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为研究细通道内气液段塞流的流体力学性质,对细通道内空气和水两相段塞流进行了数值模拟。以直径为1.6 mm的错流T型管为模型,使用计算流体力学(CFD)研究了气液流速、液相粘度和表面张力以及入口结构对段塞形成的影响,确定了气塞长度与两相流率、液相粘度和表面张力有关。气塞长度随分散相流率和表面张力的增大而增大,随连续相流率增大而减小;液相粘度在低液速时对段塞长度有较大的影响;确定了段塞形成的挤压和剪切关联式。 相似文献
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利用相干态正交化展开方法,在非旋波近似下研究了原子的布居反转随时间的演化情况.数值计算的结果表明了,场频以及耦合强度不随时间变化时,布居反转的周期随着平均光子数的增加而增大,虚光子效应引起的快速振荡随耦合强度的增大而逐渐增大.当光场随时间做正弦调制时,光场的振幅α和角频率β对布居反转的演化都会产生很大影响.光场随时间做方波形式变化,会导致原子布居反转出现新的塌缩回复现象.无论是正弦调制还是方波调制,都会对由虚光子效应产生的小锯齿状的振荡产生影响.
关键词:
相干态正交化展开
非旋波近似
原子布居数反转 相似文献
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使用非平衡分子动力学模拟方法分析了微通道脉冲管(MPT)中由正弦速度活塞提供驱动力时He气交替振荡的微观动力学过程,并对MPT的冷却机制进行了分析.结果表明,MPT的压缩和膨胀过程之间存在一个交替的振荡过程,两个过程具有不对称的属性分布,膨胀过程具有比压缩过程更大的轴向压力梯度.当充气压力较低时,循环时间对冷端温度的影响很小,但是当充气压力高于20 bar时,冷端温度对时间较为敏感,随着时间的减少,冷端温度进一步降低,而冷端瞬时平均温度随着充气压力的增加而增加.另外,压比随着时间的减少而增加,并且明显不受充气压力的影响,但它会在MPT的轴向上产生较大的温度梯度.综上所述,在热端使用不同形式的换热器和调相元件会释放或回收额外的声功率.固定工作模式和尺寸参数的MPT具有最佳频率,可以在冷端获得最低的空载温度.仿真结果增进了对脉冲管制冷机的认识,并为微通道脉冲管制冷机的优化设计提供理论支持. 相似文献
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热声发动机驱动的脉管制冷机是一种完全无运动部件的低温制冷机,具有非常好的应用前景,本文介绍了本实验室在这方面取得的最新进展。首先我们对驻波热声发动机进行了改进设计,提高了其驱动压比,用氦气作为工质最大压比达到了1.15。在此基础上我们用其驱动同轴双向进气小孔型脉管制冷机,通过调整热声发动机的振荡频率,使之与脉管达到匹配,最终达到了84.3K的最低制冷温度,这也是目前用驻波热声发动机驱动脉管所达到的最低制冷温度。同时,在此实验过程中,一些抑制跳频的方法也得到了实验验证。 相似文献
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Peng Dai Zheng Chen Xiaohua Gan Mikhail A. Liberman 《Proceedings of the Combustion Institute》2021,38(4):5905-5913
The advancement of highly boosted internal combustion engines (ICEs) with high thermal efficiency is mainly constrained by knock and super-knock, respectively, due to the end gas autoignition and detonation development. The pressure wave propagation and reflection in a small confined space may strongly interact with local end gas autoignition, leading to combustion characteristics different from those in a large chamber or open space. The present study investigates the transient autoignition process in an iso-octane/air mixture inside a closed chamber under engine-relevant conditions. The emphasis is given to the assessment of effects of the pressure wave-wall reflection and the mechanism of extremely strong pressure oscillation typical for super-knock. It is found that the hot spot induced autoignition in a closed chamber can be greatly affected by shock/pressure wave reflection from the end wall. Different autoignition modes respectively from the hot spot and the end wall reflection are identified. A non-dimensional parameter quantifying the interplay between different length and time scales is introduced, which helps to identify different autoignition regimes including detonation development near the end wall. It is shown that detonation development from the hot spot may cause super-knock with devastating pressure oscillation. However, the detonation development from the end wall can hardly produce pressure oscillation strong enough for the super-knock. The obtained results provide a fundamental insight into the knocking mechanism in engines under highly boosted conditions. 相似文献
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Nonlinear gas oscillations excited in an open tube by a flat piston at one of the tube ends are studied. The sinusoidal piston oscillations in the shock-free wave mode are created by a vibration exciter near the first eigenfrequency. Expressions for gas pressure oscillations are obtained for a tube with a nonrounded end without a flange and secondary flow velocity components. The influence of the piston displacement amplitude on the pressure range and secondary flow velocity of gas is studied. The theoretical calculations of the gas pressure are compared with experimental data. An estimate for the velocity of particle motion along the tube axis is presented with calculated values of the secondary flow velocity. 相似文献