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Frontiers in Energy

ISSN 2095-1701 (Print)
ISSN 2095-1698 (Online)
CN 11-6017/TK
Postal Subscription Code 80-972
Formerly Known as Frontiers of Energy and Power Engineering in China
2018 Impact Factor: 1.701

, Volume 14 Issue 1

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RESEARCH ARTICLE
A space power system of free piston Stirling generator based on potassium heat pipe
Mingqiang LIN, Jian MOU, Chunyun CHI, Guotong HONG, Panhe GE, Gu HU
Front. Energy. 2020, 14 (1): 1-10.  https://doi.org/10.1007/s11708-019-0655-6
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The power system of a free piston Stirling generator (FPSG) based on potassium heat pipes has been developed in this paper. Thanks to the advantages of long life, high reliability, and high overall thermal efficiency, the FPSG is a promising candidate for nuclear energy, especially in space exploration. In this paper, the recent progress of FPSG based on nuclear reactor for space use was briefly reviewed. A novel FPSG weighted only 4.2 kg was designed, and one dimensional thermodynamic modeling of the FPSG using Sage software was performed to estimate its performance. The experiment results indicated that this FPSG could provide 142.4 W at a thermal-to-electric efficiency of nearly 17.4%. Besides, the power system integrated with four FPSGs and potassium heat pipes was performed and the single machine failure test was conducted. The results show that this system could provide an electrical power of 300 W at an overall thermal efficiency of 7.3%. Thus, it is concluded that this power system is feasible and will have a great prospect for future applications.

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An adsorption study of 99Tc using nanoscale zero-valent iron supported on D001 resin
Lingxiao FU, Jianhua ZU, Linfeng HE, Enxi GU, Huan WANG
Front. Energy. 2020, 14 (1): 11-17.  https://doi.org/10.1007/s11708-019-0634-y
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Nanoscale zero-valent iron (nZVI) supported on D001 resin (D001-nZVI) was synthesized for adsorption of high solubility and mobility radionuclide 99Tc. Re(VII), a chemical substitute for 99Tc, was utilized in batch experiments to investigate the feasibility and adsorption mechanism toward Tc(VII). Factors (pH, resin dose) affecting Re(VII) adsorption were studied. The high adsorption efficiency of Re(VII) at pH= 3 and the solid-liquid ratio of 20 g/L. X-ray diffraction patterns revealed the reduction of ReO4 into ReO2 immobilized in D001-nZVI. Based on the optimum conditions of Re(VII) adsorption, the removal experiments of Tc(VII) were conducted where the adsorption efficiency of Tc(VII) can reach 94%. Column experiments showed that the Thomas model gave a good fit to the adsorption process of Re(VII) and the maximum dynamic adsorption capacity was 0.2910 mg/g.

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Soot size distribution in lightly sooting premixed flames of benzene and toluene
Wang LIU, Jiaqi ZHAI, Baiyang LIN, He LIN, Dong HAN
Front. Energy. 2020, 14 (1): 18-26.  https://doi.org/10.1007/s11708-020-0663-6
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The evolution of particle size distribution function (PSDF) of soot in premixed flames of benzene and toluene was studied on a burner stabilized stagnation (BSS) flame platform. The cold gas velocities were changed to hold the maximum flame temperatures of different flames approximately constant. The PSDFs of all the test flames exhibited a bimodal distribution, i.e., a small-size nucleation mode and a large-size accumulation mode. It was observed that soot nucleation and particle growth in the benzene flame were stronger than those in the toluene flame at short residence times. At longer residence times, the PSDFs of the two flames were similar, and the toluene flame showed a larger particle size distribution range and a higher particle volume fraction than the benzene flame.

