Rheological Properties Of Corn Stover Slurries And Their Influence On Mixing Performance Of Helical Ribbon Impeller

It is important to understand the rheological properties of corn stover (CS) slurries for their transportation and mixing. The rheological characteristics of CS slurries were studied using ARES rheometer with parallel plate geometry. The steady rheological tests investigated the effects of CS weight fraction, particle size and alkaline microwave pretreatment on apparent viscosity of CS slurries and rheological parameters were gained by fitting the viscosity data with power-law equation, moreover the yield stresses of CS slurries were also acquired by Bingham equation. The results showed that CS slurries were highly shear-thinning fluids. The viscosity, consistency index and Bingham yield stress of CS slurries increased as CS weight fraction increased. The viscosity of CS slurries without pretreatment increased first then decreased sharply as CS particle size decreased, while that of CS slurries with milling after alkaline microwave pretreatment remained constant as CS particle size ranged from 80-100 mesh to 180-200 mesh. Compared to CS slurries without alkaline microwave pretreatment, the effect of milling after alkaline microwave pretreatment on viscosity depended on CS particle size and CS weight fraction while the process of milling before alkaline microwave pretreatment increased viscosity, consistency index of CS slurries and enhanced shear-thinning ability. The dynamic rheological tests studied the effect of alkaline microwave pretreatment on linear viscoelastic range, storage modulus and loss modulus of CS slurries. The dynamic yield stresses were compared with Bingham yield stresses. As shear-thinning ability changes due to conversion of biomass to biofuel, this work investigated the effects of changing rheological properties on mixing performance of helical ribbon impeller by using different concentration of xanthan gum(XG) and carboxyl methyl cellulose(CMC) solutions as model fluids. The results showed that power consumption constants Kpn of highly shear-thinning XG solutions increased as concentration increased, while Kpn of less shear-thinning CMC solutions decreased as concentration increased. The dimensionless mixing times of XG solutions were constant at low Reynolds number, while that of CMC solutions decreased after first increasement as Reynolds number became larger.