore, we infer that the proposed saturation equation generally satisfies the evaluation criteria for carbonate reservoirs.展开更多
Complex-valued double-sideband direct detection(DD)can reconstruct the optical field and achieve a high electrical spectral efficiency(ESE)comparable to that of a coherent homodyne receiver,and DD does not require a c...Complex-valued double-sideband direct detection(DD)can reconstruct the optical field and achieve a high electrical spectral efficiency(ESE)comparable to that of a coherent homodyne receiver,and DD does not require a costly local oscillator laser.However,a fundamental question remains if there is an optimal DD receiver structure with the simplest design to approach the performance of the coherent homodyne detection.This study derives the optimal DD receiver structure with an optimal transfer function to recover a quadrature amplitude modulation(QAM)signal with a near-zero guard band at the central frequency of the signal.We derive the theoretical ESE limit for various detection schemes by invoking Shannon’s formula.Our proposed scheme is closest to coherent homodyne detection in terms of the theoretical ESE limit.By leveraging a WaveShaper to construct the optimal transfer function,we conduct a proof-of-concept experiment to transmit a net 228.85-Gb/s 64-QAM signal over an 80-km single-mode fiber with a net ESE of 8.76 b/s/Hz.To the best of our knowledge,this study reports the highest net ESE per polarization per wavelength for DD transmission beyond 40-km single-mode fiber.For a comprehensive metric,denoted as 2ESE×Reach,we achieve the highest 2ESE×Reach per polarization per wavelength for DD transmission.展开更多
The performance of a 3-phase 6-pole 400 W inverter-drive induction motor was investigated using a variety of non-oriented electrical steels for stator core at PWM inverter fundamental wave frequencies of 30 to 300 Hz....The performance of a 3-phase 6-pole 400 W inverter-drive induction motor was investigated using a variety of non-oriented electrical steels for stator core at PWM inverter fundamental wave frequencies of 30 to 300 Hz. There existed an optimum Si content of the material depending on the tooth flux density. Both reduction of material thickness and stress-relief annealing of the stator core improved the motor efficiency. The influence of Si content on the efficiency was small at lower PWM frequencies, while at higher frequencies the motor efficiency increased with increasing Si content. The Cu loss WC increased and the Fe loss Wi counteractiveiy decreasedwith increasing Si content at lower frequencies; while at higher frequencies Wi had dominant effect on the efficiency. Newly developed materials RMA, having lower Fe losses after stress-relief annealing and higher flux densities with lower Si contents, showed motor efficiencies superior to conventional J1S grade materials with comparable Fe losses.展开更多
Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It...Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmetrical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maximum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis.展开更多
As the quality of power LED improves and the cost of power LED reduces, semiconductor lighting will replace incandescent and fluorescent lighting gradually, causing another revolution on the lighting history. And its ...As the quality of power LED improves and the cost of power LED reduces, semiconductor lighting will replace incandescent and fluorescent lighting gradually, causing another revolution on the lighting history. And its driving solution has been greatly accelerated. Based on the white power LED I-V characteristics and the application ambiance, proposed is a new LED lighting solution, suiting indoor and outdoor illumination. According to the test results, the design is optimized, and the electrical efficiency is 95% and the output current deviation is 13.0%.展开更多
A novel method to calculate fuel-electric conversion factor for full hybrid electric vehicle（HEV）equipped with continuously variable transmission（CVT）is proposed.Based on consideration of the efficiency of pivotal...A novel method to calculate fuel-electric conversion factor for full hybrid electric vehicle（HEV）equipped with continuously variable transmission（CVT）is proposed.Based on consideration of the efficiency of pivotal components,electric motor,system efficiency optimization models are developed.According to the target of instantaneous optimization of system efficiency,operating ranges of each mode of power-train are determined,and the corresponding energy management strategies are established.The simulation results demonstrate that the energy management strategy proposed can substantially improve the vehicle fuel economy,and keep battery state of charge（SOC）change in a reasonable variation range.展开更多
Solar energy is a valuable renewable energy source,and photovoltaic(PV)systems are a practical approach to harnessing this energy.Nevertheless,low energy efficiency is considered a major setback of the system.Moreover...Solar energy is a valuable renewable energy source,and photovoltaic(PV)systems are a practical approach to harnessing this energy.Nevertheless,low energy efficiency is considered a major setback of the system.Moreover,high cell temperature and reflection of solar irradiance from the panel are considered chief culprits in this regard.Employing pulsating heat pipes(PHPs)is an innovative and useful approach to improving solar panel performance.This study presents the results of the power performance of a PV panel attached to a newly designed spiral pulsating heat pipe,while graphene oxide nanofluid with three different concentrations was used as a working fluid to maximize the efficacy of the solar panel.The study proved that the cooling method delivered high efficiency by reducing the temperature,especially in the middle of the day.Using nanofluid graphene oxide at concentrations of 0.2,0.4,and 0.8 gr/lit as the working fluid can reduce the thermal resistance of PHPs by over 30%,24%,and 15%,respectively.This,in turn,enhances the system’s electrical power output by approximately 9%,7%,and 6%,respectively.展开更多
