Frontiers in Energy

ISSN 2095-1701

ISSN 2095-1698(Online)

CN 11-6017/TK

Postal Subscription Code 80-972

2018 Impact Factor: 1.701

   Online First

Administered by

, Volume 4 Issue 3

For Selected: View Abstracts Toggle Thumbnails
Research articles
Renewable power for China: Past, present, and future
Eric MARTINOT
Front. Energy. 2010, 4 (3): 287-294.  
https://doi.org/10.1007/s11708-010-0120-z

Abstract   PDF (128KB)
This paper briefly examines the history, status, policy situation, development issues, and prospects for key renewable power technologies in China. The country has become a global leader in wind turbine and solar photovoltaic (PV) production, and leads the world in total power capacity from renewable energy. Policy frameworks have matured and evolved since the landmark 2005 Renewable Energy Law, updated in 2009. China’s 2020 renewable energy target is similar to that of the EU. However, China continues to face many challenges in technology development, grid-integration, and policy frameworks. These include training, research and development, wind turbine operating experience and performance, transmission constraints, grid interconnection time lags, resource assessments, power grid integration on large scales, and continued policy development and adjustment. Wind and solar PV targets for 2020 will likely be satisfied early, although domestic demand for solar PV remains weak and the pathways toward incorporating distributed and building-integrated solar PV are uncertain. Prospects for biomass power are limited by resource constraints. Other technologies such as concentrating solar thermal power, ocean energy, and electricity storage require greater attention.
References | Related Articles | Metrics
Modeling China’s energy dilemma: conflicts among energy saving, energy security, and CO 2 mitigation
Feng FU, Zheng LI, Linwei MA,
Front. Energy. 2010, 4 (3): 295-300.  
https://doi.org/10.1007/s11708-010-0104-z

Abstract   PDF (339KB)
This study analyzes China’s future energy scenarios stretching until 2050 under different policy portfolios of energy security (e.g., oil import dependency) and CO2 emissions control. Four scenarios, namely, ① business as usual, ② strong oil import dependency (OID) control, ③ strong CO2 emissions control, and ④ twofold emphasis on OID and CO2 emissions control, are designed. The results reveal the existence of conflicts among China’s multiple objectives, particularly energy saving, energy security, and CO2 mitigation. Based on the analysis, an improvement in China’s efficiency in fossil energy conversion and the promotion of the utilization of non-fossil energy such as nuclear, wind, and hydro energy are recommended. The over-development of coal-derived fuels should also be avoided because of incremental coal consumption and CO2 emissions. Furthermore, research on and development of carbon capture and storage technologies should be promoted, while the energy efficiency loss caused by integrating these technologies into energy systems should be reduced in view of the high possibility of stricter standards for CO2 emissions in the future.
References | Related Articles | Metrics
Entropy flow, entropy generation, exergy flux, and optimal absorbing temperature in radiative transfer between parallel plates
Zeshao CHEN, Songping MO, Peng HU, Shouli JIANG, Gang WANG, Xiaofang CHENG,
Front. Energy. 2010, 4 (3): 301-305.  
https://doi.org/10.1007/s11708-010-0006-0

Abstract   PDF (144KB)
Taking nonequilibrium radiative heat transfer between two surfaces as an example, the nonequilibrium thermodynamics of radiation is studied and discussed. The formulas of entropy flow, entropy generation, exergy flux, and optimal temperature of absorbing surface for maximum exergy output are derived. The result is a contribution to the thermodynamic analysis and optimization of solar energy utilization and can be applied in more complex radiative heat transfer cases.
References | Related Articles | Metrics
Air-side heat transfer and friction characteristics of biofouled evaporator under wet conditions
Hui PU, Guoliang DING, Xiaokui MA, Haitao HU, Yifeng GAO,
Front. Energy. 2010, 4 (3): 306-312.  
https://doi.org/10.1007/s11708-009-0067-0

