Arde Barinco Reversible Homogenizing Laboratory Mixer

Tests were carried out with RealShear™ F-400 and F-8K shear stress sensors to measure the shear stress at the inner wall of the stator in a CJ-4E Arde Barinco reversible homogenizing mixer. This kind of mixer can be set for either downward flow or upward flow into a baffle plate. The sensor was attached to the stator with a custom 1/4”-80 threaded hole (see photos) such that the sensor face was flush with the inner wall of the stator with a small gap separating it from the blades of the impeller. Presented are plots of the time-dependent shear stress signal (in glycerol) showing the ability of the sensor to resolve individual passes of the impeller blades. Data such as this can be used to ensure proper processing or evaluate new mixer designs.

Mixing head of the Arde Barinco reversible mixer with sensor attached to the cylindrical stator element. Inset shows the head with the stator removed, revealing the impeller blades.

Shear stress signal as mixer is turned on and off.

Shear stress signal for steady state operation. The peaks in the signal represent moments when the impeller blade passes by the sensor face.

Close-up of the shear stress signal as the mixer is turned on. The increasing frequency of the impeller rotation can be seen.

Close-up of the shear stress signal as the mixer is turned off.

Below are plots of the dependence of shear stress on the rotational rate of the impeller for both glycerol (Newtonian) and shampoo (shear-thinning).

Shear stress versus RPM for glycerol in the reversible mixer. Positive values of RPM indicate upward flow and vice versa.

Shear stress versus RPM for shampoo in the reversible mixer. Positive values of RPM indicate upward flow and vice versa.

Two-Disk Simulated Mixer

RealShear™ sensors have been tested in a rotating disk experimental setup at Lenterra. The sensor is mounted vertically in a threaded hole in a 9″ diameter stationary disk such that the face of the sensor is flush with the bottom surface of the disk. A second disk is below the first, separated from it by a variable distance (several millimeters), and is attached to a rotating shaft. This second disk has two raised portions (teeth) located opposite from one another on the disk, are 30 and 67 degrees in angular extent, and are 0.9 and 1.2 mm from the upper stationary disk, respectively. The assembly is immersed in a testing fluid which exerts shear stress on the sensor face when the lower disk is rotating.

The figure below shows shear stress data measured by the sensor using glycol as the test fluid with the lower disk rotating at a rate of 122 RPM. Two full rotations are shown in which the small and large tooth pass by the sensor twice each. As expected, the smaller gap (0.9 mm) above the smaller tooth results in a stronger peak shear stress (1500 Pa at approximately t = 0.2 and 0.65 seconds) compared with the larger tooth (1200 Pa at t = 0.4 and 0.9 seconds with a gap of 1.2 mm). Note the fine detail captured during the large tooth passes revealing complexities in the fluid dynamics.

An identical experiment was performed with air bubbles introduced behind each tooth and measurements are shown in the figure below. Once injected the bubbles remain trapped as the disk rotates. Air is substantially less viscous than glycol and exerts far less wall shear stress on the top disk. Consequently, the sensor response drops to zero as each bubble passes underneath. This result illustrates the capability of the sensor to identify the presence of multiple components or phases in a mixture.