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This paper investigates the flow field and particle trajectories in the GE90 pyrometer purge air design in order to illustrate the fouling mechanism that drives the deposition of particulates onto the lens. It is shown that the predominant flow feature within the purging system is a swirl pattern that develops at the mouth of the unit's still tube. This feature has the ability to draw contaminant particles into the still tube and thus significantly increase the likelihood of particle deposition resulting in optical fouling of the pyrometer's optics. 相似文献
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Results of a comprehensive study on the flow friction factor data collected on suspensions of solid granular particles of semolina, fly ash, and alumina having a size range of 75.5?µm ≤ dp ≤ 275?µm in air are presented. The experimental study was composed of 250 separate test cases in which airflow Reynolds number Re = UD/ν and loading ratio Mp/Ma were varied systematically covering the ranges of 50,000 ≤ Re ≤ 100,000 and 5% ≤ Mp/Ma ≤ 25%. An upward flow field with variable inclinations α of 10°, 20°, and 30° with the horizontal plane and a horizontal flow field, i.e, 0° inclination, were used to determine the influence of gravitational forces. Local static pressure gradients measured along the flow field with distance x were used to determine local air-particle friction factor fp + a, which was observed to be under the influence of particle type, Mp/Ma, Re, and flow line inclination, α. The proposed correlation for the variation of fp + a with x/D was evaluated to reach a generalized form exhibiting interactive influence of Re, Mp/Ma?, α, and particle type. 相似文献
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The aim of this paper is to investigate into flow mechanism with the help of pressure signal fluctuations analysis and modeling solids friction in case of solids–gas flows for fluidized-dense-phase pneumatic conveying of fine powders. Materials conveyed include fly ash (median particle diameter 30 µm; particle density 2300 kg m?3; loose-poured bulk density 700 kg m?3) and white powder (median particle diameter 55 µm; particle density 1600 kg m?3; loose-poured bulk density 620 kg m?3). These were conveyed in different flow regimes varying from fluidized-dense-to-dilute phase. To obtain information on the nature of flow inside pipeline, static pressure signals were studied using technique of Shannon entropy. Increase in the values of Shannon entropy along the flow direction through the straight-pipe sections were found for both the powders. However, drop occurred in the Shannon entropy values after the flow through bend(s). Change in slope of straight-pipe pneumatic conveying characteristics along the flow direction is another factor which provided indication regarding change in flow mechanisms along the flow. A new technique for modeling solids friction factor has been developed using a solids volumetric concentration and ratio of particle terminal settling velocity to superficial air velocity by replacing the conventional use of solids loading ratio and Froude number, respectively. The new model format has shown promise for predictions under diameter scale-up conditions. 相似文献
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系统测量了不同颗粒尺度纳米 SnO_2固体的内耗和模量,发现60℃附近存在一个内耗峰,对应的模量出现异常.烧结温度升高,峰高变化不明显,模量异常减弱.当烧结温度高于400℃时,模量曲线在-15℃附近出现异常,这种模量异常随烧结温度升高而加强,对应的内耗曲线出现一小峰.初步认为,60℃附近内耗峰和模量异常与纳米固体中的结构再有序有关,而-15℃处的模量异常为结构相变引起. 相似文献
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对现有吸收式换热器存在占地面积大、成本高、一次侧热水回水温度高等问题的原因进行了分析,指出问题根源在于吸收机内部存在大量“三角形”传热过程。介绍了全新的多级立式大温差发生-冷凝和蒸发-吸收基本单元,分析了其不仅能消除原吸收式换热器内不匹配的传热现象,而且做到结构紧凑的原理。由以上基本单元构建了新型吸收式换热器,称之为多级立式大温差吸收式变温器。建立了吸收式变温器的模拟分析模型,将其性能与传统单级吸收式换热器进行了比较。结果表明:吸收式变温器可制取的最低一次侧热水回水温度更低,从26℃降至20℃以下;总传热面积更小,当一次侧回水温度为26℃时,吸收式变温器的总KA(传热系数K与传热面积A的乘积)比单级吸收式换热器减小25%~32%,与此同时溶液泵总功率比单级吸收式换热器高出19%~48%,并没有显著增加。吸收式变温器相对于单级吸收式换热器具有明显性能优势。 相似文献
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竖向谐振荷载下摩擦桩的横向振动性能研究 总被引:1,自引:1,他引:1
根据弹性稳定理论研究了摩擦桩在竖向谐振荷载下的横向振动问题,在基桩小变形下导出了基桩产生参数共振频率和振幅近似计算式,讨论了桩侧土抗力、外激振频率、桩的截面几何特征、桩土阻尼等因素对基桩动力能的彤响。研究表明,基桩的动力不稳定定区域有多个,桩侧摩擦力、桩长和桩直径、桩土阻尼对桩的横向振动性能影响较大。并给出了摩擦桩的相关计算参数,提出了在实际工程中如何减小或避免基桩共振的相关措施。 相似文献
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针对多孔介质中聚合物溶液的粘弹特性难描述的问题,通过对其在多孔介质中流动特征的分析,提出将粘弹性流体在孔喉模型中流动过程分为入口收敛阶段、通过孔喉阶段和挤出孔喉阶段,并将各个阶段压降分解为粘性耗散压降和弹性拉伸压降。通过张量分析的方法,综合考虑了聚合物溶液的假塑性、弹性和弹性回复特性以及多孔介质的孔喉比和孔隙因子(喉道长度与喉道直径之比)等因素,推导了各个阶段的粘性耗散压降和弹性拉伸压降的表达式,建立了粘弹性聚合物溶液通过孔喉模型的压降数学模型。实例计算结果表明,建立粘弹性本构模型时,必须考虑通过孔喉阶段和挤出孔喉阶段以及弹性流体的弹性回复;弹性特性是造成压降损失的影响因素,在聚驱过程中不可忽略。 相似文献
