CN110927022A

CN110927022A - How to measure the coefficient of surface tension of liquids

Info

Publication number: CN110927022A
Application number: CN201911142905.1A
Authority: CN
Inventors: 胡再国
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2019-11-20
Filing date: 2019-11-20
Publication date: 2020-03-27

Abstract

The measurement method of the liquid surface tension coefficient involves the determination of the physical parameters of the liquid. The technical scheme is: there is a horizontal bubble on the bottom surface of the inner side of the cylindrical container, a water outlet pipe is fixed on the bottom surface of the cylindrical container, and the outer diameter of the outlet pipe is d; The bottom surface of the inner side of the container is horizontal; a recovery container is placed under the outlet of the water outlet of the cylindrical container, and liquid is injected into the cylindrical container until the droplets flow from the outlet of the water outlet to the recovery container, and the droplets are no longer dripped from the outlet of the water outlet. When measuring the distance h between the upper liquid level and the outlet level, the inner diameter of the cylindrical container is more than 100 times the outer diameter of the outlet pipe; then the surface tension coefficient of the liquid σ=ρ*g*h*d/4 , where ρ is the density of the liquid and g is the acceleration of gravity. The measurement method is simple and accurate.

Description

Method for measuring surface tension coefficient of liquid

Technical Field

The invention relates to the determination of physical parameters of liquids, in particular to the measurement of the surface tension coefficient of liquids.

Background

The methods adopted for measuring the surface tension coefficient of the liquid include a capillary method, a drop weight method, a pull-off method and the like, the capillary method needs to measure the included angle (contact angle) between the liquid level and the pipe wall, and the measurement is inconvenient; the drop weight method and the pull-off method belong to dynamic measurement, part of liquid can be retracted by the drop weight method, and part of liquid is adhered to a pull ring by the pull-off method, so that the measurement is inaccurate.

Disclosure of Invention

The present invention measures the surface tension coefficient of a liquid from a pressure perspective (i.e., steady state, static).

The invention adopts the technical scheme that the purpose of the invention is realized by: the method for measuring the surface tension coefficient of the liquid is characterized by comprising the following steps: a cylindrical container, wherein a horizontal bubble is arranged on the bottom surface of the inner side of the cylindrical container, a water outlet pipe is fixed on the bottom surface of the cylindrical container, the difference between the inner diameter and the outer diameter of an outlet of the water outlet pipe is 0.2-0.3mm, and the outer diameter of the outlet of the water outlet pipe is d; the edge of the top of the cylindrical container protrudes outwards to form a supporting ring, the supporting ring is placed on a circular supporting platform, and three adjusting screws of the supporting ring are adjusted so as to change an included angle between the lower surface of the supporting ring and the upper surface of the supporting platform, so that the horizontal bubble on the bottom surface of the inner side of the cylindrical container displays the level of the bottom surface of the inner side of the cylindrical container; placing a recovery container below the outlet of the water outlet pipe of the cylindrical container, injecting liquid into the cylindrical container until liquid drops flow into the recovery container from the outlet of the water outlet pipe, and measuring the distance h between the liquid level at the upper end and the horizontal plane of the outlet when the liquid drops do not drop at the outlet of the water outlet pipe any more, wherein the liquid level at the upper end is the plane part of the center of the liquid level; the diameter of the inner side of the cylindrical container is more than 100 times of the outer diameter of the outlet of the water outlet pipe; the surface tension coefficient of the liquid is σ = ρ × g × h × d/4, where ρ is the density of the liquid and g is the acceleration of gravity. If the surface tension of the liquid level at the upper end is not ignored, the diameter of the inner side of the cylindrical container is d1, and the outer diameter of the outlet of the water outlet pipe is d 2; the surface tension coefficient of the liquid σ = ρ × g × h × d1 × d 2/(4 (d1+ d 2)).

The measuring method of the distance h between the liquid level and the outlet of the water outlet pipe is that a graduated scale is arranged in the vertical direction at the outer side of the cylindrical container, the zero point of the graduated scale is the horizontal plane of the outlet of the water outlet pipe, namely the plane of the outlet of the water outlet pipe is parallel to the bottom surface of the inner side of the cylindrical container; the cylindrical container is a transparent container, the liquid level inside the cylindrical container is observed by eyes, namely the liquid is transparent liquid, and the liquid level, the scale marks and the eyes read the reading of the scale in a straight line. The scale mark of the graduated scale is annular.

