共查询到19条相似文献,搜索用时 90 毫秒
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以煤粉锅炉积灰过程为研究背景,在常温常压环境下对飞灰颗粒与平板表面撞击过程进行实验研究,分析飞灰颗粒入射法向速度对颗粒法向反弹速度的影响,以及飞灰颗粒粒径对临界捕集速度的影响。实验结果表明,飞灰颗粒粒径相同时,法向恢复系数随入射法向速度的增大先增大后平缓最后减小,在增大区域具有相当陡的斜率,反映了不同形式的力在不同阶段所占的比重不同;颗粒入射法向速度相同时,法向恢复系数随着颗粒粒径的增大而增大;而临界捕集速度随颗粒粒径的增大而减小。 相似文献
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微通道中的冷凝在微热管及微型燃料电池等器件中有着广泛的应用。本文综述了当前国内外微通道冷凝研究的现状,展望了该领域的未来研究方向。大量研究表明,控制微通道中冷凝与两相流动的主要作用力不是重力或浮力,而是表面张力。最新实验结果发现,随着通道直径的减小,微通道中主要的冷凝流型是间断的喷射流/弹状流/泡状流,而不是传统大直径通道中出现的由重力作用而导致的分层环状流。因此,未考虑表面张力的大尺度冷凝模型已不能完整描述微通道内的流动冷凝过程。对于间断流型,基于实验数据的半理论模型或经验关联式可能更为实用有效。润湿性和表面粗糙度等通道表面特性在微通道流动冷凝中有着重要的影响,这些因素的优化将会强化微通道中的冷凝换热。 相似文献
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热重法研究煤的燃烧行为及其动力学模型 总被引:1,自引:0,他引:1
采用热重法(TG)考察了六枝(LZ)、遵义(ZY)和吴家坪(WJP)原煤、脱灰煤及其脱黄铁矿煤的燃烧性能,并对其燃烧性能进行了动力学研究.研究表明:LZ,ZY和WJP脱灰煤的着火温度和燃烧峰温都较其原煤低,其燃烧特性指数较其原煤高,这是由于脱灰煤的燃烧活化能E较其原煤低的缘故.ZY和WJP脱黄铁矿煤的燃烧特性指数S与其脱灰煤相比基本没发生变化,这是由于脱黄铁矿煤的燃烧活化能E和指前因子A都较其脱灰煤大大增加,是二者相互影响的结果.对煤的燃烧行为进行动力学研究发现:LZ,ZY和WJP原煤、脱灰煤及其脱黄铁矿煤在燃烧区间的某一温度段满足一级反应模型,且线性相关性较好,相关系数大都在0.98以上. 相似文献
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在1 000℃、缺氧条件下研究了催化助燃剂NaC1、KNO3、锰矿物质对无烟煤的燃烧率的影响.结果表明:复配不同催化助燃剂比例的复合添加剂1#、2#、3#,KNO3的催化效果好于NaCl和锰矿物质,复合添加剂的催化效果1 #>3#>2#;随着添加剂量的增加,燃烧率在添加量1%处出现了拐点. 相似文献
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褐煤是一种高水分、易挥发、低密度和中低热量的低劣煤。为了提高褐煤利用效率,采用褐煤热解制备一氧化碳。通过Ellingham图筛选出有助于褐煤热解分解制备一氧化碳的氧化物,并且利用热力学对该过程进行分析,同时对该过程的反应动力学及反应机理进行探索。通过热力学分析发现,CeO_2褐煤可以制备一氧化碳,其转化率最高可以达到99.00%。该过程主要分为两个部分:925℃以下褐煤的自身气化和高温阶段的CeO_2与C的反应,且高温对该反应有促进作用。通过Kissinger和Flynn-Wall-Ozawa(FWO)方法对CeO_2褐煤分解过程的活化能研究以及通过Coats-Redfem方法对反应机理的探索,最终确定CeO_2褐煤制备一氧化碳的反应动力学模型。该研究为褐煤热解提出一条途径。 相似文献
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利用微型流化床加热速度快、温度分布均匀以及气体近平推流等优势,在直径20 mm自动控温的微型流化床反应分析仪中研究了粒度分布为1.7~3.35 mm和0.12~0.23 mm两种典型尺寸燃煤颗粒在790~900℃温度范围内的富氧燃烧行为。通过快速响应过程质谱对燃烧产生的烟气进行实时监测,成功地识别和记录了粗颗粒燃烧过程中经历的挥发分燃烧和原位新生半焦燃烧两个主要阶段。挥发分析出速度最快,然后快速燃烧,而半焦燃烧速度较慢。相比之下,细颗粒燃烧的这两个阶段具有几乎相同的速率,因而相互耦合而难以区分。根据实验结果,挥发分析出和燃烧为快速反应,煤颗粒燃烧过程速率受原位新生半焦燃烧过程控制。进一步研究了挥发分和原位新生半焦燃烧动力学行为,获得其本征动力学的活化能分别为107.2和143.9 kJ/mol。 相似文献
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《化学世界》2019,(10)
褐煤是一种高水分、易挥发、低密度和中低热量的低劣煤。为了提高褐煤利用效率,文章采用褐煤热解制备CO。通过Ellingham 图筛选出有助于褐煤热解分解制备CO的氧化物,并且利用热力学对该过程进行分析,同时对该过程的反应动力学及反应机理进行探索。通过热力学分析CeO2褐煤可以制备CO,其转化率最高可以达到99.00%。该过程主要分为两个部分:925oC以下褐煤的自身气化和高温阶段的CeO2与C的反应且高温对该反应有促进作用。通过Kissinger和FWO方法对CeO2褐煤分解过程的活化能的研究以及通过Coats-Redfem 方法对反应机理的探索,最终确定CeO2褐煤制备CO的反应动力学模型。该研究为褐煤热解提出一条新途径,并且对该过程做出了一定理论基础。 相似文献
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采用非等温热重分析技术对比研究了Na2CO3,BaCO3和CaCO3对高灰分煤粉(灰分〉44%)燃烧反应动力学参数的影响。非等温热重分析以20℃/min的升温速率从室温升到1000℃,动力学参数采用Coats—Redfern方程进行计算.结果表明:与空白煤样对比,掺有碳酸盐的煤样着火温度均有不同程度的降低,而煤样的最大燃烧速率增大且燃烧最大速率出现的温度前移;当煤粉样品中分别掺有3%的Na2CO3,BaCO3和CaCO3时,煤粉燃烧的活化能比纯煤粉分别降低了15.63%,12.39%和14.23%,且指前因子与活化能之间存在着线形关系,其关系为In(А)=0.2783E-12.882。 相似文献
