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实验研究了外加线性变化热流条件下木材点燃时间与热流变化率之间的关系,测量了不同种类木材在不同热流变化率下的点燃时间。通过分析实验数据发现,点燃时间和热流变化率之间符合很好的幂函数关系,而密度是影响木材着火的一个关键因素。 相似文献
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研究R290在管径为3、2和1 mm的水平不锈钢微细通道内,质量流率为73~505 kg/(m~2·s)、热流密度为12. 74~66. 05 k W/m~2、饱和温度为-10~25℃、干度为0~1的范围内的摩擦压降特性,分析R290流动沸腾过程中的摩擦压降变化。结果表明:换热管径尺度微型化使相同条件下的管内压降剧烈上升,质量流率对压降的影响最显著;热流密度的增加对压降的影响很小,几乎为零; R290不同饱和温度物性的改变是造成其不同温度时压降特性差异的主要原因,随着饱和温度的升高,摩擦压降变小;压降随着干度的变化在某个干度存在极值。 相似文献
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对R290在5 mm小管径内的凝结换热特性进行了实验。实验工况:热流密度5~10 kW/m~2、质量流率180~250 kg/(m~2·s)、饱和温度40~55℃、管径5 mm。研究了质量流速、饱和温度、热流密度及管型对管内换热系数的影响。研究表明:换热系数随质量流率的增大而增大,随饱和温度的上升而下降,且在干度较大区域,影响更加明显;换热系数随热流密度的增大而增大,且存在最佳热流密度使其达到最大值;相同工况下,内肋管换热系数大于光管,在质量流速低、干度小的区域内肋管的强化效果更优。 相似文献
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本文阐述了在我校高压电加热水回路装置上所进行的亚临界及近临界压力区水平沸腾管传热特性的试验研究结果。试验管为φ25×2mm不锈钢管,试验参数范围为压力从16.7MPa到22.6MPa、质量流速从600kg/m~2·s到1200kg/m~2·s、热负荷从200kw/m~2到530kw/m~2。试验得出了亚临界及近临界压力区水平沸腾管中不同质量流速、热负荷和含汽率条件下沿管子周界的壁温分布曲线,确定了水平沸腾管中发生传热恶化的位置和壁温飞升值。 相似文献
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针对CO_2水平微细管内流动沸腾换热流态及流态转变特性进行实验研究。实验工况:热流密度(5~35 k W/m~2)、质量流率(50~600 kg/(m~2·s))、饱和温度(-40~0℃)、管径(0.5~1.5 mm)。实验表明:CO_2在微细管内实际流态分别是泡状流、弹状流、间歇流、层流、波状流、混状流、环状流和雾状流;干涸过程中的流态主要为环状流-雾状流、波状流-雾状流的过程及不稳定的环状流;通过理论计算获得CO_2微细管内流动沸腾换热流态图,流态图显示热流密度对高干度区域流态转变有显著影响,质量流率大小直接决定了换热过程所经历的流态;不同饱和温度工质热物性不同改变了流型;理论分析所采用的流态形式与实际CO2在微细管内所具有的流态类型基本一致。 相似文献
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为分析饱和温度、热流密度、质量流率和管径对CO_2流动沸腾换热特性和干涸特性的影响,对水平微细管内CO_2流动沸腾换热进行了实验研究。实验工况:饱和温度-40~25℃,热流密度5~40 kW/m~2,质量流率180~1 400 kg/(m~2·s),管径0. 50、1. 0和1. 5 mm。实验结果表明:热流密度的增加显著影响核态沸腾换热,加快干涸发展进程的同时,降低干涸起始干度;换热系数受质量流量的影响较小,但质量流率的增加会降低干涸起始干度,干涸后的换热系数有所增加;不同饱和温度下换热特性差异的主要原因是CO_2的热物性受饱和温度的影响较大,饱和温度升高后干涸起始干度具有降低的趋势,且干涸后换热系数下降更为剧烈;在符合微尺度效应的前提下,管径的减小会极大地提高换热系数,同时降低干涸起始干度,干涸后换热系数下降剧烈。 相似文献
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PVC输送带点燃温度判据及应用 总被引:1,自引:0,他引:1
利用锥形量热计对800S PVC整芯阻燃输送带的点燃性能进行了实验研究;在实验数据的基础上,采用传热模型计算出实验时输送带的点燃温度,其平均点燃温度为384℃.利用此温度判据,对输送带在实验巷道中火焰蔓延情况进行了数值模拟.计算结果表明,在小尺寸实验巷道中,1m/s的风速条件下,600 s时间内火焰在输送带表面上蔓延的长度约为0.3 m. 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