A solar PV panel works with maximum efficiency only when it is operated around its optimum operating point or maximum power point.Unfortunately,the performance of the solar cell is affected by several factors like sun...A solar PV panel works with maximum efficiency only when it is operated around its optimum operating point or maximum power point.Unfortunately,the performance of the solar cell is affected by several factors like sun direction,solar irradiance,dust accumulation,module temperature,as well as the load on the system.Dust deposition is one of the most prominent factors that influence the performance of solar panels.Because the solar panel is exposed to the atmosphere,dust will accumulate on its surface,reducing the quantity of sunlight reaching the solar cell and diminishing output.In the proposed work,a detailed investigation of the performance of solar PV modules is carried out under the tropical climatic condition of Chennai,India,where the presence of dust particles is very high.The data corresponding to four different dust samples of various densities at four solar irradiation levels of 220,525,702,and 905 W/m^(2)are collected,and performance analysis is carried out.Based on the analysis carried out,the maximum power loss is found to be 73.51%,66.29%,65.46%,and 61.42%,for coal,sand,brick powder,and chalk dust respectively.Hence,it can be said that coal dust contributes to the maximum power loss among all four dust samples.Due to heat dissipation produced by dust deposition,the performance of solar PV modules is degraded as the temperature rose.展开更多
This research presents the results of system validation tests for an SOFC power system. In the study, the system was heated up without electric device, i.e., the fuel providing the required thermal energy through an i...This research presents the results of system validation tests for an SOFC power system. In the study, the system was heated up without electric device, i.e., the fuel providing the required thermal energy through an integrated BOP （balance of plant）. The ex-situ experiments, without an SOFC stack installed in the system, were fast conducted to investigate the operability of a BOP apparatus. It was found that the BOP possessed high conversion rates for both steam reforming and water gas shift reactions. The total fuel concentration of hydrogen and carbon monoxide from the reformer was around 91.2%. The system validation tests showed that, with the natural gas as fuel, the output power from the stack reached to 1,060 W, while the fuel utilization efficiency and electrical efficiency were 67.16% and 45.0%, respectively. A steady 600-hour system operation test was carried out at an average system temperature of 694℃. Of which, a 36-cell stack was employed for the test. Meanwhile, the current, voltage and output power were 26 A, 32.3 V and 840 W, respectively, and its electrical efficiency was around 33.4%.展开更多
In this study,a model of combined cooling,heating and power system with municipal solid waste(MSW)and liquefied natural gas(LNG)as energy sources was proposed and developed based on the energy demand of a large commun...In this study,a model of combined cooling,heating and power system with municipal solid waste(MSW)and liquefied natural gas(LNG)as energy sources was proposed and developed based on the energy demand of a large community,andMSW was classified and utilized.The systemoperated by determining power by heating load,and measures were taken to reduce operating costs by purchasing and selling LNG,natural gas(NG),cooling,heating,and power.Based on this system model,three operation strategies were proposed based on whether MSW was classified and the length of kitchen waste fermentation time,and each strategy was simulated hourly throughout the year.The results showed that the strategy of MSW classified and centralized fermentation of kitchen waste in summer(i.e.,strategy 3)required the least total amount of LNG for the whole year,which was 47701.77 t.In terms of total annual cost expenditure,strategy 3 had the best overall economy,with the lowest total annual expenditure of 2.7730×108 RMB at LNG and NG unit prices of 4 and 4.2 RMB/kg,respectively.The lower heating value of biogas produced by fermentation of kitchen waste from MSW being classified was higher than that of MSW before being classified,so the average annual thermal economy of the operating strategy of MSW being classified was better than that of MSW not being classified.Among the strategies in which MSW was classified and utilized,strategy 3 could better meet the load demand of users in the corresponding season,and thus this strategy had better thermal economy than the strategy of year-round fermentation of kitchen waste(i.e.,strategy 2).The hourly analysis data showed that the net electrical efficiency of the system varies in the same trend as the cooling,heating and power loads in all seasons,while the relationship between the energy utilization efficiency and load varied from season to season.This study can provide guidance for the practical application of MSW being classified in the system.展开更多
