Electro-Mechanical Design and Testing of a Prototype Low-Cost Rheometer

Abstract

Rheology is a key part of modern society, but the devices used to measure complex fluids are large and expensive, making them unobtainable for individuals or small organizations. This thesis presents the first and second prototypes of an effort to design an accurate but low-cost (<$200) rheometer using fused deposition modeling 3-dimensional printing (FDM 3D printing) and off-the-shelf components. Both designs utilized a cylinder rotating concentrically inside a cylindrical cup of sample fluid. The first prototype used an encoded direct current (DC) motor to rotate at a constant rate while measuring the motor current draw to estimate torque and was able to measure a fluid viscosity standard with η = 100 Pa.s within 17% of the known value. The second prototype used a microstepping stepper motor to rotate at a constant rate while using a loadcell to measure the reaction torque on the cup used to hold the sample and was able to measure a η = 0.1 Pa.s sample within 18% of the actual value. The second prototype was also able to measure viscosity vs shear rate curves for shear-thinning fluids over shear rates from 22.6 to 3.8 s-1 all at a cost less than 0.4% that of a laboratory rheometer (DHR-3; TA Instruments) which was used to obtain the comparison data. Finally, this thesis suggests changes to improve the accuracy and versatility of future designs.