共查询到20条相似文献,搜索用时 15 毫秒
1.
通过对百叶窗翅片平行流蒸发器空气侧换热性能进行数值模拟,分析了翅片间距、百叶窗间距和角度对空气侧流动特性、换热性能和结露过程的影响,得到了不同情况下空气侧进出口压降、换热系数及蒸发器表面凝结水量的变化规律。研究表明:百叶窗间距增加导致空气进出口压降增大,空气侧换热系数和蒸发器表面凝水量则随之呈现先增后减的趋势;翅片间距增加造成空气侧进出口压降、换热系数和蒸发器表面凝结水量逐渐减小;百叶窗角度增加使空气侧进出口压降、换热系数和蒸发器表面凝水量逐渐增大。综合考虑,当压降在可以接受的范围内时,可考虑选择较小的翅片间距、较大的百叶窗角度,百叶窗间距范围在1.4mm~1.6mm间为佳。 相似文献
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利用落塔设施创造的短时间微重力条件, 研究了不同尺寸的正方形和三角形截面的毛细管中的流体在微重力条件下的流动行为, 并与圆形毛细管中的毛细流动进行了对比, 总结出了毛细管尺寸和截面形状对界面张力主导的毛细流动行为的影响规律. 结果显示, 对于同样形状的毛细管, 其尺寸对于毛细流动的影响规律基本相同; 而对于不同的截面形状, 方形管和三角形管都与截面积小得多的圆形管有一定的类似性. 相关结果对于深入理解不同条件下的界面张力主导的毛细流动特性, 以及在空间微重力条件下通过改变毛细管的形状来实现流速和流量的独 立控制等方面都具有明显的现实意义.
关键词:
微重力
毛细流动
毛细管形状 相似文献
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利用落塔的短时微重力条件, 实验研究了与容器连通的毛细管中的流体在微重力条件下的毛细流动过程, 并通过理论分析建立了相应的毛细管中弯月液面高度随时间变化的微分方程. 结果表明, 对于不同的接触角和不同的容器/毛细管参数, 由建立的理论公式得到的数值解结果都与实验结果在定量上较为一致. 此外, 实验中发现, 改变乙醇和去离子水混合液的比例可以明显地改变接触角参数, 但对毛细流动的影响很小, 建立的理论公式也对这一现象给出了合理的解释. 该研究对于预测和分析微流道及空间微重力条件下的毛细流动行为具有明显的应用价值. 相似文献
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Effect of cavity location on combustion flow field of integrated hypersonic vehicle in near space 总被引:2,自引:0,他引:2
Abstract
The cavity has been widely employed as the flame holder to prolong the residence time of fuel in supersonic flows since it improves the combustion efficiency in the scramjet combustor, and also imposes additional drag on the engine. In this paper, the two-dimensional coupled implicit Reynolds Average Navier–Stokes equations, the RNG k–ε turbulence model and the finite-rate/eddy-dissipation reaction model have been employed to numerically simulate the combustion flow field of an integrated hypersonic vehicle. The effect of cavity location on the combustion flow field of the vehicle has been investigated, and the fuel, namely hydrogen, was injected upstream of the cavity on the walls of the first stage combustor. The obtained results show that the viscous lift force, drag force and pitching moment of the vehicle are nearly unchanged by varying the cavity location over the location range and designs considered in this article, namely the configurations with single cavity, double cavities in tandem and double cavities in parallel. The variation of the fuel injection strategy affects the separation of the boundary layer, and the viscous effect on the drag force of the vehicle is remarkable, but the viscous effects on the lift force and the pitching moment are both small and they can be neglected in the design process of hypersonic vehicles. In addition to varying the location of the cavities, three fuel injection configurations were considered. It was found that one particular case can restrict the inlet unstart for the scramjet engine. 相似文献5.
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本文研究雷诺数(Re)对圆形渐缩喷嘴湍流射流的影响.实验在射流出口雷诺数为 Re = 4050—20100 的范围内进行,分别测量了射流出口、中心线的平均及湍流流场以及部分径向剖面速度分布.所有测量均采用单热线恒温热线风速仪进行高频采样,所测流场范围在轴向上为 0—30d(这里d为射流出口直径).虽然出口速度分布均为"平顶帽"形,但测量结果依然反映出Re对射流出口以及下游流场有强烈的影响.当Re小于临界值(~10000)时
关键词:
雷诺数
圆形射流
热线风速仪 相似文献
9.
