共查询到19条相似文献,搜索用时 125 毫秒
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槽式太阳能集热器集热性能分析 总被引:4,自引:1,他引:3
本文运用蒙特卡罗光线追踪法(MCRT)模拟了抛物槽式系统聚光特性,并与计算流体与传热有限容积方法(FVM)结合,进一步研究了吸热管内耦合传热过程.聚光特性分析中考察了光不平行夹角、几何聚光比和边界角对太阳热流密度分布的影响;耦合传热模拟中考虑了液体油热物性随温度的变化以及吸收管外管壁辐射换热.模拟计算表明;模拟计算结果与文献数据对比符合较好,验证了计算方法与模拟程序的正确性.光不平行夹角主要对热流密度圆周方向分布产生影响,使其分布平缓,对热流密度轴向分布影响不大;随着几何聚光比的增大,太阳热流衰减区的角度跨度增大;随着边界角的增大,热流密度圆周分布曲线向圆周角90°方向平移,同时热流密度极大值降低.在太阳直射强度大致相同情况下,入口流速与入口温度对接收管表面对流换热与最大温差影响很大;同时变物性对流体对流换热影响也较大. 相似文献
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由于开口处阳光能流密度的不均匀分布以及阳光的单侧投射使得太阳能腔式吸热器内部吸热管表面的热流密度分布呈现出高度得不均匀性,严重影响吸热器运行的安全可靠性。采用建立的耦合计算模型对一个饱和蒸汽太阳能腔式吸热器的热性能进行了数值模拟,提出了一种沸腾管表面反射率的优化分布方式,从而改善了吸热器内部沸腾管表面热流密度和温度分布的不均匀性. 相似文献
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本文设计搭建了带有蒸发器的两相闭式热虹吸管的气液两相流动与传热特性的可视化实验平台,制备了多种尺寸的光滑表面蒸发器,并采用电镀的方法制备了微纳米尺度的多孔表面蒸发器,研究了光滑表面蒸发器和微纳米尺度多孔表面蒸发器内工质R134a的气液两相运行状态和相变传热过程。研究结果表明:光滑表面蒸发器的流道尺寸会影响其在不同热流密度条件下的传热系数;多孔表面蒸发器的传热效果要远高于光滑表面的蒸发器,最高达到光滑表面蒸发器传热系数的4倍;不同尺寸的光滑表面蒸发器和多孔表面蒸发器热流密度从零到临界热流密度所经过的沸腾状态也存在较大差异。 相似文献
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电弧电流密度分布决定着电弧热流密度、电弧压力的分布,是了解焊接电弧物理本质,建立 焊接过程数学模型的基础.根据电弧物理的基本原理,建立了电弧电流密度在变形熔池表面 上的分布模型,定量分析了熔池表面形状对电流密度分布的影响规律.计算表明,电流密度 在电弧中心线附近呈双峰分布,在离开电弧中心线一定距离处变为单峰分布,熔池表面形状 对电流密度分布有明显的影响.基于该模型计算的焊缝几何形状与实测结果符合得较好.
关键词:
熔池表面变形
电流密度
分布模型 相似文献
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对于沸腾换热,一个主要的约束条件就是临界热流密度(Critical Heat Flux,简称CHF)。这个约束条件对沸腾换热量有一个最高值的限制。文中对矩形微槽道中的流动沸腾临界热流密度进行了实验研究。实验数据是在不同尺寸(0.15mm;0.4mm;1mm)微槽道中,在较大范围的面积质量流速和不同进口过冷度下,以去离子水为工质得到的。实验过程中发现,达到CHF时,靠近出口壁面温度会突然升高,此时传热效率迅速下降。实验数据分析结果表明:CHF随质量流量的增加而增加;进口过冷度对CHF没有明显影响;CHF随着出口干度的增加而降低。 相似文献
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基于变换热力学, 采用坐标斜变换和旋转变换得到定向传热结构单元的热导率分布表达式, 并利用隔热材料和铜分层排布实现了定向传热结构单元. 将定向传热结构单元周期性排列, 得到二维平板定向传热结构. 数值计算结果表明: 当外部热流流向该结构上表面时, 热量主要向两侧流动, 从而使上下表面保持低温. 与同厚度二氧化硅气凝胶隔热材料相比, 上表面温度降低33.3%, 下表面温度降低4.3%, 而侧面温度上升40.1%. 定向传热结构上表面温度的降低表明能够及时导走热量, 从而降低上表面的红外辐射; 下表面温度的降低说明定向传热结构比二氧化硅隔热材料具有更好的隔热效果; 上表面热量主要向两侧传输造成侧面温度急剧升高, 有利于热能的有效利用. 定向传热结构在红外隐身、热防护领域具有潜在的应用价值. 相似文献
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O. V. Vysokomornaya G. V. Kuznetsov P. A. Strizhak 《Journal of Engineering Thermophysics》2011,20(1):34-41
The plane problem of heat and mass transfer in a focused radiation flux-liquid condensed substance film-oxidizer system is
numerically solved. Peculiarities of heat and mass transfer at radiation energy absorption by a vapor-gas mixture near the
liquid surface are analyzed. The influence of the radiation density distribution in a flux and the liquid and oxidizer parameters
on the conditions of heat and mass transfer is assessed. 相似文献
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采用粒子模拟研究方法,利用PEGASUS 程序对等离子体环境下面向等离子体部件的沉积特性进行了模拟研究。结果显示部件表面连接缝隙尺寸、表面粗糙度、粒子入射的角度以及流量对沉积影响显著。在能量较小、溅射可忽略时,能量对沉积的影响很小。粗糙度越小,沉积量越小;同一种粗糙度,不同轮廓也会使沉积发生较大变化,轮廓一致的更有利于减小沉积。该模拟对研究等离子体与材料相互作用,分析瓦片缝隙尺寸、瓦片加工工艺和等离子体参数对面向等离子体部件沉积行为的影响具有重要意义。 相似文献
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V. V. Cheverda I. V. Marchuk A. L. Karchevsky E. V. Orlik O. A. Kabov 《Thermophysics and Aeromechanics》2016,23(3):415-420
Heat transfer at rivulet water flow over the constantan foil with the length of 80 mm, width of 35 mm, and thickness of 25 mm was studied experimentally. The foil surface temperature was measured by an IR-scanner. Distributions of heat flux density on the surface of the foil, where the liquid flowed, were obtained. To determine the heat flux density from the foil to liquid near the contact line, the Cauchy problem was solved for the stationary heat equation using the thermographic data. Calculation results showed that the maximal heat flux occurs in the area of the contact line and exceeds the average heat flux from the entire foil surface by several times. This is explained by the influx of heat from the periphery of foil to the rivulet due to the relatively high value of heat conductivity coefficient of the foil material and high evaporation rate in the region of the contact line. 相似文献
