| In gas-liquid two-phase flow,bubbles,as dispersed phase,are bridges and bonds connecting micro-scale and macro-scale.Bubble size characteristics are the key factors affecting mass transfer and heat transfer efficiency.Reducing bubble diameter,shortening mass transfer distance and increasing gas-liquid mass transfer area are effective means to improve gas-liquid two-phase heat transfer and mass transfer efficiency.In this paper,the cutting behavior of a single bubble rising process is experimentally measured and numerically simulated based on the bubbles affecting mass transfer and heat transfer efficiency.In this paper,the cutting behavior of a single bubble rising process is experimentally measured and numerically simulated based on the bubbles affecting mass transfer and heat transfer efficiency.By installing a bubble breaker on the sieve tray tower,the changes of bubble characteristics before and after installation were explored.Under the pure glycerol system in rectangular PMMA bubble cell,the bubble cutting behavior was measured by bubble flow visualization experiment.The changes of bubble rising speed and bubble surface area before and after cutting were compared.The numerical simulation of the cutting behavior during the rising process of bubbles was carried out by using ANSYS software.The experimental and simulation results show that the rising speed of the two sub-bubbles is less than that of the mother bubbles,and the sum of the surface areas of the two sub-bubbles is larger than that of the mother bubbles.In the experiment,the rising speed of the mother bubble is about6.7 cm/s,while the rising speed of the two sub-bubbles is only 5.4 cm/s and 4.1 cm/s.The surface area of the mother bubbble is 0.82 cm~2,while the sum of the surface areas of the two sub-bubbles is 1.11 cm~2.Three kinds of bubble-breaking components with apertures of 250,425 and 600microns were installed in the self-designed experimental device of sieve tray tower.The changes of pressure drop,gas holdup and bubble characteristics of the wet plate before and after installation were compared.The results show that the smaller the pore size,the higher the average wet tray pressure drop is,and the gas holdup of the sieve plate with 425 and 600 micron bubble-breaking components is 4.5-8 percentage points higher than that of the ordinary sieve tray and the sieve tray with 250 micron bubble-breaking components.The average diameter of bubbles on the sieve tray of the bubble-breaking components with installed apertures of 425 and 600 microns is only2.357 cm and 3.261 cm,while the average diameter of bubbles on the ordinary sieve tray is 43.57 cm.Operating conditions with apparent gas velocity of 0.31m/s,the maximum rising speed of bubbles on the sieve tray of the bubble-breaking components with aperture 425 and 600 microns is only 13.25 cm/s and 15 cm/s,while the maximum rising speed of bubbles on the ordinary sieve plate is 21 cm/s.The radial distribution of bubbles before and after installation of the bubble-breaking components is basically similar,showing a trend of decreasing the diameter of bubbles from the center of the tower to the wall of the tower.The Euler-Euler two-phase flow model was used to simulate the changes of gas-liquid flow field on the tray before and after adding bubble-breaking components.The simulation results show that:The gas holdup of the sieve tray with the bubble-breaking components assembly is obviously higher than that of the ordinary sieve plate,and the gas holdup distribution is more uniform.In addition,the non-uniform distribution of gas velocity on the sieve tray was improved by the bubble-breaking components,and the backmixing area and entrainment phenomenon of mist were reduced accordingly.The results of this study can provide theoretical guidance for enhancing mass and heat transfer. |
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