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Impact of inter-fuel substitution on energy intensity in Ghana
Boqiang LIN, Hermas ABUDU
Front. Energy. 2020, 14 (1): 27-41.  https://doi.org/10.1007/s11708-019-0656-5
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Energy intensity and elasticity, together with inter-fuel substitution are key issues in the current development stage of Ghana. Translog production and ridge regression are applied for studying these issues with a data range of 2000–2015. The current energy dynamics reveal the expected inverse relationship: higher energy intensity and lower elasticity with economic growth. There are evidences of energy-economic challenges: high energy cost, inefficiency and backfire rebound effect. The implications are higher energy losses in the system, more consumption of lower-quality energy together with low energy technology innovation. Energy is wasted and directly not productive with economic activities. It is observed further that the higher energy intensity invariably increases CO2 emission because approximately 95% of total energy is derived from hydrocarbons and biomass. An inter-fuel substitution future scenario design was further conducted and the results were positive with growth, lower energy intensity, and improved energy efficiency. Therefore, government and energy policymakers should improve energy efficiency, cost, and productiveness. That is, they should change energy compositions and augment energy technology innovation, thus, increasing renewable share to 15% by 2026, reducing wood and charcoal by about 69%, and increasing natural gas to about 776%. Energy policymakers should enhance the installation of smart energy, cloud energy solution, tokenization of energy system and storage.

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Evaluation of renewable energies production potential in the Middle East: confronting the world’s energy crisis
Hamid BAHRAMPOUR, Amir Khosro BEHESHTI MARNANI, Mohammad Bagher ASKARI, Mohammad Reza BAHRAMPOUR
Front. Energy. 2020, 14 (1): 42-56.  https://doi.org/10.1007/s11708-017-0486-2
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Oil and fossil fuels, the main source of energy in the Middle East have obviously the most destructive effects on the environment and public health. The developed countries of the Middle East are faced with the crisis and energy security. This paper is about evaluating the energy demand /consumption in the Middle East. First, the position of energy consumption in the world and the Middle East is discussed. Next, the evaluation of the current potential of clean energy production from renewable energies is explained. Finally, according to related maps, charts and information presented for the condition of renewable energy which has been approved by the countries of the Middle East, the greatest places in some countries of this region are introduced and discussed.

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Does environmental infrastructure investment contribute to emissions reduction? A case of China
Xiaoqian SONG, Yong GENG, Ke LI, Xi ZHANG, Fei WU, Hengyu PAN, Yiqing ZHANG
Front. Energy. 2020, 14 (1): 57-70.  https://doi.org/10.1007/s11708-019-0654-7
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Environmental infrastructure investment (EII) is an important environmental policy instrument on responding to greenhouse gas (GHG) emission and air pollution. This paper employs an improved stochastic impact by regression on population, affluence and technology (STRIPAT) model by using panel data from 30 Chinese provinces and municipalities for the period of 2003–2015 to investigate the effect of EII on CO2 emissions, SO2 emissions, and PM2.5 pollution. The results indicate that EII has a positive and significant effect on mitigating CO2 emission. However, the effect of EII on SO2 emission fluctuated although it still contributes to the reduction of PM2.5 pollution through technology innovations. Energy intensity has the largest impact on GHG emissions and air pollution, followed by GDP per capita and industrial structure. In addition, the effect of EII on environmental issues varies in different regions. Such findings suggest that policies on EII should be region-specific so that more appropriate mitigation policies can be raised by considering the local realities.