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Drying characteristics and modeling of yam slices under different relative humidity conditions 总被引:6,自引:0,他引:6
Hao-Yu Ju Hamed M. El-Mashad Xiao-Ming Fang Zhongli Pan Yan-Hong Liu 《Drying Technology》2016,34(3):296-306
The drying characteristics of yam slices under different constant relative humidity (RH) and step-down RH levels were studied. A mass transfer model was developed based on Bi-Di correlations containing a drying coefficient and a lag factor to describe the drying process. It was validated using experimental data. Results showed that the drying air with constant RH levels of 20, 30, and 40%, temperature of 60°C, and air velocity of 1.5 m/s had an insignificant effect on drying time. This phenomenon was likely attributed to the fact that higher RH led to a rapid increase in sample’s temperature. The higher sample temperature could provide an additional driving force to water diffusion and thereby promote the moisture movement, which could minimize the negative effect of lower the drying rate in the initial drying stage. Applying air with 40% RH for 15 min in the initial stage achieved the desired color and reduced the drying time by 25% compared to the drying time under continuous dehumidification from an initial RH of 40%. Using the developed Bi-Di correlation, the estimated Biot number, effective moisture diffusivity, and mass transfer coefficient ranged from 0.1024 to 0.1182, 1.1133 × 10?10 to 8.8144 × 10?9 m2/s, and 1.8992 × 10?9 to 1.7364 × 10?7 m/s, respectively. A rather high correlation coefficient of determination (R2 between 0.9871 and 0.9971) was determined between the experimental and predicted moisture contents. The present findings contribute to a better understanding of the effect of relative humidity on drying characteristics. The developed Bi-Di correlation provided a new method to determine the effective diffusivity of moisture in drying. 相似文献
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Aaron J. Harrison Stephen P. Beaudoin 《Journal of Adhesion Science and Technology》2016,30(11):1165-1177
A lattice gas model is used with Wang-Landau Monte Carlo sampling to predict the capillary force between a model of an atomic force microscopy (AFM) probe and a smooth surface as a function of separation, relative humidity (RH), and tip hydrophilicity. Completely wetting AFM tips exhibit a maximum in the capillary force as the RH increases, while the magnitude of the capillary force in the presence of partially wetting and partially drying tips is relatively independent of the RH. Capillary forces can also be significant in low RH environments and should not be discounted in AFM studies involving hydrophilic surfaces. 相似文献