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The distribution of the peak temperature and energy flux on the surface of a steel anode in a pulsed high-current vacuum arc was determined by studying the spatial location of the borderline separating the region of hardened steel, produced by the pulse of energy flux to the anode, and the region of the anode which did not undergo a phase transition. The arc was run between a 14-mm-diameter stainless steel cathode and a 25-mm 4340 steel anode, separated by a 4-mm gap, with peak currents up to 1000 A and 71 ms full-width half-amplitude (FWHA) duration. The phase transition of the steel occurs at 727°C and the above-mentioned borderline is thus the geometrical location of all points which reached a peak temperature of 727°C. The peak anode surface temperature was calculated from the borderline position by approximate solution of the three-dimensional heat conduction equation. The effect of an axial magnetic field on the anode surface temperature and energy flux distribution was also studied showing that with no magnetic field the distribution had a pronounced maximum on the axis of the arc, while with the presence of a magnetic field the distribution became annular with a maximum at about mid-radius. In comparison, the shape of the distribution of the cathode mass deposited by the arc on the anode was uniform without a magnetic field. The peak of the anode temperature and the energy flux amplitude also depended on the magnetic field, first decreasing and then increasing almost linearly with it. 相似文献
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Byung Chan Eu 《Physics letters. A》1984,101(9):497-500
It is shown that the nonlinear heat flux calculated by means of the modified moment method applied to the Vlasov-Landau kinetic equation is adequate to account for the heat flux inhibition in laser-driven plasmas, if the nonlinear heat flux so obtained is used in the steady state energy balance equation to calculate the temperature profile self-consistently. Heat flux limit formulas are obtained for supersonic and subsonic fluid speeds. The flux limit factors have an upper bound of 0.14 in the case of the hydrogen plasma. This bound would be reduced, if the temperature at the sonic surface was less than the electron temperature at the critical density surface. 相似文献
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Numerical investigation on properties of attack angle for an opposing jet thermal protection system 下载免费PDF全文
The three-dimensional Navier-Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow conditions.The numerical method is validated by the relevant experiment.The flow field parameters,aerodynamic forces,and surface heat flux distributions for attack angles of 0°,2°,5°,7°,and 10° are obtained.The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters,aerodynamic force,and surface heat flux distribution of the supersonic vehicle nose-tip with an opposing jet thermal protection system.When the attack angle reaches 10°,the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system,thus the thermal protection has failed. 相似文献