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Thermodynamic assessment of hydrogen production via solar thermochemical cycle based on MoO2/Mo by methane reduction
Jiahui JIN, Lei WANG, Mingkai FU, Xin LI, Yuanwei LU
Front. Energy. 2020, 14 (1): 71-80.  https://doi.org/10.1007/s11708-019-0652-9
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Inspired by the promising hydrogen production in the solar thermochemical (STC) cycle based on non-stoichiometric oxides and the operation temperature decreasing effect of methane reduction, a high-fuel-selectivity and CH4-introduced solar thermochemical cycle based on MoO2/Mo is studied. By performing HSC simulations, the energy upgradation and energy conversion potential under isothermal and non-isothermal operating conditions are compared. In the reduction step, MoO2: CH4 = 2 and 1020 K<Tred<1600 K are found to be most favorable for syngas selectivity and methane conversion. Compared to the STC cycle without CH4, the introduction of methane yields a much higher hydrogen production, especially at the lower temperature range and atmospheric pressure. In the oxidation step, a moderately excessive water is beneficial for energy conversion whether in isothermal or non-isothermal operations, especially at H2O: Mo= 4. In the whole STC cycle, the maximum non-isothermal and isothermal efficiency can reach 0.417 and 0.391 respectively. In addition, the predicted efficiency of the second cycle is also as high as 0.454 at Tred = 1200 K and Toxi = 400 K, indicating that MoO2 could be a new and potential candidate for obtaining solar fuel by methane reduction.

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REVIEW ARTICLE
Room temperature liquid metal: its melting point, dominating mechanism and applications
Junheng FU, Chenglin ZHANG, Tianying LIU, Jing LIU
Front. Energy. 2020, 14 (1): 81-104.  https://doi.org/10.1007/s11708-019-0653-8
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The room temperature liquid metal (LM) is recently emerging as a new class of versatile materials with fascinating characteristics mostly originated from its simultaneous metallic and liquid natures. The melting point is a typical parameter to describe the peculiarity of LM, and a pivotal factor to consider concerning its practical applications such as phase change materials (PCMs) and advanced thermal management. Therefore, the theoretical exploration into the melting point of LM is an essential issue, which can be of special value for the design of new LM materials with desired properties. So far, some available strategies such as molecular dynamics (MD) simulation and classical thermodynamic theory have been applied to perform correlative analysis. This paper is primarily dedicated to performing a comprehensive overview regarding typical theoretical strategies on analyzing the melting points. It, then, presents evaluations on several factors like components, pressure, size and supercooling that may be critical for melting processes of liquid metal. After that, it discusses applications associated with the characteristic of low melting points of LM. It is expected that a great many fundamental and practical works are to be conducted in the coming future.

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RESEARCH ARTICLE
Experimental study on performance of passive and active solar stills in Indian coastal climatic condition
R. LALITHA NARAYANA, V. RAMACHANDRA RAJU
Front. Energy. 2020, 14 (1): 105-113.  https://doi.org/10.1007/s11708-018-0536-4
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This present work is aimed to examine the effect of mass flow rate on distillate output and performance of a solar still in active mode. Outdoor experiments were conducted at the coastal town, Kakinada (16°93′N/83°33′E), Andhra Pradesh, India. A solar still with a 30° of fixed cover inclination, 1m2 of effective basin area, and a flat-plate collector (FPC) with an effective area of 2 m2 were used. An attempt was also made earlier in passive mode to optimize the water depth for the same solar still for maximum yield and distillation efficiency. For the passive still, it is observed that the capacity of heat storage and heat drop are significant parameters that affect the still performance. For the selected still design, the study reveals that 0.04 m water depth is the optimum value for specific climatic conditions. In the active solar still, with the optimum water depth, different flow rates of 0.5, 1 and 1.5 L/min are considered through FPC. It is observed that both the mass flow rate and the variation of internal heat transfer coefficients with the mass flow rate have a significant effect on the yield and performance of the still. The experimental results show that the combination of 1.5 L/min mass flow rate and an optimum water depth of 0.04 m leads to a maximum yield for the active solar still. The enhanced yield of the active solar still is 57.55%, compared with that of the passive solar still, due to increase in area of radiation collection and more heat absorption rate.

