Effect of fiber length, flow rate, and concentration on velocity profiles of cellulosic fiber suspensions

Abstract

Conversion of cellulosic biomass to useful products involves pumping and mixing of fiber suspensions. Depending upon the concentration, the fibers may entangle to form flocs and networks. The fibers in these suspensions may settle both as individual fibers and fiber flocs. The flow of cellulosic suspensions has been previously modeled using generalized Newtonian rheological models. Under some flow conditions, those models do not apply due to strong gravitational effects that result in concentration gradients. Magnetic resonance flow imaging was used to obtain velocity profiles of fiber suspensions in horizontal pipe flow as a function of fiber length, concentration, and flow rates. Measures of flatness and asymmetry are used to characterize the shape of the velocity profiles. The largest asymmetry is found near a crowding number of roughly three. At higher crowding numbers, the velocity profiles tended to become flat, more symmetric, and pressure drops per unit length depend strongly on concentration.