| The early 90s of last century, In order to meet sustainable development and the needs of high-tech development,Micro-chemical technology was becoming interdisciplinary field of science and technology frontier within the chemical industry. Compared with conventional chemical process, Micro-chemical technology is effective, fast, flexible, lightweight, easy control, and of highly integrated.Since the concept of the MEMS / NEMS was put forward, characteristics of two-phase flow in small channels quickly became the focus of attention all over the world. Although related papers published at home and abroad are endless,different authors use different research methods,which lead to a variety of conclusions.In order to avoid differences of experimental results in different experimental systems, characteristics of nitrogen-water two-phase flow in small rectangular channel and small triangular channel with diameter of 1.15mm are studied by visualization method in the same experimental system. the flow pattern, void fraction and pressure drop of gas-liquid two-phase flow in the two mini-channels are researched by comparison.Within the superficial liquid velocity 0.01m/s-5m/s and the superficial gas velocity 0.1m/s-30m/s, Flow patterns of nitrogen-water two-phase flow in two small non-circular cross-sectional channels were obtained by High-speed camera.In the gas-liquid two-phase flow vertical upward direction, dispersed bubble flow, slug flow, churn flow and annular flow were observed in small rectangular channel,and dispersed bubble flow, capillary bubbly flow, slug flow, elongated slug flow, churn flow and annular flow were observed in small triangular channel; By comparison, we know that the section shape of small channel has a great impact on flow pattern transition.At the same time , flow patterns of two-phase flow in small rectangular channel were studied experimentally in the horizontal direction, In the lower two-phase superficial velocity, stratified flow was observed which rarely occurs in mini-channels, and dispersed bubble flow, capillary bubbly flow, slug flow, elongated slug flow, churn flow and annular flow were also observed in this direction.For the study of void fraction, A method about calculating volume fraction of slug flow was proposed in this paper. According to nonoverlapping among slug bubbles, the flow pattern images were processed by image processing techniques, noise elimination,the edge detection,binarization,area designation and picture fills. According to the proposed three-dimensional volume of gas volume model, volume fraction was obtained.Finally, void fraction which was obtained by Digital Image Processing was used to calculate pressure drop, comparison of the calculated results with the homogeneous flow model and the separated flow model, we find that for two-phase flow in small vertical rectangular channel, the calculated results can not be predicted by the existing pressure drop model and for two-phase flow in small triangular channel, Homogeneous flow model can better predict the pressure drop characteristics within±20%. Therefore, according to experimental data, modified Chisholm model can accurately predict two-phase flow pressure drop in the small rectangular channel.
|
PDF Full Text Request