Li Chi-Pei, Chen Sheng-Fu, Lo Chi-Wen, Lu Po-Chien
Department of Water Resources and Environmental Engineering, Tamkang University, 151 Ying-Chuan Road, Tamsui, New Taipei 251, Taiwan.
J Artif Organs. 2012 Mar;15(1):57-64. doi: 10.1007/s10047-011-0612-6. Epub 2011 Oct 21.
Bubble cavitation occurs in the flow field when local pressure drops below vapor pressure. One hypothesis states that low-pressure regions in vortices created by instantaneous valve closure and occluder rebound promote bubble formation. To quantitatively analyze the role of vortices in cavitation, we applied particle image velocimetry (PIV) to reduce the instantaneous fields into plane flow that contains information about vortex core radius, maximum tangential velocity, circulation strength, and pressure drop. Assuming symmetrical flow along the center of the St. Jude Medical 25-mm valve, flow fields downstream of the closing valve were measured using PIV in the mitral position of a circulatory mock loop. Flow measurements were made during successive time phases immediately following the impact of the occluder with the housing (O/H impact) at valve closing. The velocity profile near the vortex core clearly shows a typical Rankine vortex. The vortex strength reaches maximum immediately after closure and rapidly decreases at about 10 ms, indicating viscous dissipation; vortex strength also intensifies with rising pulse rate. The maximum pressure drop at the vortex center is approximately 20 mmHg, an insignificant drop relative to atmospheric vapor pressures, which implies vortices play a minor role in cavitation formation.
当局部压力降至蒸汽压以下时，流场中会发生气泡空化现象。一种假设认为，瞬时阀门关闭和封堵器回弹产生的涡流中的低压区域会促进气泡形成。为了定量分析涡流在空化中的作用，我们应用粒子图像测速技术（PIV）将瞬时流场简化为平面流，该平面流包含有关涡核半径、最大切向速度、环流强度和压降的信息。假设沿圣犹达医疗25毫米瓣膜中心的流动是对称的，在循环模拟回路的二尖瓣位置使用PIV测量关闭瓣膜下游的流场。在封堵器与外壳撞击（O/H撞击）后紧接着的连续时间阶段进行流量测量。涡核附近的速度剖面清楚地显示出典型的兰金涡。涡流强度在关闭后立即达到最大值，并在约10毫秒时迅速下降，表明粘性耗散；涡流强度也随着脉率的增加而增强。涡旋中心的最大压降约为20 mmHg，相对于大气蒸汽压而言降幅不大，这意味着涡流在空化形成中起的作用较小。