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Experimental study on combined buoyant-thermocapillary flow along with rising liquid film on the surface of a horizontal metallic mesh tube
Manuel J. GOMES, Ning MEI
Front. Energy. 2020, 14 (1): 114-126.  https://doi.org/10.1007/s11708-017-0483-5
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Temperature distribution and variation with time has been considered in the analysis of the influences of the initial level of immersion of a horizontal metallic mesh tube in the liquid on combined buoyant and thermo-capillary flow. The combined flow occurs along with the rising liquid film flow on the surface of a horizontal metallic mesh tube. Three different levels of immersion of the metallic mesh tube in the liquid have been tested. Experiments of 60 min in duration have been performed using a heating metallic tube with a diameter of 25 mm and a length of 110 mm, sealed outside with a metallic mesh of 178 mm by 178 mm, and distilled water. These reveal two distinct flow patterns. Thermocouples and infrared thermal imager are utilized to measure the temperature. The level of the liquid free surface relative to the lower edge of the tube is measured as angle q. The results show that for a smaller q angle, or a low level of immersion, with a relatively low heating power, it is possible to near fully combine the upwards buoyant flow with the rising liquid film flow. In this case, the liquid is heated only in the vicinity of the tube, while the liquid away from the flow region experiences small changes in temperature and the system approaches steady conditions. For larger q angles, or higher levels of immersion, a different flow pattern is noticed on the liquid free surface and identified as the thermo-capillary (Marangoni) flow. The rising liquid film is also present. The higher levels of immersion cause a high temperature gradient in the liquid free surface region and promote thermal stratification; therefore the system could not approach steady conditions.

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Effects of slip length and hydraulic diameter on hydraulic entrance length of microchannels with superhydrophobic surfaces
Wenchi GONG, Jun SHEN, Wei DAI, Zeng DENG, Xueqiang DONG, Maoqiong GONG
Front. Energy. 2020, 14 (1): 127-138.  https://doi.org/10.1007/s11708-020-0661-8
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This paper investigated effects of slip length and hydraulic diameter on the hydraulic entrance length of laminar flow in superhydrophobic microchannels. Numerical investigations were performed for square microchannels with Re ranging between 0.1 and 1000. It is found that superhydrophobic microchannels have a longer hydraulic entrance length than that of conventional ones by nearly 26.62% at a low Re. The dimensionless hydraulic entrance length slightly increases with the increasing slip length at approximately Re<10, and does not vary with the hydraulic diameter. A new correlation to predict the entrance length in square microchannels with different slip lengths was developed, which has a satisfying predictive performance with a mean absolute relative deviation of 5.69%. The results not only ascertain the flow characteristics of superhydrophobic microchannels, but also suggest that super hydrophobic microchannels have more significant advantages for heat transfer enhancement at a low Re.

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A genetic algorithm based improved optimal sizing strategy for solar-wind-battery hybrid system using energy filter algorithm
Aeidapu MAHESH, Kanwarjit Singh SANDHU
Front. Energy. 2020, 14 (1): 139-151.  https://doi.org/10.1007/s11708-017-0484-4
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In this paper, the genetic algorithm (GA) is applied to optimize a grid connected solar photovoltaic (PV)-wind-battery hybrid system using a novel energy filter algorithm. The main objective of this paper is to minimize the total cost of the hybrid system, while maintaining its reliability. Along with the reliability constraint, some of the important parameters, such as full utilization of complementary nature of PV and wind systems, fluctuations of power injected into the grid and the battery’s state of charge (SOC), have also been considered for the effective sizing of the hybrid system. A novel energy filter algorithm for smoothing the power injected into the grid has been proposed. To validate the proposed method, a detailed case study has been conducted. The results of the case study for different cases, with and without employing the energy filter algorithm, have been presented to demonstrate the effectiveness of the proposed sizing strategy.

