A new type of high-pressure low-flow metering valve for continuous decompression: First experimental results on degassing of rhyodacitic melts
A new type of high-pressure low-flow metering valve for continuous decompression: First experimental results on degassing of rhyodacitic melts
复制标题
新型连续减压高压小流量计量阀：流英安岩熔体脱气首次实验结果
DOI：
10.2138/am.2011.3786
复制
发表时间：
2011
影响因子：
3.1
通讯作者：
Willi Hurkuck
中科院分区：
文献类型：
--
作者：
M. Nowak;S. Cichy;R. Botcharnikov;N. Walker;Willi Hurkuck
摘要 设计了一种新型高压低流量计量阀，用于在压力高达 500 MPa、温度高达 1500 °C 的内加热压力容器 (IHPV) 中进行连续减压实验。它由改进的高压阀和压电纳米定位系统组成。压电致动器 (1) 在纳米级上以非常高的精度静态定位阀门针，以实现无限缓慢的减压，或者 (2) 在几毫秒内完全打开和关闭阀门，以实现仅受高压管直径和高压釜系统整个体积限制的快速压降。连接到 IHPV 的阀门已成功进行测试，可模拟含挥发物岩浆的连续减压。在1050 ℃和300 MPa下合成水饱和流纹英安岩熔体，随后采用连续减压以及单步和多步减压技术，以0.28 MPa/s的积分减压速率减压至50 MPa。三种方法的实验结果显示出显着差异，对于解释天然火山岩中观察到的纹理具有重要意义。气泡数密度 (BND) 值从连续减压到多步减压再到单步减压增加了两个数量级。气泡尺寸分布 (BSD) 也存在显着差异。单步减压的 BSD 曲线显示气泡大小和种群密度的变化最大，而多步减压样本的 BSD 趋势显示气泡大小和种群密度的变化最小。连续减压样品的 BSD 表明不同尺寸的气泡比例相似。单步减压样品中通道的形成可能表明流体从过压气泡中通过熔体逸出。单步和连续减压方式代表了岩浆脱气的两种极端情况，其中气泡成核和气泡生长分别是主要过程，而多步减压则类似于中间情况。
Abstract A novel type of high-pressure low-flow metering valve has been designed for experiments at continuous decompression in internally heated pressure vessels (IHPV) at pressures up to 500 MPa and temperatures up to 1500 °C. It consists of a modified high-pressure valve coupled with a piezoelectric nanopositioning system. The piezoelectric actuator (1) positions the needle of the valve statically with very high precision on a nanometer scale for infinitesimally slow decompression and, alternatively, (2) opens and closes the valve completely, within milliseconds, to achieve a fast pressure drop only limited by the diameter of the high-pressure tubing and the entire volume of the autoclave system. The valve connected to an IHPV has been successfully tested to simulate continuous decompression of volatile-bearing magma. Water saturated rhyodacitic melt was synthesized at 1050 °C and 300 MPa and subsequently decompressed to 50 MPa at an integrated decompression rate of 0.28 MPa/s using continuous decompression as well as single-step and multi-step decompression techniques. The experimental results of the three methods show significant differences, having important implications for the interpretation of textures observed in natural volcanic rocks. Bubble number density (BND) values increase from continuous to multi-step and to single-step decompression by two orders of magnitude. Bubble size distribution (BSD) also differs significantly. The BSD curve of the singlestep decompression shows largest variation both in size and in population number density, whereas the BSD trend for the sample of multi-step decompression shows the smallest variation between size and population density of bubbles. The BSD of the continuously decompressed sample indicates similar proportions of bubbles with different size. Channel formation in the sample of single-step decompression may indicate fluid escape from over-pressurized bubbles through the melt. Singlestep and continuous decompression style represent two extreme cases of magma degassing in which bubble nucleation and bubble growth are predominant processes, respectively, whereas multi-step decompression resembles the intermediate case.