高温集热管真空寿命预测研究

针对高温真空集热管真空老化性能展开真空度预测和寿命评价研究。模拟电站高温集热管运行环境,在400℃进行热循环模拟和热损测试,在450℃进行过热加速循环试验。结果表明：集热管封离后,室温条件下其内初始真空度达4.7×10^-4Pa,在400和450℃经过400次循环后,管内真空度分别为5×10^-3Pa和6×10^-2Pa。室温状态下集热管在吸收涂层法向发射比为0.08,真空度为10^-3Pa时,400℃下热损为216 W/m,显示出良好的热性能。拟合结果表明在400℃条件下集热管使用寿命满足25年要求。     

残存气体对高温真空集热管热损失的影响研究

从理论上分析了残存气体在不同压强下的传热机理,同时以东南大学和三乐集团近期开发的新型高温真空集热管为研究对象,采用特制的排气系统和真空计,在集热管环状空间不同真空度条件下测试了相应的热损失。结果表明实验与理论分析吻合,残存气体会在传热机理和材料特性两方面同时造成真空集热管的热损失显著提高。     

A UNIFIED ENGINEERING MODEL FOR STEADY AND QUASI-STEADY SHEAR-DRIVEN GAS MICROFLOWS

We analyze one-dimensional plane Couette flows in the entire Knudsen regime with the objective of modeling shear-driven rarefied gas flows encountered in various microelectromechanical system (MEMS) components. Using the linearized Boltzmann solutions available in the literature and hard sphere direct simulation Monte Carlo (DSMC) results, we develop a unified empirical model that includes analytical expressions for the velocity distribution and shear stress for steady plane Couette flows. We also present extension of this model to time-periodic oscillatory Couette flows. Comparisons between the extended model and ensemble averaged unsteady DSMC computations show good agreements in the quasi-steady flow limit, where the Stokes number (β) based on the plate separation distance and oscillation frequency is ≤ 0.25. Overall, the new model accurately predicts the velocity distribution and shear stress for steady and quasi-steady (β ≤ 0.25) flows in a wide Knudsen number range (K_n ≤ 12), and it is strictly valid for low subsonic flows with Mach number ≤ 0.3.     

抛物槽式集热器热效率研究

介绍槽式集热器的结构及其工作过程,对集热器进行热性能分析,研究已有集热器热力学模型,并对其进行优化,利用该模型计算各个部位的热损失大小以及集热器热效率,分析得出影响集热器热效率的主要因素,定量分析这些因素对集热器效率的影响趋势,并解释其原因。     

Numerical investigation of parabolic trough receiver performance with outer vacuum shell

The useful heat gain of a parabolic collector system is directly dependent on the heat loss from the absorber at its operating temperature. Selective coatings with evacuated/non evacuated glass tubes are employed to control radiative and convective heat losses. A concentric glass shell under vacuum is investigated for its thermal performance as this method circumvents the need for direct sealing between the glass envelope and the metal receiver to maintain vacuum and its related technical challenges. The performance is compared against a non evacuated receiver and its influence under different wind velocities; emissivities are calculated by a one dimensional theoretical model and solved by an iterative method.     

球形腔式太阳能吸热器性能的数值研究

利用蒙特卡洛光线追踪法分析了6种不同开口比(D/d)的球形腔式吸热器的光学性能,并以光学模拟所得壁面能流作为热分析的边界条件导入CFD软件中,运用CFD软件对6种不同开口比的球形腔式吸热器进行流固耦合传热计算,获得了球形腔式吸热器和内部流体的温度场分布。通过计算球形腔式吸热器的反射光损失、对流热损失和热辐射损失,得到聚光器/球形腔式吸热器系统的光热转化效率为81.9%～84.4%,球形腔式吸热器的最佳开口比1相似文献   

抛物槽集热器的能量效率

对以镜面不锈钢板为反光材料的抛物槽集热器的能量效率进行了研究,分析了光学效率、热损失对能量效率的影响,计算出有空气夹层的接收器的总热损系数。试验测得的能量效率为21.1%,光学效率为23.9%,总热损系数为10.45W/(m2.℃)。通过对试验数据的分析得知,光学效率是影响能量效率的主要因素,吸收管的传导热损失较辐射热损失大,若将接收器内的空气夹层抽成真空,会大大地减少热损失。     

A multi-scale flow analysis in hydrogen separation membranes using a coupled DSMC-SPH method