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Analysis of resonant coupling coil configurations of EV wireless charging system: a simulation study
M. LU, A. JUNUSSOV, M. BAGHERI
Front. Energy. 2020, 14 (1): 152-165.  https://doi.org/10.1007/s11708-019-0615-1
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Nowadays, internal combustion engine vehicles are considered as one of the major contributors to air pollution. To make transportation more environmentally friendly, plug-in electric vehicles (PEVs) have been proposed. However, with an increase in the number of PEVs, the drawbacks associated with the cost and size, as well as charging cables of batteries have arisen. To address these challenges, a novel technology named wireless charging system has been recently recommended. This technology rapidly evolves and becomes very attractive for charging operations of electric vehicles. Currently, wireless charging systems offer highly efficient power transfer over the distances ranging from several millimeters to several hundred millimeters. This paper is focused on analyzing electromagnetically coupled resonant wireless technique used for the charging of EVs. The resonant wireless charging system for EVs is modeled, simulated, and then examined by changing different key parameters to evaluate how transfer distance, load, and coil’s geometry, precisely number of coin’s turns, coin’s shape, and inter-turn distance, influence the efficiency of the charging process. The simulation results are analyzed and critical dimensions are discussed. It is revealed that a proper choice of the dimensions, inter-turn distance, and transfer distance between the coils can result in a significant improvement in charging efficiency. Furthermore, the influence of the transfer distance, frequency, load, as well as the number of the turns of the coil on the performance of wireless charging system is the main focus of this paper.

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Performance analysis of series/parallel and dual side LCC compensation topologies of inductive power transfer for EV battery charging system
P. Srinivasa Rao NAYAK, Dharavath KISHAN
Front. Energy. 2020, 14 (1): 166-179.  https://doi.org/10.1007/s11708-018-0549-z
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In an inductive battery charging system, for better power transfer capability and attaining required power level, compensation is necessary. This paper analyzes series/parallel (S/P) and dual side inductor-capacitor-capacitor (LCC) compensation topologies for inductive power transfer of electric vehicle (EV) battery charging system. The design and modeling steps of inductive power transfer for electric vehicle battery charging system are presented. Besides, the equivalent electrical circuits are used to describe the circuit compensation topologies. The results convey that the efficiency of dual side LCC compensation is higher than that of S/P compensation at variable mutual inductance (misalignment).

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Robust nonlinear control via feedback linearization and Lyapunov theory for permanent magnet synchronous generator-based wind energy conversion system
Ridha CHEIKH, Arezki MENACER, L. CHRIFI-ALAOUI, Said DRID
Front. Energy. 2020, 14 (1): 180-191.  https://doi.org/10.1007/s11708-018-0537-3
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In this paper, the method for the nonlinear control design of a permanent magnet synchronous generator based-wind energy conversion system (WECS) is proposed in order to obtain robustness against disturbances and harvest a maximum power from a typical stochastic wind environment. The technique overcomes both the problem of nonlinearity and the uncertainty of the parameter compared to such classical control designs based on traditional control techniques. The method is based on the differential geometric feedback linearization technique (DGT) and the Lyapunov theory. The results obtained show the effectiveness and performance of the proposed approach.

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Implementation and performance evaluation of advance metering infrastructure for Borneo-Wide Power Grid
Mujahid TABASSUM, Manas K. HALDAR, Duaa Fatima S. KHAN
Front. Energy. 2020, 14 (1): 192-211.  https://doi.org/10.1007/s11708-016-0438-2
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In this paper, a supervisory computer network for Borneo-Wide Power Grid system have been proposed and implemented, which includes a renewable power generation and advanced metering infrastructure. An Internet-based communication network running on multiprotocol label switching (MPLS) has been implemented for a smart power grid, with the addition of the renewable energy monitoring system. The centralized supervisory control and data acquisition systems (SCADA) are replaced by a wide area monitoring system(WAMS) comprising of a phasor measurement unit (PMU). The implemented communication network used advanced metering infrastructure that operates on worldwide interoperability for microwave access (WiMAX), wireless fidelity (Wi-Fi) and low power Wi-Fi, which are proposed for the distribution systems of Sarawak Energy. The proposed wide area network (WAN) is simulated using OPNET Modeler and the results are compared with the existing WAN used by Sarawak Energy.

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