Viscoity, Surface Tension and Density Measurements

Fluid properties such as viscosity, surface tension and liquid density can have a significant effect on spray quality.  Therefore, the ability to quantify these fluid properties is extremely important and useful in determining the optimal spray operating conditions for a successful spray application.

Spraying Systems Co quantifies the fluid properties using the following techniques.

Viscosity

Brookfield Programmable DV-II+ Viscometer, manufactured by Brookfield Engineering Laboratories, Inc, Middleboro, MA, measures fluid viscosity at given shear rates.

The DV-II+ Viscometer inserts a spindle immersed into the test fluid. The viscous drag of the fluid against the spindle is measured by the spring deflection. Spring deflection is measured with a rotary transducer.  The measurement range is determined by the rotational speed of the spindle, the size and shape of the spindle, the container the spindle is rotating in, and the full scale torque of the calibrated spring. The higher the torque calibration, the higher the measurement range.

Surface Tension and Density

The EasyDyne Tensiometer by Krüss GmbH, Hamburg, Germany, measures surface and interfacial tension of liquids using the Wilhelmy Plate or the Du Nouy Ring method. The ring/plate method is used to measure the surface/interfacial tension using a standardized ring with a ring/plate tensiometer. The ring is immersed into the liquid and then drawn out. This forms a liquid lamella that is stretched to its maximum. The surface/interfacial tension is calculated from the resulting force. The calculated value must be corrected.

EasyDyne provides an accurate method for determining the density of liquids. In order to determine densities a density determination set is required.

The density of a fluid can be measured with the EasyDyne. It uses the principal that the weight of a solid suspended in a liquid is less than the weight for that solid measured in air. The mass of the liquid displaced corresponds to the difference in weight. As long as the density of the measuring probe is known the density of the liquid can be determined by the concept of differential weighing.

Index of Refraction

The Reichert AR200 Digital Hand-Held Refractometer provides index of refraction (n) measurement for a wide range of liquids. Index of refraction is the degree that light is bent as it passes from one medium to another at a non-normal incident angle (ex: from air into a water droplet). The index of refraction becomes important in Spraying Systems Co. testing services with the use of phase Doppler analyzers such as the PDPA and PDI. The capability to measure this material property directly allows for the most accurate and reliable drop size results when various spray materials are to be characterized.