• Energy Research
• 7. Clean energy close
• 4. Education close
• Chinese Academy of Sciences close

Microturbine is widely applied now in distributed generation. Here the capacity of microturbine is defined as about 200 kW power. Commonly when the load changes, the generating gas turbine has still to run at design rotating speed. This results in lower part-load efficiency. However, the part-load performance of microturbine can be improved by variable speed operation since constant frequency of electricity can be guaranteed through the control of the electronic equipment. This optimum operation mode has not yet been theoretically studied thoroughly. The paper firstly analytically investigates the general optimum speed variation for off-design efficiency with an analytical approach proposed by the last two authors. Furthermore, the study shows that the optimum part-load performance is basically not influenced by the design temperature ratio and pressure ratio. Because of using a typical component performances and analytical approach of off-design performance analysis, the conclusions are general and typical for common microturbines but not fully accurate for any special microturbine.

Abstract Biomass gasification using lattice oxygen (BGLO) of natural hematite coupling with steam was conducted in a fluidized bed reactor. The presence of hematite particles evidently facilitated to biomass gasification. Comparing with biomass steam gasification (BSG), carbon conversion and gas yield increased by 7.47% and 11.02%, respectively, and tar content lowered by 51.53%, in BGLO with an S/B of 0.85 at 800 °C. In this case, 62.30% of the lattice oxygen in the hematite particles was consumed in the biomass gasification. The reaction temperature, steam-to-biomass ratio (S/B) and reaction time on the performance of hematite particles were extensively investigated, in terms of gas distribution, heating value, yield and carbon conversion. With the reaction temperature increasing from 750 to 850 °C, the gas yield increased from1.12 to 1.53Nm3/kg, and carbon conversion increased from 77.21% to 95.49%. An optimal S/B ratio of 0.85 was obtained in order to maximize the carbon conversion and gas yield of BGLO. At this ratio, the gas yield reached 1.41Nm3/kg with carbon conversion of 92.98%. The gas concentration was gradually close to that of BSG at the end stage of BGLO due to the active lattice oxygen was depleted with the proceeding of reactions.

Analytical method is used to obtain the geometrical shape for non-imaging secondary (NIS) mirror in the application of concentrated photovoltaic (CPV). It is discussed in beam down optical system, NIS presents advantages to eliminate dark image, to reduce the solar disc effect, to improve the uniformity of the illumination, etc. comparing to the imaging secondary. The authors have emphasized that the geometrical shape of optical components in non-imaging optics can generally be high order surfaces not restricted to the quadratic surface in imaging optics and mostly "CPC" in early developed non-imaging optics. This paper has discussed the general criteria and two practical approaches for designing NIS. We listed some of the examples in this paper to form NIS by rotating a segment of linear or quadratic or cubic curve around the central axis of primary reflector. The method to calculate the parameters of such segment is described. Although in present discussion, we are referring the usage in PV concentrator, the method is generally applied in other optical fields. (C) 2013 Elsevier Ltd. All rights reserved.

A new type of photovoltaic system with higher generation power density has been studied in detail. The feature of the system is a V-shaped module (VSM) with two tilted monocrystalline solar cells. Compared to solar cells in a flat orientation, the VSM enhances external quantum efficiency and leads to an increase of 31% in power conversion efficiency. Due to the VSM technique, short-circuit current density was raised from 24.94 to 33.7mA/cm(2), but both fill factor and open-circuit voltage were approximately unchanged. For the VSM similar results (about 30% increase) were obtained for solar cells fabricated by using mono-crystal line silicon wafers with only conventional background impurities. (c) 2004 Elsevier B.V. All rights reserved.

A 117.8 l three-dimensional pressure vessel is used to study the methane hydrate dissociation with the steam assisted gravity drainage (sagd) method. it is called the pilot-scale hydrate simulator (phs). this study proposes the evaluation and the comparisons of the gas production performance by sagd method from the methane hydrate reservoir with different steam injection rates. it indicates that the experiment could be divided into three main stages: the original gas releasing stage, the original and the hydrate-originating gas releasing stage, and the hydrate-originating gas releasing stage (the sagd process). furthermore, the temperature change consists of the four periods: decreasing dramatically, keeping stable, rising gradually, and keeping steady. with the injected steam flowing downwards and sideways, the steam chamber is expanding. the gas production rate increases with the steam injection rate, while the energy efficiency ratio (eer) and gas-to-water ratios are improved by the decrease of the steam injection rate. (c) 2013 elsevier ltd. all rights reserved.

