New Vision Probe Based On Teclecentric Photography And Its Demonstrative Applications In Multiphase Stirred Reactor

Local characteristics of dispersed phases in multiphase reactors not only decide the performance of chemical reactors,but also provide important evidence for their optimization,design and scale-up.Besides,they can help in building dynamic models for the simulation of multiphase reactors.However,nowadays measurement methods on local characteristics in multiphase reactors have their own limitations,especially for measurements in gas-liquid-solid three phase systems that contain more than one dispersed phase.A new vision probe based on telecentric photography has been proposed for two-phase and three-phase measurements,and its measurement method has also been defined.Pictures of the fluid flow at the measured position can be obtained from the probe installed on the measured reactor,according to the preset synchronous control system for the strobe light and CMOS.Particle size and its holdup are calculated with aid of the image processing software,Image-Pro Plus.Four outstanding advantages of the probe are as follows:(ⅰ)Sharp pictures with little image distortion can be obtained because of the distinctive parallel light paths from the telecentric lens;(ⅱ)The probe is slim and long so that it can be positioned everywhere in very large reactors;(ⅲ)Local characteristics such as particle(solid particle,drop or bubble)size,holdup and interfacial area in one or even more dispersed phases can be measured at the same time;(ⅳ)The limitations(e.g.transparent reactor wall)of non-invasive vision methods is overcome.Comparing with the diameter results of 100 plastic spherical particles(the diameters all around 1 mm)measured by a Vernier caliper,the size distribution measured by the probe accounts for an error about 0.92%.When measuring various particle concentrations under different expansion heights in a fluidized bed,the maximum measurement error is 13.1%and the average error is 7.1%.Therefore,the probe shows its rationality in the measurements of particles size and concentration distributions.After tests on particles with different reflectivity,irregular shaped particles and systems with more dispersed phases,the probe shows its adaptability for multiphase systems under the control system or with the help of a reflective panel in special conditions(particles with low reflectivity).The local solid holdup distribution of a solid-liquid system in a stirred tank is measured by the probe,and the results coincide with the current knowledge.The bubble size distribution measurement in a gas-liquid stirred tank turns out that the probe can even measure bubble size smaller than 100 μm,and this is an obvious advantage over other probe measurements.The bubble size and solid particle size distribution measurements in a gas-liquid-solid stirred tank indicate that the probe can be used in the measurements for multiphase systems with more than one dispersed phase.