The membrane separation process has been developed as an effective and efficient method for obtaining ultra-high purity hydrogen from impure feed streams. A typical membrane gas flow possesses multi-scale flow characteristics, comprising a macroscopic flow regime on both sides of the membrane and a microscopic flow regime in the pores within the membrane. A better understanding of the fundamentals of such flow behaviors and mass transfer at a multi-scale level is therefore crucial for a better membrane architecture design, which could lead to better membrane separation efficiency and reliability for hydrogen productions in fuel cells. In this paper, a novel numerical analysis method combining the direct simulation Monte Carlo (DSMC) method with the smoothed particle hydrodynamics (SPH) method is presented for the multi-scale flow prediction in a membrane. Using the coupled method, the rarefied flow behaviors within a micro-orifice pore can be predicted by the DSMC method, while the continuum flow behaviors on both sides of the membrane can be simulated by the SPH method simultaneously. To investigate the various flow behaviors and mass transfer between different components, such as H₂ and CO in the membrane, the pressure, velocity, molar concentration, mass flowrate and rarefaction of the H₂ and CO components are compared in details. The influences to the multi-scale flow from the orifice feature and size are discussed. Some unique phenomena are observed to be quite different from that observed in either a solely macroscopic or microscopic flow. The results can be greatly beneficial for the understanding of the mechanism of membrane separation, and the designing of the membranes for hydrogen productions in fuel cell applications.     

凝汽器喉部蒸汽流动的三维数值模拟

应用具有超粒子模型的直接模拟蒙特卡罗方法,对汽轮机凝汽器喉部进行区域分解和数学建模,及对具有典型结构的凝汽器喉部蒸汽流动进行了三维数值模拟,重点分析了凝汽器喉部流场的流动分布情况,揭示了喉部流场不均匀性流动特点及其产生原因。     

槽式太阳能集热器热损失计算模型适用性分析

为精确预测太阳能槽式集热器（parabolic trough collector, PTC）的传热损失,基于美国桑迪亚国家实验室（Sandia National Laboratory, SNL）、西班牙太阳能热发电站（Plataforma Solar de Almería, PSA）以及美国安柏瑞德航空航天大学（Embry-Riddle Aeronautical University, ERAU）的实测数据,对16个既有的PTC热损失模型的准确性和适用性进行了分析。结果表明,WANG等模型与SNL的实测数据吻合度最高;DICKES模型与ERAU的实测数据吻合度最高;PATNODE模型与PSA的实测数据吻合度最高。整体而言,在30 ~ 450℃ PTC载热介质工作温度范围内,PATNODE模型计算精度最高,适用性最好;直射辐射强度、入射角以及载热介质温度对集热器热损失的大小起着决定性的作用。     

Simulation-based life cycle assessment of energy efficiency of biomass-based ethanol fuel from different feedstocks in China

Interests in biomass-based fuel ethanol (BFE) have been re-boosted due to oil shortage and environmental deterioration. Biomass-based fuel ethanol is renewable and, apparently, environmentally friendly. Biomass-based E10 (a blend of 10% ethanol and 90% gasoline by volume) is a promising conventional gasoline substitute, because vehicle engines require no modifications to run on E10 and vehicle warranties are unaffected. This paper presented life cycle assessments (LCAs) of energy efficiency of wheat-based E10 from central China, corn-based E10 from northeast China, and cassava-based E10 from southwest China. The respective energy flow-based evaluation model of wheat-, corn-, and cassava-based E10 was built based on data from pilot BFE plants. Monte Carlo method is applied to deal with the uncertain parameters and input and output variables of the evaluation model because of its wide application and easy development of statistical dispersion of calculated quantities. According to the assessment results, the average energy input/output ratio of wheat-based fuel ethanol (WFE), corn-based fuel ethanol (CFE), and cassava-based fuel ethanol (KFE) is 0.70, 0.75, and 0.54, respectively, and biomass-based E10 vehicle can have less fossil energy demand than gasoline-fueled ones.     

Energy efficiency assessment by life cycle simulation of cassava-based fuel ethanol for automotive use in Chinese Guangxi context

Interest has been renewed in bio-ethanol products for their contributions in moderating oil crises. So far, most research on bio-ethanol in China is based on pilot-level experimental studies. But this work only discloses information regarding material balances and reached yields without any further energy analysis.     

