内嵌螺管式冷冻沉积物采样器的研制及其性能研究

发布时间：2018-04-22 23:04

  本文选题：沉积物 + 采样器　； 参考：《安徽工业大学》2015年硕士论文

【摘要】：了解沉积物是认识环境变迁历史和预测未来环境变化的基础。作为流域地表物质迁移的主要宿体,湖泊较差的流动性,使得其中的环境物质沉积相对稳定,沉积物的层次结构中蕴含了丰富的环境信息,因而成为目前诸多自然环境变迁记录研究的热点。由于现有的采样器通常破坏了沉积物的原始层序,导致了对沉积时期研究的准确度普遍偏低。本文总结了现有沉积物采样器的不足,依据结构功能原理,设计了内嵌螺管式冷冻沉积物采样器的详细结构并制作出了样机。基于Fluent软件对该采样器的冻结规律进行了数值模拟,通过室内试验与数值模拟结果进行了对照,检测了该采样器的基本性能,并制定了野外采样的操作方案。样机的基本结构参数为:采样管长1000mm,内径137mm;冷源宽度250mm,冷源下边界距采样管口距离200mm。采样管材质为201不锈钢,螺旋冷冻管材质为铜管,防水保护套管材质为UPVC给水管。对采样器的冻结规律进行了数值模拟,得出了模拟条件下采样管腔近壁面呈弓形,中心处呈“H”形的对称温度分布特征以及样品的对称弓形相变特征。获取了样品理论闭合点的位置,并绘制出样品轴向闭合高度随时间的变化曲线。开展清水试验并与数值模拟的结果进行了对照,得出理论闭合点冻结过程经历了“匀速期”、“平台期”、“跌落期”和“减速期”,各时段占比依次为22.2%、44.4%、11.1%和22.2%,其中“平台期”对整个冷冻周期起控制作用。开展了室内模拟湖泊沉积物采样试验,试验进行了8小时,从初始水温为12.7℃的环境中采集到了界面清晰的沉积物及其上覆水冻结样品。其中沉积物厚164.8mm,上覆水厚151.4mm,样品直径137mm,表明了该采样器实施冷冻采样可行。进行了含水率与冷冻膨胀率以及融化收缩率的关系试验,并制定了野外采样操作方案。含水率与冷冻膨胀率的相关系数为0.81,与融化收缩率的相关系数为0.97。沉积物样品的冷冻膨胀率小于5%而融化收缩率总体介于10%到40%之间。
[Abstract]:Understanding sediment is the basis of understanding the history of environmental change and predicting future environmental change. As the main host of surface matter migration, the poor fluidity of lakes makes the deposition of environmental materials relatively stable, and the stratification of sediments contains rich environmental information. As a result, it has become a hot spot in the research of many natural environment change records. Because the existing samplers usually destroy the original sequence of sediments, the accuracy of the study on sedimentary period is generally low. In this paper, the shortcomings of the existing sediment sampler are summarized. According to the principle of structure and function, the detailed structure of the snail tube frozen sediment sampler is designed and a prototype is made. The freezing law of the sampler is numerically simulated based on Fluent software. The basic performance of the sampler is tested by comparing the results of indoor test and numerical simulation, and the operation scheme of field sampling is worked out. The basic structural parameters of the prototype are as follows: the length of the sampling tube is 1000mm, the inner diameter is 137mm, the width of the cold source is 250mm, and the distance between the lower boundary of the cold source and the sampling port is 200mmm. The sample tube is 201 stainless steel, the screw freezing tube is copper tube, the waterproof protective casing is UPVC feed pipe. The freezing law of the sampler is numerically simulated, and the symmetrical temperature distribution characteristics of the sampling tube cavity near the wall, the "H" shape at the center and the symmetrical arch phase transition of the sample are obtained under the simulated conditions. The position of the theoretical closure point of the sample was obtained and the curve of the axial closure height of the sample with time was plotted. The results of clean water test and numerical simulation show that the freezing process of the theoretical closed point has experienced "constant velocity period", "platform period", "drop period" and "deceleration period". The proportion of each period was 22.2and 44.4%, respectively, and the "platform period" controlled the whole freezing cycle. The indoor simulated lake sediment sampling test was carried out, and the samples with clear interface and frozen water were collected from the initial water temperature of 12.7 鈩，

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