The upper end of the water outlet pipe is provided with a circular platform, the lower surface of the circular platform is attached to a circular groove in the inner bottom surface of the cylindrical container, the lower surface of the circular platform and the circular groove in the inner bottom surface of the cylindrical container are sealed through a gasket to prevent liquid from seeping out, the outer side of the bottom surface of the cylindrical container is fixed with the water outlet pipe through matching of internal threads of a nut and external threads of the water outlet pipe, and the upper surface of the water outlet pipe and the inner bottom surface of the cylindrical container are in the same plane through.

The relation between the liquid level height h and the pipe diameter d outside the outlet of the water outlet pipe is observed by changing the pipe diameter d outside the outlet of the water outlet pipe, namely changing the taper of the conical surface inside the water outlet pipe, and the relation that the surface tension is in direct proportion to the pipe diameter d outside the outlet of the water outlet pipe is verified.

The invention has the beneficial effects that: the contact angle of the liquid is not considered, the method belongs to static measurement, the phenomena of contraction and adhesion of liquid drops are avoided, and the measurement method is simple and accurate.

Drawings

FIG. 1 is a schematic view of the apparatus; FIG. 2 is a schematic view of the outlet pipe; FIG. 3 is a schematic view of a nut;

wherein, 1, a cylindrical container; 2. horizontal bubble; 3. a water outlet pipe; 4. a support ring; 5. a screw; 6. an outlet; 7. a nut; 8. a graduated scale; 9. and (4) threading.

Detailed Description

According to the method for measuring the surface tension coefficient of the liquid by a drop weight method, the relation between the mass m of the liquid drop and the pipe diameter d (the outer diameter is the wetting condition, and the inner diameter is the non-wetting condition) of the dropper satisfies the condition that m & ltg & gt = pi & ltd & gt sigma, namely sigma = m & ltg & gt/(pi & ltd & gt); there are problems in that: when the liquid is broken into droplets, part of the liquid shrinks back, so that the mass m of the dropped droplets is reduced, and the correction is needed, and the measurement method is not simple and even difficult to understand.

The present invention discusses this problem in another aspect, and the drop of the liquid drop is caused by insufficient surface tension to pull the liquid, i.e. the pressure (pressure) of the liquid column, and therefore, we discuss the following: the liquid has surface tension on the upper surface of the container and the outlet 6 end of the dropper, the pipe diameter of the outlet 6 end is d, the pipe diameter of the upper end is 100d (which is a design parameter of the invention), the height of the liquid column is h, the pressure difference is rho g h, wherein rho is the density of the liquid, g is the acceleration of gravity, and h is the distance between the liquid level at the upper end and the outlet 6 of the water outlet pipe 3; the outlet 6 of the lower outlet pipe 3 has a pipe diameter (the infiltration liquid is an outer diameter, the invention is suitable for infiltration liquid) of d, a surface tension of pi x d sigma and a supportable pressure of pi x d sigma/S, wherein S is the area of the outlet 6 of the outlet pipe 3, i.e. pi x (d/2)²(ii) a Pi × d σ/S =4 σ/d; also at the upper end of the liquid surface there is an acceptable pressure =4 σ/(100 d), and due to the difference of 100 times, the pressure 4 σ at the upper endIf not, the correction can be made to 4 σ/d +4 σ/(100 d) = ρ × g × h. When the droplet is not landing, the pressure of surface tension build-up is balanced with the pressure of the liquid column, so that σ = ρ × g × h × 4; after correction σ = ρ × g × h × d1 × d 2/(4 (d1+ d 2)), where d1 and d2 are the diameter of the upper end liquid surface and the tube diameter of the lower end outlet 6 (mostly wetted, and therefore mostly outer diameter), respectively. The method of the invention is only suitable for immersion liquids (non-immersion liquids cannot be measured, which are also a few of the liquids that are routinely found).