Abstract   PDF (327KB)
The effects of biofouling on air-side heat transfer and friction characteristics under wet conditions of three biofouled finned tube heat exchangers and one clean finned tube heat exchanger were investigated experimentally. Experimental results indicate that the biofouled fin efficiency of the evaporator decreases by 15.5% compared with the clean evaporator under the condition of the biofouled area ratio of 60% at the inlet air velocity of 2.0m/s; The ranges of friction fouling factor and heat transfer fouling factor are 19.8%―43.1% and ―15.6%―13.1%, respectively; a small quantity of biofouled particles can enhance heat transfer at low Reynolds number, and the enhancement effect decreases with the increase of Reynolds number.
References | Related Articles | Metrics
Augmentation of natural convective heat transfer by acoustic cavitation
Jun CAI, Xiulan HUAI, Shiqiang LIANG, Xunfeng LI,
Front. Energy. 2010, 4 (3): 313-318.  
https://doi.org/10.1007/s11708-009-0064-3

Abstract   PDF (215KB)
An experimental study was conducted to investigate the effects of acoustic cavitation on natural convective heat transfer from a horizontal circular tube. The experimental results indicated that heat transfer could be enhanced by acoustic cavitation and had the best effect when the head of the ultrasonic transducer was over the midpoint of the circular tube, and the distance between the head and the tube equaled 15 mm. The augmentation at low heat flux was better than that in the case of high heat flux. Based on experimental results, the correlation formula of Nusselt number for water was obtained.
References | Related Articles | Metrics
Liquefaction and impurity separation of oxygen-bearing coal-bed methane
Qiuying LI, Yonglin JU, Li WANG,
Front. Energy. 2010, 4 (3): 319-325.  
https://doi.org/10.1007/s11708-010-0115-9

Abstract   PDF (225KB)
Coal-bed methane (CBM) is a type of clean energy. However, most oxygen-bearing CBM have not yet to be utilized due to limited techniques, and when utilized, the discharged gas leads to resource wastage and environment pollution. In this paper, a liquefaction process is proposed and designed for the specified oxygen-bearing CBM obtained from the Daqing Qingshen gas field. The distillation column is employed to separate the oxygen and nitrogen components present in the CBM. HYSYS software is adopted to simulate the process, and the results reveal that the energy consumption of the whole liquefaction process is low. Moreover, oxygen and nitrogen are nearly removed completely, achieving a high-purity liquefied natural gas product with a high methane recovery rate. The applicability and safety of the liquefaction process are also analyzed. The simulation results can offer references for the separation of the oxygen component from CBM.
References | Related Articles | Metrics
Entropy production analysis of swirling diffusion combustion processes
Deodat MAKHANLALL, Linhua LIU,
Front. Energy. 2010, 4 (3): 326-332.  
https://doi.org/10.1007/s11708-009-0058-1

Abstract   PDF (254KB)
A critical factor in the design of combustion systems for optimum fuel economy and emission performance lies in adequately predicting thermodynamic irreversibilities associated with transport and chemical processes. The objective of this study is to map these irreversibilities in terms of entropy production for methane combustion. The numerical solution of the combustion process is conducted with the help of a Fluent 6.1.22 computer code, and the volumetric entropy production rate due to chemical reaction, viscous dissipation, and mass and heat transfer are calculated as post-processed quantities with the computed data of the reaction rates, fluid velocity, temperature and radiative intensity. This paper shows that radiative heat transfer, which is an important source of entropy production, cannot be omitted for combustion systems. The study is extended by conducting a parametric investigation to include the effects of wall emissivity, optical thickness, swirl number, and Boltzmann number on entropy production. Global entropy production rates decrease with the increase in swirl velocity, wall emissivity and optical thickness. Introducing swirling air into the combustion system and operations with the appropriate Boltzmann number reduces the irreversibility affected regions and improves energy utilization efficiency.
References | Related Articles | Metrics
Transversal tube pitch effects on local heat transfer characteristics of the flat tube bank fin mounted vortex generators and their sensitivity to nonuniform temperature of the fin
Liangbi WANG, Zhimin LIN, Kangjie SUN, Yuanxin DONG, Song LIU, Yongheng ZHANG,
Front. Energy. 2010, 4 (3): 333-345.  
https://doi.org/10.1007/s11708-009-0061-6