The solar chimney can generate airflow through the living space of the building to provide cooling. Hence, solar energy represents the best renewable, environmentally friendly source of energy that can be used for hea...The solar chimney can generate airflow through the living space of the building to provide cooling. Hence, solar energy represents the best renewable, environmentally friendly source of energy that can be used for heating and cooling of houses. The present paper reports the numerical study of the performance of the mixed convection in the associated hybrid Photovoltaic/Thermal chimneys integrated into building for natural habitat ventilation. The front side glass plate of the chimneys is heated by a non-uniform daily solar radiation flux. Air is considered to be the cooling fluid. The stream fucntion-vorticity formulation with a finite difference numerical discretization solution scheme has been adopted. The system of algebraic governing equations is solved by Thomas algorithm method. The aim of the present paper is to study and to predict the dynamic fields and particularly of the mass flow rate of the air thermosiphon drawing in the associated hybrid Photovoltaic-Thermal chimneys integrated into a building for passive cooling in the habitats. The effects of the governing parameters, namely Reynolds number (30 ≤ Re ≤ 200), Rayleigh number (103 ≤ Ra≤ 105), the integrated chimney width on the fluid flow and the heat transfer characteristics, are studied in detail. The local Nusselt number, streamlines, isotherms, PV cells electrical efficiency and the outlet velocity at the top of the channels are the results represented versus the above controlling parameters.展开更多
Electricity shortages present a significant constraint on manufacturers,who rely on electricity as an important input into production.In China,electricity supply has been growing rapidly.However,the rapid industrializ...Electricity shortages present a significant constraint on manufacturers,who rely on electricity as an important input into production.In China,electricity supply has been growing rapidly.However,the rapid industrialization sometimes makes the power supply still unable to meet the demand.Using a survey of 1673 Chinese manufacturing firms,this paper explores how firms response to electricity shortages and its impact on productivity.We find that self-generation of electricity and investment in Research and Development(R&D)have significant positive relationships with electricity shortages.Further investigations reveal that self-generation is the most common way to deal with electricity shortages.However,it aggravates productivity loss.Though investment in Research and Development can promote productivity,it cannot offset the negative impact of electricity shortages on productivity.Analyses on subsamples show heterogeneity in the impacts of electricity shortages across firms.In particular,large firms are more inclined to invest in R&D than small and medium-sized firms are.They are also the one who suffer significant productivity loss due to self-generation of electricity.Though it is possible for medium-sized firms to reduce productivity loss through R&D,they are not likely to invest in R&D as a response to electricity shortages.This study illustrates that firms can hardly have effective solutions to electricity shortages,and policy makers should take great efforts to increase electricity supply.展开更多
The aim of this paper is to present a new topology of a DC-DC power converter for conditioning the current and voltages behaviors of embarked energy sources used in electrical vehicles. The fuel cells in conjunction w...The aim of this paper is to present a new topology of a DC-DC power converter for conditioning the current and voltages behaviors of embarked energy sources used in electrical vehicles. The fuel cells in conjunction with ultra-capacitors have been chosen as the power supply. The originality of the proposed converter is to use a variable voltage of the DC bus of the vehicle. The goal is to allow a better energy management of the embedded sources onboard the vehicle by improving its energy efficiency. After presenting and explaining the topology of the converter, some simulation and experiments results are shown to highlight its different operation modes.展开更多
A novel tank-Photovoltaic-thermal(PV/T) system is presented in this paper, and its energy performance has been compared with a traditional heat pipe PV/T system. The novel tank PV/T system combines photovoltaic cell, ...A novel tank-Photovoltaic-thermal(PV/T) system is presented in this paper, and its energy performance has been compared with a traditional heat pipe PV/T system. The novel tank PV/T system combines photovoltaic cell, heat absorbing plate and hot-water storage tank which expands the heat exchange area, shortens the heat transfer path and saves the module installation space. A prototype system is constructed and tested in a cold weather condition and then compared with a heat pipe PVT system. The experimental results indicate that during the 10 days’ testing, the electrical, thermal and overall efficiency of the tank PV/T system ranges from 14.3% to 15.6%, 38.6% to 43.8% and 53.1% to 58.1%, respectively, while the heat pipe PVT system ranges from 10.9% to 12.2%, 39.3% to 41.2% and 50.5% to 53.4%, respectively. Based on these data, the electrical and thermal efficiency curve of the system with the novel tank-PVT system and heat pipe PVT system were generated. According to the comparison result, it shows that the novel tank-PVT system has a better thermal and electrical efficiency. This system provides a new design method for the development of the PV/T systems, which has a potential for PV/T systems building integration in the future.展开更多