According to the above discussion, the embodiments are: a horizontal bubble 2 is arranged on the bottom surface of the inner side of a cylindrical container 1, a water outlet pipe 3 is fixed on the bottom surface of the cylindrical container 1, the difference between the inner diameter and the outer diameter of an outlet 6 of the water outlet pipe 3 is 0.2-0.3mm (namely the thickness of the pipe wall is 0.10-0.15 mm), and the outer diameter of the outlet 6 of the water outlet pipe 3 is d; the top edge of the cylindrical container 1 protrudes outwards to form a supporting ring 4, the supporting ring 4 is placed on a ring-shaped supporting platform (common equipment, not shown in fig. 1-3), and three adjusting screws 5 (three points determine a plane principle) of the supporting ring 4 are adjusted so as to change the distance between the lower surface of the supporting ring 4 and the upper surface of the supporting platform (namely change the included angle between the lower surface of the supporting ring 4 and the upper surface of the supporting platform), so that the horizontal bubble 2 on the inner bottom surface of the cylindrical container 1 displays that the inner bottom surface of the cylindrical container 1 is horizontal; a recovery container is arranged below an outlet 6 of an outlet pipe 3 of a cylindrical container 1, liquid is injected into the cylindrical container 1, until liquid drops flow to the recovery container from the outlet 6 of the outlet pipe 3, when the liquid drops do not drop from the outlet 6 of the outlet pipe 3, the distance h between the liquid level at the upper end and the horizontal plane of the outlet 6 is measured (namely the plane of the outlet 6 of the outlet pipe 3 is parallel to the upper end plane of the outlet pipe 3, the upper end plane is superposed with the bottom surface of the cylindrical container 1, the plane of the central part of the liquid level at the upper end is always in the horizontal plane), and the liquid level at the upper end refers to the plane part (not the part of the edge which is upwards stretched and; the diameter of the inner side of the cylindrical container 1 is more than 100 times of the outer diameter of the outlet 6 of the water outlet pipe 3 (the influence of the surface tension of the upper end of the cylindrical container 1 can be ignored at the moment); the surface tension coefficient of the liquid is σ = ρ × g × h × d/4, where ρ is the density of the liquid and g is the acceleration of gravity.

The method for measuring the distance h between the liquid level and the outlet 6 of the water outlet pipe 3 is that a graduated scale 8 is arranged on the outer side of the cylindrical container 1 in the vertical direction, the zero point of the graduated scale 8 is the horizontal plane where the outlet 6 of the water outlet pipe 3 is located, the cylindrical container 1 is a transparent container, the liquid level on the inner side is observed by eyes, and the liquid level, the graduated line and the eyes read the reading of the graduated scale 8 in a straight line.

The upper end of the water outlet pipe 3 is provided with a circular platform, the lower surface of the circular platform is attached to a circular groove on the inner bottom surface of the cylindrical container 1, the lower surface of the circular platform and the circular groove on the bottom surface of the cylindrical container 1 are sealed through a gasket to prevent liquid from seeping out, the outer side of the bottom surface of the cylindrical container 1 is matched with the external thread 9 of the water outlet pipe 3 through the internal thread 9 of the nut 7 to fix the water outlet pipe 3, and the upper surface of the water outlet pipe 3 and the inner bottom surface of the cylindrical container 1 are in the same plane through. Washers and nuts are common sealing fixtures and methods of use are well known to those skilled in the art, and therefore the washers are not shown in fig. 1-3.

By changing the pipe diameter d (outer diameter) of the outer side of the outlet 6 of the water outlet pipe 3, namely changing the taper of the conical surface of the inner side of the water outlet pipe 3 (keeping the pipe wall thickness unchanged), observing the relation between the liquid level height h and the pipe diameter d of the outer side of the outlet 6 of the water outlet pipe 3, and verifying the proportional relation between the surface tension and the pipe diameter d of the outer side of the outlet 6 of the water outlet pipe 3.

The implementation performance is as follows: the standard value of the surface tension coefficient of pure water at 19.7 ℃ was 7.280 x 10^-2N/m; the gravity acceleration is 9.8m/s²(ii) a Rho is 1000kg/m³(ii) a The diameter (outer diameter) d of an outlet 6 of the water outlet pipe 3 is 2mm =0.002 m; then σ = ρ × g × h × d/4=7.280 × 10^-2N/m=1000 kg/m³*9.8m/s²H 0.002m/4, h =1.5 cm. If d takes 1mm, h =3.0 cm. If d takes 0.5mm, h =6.0 cm. The length of the water outlet pipe 3 is within 1cm, which is more suitable. The water outlet pipe 3 can also be formed by protruding outwards from the cylindrical container 1 (i.e. the water outlet pipe and the cylindrical container 1 are an integral structure).