Abstract   PDF (407KB)
The tube bank fin is commonly used to increase the area of the heat transfer surface with a small heat transfer coefficient of a heat exchanger. If vortex generators (VGs) are punched on the fin surface, the heat transfer performance of the fin can be improved. This paper focused on the effect of transversal tube pitch on the local heat transfer performance of the three-row flat tube bank fin mounted with VGs. On the fin surface, constructing the flow channel but without mounted VGs, the transversal tube pitch was greater, and the span averaged Nusselt number downstream was larger because fewer interactions of vortices would be generated from different VGs located upstream. When the area goodness factor was used as the criteria on the condition of one tube unit of heat exchanger for commonly used fin materials and fin thickness, the transversal tube pitch has considerable effect on the heat transfer enhancement of VGs. Large transversal tube pitch is more sensitive to fin material than to fin thickness.
References | Related Articles | Metrics
Evaluation of the power-generation capacity of wearable thermoelectric power generator
Yang YANG, Jing LIU,
Front. Energy. 2010, 4 (3): 346-357.  
https://doi.org/10.1007/s11708-010-0112-z

Abstract   PDF (747KB)
Employing thermoelectric generators (TEGs) to gather heat dissipating from the human body through the skin surface is a promising way to supply electronic power to wearable and pocket electronics. The uniqueness of this method lies in its direct utilization of the temperature difference between the environment and the human body, and complete elimination of power maintenance problems. However, most of the previous investigations on thermal energy harvesters are confined to the TEG and electronic system themselves because of the low quality of human energy. We evaluate the energy generation capacity of a wearable TEG subject to various conditions based on biological heat transfer theory. Through numerical simulation and corresponding parametric studies, we find that the temperature distribution in the thermopiles affects the criterion of the voltage output, suggesting that the temperature difference in a single point can be adopted as the criterion for uniform temperature distribution. However, the criterion has to be shifted to the sum of temperature difference on each thermocouple when the temperature distribution is inconsistent. In addition, the performance of the thermal energy harvester can be easily influenced by environmental conditions, as well as the physiological state and physical characteristics of the human body. To further validate the calculation results for the wearable TEG, a series of conceptual experiments are performed on a number of typical cases. The numerical simulation provides a good overview of the electricity generation capability of the TEG, which may prove useful in the design of future thermal energy harvesters.
References | Related Articles | Metrics
Heat transfer with water flowing upward in a tube for pressures up to supercritical region
Yuzhou CHEN, Chunsheng YANG, Shuming ZHANG, Minfu ZHAO, Kaiwen DU,
Front. Energy. 2010, 4 (3): 358-365.  
https://doi.org/10.1007/s11708-009-0071-4

Abstract   PDF (343KB)
A heat transfer experiment was conducted in a tube of 6.07mm in diameter with water flowing upward, covering the ranges of pressure of 10―23MPa, mass flux of 288―1298kg/(m2·s), local water temperature of 78°C―270°C, heat flux of 0.23―1.18MW/m2 and Reynolds number of 5.5×103―3.9×104. The experimental results were compared with the predictions of the Dittus-Boelter correlation, Jackson correlation, Bishop correlation, Swenson correlation and Yamagata correlation. Significant deterioration in heat transfer was observed in both subcritical and supercritical region due to the effect of buoyancy force, but it was not predicted reasonably by the existing correlations.
References | Related Articles | Metrics
Development of an experimental platform for research in energy and electrical machine control
Ali HMIDET, Rachid DHIFAOUI, Driss SAIDANI, Othman HASNAOUI,
Front. Energy. 2010, 4 (3): 366-375.  
https://doi.org/10.1007/s11708-010-0106-x

