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鉴于水跃跃后水深作为消力池体形设计的重要参数,通过建立水跃区跃前和跃后断面的能量方程,分析了突扩式消力池S型水跃局部水头损失系数和共轭水深比的变化规律。研究发现,S型水跃相对局部水头损失系数是跃前断面弗劳德数函数,并随着弗劳德数的增大而增大;相对局部水头损失系数随跃前断面弗劳德数的变化规律既可用线性公式表示又可用乘幂公式表示;水跃共轭水深比是跃前断面弗劳德数和消力池突扩比的函数。通过能量方程求解的S型水跃跃后水深公式具有较高的计算精度和较好的通用性,且能作为矩形明渠水跃共轭水深的求解公式。 相似文献
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为了解折坡扩散消力池的水跃特性及相关参数、判别其消能效果,通过模型试验的方法对折坡扩散消力池水跃进行了研究,提出了共轭水深计算公式,分析了水跃长度、共轭水深比、消能率等相关水力参数及其变化规律。结果表明,在试验条件下,公式计算结果与实测值相比误差较小,精度较高;水跃长度与共轭水深比、佛劳德数均遵循正比例变化规律;水跃消能率与佛劳德数呈正比。 相似文献
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在很多水电站中,不论河床式水电站的溢流坝、泄水闸或者是引水道,底流水跃常被用来作为下游消能的一种有效措施.而这种水跃往往是低佛氏数的,例如引水闸或泄水闸的低堰上,或者大单宽中等高度的溢流坝下游的水跃均是跃前佛氏数小于4.5的低佛氏数水跃.对水跃的研究已有一个多世纪的历史,尤其是对于平底矩形水槽内的二元自由水跃,已取得了大量的试验资料和比较完整的可靠的水力设计方法.但对于低佛氏数水跃的消能机理研究还是从本世纪50年代开始的.低佛氏数水跃消能的显著特点是来流的泄水功率高而水跃消能率低,例如当Fr=2~5时,其时均消能率只有20~45%,这说明在水跃下游的水流中,还有大量地未被消散掉的余能(即紊动能和波动能)将造成跃后水流强烈的紊动和波动,需要流经一段距离后才能消失,给下游消能防冲带来较大的困难.因此,近年来国内外 相似文献
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针对低弗劳德数水流在消力池内极易形成弱水跃且水面大幅波动的问题,在低弗劳德数情况下,利用RNGκ-ε紊流模型,分别对趾墩悬栅联合消能工与单一悬栅消能工所处流场进行数值模拟,系统分析了水深沿程变化及流速分布规律,得到联合消能结构作用下消力池内部水流流态及过栅绕流涡旋分布。结果表明,联合消能工能增大回流区漩涡尺度,加剧水流卷吸掺混强度,大幅提高掺气浓度,迫使跃前断面向下游推移,相对推移比接近26%,淹没度下降约10%左右,从而显著降低陡坡水流脉动;悬栅附近涡群具有更强的漩涡运动,主、回流间紊动混掺加剧,增强了下泄水流能量耗散。研究结果为同类工程中解决消能防冲问题提供了新思路和参考依据。 相似文献
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本文应用CDL-86型超声多普勒流速仪,对佛氏数Fr=2.16~4.34的水跃跃前断面和跃后水流的紊动特性进行了试验研究;分析了跃后水流的紊动能量、紊动强度衰减率和水跃消能率等;Fr=2.99可能是这些量变化的突变点或转折点;并通过对试验资料的回归计算得出了跃后水流的紊动能和紊动强度及其衰减率随佛氏数变化的计算式,给出了计入多种影响因素的水跃消能率计算式.认为低佛氏数水跃跃前断面流速分布不均匀以及紊动值的大小对跃后水流有较大影响,近低区较大流速梯度和较大的水流紊动作用是造成水跃下游河床冲刷破坏的主要原因之一. 相似文献
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给出梯形明渠水跃共轭水深的显式精确计算公式。根据梯形明渠的水跃方程和一元四次方程的求解方法,研究了梯形明渠水跃共轭水深的精确解法。提出了梯形明渠水跃共轭水深的显式精确计算公式、计算步骤,并与其他迭代公式进行比较。给出的梯形明渠水跃共轭水深的计算方法为显式精确解,比试算法、查图法和迭代法简单、方便、精度高。 相似文献
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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. 相似文献
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《热能动力工程》2014,(5)
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%. 相似文献
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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. 相似文献
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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. 相似文献
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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. 相似文献
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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. σred = σ1 β + (1 − β)σi, where: σ1-maximal principal stress, σi-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. 相似文献
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Jaime Massanet-Nicolau Alan Guwy Richard Dinsdale Giuliano Premier Sandra Esteves 《International Journal of Hydrogen Energy》2010
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. 相似文献