Over 25 percent of the world’s population lives without access to electricity from a utility-supplied grid[1].In underdeveloped and developing countries,the reason is primarily a lack of government-sponsored utility ...Over 25 percent of the world’s population lives without access to electricity from a utility-supplied grid[1].In underdeveloped and developing countries,the reason is primarily a lack of government-sponsored utility infrastructure due to the high cost of power line extension.In developed countries,power line extension costs are again the primary factor in lack of a grid connection,as in most cases the end user must foot the bill for such improvements.In the United States,power line extension can cost over$50,000 per kilometer[2],so the cost of an off-grid electrical system that uses renewable sources to charge a large battery bank for energy storage can compare favorably to that of grid extension-but not always.However,both the design and implementation of such off-grid renewable energy systems differ greatly from more common grid-tied applications,where the utility grid is used as“battery”with which the system can buy and sell electrical energy from and to the utility as needed.Energy efficiency and conservation are paramount in all off-grid renewable energy system designs,as these measures extend at low cost the hours or days of autonomous operation time before a backup power source(usually an internal-combustion generator)must be used for battery charging during periods of no input from renewable solar,wind,or hydroelectric sources.The techniques used in designing and operating an off-grid building can seem extreme compared to the norm,and provide a whole set of new challenges if the retrofitting of an existing structure is required.But the lessons learned from these experiences are quite relevant to modern buildings in urban and suburban areas,as the goal is the same-first reduce energy consumption through efficiency and conservation,rather than simply increasing energy production.With off-grid systems,the payback from these measures simply has a more immediate effect.And at the end of the day,non-electrical energy efficiency measures prove to be at least as effective as electrical ones.展开更多
The extensive environment,especially low temperature and weak lighting in winter and spring,which limits the growth of pepper(Capicum annuum L.)seedlings,the use of plant factory with artificial lighting technology ca...The extensive environment,especially low temperature and weak lighting in winter and spring,which limits the growth of pepper(Capicum annuum L.)seedlings,the use of plant factory with artificial lighting technology can effectively control the lighting environment to produce high-quality seedlings.In this study,white LED lamps with R:B ratio of 0.7(L0.7)and 1.5(L1.5)and red-blue LED lamps with R:B ratio of 3.5(L3.5)were used to cultivate seedlings of“CAU-24”pepper in the light intensity of 250μmol/m^(2)·s and photoperiod of 12 h/d,white fluorescent lamps with R:B ratio of 1.7(F1.7)was used as control.The results showed that plant height,stem diameter,hypocotyl length,biomass accumulation,light energy use efficiency(LUE)and electric energy use efficiency(EUE)of pepper seedling under L1.5 were the highest.After 36 days of sowing,the dry weight of shoot reached 302.8±45.2 mg/plant.Leaf area reached maximum value of 153.5±22.0 cm^(2) under L0.7.The contents of chlorophyll a,chlorophyll b and total chlorophyll of pepper seedling leaves under all kinds of LED light were greater than F1.7,but there was no significant difference in net photosynthetic rate.The total dry weight with lamp electric power consumption of L1.5 were 3.0 g/(kW·h)which was 1.5,2,and 3 times greater than that of L3.5,L0.7,and F1.7,respectively.Therefore,compared with fluorescent lamp and other LED lamps,the white LED light quality with R:B ratio of 1.5 is suitable for pepper seedling production in plant factory because of the high LED lighting efficiency,greater LUE and EUE.展开更多
Understanding the effectiveness of cabin air filters is important for assessing human exposure to ultra- fine particles （UFPs） of vehicular origin. The filtration efficiency of vehicular UFPs with electric charges w...Understanding the effectiveness of cabin air filters is important for assessing human exposure to ultra- fine particles （UFPs） of vehicular origin. The filtration efficiency of vehicular UFPs with electric charges was investigated for different electric charge characteristics （charge state, charge polarity）. The average filtration efficiency increased ~10% as the electric charge state on the particles changed in distribution from lightly charged to highly charged. The enhancement of filtration efficiency due to electric charge was different at various filter-face air velocities. As electric charges increased, the filtration efficiency increased 12% and 9% at low air velocity （0.1 m/s） and high air velocity （0.S m/s）, respectively. The filter fiber material poses somewhat effect on the filtration efficiency change due to the electric charge. The effects of filter usage and charge polarity on filtration efficiency due to the electric charge were negligi- ble. A coefficient was empirically derived and successfully accounts for the electric charge effect on UFP filtratinn efficiency.展开更多
