共查询到18条相似文献,搜索用时 515 毫秒
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设计了蒸发器盘管排列密度可以改变的直接蒸发冰盘管蓄冷装置,在高、中、低三种盘管排列密度情况下,进行了蓄冷槽内载冷剂在自然对流和强制对流下的静态和动态蓄冷实验,研究了盘管排列密度和蓄冷状态对蓄冷速率的影响。结果显示:高密度系统平均蓄冷速率较低密度系统提高27.9%以上,动态系统平均蓄冷速率较静态系统提高2%左右。 相似文献
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以竖直盘管直接蒸发内融冰式冰蓄冷空调蓄冰槽内的传热过程为基础,利用热阻网络法和能量平衡建立了融冰过程的数学模型,对其融冰机理进行了理论分析。计算结果表明,融冰过程中蓄冰槽盘管出口的制冷剂温度随时间逐渐升高,但在后期存在一个因冰柱碎裂上浮导致自然对流瞬时得到强化从而引起的短时间轻微下降现象。另外,蓄冰槽内的传热系数经历了先骤然降低,然后维持稳定,最后又快速上升的过程。该现象与盘管外由于冰融化所形成的水环直径有关,水环直径越大,释放冷量的速度就越小。通过与实验数据的对比,验证了计算模型的合理性和准确性。 相似文献
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通过对蒸发式新风机组加干式风机盘管空调系统进行性能研究,改变室外相对湿度及新风量,测试新风机组性能;改变风机盘管供水温度、回风量、水流量,测试风机盘管性能。结果表明,随室外相对湿度的升高,新风机组制冷量、新风机组潜热制冷量均增加,新风机组显热制冷量降低;随新风量的增加,新风机组总制冷量、显热制冷量、潜热制冷量都增加。随风机盘管供水温度的升高,风机盘管总制冷量、显热制冷量、潜热制冷量均降低,其中,最佳供水温度为16℃,既可以保证风机盘管完全处于干工况运行,又可以保证风机盘管最大制冷量;随风机盘管回风量的增加,风机盘管总制冷量、显热制冷量增加,潜热制冷量降低;随风机盘管水流量的增加,风机盘管总制冷量、显热制冷量、潜热制冷量均增加。 相似文献
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Kohno S. Teramoto Y. Lisitsyn I.V. Katsuki S. Akiyama H. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(3):778-785
The characteristics of a plasma generated by cable plasma guns have been studied by a laser interferometer. Cable plasma guns are frequently used as a plasma source in plasma opening switches. In our experiments, the plasma source consists of eight coaxial cable guns mounted on the outer electrode of concentric coaxial electrodes. The reproducibility of the gun in subsequent shots is found to be better than 10%, and the gun-to-gun difference is less than 15%. Assuming a symmetry of eight guns, the contour maps of the electron plasma density are plotted as functions of time. The plasma density becomes maximum near the gun nozzle and near the inner coaxial electrode. The plasma density is low in the area between the coaxial electrodes during the early time of the discharge. At a later time, the plasma fills the space between the two guns more uniformly. Still photographs of the plasma luminosity show a good correspondence with the plasma density plots which were taken 10 μs after the discharge initiation. The plasma gun system is designed for use in a 400-kA inductive voltage adder with the inductive energy storage system 相似文献
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为了分析感应式脉冲放电等离子体推力器中时变电磁场作用下等离子体的放电参数分布及其随着磁场强度变化的影响,引入了利用双曲型散度清除方法的二维轴对称瞬态等离子体流动的磁流体力学数值模型.计算结果表明,随着输入能量的增加,等离子体团出现速度峰值的时刻提前,等离子体中同时存在的异号电流环对其加速具有阻滞作用.等离子体的加速效率随着磁场强度非线性增大,磁场大于某一临界值时(几何构型下峰值磁场强度大于0.45 T),有限空间情况下等离子体的加速效率获得显著提高. 相似文献
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Wind tunnel experiments on flow separation control of an Unmanned Air Vehicle by nanosecond discharge plasma aerodynamic actuation 下载免费PDF全文
Plasma flow control(PFC) is a new kind of active flow control technology, which can improve the aerodynamic performances of aircrafts remarkably. The flow separation control of an unmanned air vehicle(UAV) by nanosecond discharge plasma aerodynamic actuation(NDPAA) is investigated experimentally in this paper. Experimental results show that the applied voltages for both the nanosecond discharge and the millisecond discharge are nearly the same, but the current for nanosecond discharge(30 A) is much bigger than that for millisecond discharge(0.1 A). The flow field induced by the NDPAA is similar to a shock wave upward, and has a maximal velocity of less than 0.5 m/s. Fast heating effect for nanosecond discharge induces shock waves in the quiescent air. The lasting time of the shock waves is about 80 μs and its spread velocity is nearly 380 m/s. By using the NDPAA, the flow separation on the suction side of the UAV can be totally suppressed and the critical stall angle of attack increases from 20° to 27° with a maximal lift coefficient increment of 11.24%. The flow separation can be suppressed when the discharge voltage is larger than the threshold value, and the optimum operation frequency for the NDPAA is the one which makes the Strouhal number equal one. The NDPAA is more effective than the millisecond discharge plasma aerodynamic actuation(MDPAA) in boundary layer flow control. The main mechanism for nanosecond discharge is shock effect. Shock effect is more effective in flow control than momentum effect in high speed flow control. 相似文献
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等离子体电磁加速器可产生高速度、高密度等离子体射流而广泛应用于核物理、天体物理等领域.本文通过光电二极管、磁探头研究了不同放电电流和初始气压条件下等离子体在平行轨道加速器内的轴向运动特性.通过电流截断的方法,采用冲击摆测量了首次等离子体射流的动量.平行轨道加速器驱动电源由14级脉冲形成网络组成,每级电容为1.5μF,每级电感约为300 nH,得到振荡衰减型方波的电流波形.实验发现,电流过零时,轨道起始处一般会发生二次击穿,并形成二次轴向运动的等离子体.放电电流为10—55 kA、初始气压为200—1000 Pa时,等离子体的轴向速度为8—25 km/s.实验获得的等离子体的运动速度为雪犁模型理论结果的60%—80%,这主要是理论模型忽略了电极表面对电弧的黏滞阻力以及电极烧蚀引起的质量增加.等离子体动量与电流的平方随时间的积分成正比.放电电流为21-51.6 kA时,首次等离子体射流的动量为1.49—9.88 g·m/s.等离子体运动过程中除了受到洛伦兹力外,还会受到电极表面的黏滞阻力,造成等离子体动量约为理论结果的75%. 相似文献
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显示屏是人机交互的重要部件,当人体静电放电发生在显示屏表面时,有可能导致软硬故障。为了研究显示屏空气式静电放电实验特性,通过一个自制的装置对显示屏空气式静电放电电流和通过显示屏的位移电流进行了实验测量。研究发现:放电电流峰值随接近速度的增加而增加,上升时间随接近速度的增加而减小。在±10~±12 kV电压范围,受电弧长度的影响,上升时间增大,电流峰值变小。随着测量点与放电点之间距离的增大,位移电流波形峰值减小、上升时间增大,正极性放电峰值更大且扩散范围更广,而负极性放电上升时间增大更加明显。由位移电流波形及其分布可以计算出电荷密度。电荷密度随距离放电位置距离的增大而减小。与正极性相比,尽管负极性放电电流峰值较低,但电荷密度较高,说明负极性放电具有造成更高等级损伤风险的危害。 相似文献
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