Fluid elasticity measurements from hole pressure error data

摘要

AbstractA slit die of variable heightH(0.135 in., 0.1975 in., or 0.2488 in.) widthW2.5 in., and variable lengthLe(12.0 in., 12.5 in., or 13.5 in.) has been designed and constructed for measuring the wall shear stress σwand the hole pressure errorPH. Values ofPHand σware obtained directly and rapidly on a chart recorder from three commercial pressure transducers by means of an electronic differencing technique. The reliability ofPHmeasurements is established by the excellent agreement between viscosity η values obtained from this apparatus and a rheogoniometer and by measuring negligible values ofPHfor the New tonian fluid, glycerine, for σw0 for σw≥ 800 dyn/cm2and values ofPH<0 for a low‐elasticity solution of polystyrene in dioctyl phthalate (DOP). Values ofPHare found to be independent of the distanceEof the transducers from the die exit and the die height which indicated thatPHis independent of the undisturbed wall pressurePwfor constant values of σw. Our values agree well with those measured by Higashitani for a similar Separan solution in a different slit die. Using this new slit die, it is shown thePHis sensitive to changes in molecular weight (MW) for a series of solutions of polystyrene in DOP and thatPHcould be used to monitor continuously the changes in molecular structure which occured during the mechanical degradation of a 2.0 aqueous poly(ethylene oxide) solution. The simple relation betweenPHandN1(PH= −cN1, wherecis a constant) is verified for solutions of polystyrene in DOP and aqueous Separan solutions over a large range of flow conditions (⋅ = 1000 sec−1). Becausecis found to vary slightly with polymer type, concentration, and molecular weight, a method is presented for obtainingN1dire