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利用相界面追踪的耦合水平集-流体体积(CLSVOF)方法,对液滴撞击超疏水管状壁面的动态特性展开研究,主要讨论粘性系数和表面张力系数对撞击过程的影响。研究结果表明:液滴粘性系数越小,液膜的铺展速度越快,回缩速度也越快,同时越早发生反弹,反弹高度也越大;随着表面张力系数的增大,液膜达到最大铺展所需时间减少,会阻碍液膜的铺展,但会促进其回缩,当表面张力系数为0.01 N/m时,液膜外边缘出现飞溅且液膜主体不发生反弹;还对液滴撞击超疏水管壁后出现的反弹、飞溅现象的机理展开分析。 相似文献
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应用数值模拟方法研究单液滴撞击薄液膜的动力学行为.在二维轴对称坐标系内,采用VOF方法与网格局部瞬时加密技术相结合,跟踪液滴和液膜与空气间的气液两相界面.结果表明,液滴撞击薄液膜的演化行为主要受液滴初始动能、表面张力以及液体黏性的影响.初始动能越大,则形成的空间液膜最大高度越大,达到稳定状态越晚,飞溅开始时刻越早,飞溅生成的二次液滴数量也越多;在扩展后期及回缩阶段,空间液膜的形成主要受液体黏度影响,增加液体黏度会阻碍空间液膜飞溅;表面张力增大,形成的空间液膜高度减小、厚度增加,同时阻碍二次液滴的生成. 相似文献
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在气液两相流VOF(volume of fluid,VOF)模型的基础上耦合CSF(continuum surface force,CSF)表面张力模型,建立了高温平板上的铺展液滴与高温空气中悬浮液滴蒸发过程中内部非稳态流动模型,对液滴蒸发过程中内部非稳态流动进行了研究。基于相变理论,采用用户自定义函数将流体相变模型加入非稳态流动模型中进行耦合计算,获得了高温平板上的铺展液滴与高温空气中悬浮液滴蒸发过程中的内部流动及变化过程。液滴蒸发过程中非稳态内部流动由液滴表面的温度梯度引发,Marangoni流动在液滴内部形成的时间非常短,流体从液滴表面高温区域流向低温区域。计算结果表明:高温平板上随着液滴蒸发的进行,液滴内部一直保持两个对称的涡流,Marangoni流动比较稳定;高温空气环境中随着液滴蒸发的进行,液滴内部四个涡流逐渐转变成两个对称的涡流;液滴内部温度分布因Marangoni流动加强传热而变得均匀,同时由于温度分布变得均匀,Marangoni流动被削弱。 相似文献
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液滴撞击壁面后的铺展行为是液滴撞壁的主要发展模式之一,对喷雾研究具有重要意义.通过对理想光滑壁面和实际粗糙壁面接触角的理论分析,发现壁面粗糙度是引起接触角滞后的主要原因,通过引入壁面阻力建立了粗糙壁面上接触角滞后模型.对接触线附近贴壁区域的流动状态进行分析,引入接触线特征参数求得固液间的黏性剪切力和气液界面上的黏性剪切力.在理论分析的基础上建立了动态接触角随接触线移动速度的变化关系式.通过研究动态接触角随接触线特征参数、液滴黏度、壁面粗糙度和气液表面张力的变化关系,获得了这些因素对液滴碰壁铺展行为的影响规律. 相似文献
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基于单组分多相流格子Boltzmann方法结合精确差分法建立了汽液相变模型,运用伪势模型以及双分布函数,结合所提出的沸腾冷凝相变模型,对微小空间内超亲水和超疏水组合表面下汽液共存沸腾时两个汽泡合并、生长、离开水平面以及蒸汽冷凝凝结成两个液滴融合、脱落的过程进行了研究。着重分析了重力加速度对汽泡脱离直径和汽泡脱离时间的影响以及流固作用强度对接触角的影响,最后拟合出了对应关系,并对汽泡和液滴运动过程进行了分析。研究发现与现有已发表的对应关系和公开实验结果基本吻合,并得出结论:随着重力加速度的增大,汽泡脱离直径和汽泡脱离时间均呈现出减小的趋势;接触角随着流固作用强度的增大呈现出减小的趋势;沸腾过程受热产生的蒸汽在模型内部在平衡移动原理作用下向着冷源移动,冷源液化消耗近似等量蒸汽产生水滴逐渐成长落入水中,实现了系统内热力平衡和循环过程。 相似文献
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建立了石灰石/石膏湿法烟气脱硫喷淋塔实验台,实验研究了重要的操作参数对喷淋塔脱硫效率的影响规律。实验结果表明,提高液气比和浆液pH值、降低烟气温度和烟气速度、降低入口烟气的SO2浓度以及强制氧化均可以提高脱硫效率。将喷淋浆液分成喷淋液滴和塔壁液膜两种存在形式,并分别建模,喷淋液滴的脱硫过程采用Gerbec液滴脱硫模型计算,将塔壁液膜的流动分为层流和波动层流两种状态,发展出了新的喷淋塔脱硫反应模型。模型计算结果表明,相对于Gerbec液滴模型,本文的模型计算结果与实验数据吻合得更好。 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