基金supported by the National Science and Technology Major Project(2011ZX05030)
文摘We derived an equation for saturation in carbonate reservoirs based on the electrical efficiency model in the case of lacking core data. Owing to the complex pore structure and strong heterogeneity in carbonate reservoirs, the relation between electrical efficiency and water porosity is either complex or linear. We proposed an electrical efficiency equation that accounts for the relation between electrical efficiency and water porosity. We also proposed a power-law relation between electrical efficiency and deep-formation resistivity and analyzed the factors controlling the error in the water saturation computations. We concluded that the calculation accuracy of the electrical efficiency is critical to the application of the saturation equation. The saturation equation was applied to the carbonate reservoirs of three wells in Iraq and Indonesia. For relative rock electrical efficiency error below 0.1, the water saturation absolute error is also below 0.1. Therefore, we infer that the proposed saturation equation generally satisfies the evaluation criteria for carbonate reservoirs.
基金supported by the National Natural Science Foundation of China(62341508).
文摘Complex-valued double-sideband direct detection(DD)can reconstruct the optical field and achieve a high electrical spectral efficiency(ESE)comparable to that of a coherent homodyne receiver,and DD does not require a costly local oscillator laser.However,a fundamental question remains if there is an optimal DD receiver structure with the simplest design to approach the performance of the coherent homodyne detection.This study derives the optimal DD receiver structure with an optimal transfer function to recover a quadrature amplitude modulation(QAM)signal with a near-zero guard band at the central frequency of the signal.We derive the theoretical ESE limit for various detection schemes by invoking Shannon’s formula.Our proposed scheme is closest to coherent homodyne detection in terms of the theoretical ESE limit.By leveraging a WaveShaper to construct the optimal transfer function,we conduct a proof-of-concept experiment to transmit a net 228.85-Gb/s 64-QAM signal over an 80-km single-mode fiber with a net ESE of 8.76 b/s/Hz.To the best of our knowledge,this study reports the highest net ESE per polarization per wavelength for DD transmission beyond 40-km single-mode fiber.For a comprehensive metric,denoted as 2ESE×Reach,we achieve the highest 2ESE×Reach per polarization per wavelength for DD transmission.
文摘The performance of a 3-phase 6-pole 400 W inverter-drive induction motor was investigated using a variety of non-oriented electrical steels for stator core at PWM inverter fundamental wave frequencies of 30 to 300 Hz. There existed an optimum Si content of the material depending on the tooth flux density. Both reduction of material thickness and stress-relief annealing of the stator core improved the motor efficiency. The influence of Si content on the efficiency was small at lower PWM frequencies, while at higher frequencies the motor efficiency increased with increasing Si content. The Cu loss WC increased and the Fe loss Wi counteractiveiy decreasedwith increasing Si content at lower frequencies; while at higher frequencies Wi had dominant effect on the efficiency. Newly developed materials RMA, having lower Fe losses after stress-relief annealing and higher flux densities with lower Si contents, showed motor efficiencies superior to conventional J1S grade materials with comparable Fe losses.
基金The Swedish International Development Cooperation Agency
文摘Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmetrical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maximum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis.
文摘As the quality of power LED improves and the cost of power LED reduces, semiconductor lighting will replace incandescent and fluorescent lighting gradually, causing another revolution on the lighting history. And its driving solution has been greatly accelerated. Based on the white power LED I-V characteristics and the application ambiance, proposed is a new LED lighting solution, suiting indoor and outdoor illumination. According to the test results, the design is optimized, and the electrical efficiency is 95% and the output current deviation is 13.0%.
基金Supported by the National Science and Technology Support Program(2013BAG12B01)Foundational and Advanced Research Program General Project of Chongqing City(cstc2013jcyjjq60002)
文摘A novel method to calculate fuel-electric conversion factor for full hybrid electric vehicle（HEV）equipped with continuously variable transmission（CVT）is proposed.Based on consideration of the efficiency of pivotal components,electric motor,system efficiency optimization models are developed.According to the target of instantaneous optimization of system efficiency,operating ranges of each mode of power-train are determined,and the corresponding energy management strategies are established.The simulation results demonstrate that the energy management strategy proposed can substantially improve the vehicle fuel economy,and keep battery state of charge（SOC）change in a reasonable variation range.