Claims

1. A method for measuring the coefficient of surface tension of a liquid, which is characterized by: a cylindrical container (1), a horizontal bubble (2) on the inner bottom surface of the cylindrical container (1), and a cylindrical container (1) fixed on the bottom surface The difference between the inner diameter and the outer diameter of the water outlet pipe (3) and the outlet (6) of the water outlet pipe (3) is 0.2-0.3mm, and the outer diameter of the outlet (6) of the water outlet pipe (3) is d; the top of the cylindrical container (1) The edge protrudes outward to form a support ring (4), the support ring (4) is placed on a circular support platform, and the three adjustment screws (5) of the support ring (4) are adjusted to change the support ring ( 4) The angle between the lower surface and the upper surface of the support platform makes the horizontal bubble (2) on the inner bottom surface of the cylindrical container (1) show that the inner bottom surface of the cylindrical container (1) is horizontal; ) A recovery container is placed under the outlet (6) of the water outlet pipe (3), and liquid is injected into the cylindrical container (1) until the droplets flow from the outlet (6) of the water outlet pipe (3) to the recovery container, and the water outlet pipe ( 3) When the outlet (6) no longer drips droplets, measure the distance h between the upper liquid surface and the horizontal surface of the outlet (6). The upper liquid surface refers to the plane part of the center of the liquid surface; the inner side of the cylindrical container (1) The diameter of the water outlet pipe (3) is more than 100 times the outer diameter of the outlet (6); then the surface tension coefficient of the liquid σ=ρ*g*h*d/4, where ρ is the density of the liquid, and g is the acceleration of gravity.

2. The method for measuring the coefficient of surface tension of liquid according to claim 1, characterized in that: the method for measuring the distance h between the liquid level and the outlet (6) of the water outlet pipe (3) is the method of measuring the distance h of the cylindrical container (1). There is a scale (8) in the vertical direction on the outside. The zero point of the scale (8) is the horizontal plane where the outlet (6) of the water outlet pipe (3) is located, that is, the plane where the outlet (6) of the water outlet pipe (3) is located is parallel to the cylindrical container ( 1) The inner bottom surface; the cylindrical container (1) is a transparent container, and the liquid level inside the cylindrical container (1) is observed with the eye level, that is, the liquid is a transparent liquid, and the liquid level, the scale line and the eyes are in a straight line to read the scale (8) readings.

3. The method for measuring the coefficient of surface tension of liquid according to claim 1, wherein the upper end of the water outlet pipe (3) has an annular platform, and the lower surface of the annular platform is connected to the inner side of the cylindrical container (1). A circular groove on the bottom surface is fitted, and a gasket is used to seal between the lower surface of the circular platform and the circular groove on the inner bottom surface of the cylindrical container (1) to prevent liquid leakage. The cylindrical container (1) ) On the outside of the bottom surface, the inner thread (9) of the nut (7) cooperates with the outer thread (9) of the outlet pipe (3) to fix the outlet pipe (3). The upper surface and the inner bottom surface of the cylindrical container (1) are in a plane.

4. The method for measuring the coefficient of surface tension of liquid according to claim 1, characterized in that: by changing the outer diameter d of the outlet (6) of the water outlet pipe (3), that is, changing the taper of the inner conical surface of the water outlet pipe (3), Observe the relationship between the liquid level height h and the outer diameter d of the outlet (6) of the outlet pipe (3), and verify that the surface tension is proportional to the outer diameter d of the outlet (6) of the outlet pipe (3).

5. The method for measuring the coefficient of surface tension of liquid according to claim 1, wherein the inner diameter of the cylindrical container (1) is d1, and the outer diameter of the outlet (6) of the water outlet pipe (3) is d2; Surface tension coefficient σ=ρ*g*h*(d1*d2)/(4(d1+d2)).

6. The method for measuring liquid surface tension coefficient according to claim 2, characterized in that: the scale line of the scale (8) is annular.

7 . The method for measuring the coefficient of surface tension of liquid according to claim 1 , wherein the outer diameter of the outlet ( 6 ) of the water outlet pipe ( 3 ) is 0.5-1 mm. 8 .