Abstract   PDF (627KB)
This paper presents the development of a test bench dedicated for electrical machines and energy control, as realized by the research team of the Power Systems and Electrical Machines Laboratory (RME) of the National Institute of Applied Sciences and Technology (INSAT) in Tunisia. The principal components of the proposed test bench are explained, and the respective characteristics are given. This paper focuses on mounting low-cost sensors and developing reliable scientific results. The relevant obtained results in photovoltaic (PV) and wind energy fields, power measurement and control, as well as alternating current (AC) machine drives are likewise presented. These are supported by two signal processing controller boards based on Technosoft MCK240 and dSPACE DS1104 kits. In the wind energy field, some results relative to Self Excited Induction Generator dedicated to supplying isolated sites are discussed; in addition, water pumping is discussed for PV energy. In the AC drives area, the results of a closed loop control are presented using a developed direct voltage control (DVC) scheme implemented on dSPACE DS1104. Maps and interesting details of some realized sensors are also presented.
References | Related Articles | Metrics
Numerical study of EGR effects on reducing the pressure rise rate of HCCI engine combustion
Gen CHEN, Norimasa IIDA, Zuohua HUANG,
Front. Energy. 2010, 4 (3): 376-385.  
https://doi.org/10.1007/s11708-010-0118-6

Abstract   PDF (705KB)
The effects of the inert components of exhaust gas recirculation (EGR) gas on reducing the pressure rise rate of homogeneous charge compression ignition engine combustion were investigated numerically by utilizing the CHEMKIN II package and its SENKIN code, as well as Curran’s dimethyl ether reaction scheme. Calculations were conducted under constant volume combustion and engine combustion (one compression and one expansion only, respectively) conditions. Results show that with constant fuel amount and initial temperature and pressure, as EGR ratio increases, combustion timings are retarded and the duration of thermal ignition preparation extends non-linearly; peak values of pressure, pressure rising rate (PRR), and temperature decrease; and peak values of heat release rate in both low temperature heat release (LTHR) and high temperature heat release decrease. Moreover, maximum PRR decreases as CA50 is retarded. With constant fuel amount, mixtures with different EGR ratios can obtain the same CA50 by adjusting the initial temperature. Under the same CA50, as EGR ratio increases, the LTHR timing is advanced and the duration of thermal ignition preparation is extended. Maximum PRR is almost constant with the fixed CA50 despite the change in EGR ratio, indicating that the influence of EGR dilution on chemical reaction rate is offset by other factors. Further investigation on the mechanism of this phenomenon is needed.
References | Related Articles | Metrics
A solar assisted heat pump drying system for grain in-store drying
Haifeng LI, Yanjun DAI, Jianguo DAI, Xibo WANG, Lei WEI,
Front. Energy. 2010, 4 (3): 386-391.  
https://doi.org/10.1007/s11708-010-0003-3

Abstract   PDF (305KB)
For grain in-store drying, a solar assisted drying process has been developed, which consists of a set including a solar-assisted heat pump, a ventilation system, a grain stirrer, etc. In this way, low power consumption, short cycle time and water content uniformity can be achieved in comparison with the conventional method. A solar-assisted heat pump drying system has been designed and manufactured for a practical granary, and the energy consumption performance of the unit is analyzed. The analysis result shows that the solar fraction of the unit is higher than 20%, the coefficient of performance about system (COPS) is 5.19, and the specific moisture extraction rate (SMER) can reach 3.05 kg/kWh.
References | Related Articles | Metrics
Effect of heat transfer space non-uniformity of combustion chamber components on in-cylinder heat transfer in diesel engine
Jizu LV, Minli BAI, Long ZHOU, Jian ZHOU,
Front. Energy. 2010, 4 (3): 392-401.  
https://doi.org/10.1007/s11708-009-0066-1

