Numerical simulations of counter-current two-phase flow experiments in a PWR hot leg model using an interfacial area density model

In order to improve the understanding of counter-current two-phase flows and to validate new physical models, CFD simulations of 1/3rd scale model of the hot leg of a German Konvoi PWR with rectangular cross section was performed. Selected counter-current flow limitation (CCFL) experiments at the Helmholtz–Zentrum Dresden–Rossendorf (HZDR) were calculated with ANSYS CFX 12.1 using the multi-fluid Euler–Euler modeling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a k-ω turbulence model for each phase. In the simulation, the surface drag was approached by a new correlation inside the Algebraic Interfacial Area Density (AIAD) model. The AIAD model allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. The goal is to provide an easy usable AIAD framework for all Code users, with the possibility of the implementation of their own correlations.     

脉宽调制亮度调节方式下冷阴极荧光灯性能的实验研究

从电学的角度看,由于冷阴极荧光灯(Cold cathode fluorescent lamp,CCFL)具有十分复杂的阻抗特性,例如,灯管的阻抗几乎随工作电流的增加而减小,因此对其亮度进行调节也十分困难,尤其是大亮度调节比的场合。在对逆变电路进行优良设计并进行同步调光的前提下,脉宽调制(Pulse width modulating,PWM)可以实现高达2000:1的亮度调节比。这种大范围亮度调节特性,可以满足机载显示器的亮度调节性能要求。另一方面,CCFL的亮度输出与PWM的占空比之间具有良好的线性关系。此外,还不会对CCFL的寿命造成任何的影响,从而保证了军用显示器件的可靠性。实验结果表明,PWM方式可以很好地调节多管并列式背光灯组的亮度,这是其他调节方式无法做到的。     

冷阴极荧光灯色度测量的实验设计

本文介绍了将冷阴极荧光灯彩色光源引入色度测量物理实验教学,并给出了测量该光源色度的实验方法．