Parameter Optimization And Mixing Performance Analysis Of Agitator Paddle For Pullulan Fermentation

Pullulan is a kind of polysaccharide which has important value.Because of the unique biological property,chemical property and physical property,pullulan has gas barrier property and is easy to form fiber and sheeting.Pullulan was widely used in food preservation,fruit package and food manufacturing.In the fermentation process,the more contact between aerobic bacteria and oxygen,the faster rate of reaction gets.It's important to increase the gas holdup of zymotic fluid.Zymotic fluid of pullulan is a kind of typical non-Newtonian fluid,so it has the rheological characteristics of non-Newtonian fluid,such as shear thinning.In this paper,power law model was used to fit non-Newtonian fluid.The effects of different agitators parameters on the gas holdup of zymotic fluid at different times were studied.During the fermentation,since pullulan is continually produced,it's hard to get the rheological characteristics of zymotic fluid real-timely,so the study on zymotic fluid at three time points was done.Taking the fermentation tank as the research object,the 3-D model of fermentation tank was established by PRO/E software.Through ICEM CFD,the mesh of 3-D model was obtained.Then through FLUENT,nephogram of velocity,vector graph of velocity and distribution of gas holdup was obtained,and the results were compared with experimental ones.Four parameters were selected to design orthogonal test: agitator type,speed of agitator,height of agitator and parameter model of zymotic fluid.the best combination of pararmeters and significance of factors were obtained.Meanwhile basic support for parameter optimization of agitator was provided.The main conclusions of the study are as follows:(1)Flow pattern of simulation were in good agreement with other literatures and the average relative error value of gas holdup was 5.95%.Computational fluid dynamics can be used to calculate the gas holdup of zymotic fluid.(2)The order of gas holdup from high to low is: disc turbine blade with four 45 degrees straight blade,open turbine blade with four 45 degrees straight blade,disc turbine blade with four straight blade.(3)The higher the viscosity is,the higher the gas holdup is.Average gas holdup of 24 h zymotic fluid was 5.25%,average gas holdup of 8h zymotic fluid was 7.10%,average gas holdup of 72 h zymotic fluid was 7.84%.(4)Taking the agitator type,speed of agitator and height of agitator as variables,combine orthogonal test and computational fluid dynamics.The optimized parameters are as follows: disc turbine blade with four 45 degrees straight blade,speed of agitator 700r/min,height of agitator 50 mm.