Abstract   PDF (1104KB)
Combustion chamber components (cylinder head-cylinder liner-piston assembly-oil film) were treated as a coupled body. Based on the three-dimensional numerical simulation of the heat transfer of the coupled body, a coupled three-dimensional calculation model for the in-cylinder working process and the combustion chamber components was built with domain decomposition and boundary coupling method, which adopts the coupled three-dimensional simulation of in-cylinder working process and the combustion chamber components. The model was applied in the investigation of the influence of space non-uniformity in heat transfer among combustion chamber components on in-cylinder heat transfer. The results show that the effect of wall temperature space non-uniform distribution of combustion chamber components on heat transfer happens mainly at the end of the compression stroke and expansion stroke. Therefore, it can be concluded that wall temperature space non-uniform distribution of combustion chamber components would influence heat transfer during the intake and exhaust stroke obviously.
References | Related Articles | Metrics
A performance analysis of integrated solid oxide fuel cell and heat recovery steam generator for IGFC system
Souman RUDRA, H. T. KIM, Jinwook LEE, L. ROSENDAHL,
Front. Energy. 2010, 4 (3): 402-413.  
https://doi.org/10.1007/s11708-010-0122-x

Abstract   PDF (474KB)
Solid oxide fuel cell (SOFC) is a promising technology for electricity generation. Sulfur-free syngas from a gas-cleaning unit serves as fuel for SOFC in integrated gasification fuel cell (IGFC) power plants. It converts the chemical energy of fuel gas directly into electric energy, thus high efficiencies can be achieved. The outputs from SOFC can be utilized by heat recovery steam generator (HRSG), which drives the steam turbine for electricity production. The SOFC stack model was developed using the process flow sheet simulator Aspen Plus, which is of the equilibrium type. Various ranges of syngas properties gathered from different literature were used for the simulation. The results indicate a trade-off efficiency and power with respect to a variety of SOFC inputs. The HRSG located after SOFC was included in the current simulation study with various operating parameters. This paper describes IGFC power plants, particularly the optimization of HRSG to improve the efficiency of the heat recovery from the SOFC exhaust gas and to maximize the power production in the steam cycle in the IGFC system. HRSG output from different pressure levels varies depending on the SOFC output. The steam turbine efficiency was calculated for measuring the total power plant output. The aim of this paper is to provide a simulation model for the optimal selection of the operative parameters of HRSG and SOFC for the IGFC system by comparing it with other models. The simulation model should be flexible enough for use in future development and capable of predicting system performance under various operating conditions.
References | Related Articles | Metrics
Applying the multi-zone model in predicting the operating range of HCCI engines
Ming JIA, Maozhao XIE, Zhijun PENG,
Front. Energy. 2010, 4 (3): 414-423.  
https://doi.org/10.1007/s11708-010-0108-8

Abstract   PDF (535KB)
In this paper, a multi-zone model is developed to predict the operating range of homogeneous charge compression ignition (HCCI) engines. The boundaries of the operating range were determined by knock (presented by ringing intensity), partial burn (presented by combustion efficiency), and cycle-to-cycle variations (presented by the sensitivity of indicated mean effective pressure to initial temperature). By simulating an HCCI engine fueled with iso-octane, the knock and cycle-to-cycle variations predicted by the model showed satisfactory agreement with measurements made under different initial temperatures and equivalence ratios; the operating range was also well reproduced by the model. Furthermore, the model was applied to predict the operating range of the HCCI engine under different engine speeds by varying the intake temperatures and equivalence ratios. The potential to extend the operating range of the HCCI engine through two strategies, i.e., variable compression ratio and intake pressure boosting, was then investigated. Results indicate that the ignition point can be efficiently controlled by varying the compression ratio. A low load range can be extended by increasing the intake temperature while reducing the compression ratio. Higher intake temperatures and lower compression ratios can also extend the high load range. Boosting intake pressure is helpful in controlling the combustion of the HCCI engine, resulting in an extended high load range.
References | Related Articles | Metrics
Fast and catalytic pyrolysis of xylan: Effects of temperature and M/HZSM-5 (M= Fe, Zn) catalysts on pyrolytic products
Xifeng ZHU, Qiang LU, Wenzhi LI, Dong ZHANG,
Front. Energy. 2010, 4 (3): 424-429.  
https://doi.org/10.1007/s11708-010-0015-z

