Method and instrument for measuring surface tension

Abstract

For measuring the surface tension between a liquid and fluid such as a gas, a capillary () is used in which the liquid slowly flows and at the end of which drops () are formed, falling off into a closed space () containing the fluid. Using a pressure sensor () the pressure is measured which can be the absolute pressure of a fluid volume enclosed in the closed space or alternatively a differential pressure measured as the pressure difference between the liquid in the capillary and fluid contained in the closed space. The pressure is measured when one or more drops are formed and full off. The obtained pressure curves are evaluated electronically () and provide a value of the surface tension. The measurement can be made within a fairly short time with a high operational reliability. The temperature difference between the drop and the surrounding fluid is small resulting in a little precipitation of salts dissolved in the liquid, reducing the risk that the liquid capillary with be blocked. A pump can be connected () to the closed space to create a subatmospheric pressure therein and thereby assist in restarting the liquid flow through the capillary if it would be blocked. The velocity of the liquid flow to the drop can be controlled using the pump.