Real option valuation of free destination in long-term liquefied natural gas supplies

This paper presents a real option model for the valuation of destination flexibility in long-term LNG supplies. Stochastic price dynamics in the different markets is modelled through geometric Brownian motion processes. Mean reversion is considered as well as correlation between markets, but instead of the usual correlation in return shocks, a price convergence term is introduced representing the arbitrage streams between markets. Model parameters are estimated from market data on LNG prices by maximum log-likelihood. The goodness of the fit for the proposed model is tested as well as for two alternative models. Confidence intervals for the parameters are given. Results for the model are calculated by Monte Carlo simulation. Frequency distributions for the main results are plotted. The effect of the main parameters of the model is studied (i.e. price volatilities, price convergence, initial prices in the markets, mean reversion, extra transportation costs, number of alternative markets). The value of destination flexibility is found to be an important share of the value of LNG.     

基于蒙特卡洛算法的SCR脱硝性能影响因素分析

为分析入口参数不均匀分布对选择性催化还原(Selective Catalytic Reduction, SCR)反应器脱硝性能的影响,通过MATLAB编程的方法建立了SCR脱硝反应三维数值模型。采用蒙特卡洛算法生成入口边界,以此调用模型,研究入口速度、温度及氨氮比分布不均条件下脱硝效率及氨逃逸率的变化规律。结果表明：当入口速度超过1.5 m/s,速度偏差对脱硝效率及氨逃逸率的影响较为显著,在入口速度为4 m/s时将速度偏差由0增大到80%,脱硝效率由46.77%降低到44.67%,而氨逃逸率由8.31%增加到12.57%;不同温度偏差变化区间对脱硝性能影响不同,当温度偏差小于10%时脱硝效率主要受到反应温度的影响,而当温度偏差大于10%时温度偏差成为影响脱硝效率的主要因素;氨氮比主要影响氨逃逸率,当氨氮比由0.8增大到1.2时,氨逃逸率由0.55%增大到1.02%,而脱硝效率由42.5%增大到57.23%。     

复合抛物面聚光器(CPC)光学分析研究

阐述了复合抛物面聚光器（CPC）的设计原理和光学原理，简单介绍了复合抛物面聚光器（CPC）与不同接收器的结合形式。主要介绍了平板型CPC和圆管型CPC的设计方法和相关量的计算公式的推导结果最后主要说明了截取比在CPC系统中对系统效率和系统的经济性的影响，认为合适的截取比可增加CPC的利用率并且可大大的节省材料，对CPC的推广应用很有利。     

A Life Cycle Analysis on a Bio-DME production system considering the species of biomass feedstock in Japan and Papua New Guinea

This paper describes the performance and/or CO₂ intensities of a Bio-DME (Biomass Di-methyl Ether) production system, considering the differences of biomass feedstock. In the past LCA studies on an energy chain model, there is little knowledge on the differences of biomass feedstock and/or available condition. Thus, in this paper, we selected Papua New Guinea (PNG) which has good potential for supply of an energy crop (a short rotation forestry), and Japan where wood remnants are available, as model areas. Also, we referred to 9 species of biomass feedstock of PNG, and to 8 species in Japan.The system boundary on our LCA consists of (1) the pre-treatment process, (2) the energy conversion process, and (3) the fuel transportation process. Especially, since the pre-treatment process has uncertainties related to the moisture content of biomass feedstock, as well as the distance from the cultivation site to the energy plant, we considered them by the Monte Carlo simulation.Next, we executed the process design of the Bio-DME production system based on the basic experimental results of pyrolysis and char gasification reactions. Due to these experiments, the gas components of pyrolysis and the gasification rate under H₂O (steam) and CO₂ were obtained. Also, we designed the pressurized fluid-bed gasification process. In a liquefaction process, that is, a synthesis process of DME, the result based on an equilibrium constant was used. In the proposed system, a steam turbine for an auxiliary power was assumed to be equipped, too. The energy efficiencies are 39.0–56.8 LHV-%, depending upon the biomass species.Consequently, CO₂ intensities in the whole system were 16.3–47.2 g-CO₂/MJ-DME in the Japan case, and 12.2–36.7 g-CO₂/MJ-DME in the PNG one, respectively.Finally, using the results of CO₂ intensities and energy efficiencies, we obtained the regression equations as parameters of hydrogen content and heating value of a feedstock. These equations will be extremely significant when we install the BTL (biomass-to-liquid, ex. Bio-DME) energy system in the near future, in order to mitigate CO₂ emissions effectively, and to estimate the energy’s efficiency.