Normal stress measurements in sheared non-Brownian suspensions
Journal of rheology
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... solutions? J. Rheol. 56, 1413Rheol. 56, (2012 Rheological and morphological study of cocontinuous polymer blends during coarsening Synopsis Measurements in a cylindrical Taylor-Couette device of the shear-induced radial normal stress in a suspension of neutrally buoyant non-Brownian (noncolloidal) spheres immersed in a Newtonian viscous liquid are reported. The radial normal stress of the fluid phase was obtained by measurement of the grid pressure P g , i.e., the liquid pressure measured behind a grid which restrained the particles from crossing. The radial component of the total stress of the suspension was obtained by measurement of the pressure, P m , behind a membrane exposed to both phases. Pressure measurements, varying linearly with the shear rate, were obtained for shear rates low enough to insure a grid pressure below a particle size dependent capillary stress. Under these experimental conditions, the membrane pressure is shown to equal the second normal stress difference, N 2 , of the suspension stress whereas the difference between the grid pressure and the total pressure, P g À P m , equals the radial normal stress of the particle phase, R p rr . The collected data show that R p rr is about 1 order of magnitude higher than the second normal stress difference of the suspension. The R p rr values obtained in this manner are independent of the particle size, and their ratio to the suspension shear stress increases quadratically with /, in the range 0 < / < 0:4. This finding, in agreement with the theoretical particle pressure prediction of Brady and Morris [J. Fluid Mech. 348, 103-139 (1997)] for small /, supports the contention that the particle phase normal stress R p rr is due to asymmetric pair interactions under dilute conditions, and may not require manybody effects. Moreover we show that the values of R p rr , normalized by the fluid shear stress, g f j_ cj with g f the suspending fluid viscosity and j_ cj the magnitude of the shear rate, are well-described by a simple analytic expression recently proposed for the particle pressure. V C 2013 The Society of Rheology. [http://dx.