文摘Solar energy is a valuable renewable energy source,and photovoltaic(PV)systems are a practical approach to harnessing this energy.Nevertheless,low energy efficiency is considered a major setback of the system.Moreover,high cell temperature and reflection of solar irradiance from the panel are considered chief culprits in this regard.Employing pulsating heat pipes(PHPs)is an innovative and useful approach to improving solar panel performance.This study presents the results of the power performance of a PV panel attached to a newly designed spiral pulsating heat pipe,while graphene oxide nanofluid with three different concentrations was used as a working fluid to maximize the efficacy of the solar panel.The study proved that the cooling method delivered high efficiency by reducing the temperature,especially in the middle of the day.Using nanofluid graphene oxide at concentrations of 0.2,0.4,and 0.8 gr/lit as the working fluid can reduce the thermal resistance of PHPs by over 30%,24%,and 15%,respectively.This,in turn,enhances the system’s electrical power output by approximately 9%,7%,and 6%,respectively.
文摘A solar PV panel works with maximum efficiency only when it is operated around its optimum operating point or maximum power point.Unfortunately,the performance of the solar cell is affected by several factors like sun direction,solar irradiance,dust accumulation,module temperature,as well as the load on the system.Dust deposition is one of the most prominent factors that influence the performance of solar panels.Because the solar panel is exposed to the atmosphere,dust will accumulate on its surface,reducing the quantity of sunlight reaching the solar cell and diminishing output.In the proposed work,a detailed investigation of the performance of solar PV modules is carried out under the tropical climatic condition of Chennai,India,where the presence of dust particles is very high.The data corresponding to four different dust samples of various densities at four solar irradiation levels of 220,525,702,and 905 W/m^(2)are collected,and performance analysis is carried out.Based on the analysis carried out,the maximum power loss is found to be 73.51%,66.29%,65.46%,and 61.42%,for coal,sand,brick powder,and chalk dust respectively.Hence,it can be said that coal dust contributes to the maximum power loss among all four dust samples.Due to heat dissipation produced by dust deposition,the performance of solar PV modules is degraded as the temperature rose.
文摘This research presents the results of system validation tests for an SOFC power system. In the study, the system was heated up without electric device, i.e., the fuel providing the required thermal energy through an integrated BOP （balance of plant）. The ex-situ experiments, without an SOFC stack installed in the system, were fast conducted to investigate the operability of a BOP apparatus. It was found that the BOP possessed high conversion rates for both steam reforming and water gas shift reactions. The total fuel concentration of hydrogen and carbon monoxide from the reformer was around 91.2%. The system validation tests showed that, with the natural gas as fuel, the output power from the stack reached to 1,060 W, while the fuel utilization efficiency and electrical efficiency were 67.16% and 45.0%, respectively. A steady 600-hour system operation test was carried out at an average system temperature of 694℃. Of which, a 36-cell stack was employed for the test. Meanwhile, the current, voltage and output power were 26 A, 32.3 V and 840 W, respectively, and its electrical efficiency was around 33.4%.
基金support provided by the Nature Science Foundation of Shandong Province(ZR201709180049)the Shandong Key Research and Development Program(2019GSF109023).
文摘In this study,a model of combined cooling,heating and power system with municipal solid waste(MSW)and liquefied natural gas(LNG)as energy sources was proposed and developed based on the energy demand of a large community,andMSW was classified and utilized.The systemoperated by determining power by heating load,and measures were taken to reduce operating costs by purchasing and selling LNG,natural gas(NG),cooling,heating,and power.Based on this system model,three operation strategies were proposed based on whether MSW was classified and the length of kitchen waste fermentation time,and each strategy was simulated hourly throughout the year.The results showed that the strategy of MSW classified and centralized fermentation of kitchen waste in summer(i.e.,strategy 3)required the least total amount of LNG for the whole year,which was 47701.77 t.In terms of total annual cost expenditure,strategy 3 had the best overall economy,with the lowest total annual expenditure of 2.7730×108 RMB at LNG and NG unit prices of 4 and 4.2 RMB/kg,respectively.The lower heating value of biogas produced by fermentation of kitchen waste from MSW being classified was higher than that of MSW before being classified,so the average annual thermal economy of the operating strategy of MSW being classified was better than that of MSW not being classified.Among the strategies in which MSW was classified and utilized,strategy 3 could better meet the load demand of users in the corresponding season,and thus this strategy had better thermal economy than the strategy of year-round fermentation of kitchen waste(i.e.,strategy 2).The hourly analysis data showed that the net electrical efficiency of the system varies in the same trend as the cooling,heating and power loads in all seasons,while the relationship between the energy utilization efficiency and load varied from season to season.This study can provide guidance for the practical application of MSW being classified in the system.