Abstract   PDF (156KB)
Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was employed to achieve fast pyrolysis of xylan and on-line analysis of pyrolysis vapors. Tests were conducted to investigate the effects of temperature on pyrolytic products, and to reveal the effect of HZSM-5 and M/HZSM-5 (M= Fe, Zn) zeolites on pyrolysis vapors. The results showed that the total yield of pyrolytic products first increased and then decreased with the increase of temperature from 350°C to 900°C. The pyrolytic products were complex, and the most abundant products included hydroxyacetaldehyde, acetic acid, 1-hydroxy-2-propanone, 1-hydroxy-2-butanone and furfural. Catalytic cracking of pyrolysis vapors with HZSM-5 and M/HZSM-5 (M= Fe, Zn) catalysts significantly altered the product distribution. Oxygen-containing compounds were reduced considerably, and meanwhile, a lot of hydrocarbons, mainly toluene and xylenes, were formed. M/HZSM-5 catalysts were more effective than HZSM-5 in reducing the oxygen-containing compounds, and therefore, they helped to produce higher contents of hydrocarbons than HZSM-5.
References | Related Articles | Metrics
Study on electrical ignition and micro-explosion properties of HAN-based monopropellant droplet
Yonggang YU, Ming LI, Yanhuang ZHOU, Xin LU, Yuzhu PAN,
Front. Energy. 2010, 4 (3): 430-435.  
https://doi.org/10.1007/s11708-010-0010-4

Abstract   PDF (332KB)
In order to study the electrical ignition characteristics of hydroxylammonium nitrate (HAN)-based liquid propellant, an experimental device for the electrical heating ignition of a liquid propellant droplet was designed. By using a high speed camera system, the ignition properties of the LP1846 single droplet were observed at different electrical heating speeds. The results show that when the LP1846 droplet is electrified, it mainly goes through an evaporization process, a periodic expansion and contraction process, a stronger thermal decomposition process, and an ignition and combustion process. The periodic expansion and contraction process accompanies the droplet micro-explosion phenomenon, and the micro-explosion mechanism is formed mainly due to the overheated water component in LP1846. When peak load voltage is from 80 to 140V/s, the ignition delay of the LP1846 droplet is linearly shortened from 0.82 to 0.62s, but the flame is lighter. Based on the above experiments, a simplified model of the electrical heating ignition of the LP1846 single droplet is established.
References | Related Articles | Metrics
Comparison of combustion characteristics of petroleum coke and coal in one-dimensional furnace
Qulan ZHOU, Qinxin ZHAO, Guangjie ZHOU, Huiqing WANG, Tongmo XU, Shien HUI,
Front. Energy. 2010, 4 (3): 436-442.  
https://doi.org/10.1007/s11708-009-0059-0

Abstract   PDF (381KB)
The effect of primary air fraction f1, outer secondary air swirl strength and excess oxygen coefficient on the combustion characteristics of petroleum coke, Hejin lean coal and Shenmu soft coal are researched on a one-dimensional furnace using a dual channel swirl burner. The results show that with the increase in primary air fraction f1, the NOx emission concentrations of both Hejin lean coal and petroleum coke increase, and the combustion worsens in the earlier stage, but the burn-out rate of Shenmu soft coal is improved. The NOx emission concentration obtains a minimum value with an increase in f1. The ignition and burn-out rate of petroleum coke and Shenmu soft coal are optimal when Ωdl is minimum and Ωdl=0.87, respectively. However, both the NOx emission concentration of petroleum coke and Shenmu soft coal are minimum when Ωdl=1.08. The increase in excess oxygen coefficient delays the ignition of petroleum coke, worsens the combustion condition and increases the NOx emission concentration, but it greatly decreases the NOx emission concentration of Shenmu soft coal.
References | Related Articles | Metrics
19 articles