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Development of an unsheared mixing technology by means of buoyant convection and ultrasound

利用浮力对流和超声波开发无剪切混合技术

基本信息

批准号：
11555059
负责人：
KOMORI Satoru
金额：
$ 8.77万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11555059/
关键词：
Thermal Stratification Buoyant convection Turbulent Mixing Chemical Reaction

项目摘要

The unsheared mixing technology is required to avoid the destruction of the biocell or polymer molecules in bio- and polymerization reactors. The purpose of.this study is, therefore, to develop an unsheared mixing technology by means of body forces such as buoyant convection. The effects of unstable thermal-stratification on the chemical reaction and turbulent mixing were experimentally investigated both in reacting grid-generated turbulence and in turbulent reacting mixing-layer. Experiments were carried out in unsheared neutrally-stratified, unsheared unstably stratified and sheared neutrally-stratified conditions. Instantaneous velocity and concentration were simultaneously measured using both a laser Doppler velocimeter and a laser-induced fluorescence technique. The Large-eddy simulation (LES) based on the large-eddy probability-density function model was applied to the same thermally stratified flows.The results show that the turbulent mixing is enhanced at both large and small scales by buoyancy under unstably stratified conditions and therefore the chemical reaction is strongly promoted. The mean shear acts to enhance the turbulent mixing mainly at large scales. However, the chemical reaction rate in the sheared flow is not so large compared to the unstably stratified case with the same turbulence level, since the mixing at small scales in the sheared neutrally stratified flow is weaker than that in the unsheared unstably-stratified flow. The unstable stratification is regarded as a better tool to attain the unsheared mixing since the shearing stress acting on the fluid is much weaker in the unstably stratified flow than in the sheared flow. The effects of the stratification on the turbulent mixing and chemical reaction were well estimated by the LES.

为了避免生物反应器和聚合反应器中生物细胞或聚合物分子的破坏，需要采用非剪切混合技术。的目的。因此，本研究旨在开发一种利用浮力对流等体力的非剪切混合技术。实验研究了不稳定热分层对反应网格湍流和湍流反应混合层中化学反应和湍流混合的影响。实验分别在未剪切中性分层、未剪切不稳定分层和剪切中性分层条件下进行。使用激光多普勒测速仪和激光诱导荧光技术同时测量瞬时速度和浓度。将基于大涡概率-密度函数模型的大涡模拟应用于同一热分层流。结果表明，在不稳定分层条件下，浮力在大尺度和小尺度上都增强了湍流混合，从而强烈地促进了化学反应。平均切变主要在大尺度上增强湍流混合。然而，在相同湍流度下，剪切流中的化学反应速率与不稳定分层情况相比没有那么大，因为剪切中性分层流中的小尺度混合比未剪切不稳定分层流中的弱。由于不稳定分层流动的剪切应力比剪切流动弱得多，因此不稳定分层被认为是实现非剪切混合的较好工具。分层对湍流混合和化学反应的影响用LES估计得很好。