内可逆四热源吸收式制冷循环的热经济性能优化

应用内可逆四热源吸收式制冷循环模型，分析吸收式制冷机受传热不可逆性影响时的热经济性能。在牛顿传热定律下，导出了循环的最佳热经济性目标和制冷系数的基本优化关系和最大热经济性目标及相应的制冷系数与比制冷率；通过数值算例，得出循环参数对循环的热经济性目标、制冷系数和比制冷率的影响关系。     

吸收式热泵等效循环模型及性能优化

应用有限时间热力学理论对吸收式热泵进行研究,将其等效为一个由不可逆卡诺热机驱动的不可逆卡诺热泵的联合循环系统,考虑了热阻及工质内部的不可逆性,建立了四热源吸收式热力循环模型,得出吸收式热泵的性能界限及取得性能界限的途径;并得出了吸收式热泵热力循环各个关键参数的通用优化关系,结果表明:两个等效循环的不可逆程度对系统最优性能的影响不同,在设计机组时,减小等效热泵循环的摩擦、热损失、内部耗散比减小等效热机循环之间的相应损失更能显著提高机组的性能;并指出吸收器与冷凝器的热分配率是热力循环优化的结果,指出以往研究者将热分配率定义为一个独立变量而得到的分析结果均不具有普遍适用性。     

不可逆双谐振通道能量选择性电子制冷机热力学性能优化北大核心CSCD

建立了考虑线性热漏的不可逆双谐振通道能量选择性电子(energy selective election,ESE)制冷机模型,导出了制冷机制冷率和制冷系数的表达式,应用有限时间热力学理论研究了系统制冷率与制冷系数最优性能,通过数值计算,详细分析了热漏、能量宽度、能量间距等设计参数对ESE制冷机最优性能的影响。研究发现,系统的制冷率和制冷系数都会随热漏的增加而减小;给定能量间距时,制冷率和制冷系数都会随能量宽度的增加而先增大后减小,存在最优的能量宽度使制冷率或制冷系数达到最大值;给定能量宽度时,制冷率和制冷系数会随能量间距的增加而先增加后减小,存在最优的能量间距使制冷率或制冷系数达到最大值。合理地选取能量宽度、能量间距等参数,可以使不可逆的双谐振ESE制冷机设计于最大制冷率或最大制冷系数的状态。     

热漏对内可逆四热源制冷系统的影响

在恒温热源内可逆四热源吸收式制冷循环的基础上，建立不可逆吸收式制冷循环的模型，考虑环境热源到制冷空间的热漏以及工质与外部热源间的热阻损失，导出牛顿定律下循环的制冷率和制冷系数的基本优化关系、最大制冷系数及相应的制冷率和最大制冷率及相应的制冷系数；并通过数值计算分析了循环参数对循环的制冷率、制冷系数的影响。     

广义不可逆联合制冷循环有限时间(火用)经济性分析与优化

研究了存在热阻、热漏和内不可逆性的广义不可逆联合制冷循环有限时间(火用)经济性能,导出在线性传热定律下循环最佳利润率和最佳制冷系数的解析式以及二者的优化关系,并用数值算例对比分析了热漏、内不可逆性和价格比对利润率和(火用)经济性能界限的影响.     

广义不可逆布雷森循环生态学性能系数分析

以反映热机循环输出和损失之比的生态学性能系数(ECOP)为目标,用有限时间热力学理论,对广义不可逆布雷森循环进行性能分析。导出了在牛顿传热律下广义不可逆布雷森循环无因次功率、效率、无因次熵产率、无因次生态学函数和生态学性能系数的解析式;并通过数值算例得到它们之间的关系。结果表明,内不可逆性对该热机各种性能参数产生一定的影响,以ECOP为目标优化具有效率较高,熵产率较低的优势。     

内可逆四热源吸收式制冷机生态学最优性能

基于能量分析的观点,建立了反映四热源吸收式制冷机制冷率与熵产率之间最佳折中的生态学准则,分析了线性(牛顿)传热定律下内可逆四热源吸收式制冷机的生态学最优性能.导出了生态学目标与制冷系数的优化关系和最大生态学目标值及其相对应的制冷系数、制冷率和熵产率,确定了循环主要参数的生态学优化选择范围.数值算例分析了制冷率目标和生态学目标的相互关系,计算表明生态学准则对吸收式制冷机优化设计是一种具有长期效应的可选优化目标.     

线性唯象传热定律下不可逆四热源制冷循环最优性能

在恒温热源内可逆四热源吸收式制冷循环的基础上，考虑环境热源到制冷空间的热漏、工质的内部耗散以及工质与外部热源问的热阻损失，建立传热服从线性唯象定律的不可逆吸收式制冷循环的模型，导出循环的制冷率和制冷系数的基本优化关系、最大制冷系数及相应的制冷率和最大制冷率及相应的制冷系数，给出了最佳换热面积，并通过数值计算分析了设计参数对循环的制冷率、制冷系数的影响。所得结果对实际吸收式制冷机的设计和运行有一定的指导意义。     

不可逆卡诺热泵的有限时间热力学最优化

本文在考虑工质与热源间热阻损失的内可逆卡诺热泵模型基础上，用一常数项表示热源间的热漏，用一带系数项表示循环中除热阻和热漏外的其余所有不可逆性（如摩擦,涡流,非平衡等），建立了一个不可逆定常态能量转换卡诺热泵模型，并对此不可逆热泵模型进行有限时间热力学分析，导出了供热率和供热系数之间的优化关系。由此模型可准确描述各种不可逆性对热泵性能的影响，能对实际热泵的工作性能起到精确的指导作用．     

不可逆半导体固态热离子制冷器性能分析和优化

建立了考虑外部有限速率传热过程和热源间热漏的不可逆半导体固态热离子制冷器模型,基于非平衡热力学和有限时间热力学理论导出了热离子制冷器的制冷率和制冷系数的表达式;对比分析了不可逆热离子制冷器与可逆热离子制冷器的发射电流密度特性、电极温度特性以及制冷系数特性;研究了不可逆系统的制冷率与制冷系数最优性能,得到了制冷率和制冷系数的最优运行区间;通过数值计算,详细讨论了外部传热以及内部导热、热源间热漏损失、热源温度、外加电压、半导体材料势垒等设计参数对热离子装置性能的影响。在总传热面积一定的条件下,进一步优化了高、低温侧换热器的面积分配以获得最佳的制冷率和制冷系数特性。结果表明,由于存在内部和外部的不可逆性,热离子装置的发射电流密度及制冷系数都会明显降低;不可逆半导体固态热离子制冷器的制冷率与制冷系数特性呈扭叶型;合理地选外加电压、势垒等参数,可以使制冷器设计于最大制冷率或最大制冷系数的状态。     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Contents in Volume 23,2014

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Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.