文摘The solar chimney can generate airflow through the living space of the building to provide cooling. Hence, solar energy represents the best renewable, environmentally friendly source of energy that can be used for heating and cooling of houses. The present paper reports the numerical study of the performance of the mixed convection in the associated hybrid Photovoltaic/Thermal chimneys integrated into building for natural habitat ventilation. The front side glass plate of the chimneys is heated by a non-uniform daily solar radiation flux. Air is considered to be the cooling fluid. The stream fucntion-vorticity formulation with a finite difference numerical discretization solution scheme has been adopted. The system of algebraic governing equations is solved by Thomas algorithm method. The aim of the present paper is to study and to predict the dynamic fields and particularly of the mass flow rate of the air thermosiphon drawing in the associated hybrid Photovoltaic-Thermal chimneys integrated into a building for passive cooling in the habitats. The effects of the governing parameters, namely Reynolds number (30 ≤ Re ≤ 200), Rayleigh number (103 ≤ Ra≤ 105), the integrated chimney width on the fluid flow and the heat transfer characteristics, are studied in detail. The local Nusselt number, streamlines, isotherms, PV cells electrical efficiency and the outlet velocity at the top of the channels are the results represented versus the above controlling parameters.
基金supported by“Philosophy and Social Sciences Planned Project of Anhui Province,China”(Grant No.AHSKY2020D37).
文摘Electricity shortages present a significant constraint on manufacturers,who rely on electricity as an important input into production.In China,electricity supply has been growing rapidly.However,the rapid industrialization sometimes makes the power supply still unable to meet the demand.Using a survey of 1673 Chinese manufacturing firms,this paper explores how firms response to electricity shortages and its impact on productivity.We find that self-generation of electricity and investment in Research and Development(R&D)have significant positive relationships with electricity shortages.Further investigations reveal that self-generation is the most common way to deal with electricity shortages.However,it aggravates productivity loss.Though investment in Research and Development can promote productivity,it cannot offset the negative impact of electricity shortages on productivity.Analyses on subsamples show heterogeneity in the impacts of electricity shortages across firms.In particular,large firms are more inclined to invest in R&D than small and medium-sized firms are.They are also the one who suffer significant productivity loss due to self-generation of electricity.Though it is possible for medium-sized firms to reduce productivity loss through R&D,they are not likely to invest in R&D as a response to electricity shortages.This study illustrates that firms can hardly have effective solutions to electricity shortages,and policy makers should take great efforts to increase electricity supply.
文摘The aim of this paper is to present a new topology of a DC-DC power converter for conditioning the current and voltages behaviors of embarked energy sources used in electrical vehicles. The fuel cells in conjunction with ultra-capacitors have been chosen as the power supply. The originality of the proposed converter is to use a variable voltage of the DC bus of the vehicle. The goal is to allow a better energy management of the embedded sources onboard the vehicle by improving its energy efficiency. After presenting and explaining the topology of the converter, some simulation and experiments results are shown to highlight its different operation modes.
基金supported by a grant from National Key R&D Program of China(Grant No.2020YFE0200300)。
文摘A novel tank-Photovoltaic-thermal(PV/T) system is presented in this paper, and its energy performance has been compared with a traditional heat pipe PV/T system. The novel tank PV/T system combines photovoltaic cell, heat absorbing plate and hot-water storage tank which expands the heat exchange area, shortens the heat transfer path and saves the module installation space. A prototype system is constructed and tested in a cold weather condition and then compared with a heat pipe PVT system. The experimental results indicate that during the 10 days’ testing, the electrical, thermal and overall efficiency of the tank PV/T system ranges from 14.3% to 15.6%, 38.6% to 43.8% and 53.1% to 58.1%, respectively, while the heat pipe PVT system ranges from 10.9% to 12.2%, 39.3% to 41.2% and 50.5% to 53.4%, respectively. Based on these data, the electrical and thermal efficiency curve of the system with the novel tank-PVT system and heat pipe PVT system were generated. According to the comparison result, it shows that the novel tank-PVT system has a better thermal and electrical efficiency. This system provides a new design method for the development of the PV/T systems, which has a potential for PV/T systems building integration in the future.
