ABSTRACT

Wire-mesh sensors (WMSs) have been used to measure various characteristics of bubbles, such as volume fraction, size and velocity. The WMS used in this study consists of a grid of nine by nine wires arranged in an orthogonal shape. Transmitter wires are activated sequentially and receiver wires pick up the electric signals and convert them to a current. Multiphase flow, the electric conductivity of each phase, allows characteristic electrical signals to flow and from this information the volume fraction can be calculated. However, deformation of bubbles and the intrusive effects of wires have yet to be considered. To address these issues, we conducted numerical simulations using commercial software. The actual behavior of a single bubble was considered to calculate the electrostatic and two-phase flow simultaneously. First, a bubble was considered stationary in a spherical shape at the center of the WMS. A user-defined function was used to calculate the governing equation of the electric field and then activate electric signals on the transmitter wires. The numerical results were compared with reference values, and the error of a volume fraction was quantified. After that, we considered a bubble rising without a change of shape in the pseudo-dynamic process. However, for the dynamic process, a volume of fluid model was added and a bubble interface that reflects its actual movement was considered. A comparison between the pseudo-dynamic and dynamic processes was conducted using the same positional relations between the wire and bubble surface. When the bubble contacted with and then separated from the wire, differences in the received signal and an overshooting phenomenon were observed owing to deformation of the bubble. Also, the range of locations where the bubble would begin to affect the electric field because of the flattened shape of the bubble was observed.

摘要

丝网传感器（WMS）已用于测量气泡的各种特征，例如体积分数，大小和速度。本研究中使用的WMS由九乘九的线以正交形状排列的网格组成。发射器导线依次激活，接收器导线拾取电信号并将其转换为电流。多相流（各相的电导率）允许特征性的电信号流过，并且可以根据此信息计算体积分数。然而，气泡的变形和金属丝的侵入效应尚未被考虑。为了解决这些问题，我们使用商业软件进行了数值模拟。考虑单个气泡的实际行为，可以同时计算静电和两相流。第一的，在WMS的中心，气泡被认为是球形固定的。使用用户定义的函数来计算电场的控制方程，然后激活发射器导线上的电信号。将数值结果与参考值进行比较，并量化体积分数的误差。此后，我们考虑了在拟动力过程中气泡上升而形状没有变化的情况。但是，对于动态过程，添加了一定体积的流体模型，并考虑了反映其实际运动的气泡界面。使用金属丝和气泡表面之间的相同位置关系，对拟动态过程和动态过程进行了比较。当气泡与金属丝接触然后脱离时，由于气泡的变形，观察到接收信号的差异和超调现象。而且，观察到由于气泡的扁平形状气泡将开始影响电场的位置范围。