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湿度对锦纶66帘线强伸性能的影响 总被引:1,自引:0,他引:1
进行了湿度对锦纶66帘线强伸性能影响的试验研究。通过统计分析断裂强力、断裂强力不匀率、定负荷伸长度、断裂伸长率、断裂伸长不匀率等旨标的试验数据并结合理论分析,得出随着相对湿度的增大,锦纶66帘线断裂强力下降,定负荷伸长率、断裂伸长率及断裂强力不匀率、断裂伸长不匀率增大的结论。 相似文献
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Operation of a proton exchange membrane (PEM) fuel cell without external humidification (or 0% relative humidity, abbreviated as 0% RH) of the reactant gases is highly desirable, because it can eliminate the gas humidification system and thus decrease the complexity of the PEM fuel cell system and increase the system volume power density (W/l) and weight power density (W/kg). In this investigation, a PEM fuel cell was operated in the temperature range of 23-120 °C, in particular in a high temperature PEM fuel cell operation range of 80-120 °C, with dry reactant gases, and the cell performance was examined according to varying operation parameters. An ac impedance method was used to compare the performance at 0% RH with that at 100% RH; the results suggested that the limited proton transfer process to the Pt catalysts, mainly in the inonomer within the membrane electrode assembly (MEA) could be responsible for the performance drop. It was demonstrated that operating a fuel cell using a commercially available membrane (Nafion® 112) is feasible under certain conditions without external humidification. However, the cell performance at 0% RH decreased with increasing operation temperature and reactant gas flow rate and decreasing operation pressure. 相似文献
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A dynamic model has been developed to simulate the normal impact of an elastic-plastic adhesive sphere with a flat surface. The model combines the extended JKR theory considering both adhesion and plastic deformation with Newton's motion equation to describe the rebound behavior of the impacting particles. Theoretical expressions for velocity, contact time and restitution coefficient are obtained. The models were validated by comparison with the experimental results. Especially, a new empirical critical capture velocity expression was proposed which can be used to determine whether the particle will stick or bounce off the surface after the impact.
Copyright © 2018 American Association for Aerosol Research 相似文献
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水蒸气纯氧燃烧技术因具有高效零污染物排放的特点而备受关注,对合成气在水蒸气纯氧条件下的燃烧特性进行了实验研究。在扩散燃烧实验台上测量了H2O/O2为2.0时,燃烧室中心气体成分和火焰温度随停留时间的变化规律,分析了过量氧气系数对合成气水蒸气纯氧燃烧过程的影响。研究结果表明:过量氧气系数为0时,H2和CO的燃烧主要在前28 ms内,H2的燃烧速率较快,能够快速燃尽;CO燃烧较慢,燃烧室出口含量依然很高。过量氧气系数从0增大到10%时,CO的浓度整体降低,燃烧速率提高,燃烧前期火焰温度提高。燃烧室出口CO浓度随过量氧气系数的增加逐渐降低,氧气微过量时CO浓度迅速下降,继续增大时,燃烧室出口CO的浓度下降缓慢。 相似文献