文摘Over 25 percent of the world’s population lives without access to electricity from a utility-supplied grid[1].In underdeveloped and developing countries,the reason is primarily a lack of government-sponsored utility infrastructure due to the high cost of power line extension.In developed countries,power line extension costs are again the primary factor in lack of a grid connection,as in most cases the end user must foot the bill for such improvements.In the United States,power line extension can cost over$50,000 per kilometer[2],so the cost of an off-grid electrical system that uses renewable sources to charge a large battery bank for energy storage can compare favorably to that of grid extension-but not always.However,both the design and implementation of such off-grid renewable energy systems differ greatly from more common grid-tied applications,where the utility grid is used as“battery”with which the system can buy and sell electrical energy from and to the utility as needed.Energy efficiency and conservation are paramount in all off-grid renewable energy system designs,as these measures extend at low cost the hours or days of autonomous operation time before a backup power source(usually an internal-combustion generator)must be used for battery charging during periods of no input from renewable solar,wind,or hydroelectric sources.The techniques used in designing and operating an off-grid building can seem extreme compared to the norm,and provide a whole set of new challenges if the retrofitting of an existing structure is required.But the lessons learned from these experiences are quite relevant to modern buildings in urban and suburban areas,as the goal is the same-first reduce energy consumption through efficiency and conservation,rather than simply increasing energy production.With off-grid systems,the payback from these measures simply has a more immediate effect.And at the end of the day,non-electrical energy efficiency measures prove to be at least as effective as electrical ones.
基金supported by the National Key Research and Development Program of China(2017YFB0403901).
文摘The extensive environment,especially low temperature and weak lighting in winter and spring,which limits the growth of pepper(Capicum annuum L.)seedlings,the use of plant factory with artificial lighting technology can effectively control the lighting environment to produce high-quality seedlings.In this study,white LED lamps with R:B ratio of 0.7(L0.7)and 1.5(L1.5)and red-blue LED lamps with R:B ratio of 3.5(L3.5)were used to cultivate seedlings of“CAU-24”pepper in the light intensity of 250μmol/m^(2)·s and photoperiod of 12 h/d,white fluorescent lamps with R:B ratio of 1.7(F1.7)was used as control.The results showed that plant height,stem diameter,hypocotyl length,biomass accumulation,light energy use efficiency(LUE)and electric energy use efficiency(EUE)of pepper seedling under L1.5 were the highest.After 36 days of sowing,the dry weight of shoot reached 302.8±45.2 mg/plant.Leaf area reached maximum value of 153.5±22.0 cm^(2) under L0.7.The contents of chlorophyll a,chlorophyll b and total chlorophyll of pepper seedling leaves under all kinds of LED light were greater than F1.7,but there was no significant difference in net photosynthetic rate.The total dry weight with lamp electric power consumption of L1.5 were 3.0 g/(kW·h)which was 1.5,2,and 3 times greater than that of L3.5,L0.7,and F1.7,respectively.Therefore,compared with fluorescent lamp and other LED lamps,the white LED light quality with R:B ratio of 1.5 is suitable for pepper seedling production in plant factory because of the high LED lighting efficiency,greater LUE and EUE.
基金This study is based on work partially supported by the National Natural Science Foundation of China （grant no. 51208372） and the Fundamental Research Funds for the Central Universities （grant no. 2013KJ020）.
文摘Understanding the effectiveness of cabin air filters is important for assessing human exposure to ultra- fine particles （UFPs） of vehicular origin. The filtration efficiency of vehicular UFPs with electric charges was investigated for different electric charge characteristics （charge state, charge polarity）. The average filtration efficiency increased ~10% as the electric charge state on the particles changed in distribution from lightly charged to highly charged. The enhancement of filtration efficiency due to electric charge was different at various filter-face air velocities. As electric charges increased, the filtration efficiency increased 12% and 9% at low air velocity （0.1 m/s） and high air velocity （0.S m/s）, respectively. The filter fiber material poses somewhat effect on the filtration efficiency change due to the electric charge. The effects of filter usage and charge polarity on filtration efficiency due to the electric charge were negligi- ble. A coefficient was empirically derived and successfully accounts for the electric charge effect on UFP filtratinn efficiency.
