SU1741020A1 - Method for determination of surface liquid tension - Google Patents

Abstract

The invention relates to a measurement technique and can be used to determine the surface tension coefficient of liquids, including high viscosity liquids, as well as in weak gravitational fields when studying liquids obtained under the conditions of new space technologies. Under the influence of an electric field created by a high voltage source between the electrodes, the liquid from the vessel is drawn into the capillary between the electrodes and forms a drop at the outlet of the capillary. The magnitude of the electric field is gradually increased until the drop is removed from the cut off of the capillary, the diameter of the drop is measured at this moment, the magnitude of the voltage between the liquid and the accelerating electrode, and the surface tension coefficient is calculated by the expression in the claims. 1 tab., 1 Il. cl

Description

The invention relates to a measurement technique and can be used to determine the surface tension coefficient of liquids, including high viscosity liquids, as well as in weak gravitational fields in the study of liquids, obtained under the conditions of new space technologies.

A known method for determining the surface tension of liquids by the method of maximum pressure in a drop using the stalagmometric method is based on the condition of balancing the force of gravity of the drop at the moment of its detachment from the end of the capillary by the forces of surface tension.

The method is suitable under conditions of slow drop formation and is static.

Closest to the present invention is a method for determining the surface tension of liquids by the method of maximum pressure in a drop, which involves squeezing a drop out of a capillary and creating maximum pressure in a drop using centrifugal forces.

The disadvantage of this method is the complexity and difficulty of its use for highly viscous liquids.

The purpose of the invention is to expand the scope of use of the method and simplify it.

The method is as follows.

H

four

ABOUT

hO

about

Due to the electric field, the investigated liquid from the vessel is drawn into the capillary, which is connected with the vessel and is located perpendicularly to two electrodes, one of which is in the liquid and the other at a distance H from the first. Under the action of an electric field, a liquid droplet forms at the end of the capillary. At the moment of detachment of the droplet from the capillary, its radius R is measured and the value of the voltage U is fixed, the magnitude of which and the distance H between the electrodes determine the strength of the uniform electric field U U / H. The surface tension coefficient is calculated by the formula

+ fpgR)

0)

where r, R are the capillary radii and drops, respectively, m;

p is the density of the test liquid, kg / m3;

g — gravitational field strength, m / s;

Ј0 8.85-F / m - electric constant.

When exposed to an electric field on the liquid, it is drawn into the capillary and forms a spherical drop at its output. The condition of the drop from the capillary:

F3 +,

(2)

where Re, Fg, F0- are the electrostatic, gravitational and surface forces acting on a liquid drop, respectively.

The electrostatic force acting on a drop of liquid is equal to

F3 Eo E2 S / 2, (3)

about

where S is the droplet surface area, m; S 47TR2.

The gravitational force acting on the drop is equal to

Fg 4jrR3 / og / 3.

(four)

The surface tension force preventing the spherical drop from the capillary is equal to

  2ffSi / r1

(five)

where o is the coefficient of surface tension of the liquid, N / m;

Si тгг2 - the area of the internal section of the capillary, m.

In formula (5) it is assumed that

drops occur along the inner radius of the capillary.

Taking into account expressions (3) - (5) from condition (2), the magnitude of the coefficient of surface tension of a fluid is determined by the formula

R2

15

cr (6

r, 0E2 + | pgR),

From expressions (2) - (5) it can be seen that in the case of a weak gravitational floor or the absence of it, it is necessary to create only

a stronger electric field in order to form a drop of liquid at the exit from the capillary and to detach it from the capillary. Thus, the electric field in the case of weak gravitational fields, up to their complete absence, is a determining factor ensuring the operability of the proposed method under the specified conditions. Similarly electric

The field is a determining factor when exposed to highly viscous liquids, when the formation of a drop only under the action of gravitational forces is difficult, and often practically impossible.

The drawing shows a diagram of the implementation of the method.

The required amount of the test liquid is drawn into the upper tank 1, made of a dielectric material, at the bottom of which electrode 2 is installed, and at the bottom of the tank a dielectric capillary 3 is fixed. Accelerating electrode 4 with a small opening for the passage of droplets is installed above the lower tank 5, which serves

to collect the test liquid, using a high voltage source 6 with a continuously adjustable voltage value, the value of which is determined by ki; lovoltmeter 7 between electrodes 3 and 4

an electric field is created, under the action of which the liquid is drawn into the caliber p 3 and forms a drop at the exit of the capillary. The electric field is increased until the drop is separated from the slice.

capillary, and the radius of the drop is fixed at this moment with an ocular microscope 8. The illumination is measured by the illuminator 9. With the radius of the capillary r, the radius of the drop R at the time of its separation from the capillary, the intensity of the electric field E between The surface tension of the liquid is determined by electrodes and the density of the test liquid A according to the formula (1).

Example. Determination of the surface tension of water.

Measurements are carried out at normal atmospheric pressure and a temperature of 20 ° C in the earth's gravity field at g 9.81 m / s2. The value of the high voltage supplied to the electrodes is smoothly varied from 0 to 10 kV and measured using an electrostatic kilovoltmeter of the type C-196. An ocular microscope and a USC-2 optical bench illuminator are used to measure the droplet diameter. The diameter of the capillary in measurements was 0.36 mm. The measurements are carried out at different interelectrode distances N. The results of the measurements are presented in the table. The table also shows the values of the surface tension coefficient 7, calculated by formula (1). The tabular value of the surface tension coefficient under similar conditions in which the measurements were made is of the order of 73-10 N / m. The discrepancy between the average value of measurement results and reference data is not more than 1.5%.

The proposed method for determining the coefficient of surface tension of a liquid can be easily put into practice, it allows measurements for liquids with high viscosity, since the action of electrical forces in this case becomes predominant over all other forces acting upon the formation of a drop of liquid.

0

five

0

five

In addition, when implementing this method, the hydrostatic field is not fundamentally necessary, it becomes the main factor responsible for the formation of a drop of liquid. Consequently, this method and device that implements it can work under conditions of weak gravitational fields, up to weightlessness.

Claims (1)

Invention Formula The method of determining the surface tension of liquids by the method of maximum pressure in a droplet squeezed out of a capillary, characterized in that, in order to expand the field of use of the method and simplify it, the maximum pressure is created using electric field forces, while at the moment of dropping the droplet from the cut off capillary The intensity of the electric field and the radius of the drop are measured, and the desired value of the surface tension is determined by the formula 0 five a (fioE2 + | yC) gR), where r and R are the radii of the capillary and the liquid droplets at the moment of separation of the droplet from the capillary, respectively, m; p is the density of the liquid, kg / m; g — gravitational field strength, m / s2; Е is the intensity of the electric field at the moment of separation of the drop from the capillary, V / m; 80 8.85 constant. v12 10 F / m - dielectric X LI 7 / r S7 f f (GT S s z fSSrS X I-o  22 OB