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This article results from an ongoing investigation aimed at developing a new validated test-design procedure for the accurate prediction of pressure drop for dense-phase pneumatic conveying of powders. Models for combined pressure drop coefficient (“K”) for solids-gas mixture were derived using the concept of “suspension density” by using the steady-state “straight pipe” pressure drop data between two different tapping locations of the same pipe and also for two different diameter pipes. It was observed that the derived models were different depending on the location of tapping points (for the same pipe) and selected pipe diameters. The derived models were then evaluated by predicting the pressure drop for pipelines with various diameters or lengths (69 mm I.D. × 168 m, 105 mm I.D. × 168 m, 69 mm I.D. × 554 m) for the conveying of power station fly ash. A comparison between the predicted pneumatic conveying characteristics (PCC) and the experimental plots showed that the models resulted in significant over-predictions. In the second part of the article, the “system” approach of scaleup was evaluated. “Total” pipeline pressure drop characteristics for test-rig pipelines were scaled up to predict the PCC for larger/longer pipes. It was found that the “system” approach generally resulted in grossly inaccurate predictions. It was concluded that further studies are needed for a better understanding of the solids-gas flow mechanism under dense-phase conditions. 相似文献
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采用平板滑动摩擦实验研究了接触压力、滑动速度、润滑油黏度和温度对合金化热镀锌钢板摩擦系数的影响,基于粘着理论深入分析了合金化热镀锌钢板摩擦系数变化的原因,并利用扫描电镜对比分析了不同摩擦条件下的镀层磨损,进一步验证了合金化热镀锌板摩擦系数的变化规律.研究表明:镀锌板摩擦系数随着接触压力、滑动速度和润滑油黏度升高均有不同程度降低;摩擦系数随着温度的增加而快速升高.摩擦系数与接触压力的1-n次方成反比;在接触压力恒定的情况下,摩擦系数的大小由模具和镀层直接接触部分占总接触面积百分比α决定;α随接触压力、温度的增加而升高,随滑动速度、润滑油黏度的增加而降低. 相似文献
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Pandaba Patro 《Particulate Science and Technology》2014,32(1):94-103
Two fluid or Eulerian modeling incorporating the kinetic theory for granular particles and accounting for four-way coupling was performed to investigate the hydrodynamics and pressure drop characteristics of gas-solid flows in horizontal pipes. The model was validated by comparison with the experimental data found in literature and the predictions agreed reasonably well with experimental results. It was found that lift force along with particle-wall collision and specularity coefficient play significant role in the simulation of horizontal gas-solid flows. Granular temperature model by Ding and Gidaspow (1990) predicts the velocity profiles of both phases accurately. The gas-solid two-phase flow in the horizontal pipe generally has an asymmetric structure in the vertical direction, which is due to the effect of gravity. An extensive investigation was also done to study the effect of various flow parameters like particle properties, gas velocity, and solid concentration on pressure drop prediction. Finally a simplified correlation was proposed for fully developed pressure drop in horizontal gas-solid flows. Unlike the existing correlations, this correlation is valid for a wide range of particle size, pipe diameter, and mass loading. 相似文献
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本文分析讨论了绞弹机摩擦离合器结构特点和工作条件,摩擦偶的接触面积,油膜厚度和摩擦表面状态的变化是影响摩擦稳定性的主要因素,为提高摩擦稳定性,选用了合适的原材料粉末粒度和工艺参数,烧结硬度控制在30~40HB,绞弹机离合器铜基摩擦片有较好的摩擦稳定性。 相似文献
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纸基摩擦材料的国内研究进展 总被引:2,自引:0,他引:2
纸基摩擦材料是一种润滑摩擦材料,其性能优劣取决于材料组成和制备技术,反过来又影响传扭/制动的品质.评述了近年来国内纸基摩擦材料研究的现状,并对其发展趋势进行了预测. 相似文献
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目的 研究焊接速度、搅拌头旋转速度和下压量对异种铝合金搅拌摩擦焊接头力学性能的影响,找出最佳工艺参数,从而进一步提高接头的力学性能。方法 采用正交实验法对1.5 mm厚5052/6061异种铝合金搅拌摩擦焊接进行实验设计,焊接完成后,观察焊缝宏观形貌,然后将试件制成标准拉伸试样进行拉伸实验,拉伸实验完成后用扫描电镜观察焊接接头的断口形貌,最后运用极差分析法和方差分析法分别对实验结果进行分析。结果 在选取的工艺参数范围内,搅拌头旋转速度影响最大,其次是焊接速度,下压量影响最小。当焊接速度为120 mm/min、转速为1400 r/min、下压量为1.5 mm时,接头抗拉强度达到了最大值194 MPa,伸长率也达到了最大值9.62%。结论 在一定工艺参数范围内,提高焊接速度或搅拌头的旋转速度能显著提高接头的力学性能,而下压量对接头力学性能影响不显著。 相似文献
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胶乳改性摩阻材料用酚醛树脂的研究 总被引:2,自引:0,他引:2
采用丁腈、羧基丁腈、丁苯、丁吡四种胶乳改性酚醛树脂。研究改性产物的微观结构与其冲击强度和摩擦性能之间的内在关系。实验结果表明 ,胶乳改性酚醛树脂在性能上有强度大且韧性好的特点 ,尤其在摩擦性能上比纯酚醛树脂有较大的改善。通过四种胶乳改性酚醛树脂发现 ,羧基丁腈胶乳改性酚醛树脂综合性能优于其它三种胶乳改性的酚醛树脂。 相似文献