Study On The Heat Transfer Of Xanthan Gum Bioreactor By Numerical Simulation

Heat and mass transfer of high viscosity pseudoplastic fluids in stirred tank reactorare very complicated. Current theories are difficult to reveal the nature of two processes.So far, with regard to heat transfer, dimensionless number equations are most derived byregression of a great quantity of experimental data. But calculated values differ greatlyfrom experimental values, and the regression equation is not applicable to all fluids. Formass transfer, the experimental apparatus of measuring the flow field is very expensive,and the measurement work is quite a waste of time, labor, money and materials.Sometimes, the flow fields within the reactor cannot be measured restrict byenvironmental constraints.Computational Fluid Dynamics (CFD) method utilize momentum, mass, energyconservation equation and experimental environment to establish mathematical model,simulate and restore various kinds of real processes by numerical calculation, and thusobtain all kinds of the field distributions directly related to the real ones. Using CFDsoftware, mass and heat transfer processes in the reactor can be directly visualized and itsgeneration mechanism can also be further analyzed, providing guidance for the experimentand saving experimental time and resources.The mixed and heat transfer characteristics of maxblend impeller in highly viscouspseudoplastic fluid,1.0wt%xanthan gum solution, are studied by CFD method in thispaper. The distribution of flow field, dead zone, temperature field, shear rate and apparentviscosity in the reactor are analyzed by numerical simulation. Furthermore, the mass andheat transfer processes of maxblend impeller in the aqueous solution of xanthan gum iscompared with those of the combination impeller. Exploringly, the heat pipe is introducedinto the reactor in the research. The heat and mass transfer mathematical model oftraditional and heat pipe bioreactors are established. The effects of heat pipe for mass andheat transfer process in the reactor were simulated to solve the heat transfer problems ofxanthan gum fermentation process.The results show that: there are all formed the "two-cycle" flow type structure in the reactor when installing maxblend impeller and the combination impeller, which forming agood subject in circulation flow in the kettle. But the maxblend impeller can reduce theboundary layer of reactor wall and bottom region effectively. So, along with the increaseof power consumption of unit volume, the temperature in the reactor is lower and moreevenly distributed. All those shows the maxblend impeller enhance the heat transfer whilehas an obvious advantages in mass transfer process. The use of heat pipe greatly improvesthe heat transfer performance in the reactor, resulting in the overall temperature decreasedsignificantly.This shows that the CFD method can be used in the study of the fermentation heat ofxanthan gum and other high viscosity of non-Newtonian fluid cannot be removed timely.It can be applied to guide the industrial production of xanthan gum and the selection andoptimization of paddle in the reactor.