《Composite Interfaces》2013,20(5):433-444
Interfacial degradation behavior of E-glass cloth reinforced vinyl ester resin under acidic conditions has been investigated. Specimens with different surface treatment conditions were prepared. Mode I fracture toughness tests were performed using DCB specimen, and the effect of surface treatment condition and immersion time on the crack propagation behavior is discussed. The crack propagation behavior changes as a function of the condition of the silane coupling agent and the immersion time due to the degradation of the interphase. A technique is proposed to evaluate the interfacial property. The change of fracture toughness of interphase and resin as a function of immersion time is studied by the crack propagation behavior and the fracture toughness of interphase and resin evaluated by this technique. The fracture toughness of interphase decreases rapidly with immersion in acidic solution. 相似文献
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The purpose of the present paper is to investigate the flow and heat transfer of a double fractional Maxwell fluid with a second order slip model. The fractional governing equations are solved numerically by using the finite difference method. By comparing the analytical solutions of special boundary conditions, the validity of the present numerical method is examined. The effects of the two slip parameters and the fractional parameters on the velocity and temperature distribution are presented graphically and discussed. The results reveal that the fractional Maxwell fluid exhibits a stronger viscosity or elasticity for different fractional parameters, and the oscillation phenomenon will gradually decrease as expected with an increase in slip parameters. 相似文献
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通过实验研究出口雷诺数对平面湍流射流自保持性的影响. 测量的射流来自相同的喷嘴但不同的雷诺数Re(≡Ujh/ν,其中Uj是出口平均速度、h是窄缝出口的厚度和ν是黏性系数),其变化范围是Re=4582—57735.所得的数据包括沿轴线的平均速度、湍流强度、积分尺度、高阶矩和能谱. 实验发现,随着Re的增大,平面射流发展减慢,平均速度和湍流强
关键词:
平面射流
雷诺数
自保持性 相似文献
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Yang-Hui Hu 《中国物理 B》2023,32(1):18901-018901
Building exit as a bottleneck structure is the last and the most congested stage in building evacuation. It is well known that obstacles at the exit affect the evacuation process, but few researchers pay attention to the effect of stationary pedestrians (the elderly with slow speed, the injured, and the static evacuation guide) as obstacles at the exit on the evacuation process. This paper explores the influence of the presence of a stationary pedestrian as an obstacle at the exit on the evacuation from experiments and simulations. We use a software, Pathfinder, based on the agent-based model to study the effect of ratios of exit width ($D$) to distance ($d$) between the static pedestrian and the exit, the asymmetric structure by shifting the static pedestrian upward, and types of obstacles on evacuation. Results show that the evacuation time of scenes with a static pedestrian is longer than that of scenes with an obstacle due to the unexpected hindering effect of the static pedestrian. Different ratios of $D/d$ have different effects on evacuation efficiency. Among the five $D/d$ ratios in this paper, the evacuation efficiency is the largest when $d$ is equal to $0.75D$, and the existence of the static pedestrian has a positive impact on evacuation in this condition. The influence of the asymmetric structure of the static pedestrian on evacuation efficiency is affected by $D/d$. This study can provide a theoretical basis for crowd management and evacuation plan near the exit of complex buildings and facilities. 相似文献