To assign fossil and nonfossil contributions to carbonaceous particles, radiocarbon ((14)C) measurements were performed on organic carbon (OC), elemental carbon (EC), and water-insoluble OC (WINSOC) of aerosol samples from a regional background site in South China under different seasonal conditions. The average contributions of fossil sources to EC, OC and WINSOC were 38 ± 11%, 19 ± 10%, and 17 ± 10%, respectively, indicating generally a dominance of nonfossil emissions. A higher contribution from fossil sources to EC (∼51%) and OC (∼30%) was observed for air-masses transported from Southeast China in fall, associated with large fossil-fuel combustion and vehicle emissions in highly urbanized regions of China. In contrast, an increase of the nonfossil contribution by 5-10% was observed during the periods with enhanced open biomass-burning activities in Southeast Asia or Southeast China. A modified EC tracer method was used to estimate the secondary organic carbon from fossil emissions by determining (14)C-derived fossil WINSOC and fossil EC. This approach indicates a dominating secondary component (70 ± 7%) of fossil OC. Furthermore, contributions of biogenic and biomass-burning emissions to contemporary OC were estimated to be 56 ± 16% and 44 ± 14%, respectively.

AbstractA series of block copolymers with fixed length of the semiconductor‐block poly(3‐butylthiophene) (P3BT) and varying length of the insulator‐block polystyrene (PS) are synthesized. These copolymers are blended with phenyl‐C61‐butyric acid methyl ester (PCBM) for the bulk heterojunction photoactive layers. With appropriate insulator‐block length and donor–acceptor ratio, the power conversion efficiency increases by one order of magnitude compared with reference devices with pure P3BT/PCBM. PS blocks improve the miscibility of the active layer blends remarkably. The P3BT‐b‐PS crystallizes as nanorods with the P3BT core covered with the PS‐block, which creates a nanoscale tunneling barrier between donor and acceptor leading to more efficient transportation of charge carriers in the semiconductors.

High frequency operation of standing wave thermoacoustic heat engines is attractive for space applications due to compact size and high reliability. To expedite practical use, further improvement and optimization should be based on deep understanding and quantitative analysis. This article focuses on using computational fluid dynamics (CFD) to investigate nonlinear phenomena and processes of a 300 Hz standing wave thermoacoustic engine (SWTE). The calculated model was tested in detail, which indicated that the co-axially stacked tube model was suitable for the simulation of SWTEs. Two methods of imposing temperature gradient across the stack were studied, and the processes of mean pressure increasing, pressure wave amplification and saturation were obtained under the thermal boundary condition of applying heating power. The acoustic fields were given, and the flow vortices and their evolution in both ends of the stack and resonator were observed. Moreover, a comparison between the simulation and experiments was made, which demonstrated the validity and power of the CFD simulation for characterizing complicated nonlinear phenomenon involved in the self-excited SWTEs.

Abstract South Korea initiated an emissions trading scheme (ETS) on January 1, 2015. Based on this environmental policy, at the 21st Conference of Parties (COP) meeting, the Korean government announced that it would decrease carbon emissions 37% from business as usual (BAU) levels by 2030. Since this target is too ambitious for the Korean economy, a number of studies have analyzed the economic impacts of emissions trading in Korea, but few have distinguished between industries covered and not covered by the ETS, notwithstanding the lack of industry-level data on quotas and emissions. This study overcomes such shortcomings by converting a dataset of 525 firms covered by the South Korea ETS (SK-ETS) into a 28-sector database consistent with the Global Trade Analysis Project (GTAP) classifications. We implement a simulation of the SK-ETS with a computational general equilibrium (CGE) model. Simulation results suggest that while SK-ETS has significant abatement effects (−2.56% from the base case), it only has mild negative impacts on GDP (0.41%) and household consumption (0.11%). Industry output on average falls by 0.54%, with the gas and air transport sectors most adversely affected. The most noticeable price changes are from the electricity sector, whose output price goes up by 3.75%. It is noteworthy that because of the export-oriented economy, many global business leaders and politicians have argued that the ETS will disadvantage exporting companies, while the simulation results showed a higher trade surplus based on enhanced competitiveness.