29E-15 |
Effect of viscoelasticity on pressure profile measurements during mixing in a continuous twin screw mixer |
R. K. CONNELLY and J. L. Kokini. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, Cook Campus, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Earlier 2-D mixer simulations showed that the pressure was extremely sensitive to changes in the level of viscoelasticity in a viscous fluid even when the fluid viscosity was constant (Connelly & Kokini, 2003). Pressure measurement at the barrel surface is easily accomplished and is representative of the entire profile. When the probes are properly positioned, it is also possible to get an estimate of single screw pressure profiles that have been simulated using viscoelastic fluid models. Using viscous Newtonian corn syrup and a constant viscosity, viscoelastic corn syrup/polyacrylamide mixture, the effect of viscoelasticity on the pressure wave produced by the turning of the blades is explored in a fully filled continuous twin screw mixer. Two pressure probes were positioned at the extreme left side of the barrel in the same z plane, combining to give a full 180 degree profile when the left blade cuts off a portion of the mixing region from the rest of the mixer. The data acquisition system continuously collected pressure, temperature and blade position data for two minutes at a mixer speed of 100 rpm. The experimental fluids were Newtonian corn syrup (Corn Products Inc.) that has a viscosity of 5400 cp at 48C with and without 100 ppm of 5-6,000,000 MW polyacrylamide (Scientific Polymer Products, Ontario, NY) to add viscoelasticity. The discharge gate was almost completely closed in order to increase the pressure drop in the z direction and insure complete fill. The data reveals the effect of pressure on the experimental pressure profile. The experimental results are also directly compared to numerical simulations conducted in the same manner as those in Connelly & Kokini (2003) using the current experimental conditions. The results of simulations can be used to design experiments that both validate the simulations and confirm conclusions revealed through the use of simulation.
Session 29E, Food Engineering: Transport processes and kinetics
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