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The effect of finite temperature on compositeness condition in the Yukawa theory is investigated in 2 and 3 space-time dimensions. It is shown that this condition remains satisfied at all temperatures in these dimensions. These findings are contrary to the results obtained by Kikuchi and Takahashi. According to them the compositeness condition has a solution at all temperatures in 2 dimensions while in 3 dimensions it has a solution at low temperature and there is no solution at high temperature. 相似文献
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XU MingTian 《中国科学:物理学 力学 天文学(英文版)》2015,(4):80-88
In this paper,based on the mean field dynamo theory,the influence of the electromagnetic boundary condition on the dynamo actions driven by the small scale turbulent flows in a cylindrical vessel is investigated by the integral equation approach.The numerical results show that the increase of the electrical conductivity or magnetic permeability of the walls of the cylindrical vessel can reduce the critical magnetic Reynolds number.Furthermore,the critical magnetic Reynolds number is more sensitive to the varying electrical conductivity of the end wall or magnetic permeability of the side wall.For the anisotropic dynamo which is the mean field model of the Karlsruhe experiment,when the relative electrical conductivity of the side wall or the relative magnetic permeability of the end wall is less than some critical value,the m=1(m is the azimuthal wave number)magnetic mode is the dominant mode,otherwise the m=0 mode predominates the excited magnetic field.Therefore,by changing the material of the walls of the cylindrical vessel,one can select the magnetic mode excited by the anisotropic dynamo. 相似文献
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通过对P沟道MOS场效应管IRF9530和N沟道MOS场效应管IRF540N的X射线和钴源γ射线的辐照对比研究,发现两种场效应管阈值电压变化随吸收剂量近似成一阶指数衰减关系。产生这种现象的原因是场效应管氧化物中的空间俘获电荷与吸收剂量近似成线性变化,对阈值电压变化和吸收剂量有近似线性的改变;而界面态对空间电荷有补偿作用,其对阈值电压的改变与吸收剂量有近似成二次方的关系。 相似文献
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研制了一套能够同时测量线缆皮线和芯线感应电流的试验系统,研究自然闪电条件下敷地线缆的耦合问题。结果表明:不同位置处的线缆皮线感应电流波形基本一致,但幅值存在一定差异,说明感应电流空间分布不均匀; 所测线缆芯线和皮线感应电流的时域波形和频谱比较相似,能量集中在1 kHz~1 MHz之间; 正负地闪芯线感应电压波形均为单一脉冲型,波形持续时间10~49 μs; 正地闪线缆感应电压的幅值范围及幅值平均值都大于负地闪相应结果,说明正地闪产生的线缆耦合作用大于负地闪; 不同雷电过程的线缆感应电压幅值与磁感应强度有较小的相关性,而同一雷电过程则基本成线性关系; 正地闪线缆感应电压波形持续时间、半峰值宽度、10%~90%上升时间的范围及均值都比负地闪的要大。 相似文献
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The effect of magnetic fields on out-of-plane orientations of liquid crystalline polymers (LCPs) under simple shear flows is numerically analyzed using the Doi–Hess equation. The evolution equation for the probability distribution function of the LCP molecules is directly solved without any approximation closure. The initial director is parallel to the vorticity direction. Two cases of the magnetic fields are considered (1) the magnetic field parallel to the flow direction, and (2) the magnetic field parallel to the velocity gradient direction. For both cases a log-rolling orientation state is detected at low shear rates. However, the director is quickly aligned along the direction of magnetic fields because of the deformation of molecules. The field affects on the scalar order parameter rather than the major orientation direction for the magnetic field parallel to the flow direction. On the other hand regarding the magnetic field along the vorticity gradient direction, the effect of the magnetic field is more remarkable on the major orientation in comparison with the effect on the scalar order parameter. Also it is be found that the order parameter is increased obviously with increasing the magnetic fields. It is an efficient way to improve the performance of LCP materials. 相似文献
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光学系统的波面不均匀性与MTF理论值的计算精度 总被引:2,自引:1,他引:2
在计算光学系统的MTF值时,无论采用什么方法,一般都假设光能在光学系统的出射波面上的分布是均匀的,即假设瞳函数的振幅为常数,但由于实际光学系统存在光阑像差,出射波面上的光能分布是非均匀的,故上述假设给MTF的计算带来了误差。本文在计算MTF值时,推导出了出射波面的相对能量公式,并通过典型光学系统的实际比较计算,分析了出射波面光能分布的不均匀程度的大小与MTF值计算精度的关系。最后得出结论:光学系统的波面不均匀性对MTF理论值的计算精度的影响是可观的,当光学系统的MTF值计算精度要求较高时,不能近似处理。 相似文献