Experimental Study On The Suspension Characteristics Of Cylindrical Particles In A Stirred Tank

Stirred bioreactors are widely used in biotechnology industries such as food fermentation and biopharmaceuticals.The solid particles of biomass,such as straw and manure,can be simplified into cylindrical,disc-shaped,etc.in shape.For solid-liquid suspension operations,most scholars nowadays focus on the solid-liquid suspension of regular spherical particles,and there are very few studies on irregularly shaped non-spherical particles(such as cylindrical,discshaped).This paper studies the suspension characteristics of multiple cylindrical particles in a solid-liquid stirred tank driven by a disk paddle under laminar flow conditions.During the experiment,two high-speed cameras located on the bottom and side of the stirring tank were used to simultaneously photograph the movement of up to 8 cylindrical particles.And with the help of Matlab software to process the data of the obtained image,the image of the movement trajectory of the cylindrical particle and the information of the movement speed are obtained.The experiment examines the changes in the suspension movement of cylindrical particles from the aspects of the change of the number of particles,the difference of the aspect ratio of the particles,the difference of the material of the particles,and the size of the stirring Reynolds number.The experimental results show that as the number of cylindrical particles increases,the speed required for the particles to begin to suspend gradually decreases.The critical suspension speed NLO will not increase monotonously with the increase of the aspect ratio,but will increase within a certain range.For cylindrical particles with the same initial position,the final offset distance roffset will decrease as the total number of particles increases.The increase of the aspect ratio will weaken the trend,while the increase of the particle density will increase the reduction range,and the change of Reynolds number will basically not affect the change trend of the final offset distance roffset of the particles.The maximum peak velocity of particles at the same initial position will decrease as the number of particles increases.When the aspect ratio increases,the number of particle velocity peaks will also change.Generally speaking,there will be two velocity peaks,but there may be only one velocity peak.The increase in the aspect ratio will cause the maximum suspension height of the particles to decrease.After the number of particles increases,the maximum elevation angle β that the particles with the same initial position can reach appears to decrease.