Method for measuring liquid flow property and apparatus for observing droplet
A method for measuring a liquid flow property is provided. The method includes controlling a droplet to drop from a preset height to a substrate, acquiring a droplet density on the substrate, a maximum radius of a tip of the droplet, a real-time height of the tip, an initial height of the tip, and a testing duration from a beginning of the droplet to fall on the substrate to an end of a test, determining that influencing factors of the tip of the droplet comprise inertial force and viscous force, and the inertial force is equal to the viscous force, and calculating a calculated viscosity of the droplet, wherein the calculated viscosity of the droplet is related to a first calculation coefficient, the droplet density, the maximum radius of the tip and the initial height of the tip, and the first calculation coefficient is equal to a ratio of a tip height change value to the testing duration, wherein the tip height change value is a difference between the initial height of the tip and the real-time height of the tip.
1 . A method for measuring a liquid flow property, comprising:
controlling a droplet to drop from a preset height to a substrate;
acquiring a droplet density on the substrate, a maximum radius of a tip of the droplet, a real-time height of the tip, an initial height of the tip, and a testing duration from a beginning of the droplet to fall on the substrate to an end of a test;
determining that influencing factors of the tip of the droplet comprise inertial force and viscous force, and the inertial force is equal to the viscous force, and calculating a calculated viscosity of the droplet, wherein the calculated viscosity of the droplet is related to a first calculation coefficient, the droplet density, the maximum radius of the tip and the initial height of the tip, and the first calculation coefficient is equal to a ratio of a tip height change value to the testing duration, wherein the tip height change value is a difference between the initial height of the tip and the real-time height of the tip.
2 . The method for measuring the liquid flow property of claim 1 , wherein before calculating the calculated viscosity of the droplet,
controlling a Weber number of the droplet to be greater than or equal to a set threshold; and
determining that influencing factors of the tip of the droplet comprise inertial force and viscous force, and the inertial force is equal to the viscous force, based on the Weber number being greater than or equal to the set threshold.
3 . The method for measuring the liquid flow property of claim 2 , wherein a calculation formula for determining the calculated viscosity of the droplet based on the inertial force being equal to the viscous force is:
ρ
∂
2
H
max
∂
t
2
R
n
2
H
max
=
η
∂
H
max
R
n
∂
t
R
n
H
max
(
1
)
where ρ is the droplet density;
ρ is the calculated viscosity;
R n is the maximum radius of the tip;
t is the testing duration from the beginning of the droplet to fall on the substrate to the end of the test;
H max is the real-time height of the tip, which varies with the testing duration t;
obtaining a formula:
Δ
H
max
H
0
=
η
t
ρ
R
n
2
(
2
)
by solving the formula (1),
obtaining:
η
=
C
1
ρ
R
n
2
H
0
by the formula (2);
where ΔH max is the tip height change value, and ΔH max =H 0 −H max ;
H 0 is the initial height of the tip when the droplet drips on the substrate;
C 1 is the first calculation coefficient, where
C
1
=
Δ
H
max
t
.
4 . The method for measuring the liquid flow property of claim 2 , wherein the preset height is greater than or equal to 11.8 cm, and the maximum radius of the tip is between 0.5 mm to 1 mm.
5 . The method for measuring the liquid flow property of claim 1 , further comprising:
controlling a Weber number of the droplet to be less than a set threshold;
determining that influencing factors of the tip comprise viscous force and surface tension, and the viscous force is equal to the surface tension, based on the Weber number being less than the set threshold;
after the step of calculating the calculated viscosity of the droplet,
determining a ratio of a third power of the tip height change value to the testing duration as a second calculation coefficient, based on the viscous force being equal to the surface tension,
calculating a surface tension coefficient of the surface tension from the calculated viscosity, the second calculation coefficient, and the maximum radius of the tip.
6 . The method for measuring the liquid flow property of claim 5 , wherein a calculation formula for calculating the surface tension coefficient of the surface tension from the calculated viscosity, the second calculation coefficient, and the maximum radius of the tip, based on the viscous force being equal to the surface tension is:
(
Δ
H
max
R
n
)
η
Δ
H
max
t
Δ
H
max
=
γ
R
n
(
3
)
where ΔH max is the tip height change value, and ΔH max =H 0 −H max ; H 0 is the initial height of the tip when the droplet drips on the substrate; H max is the real-time height of the tip, which varies with the testing duration t;
R n is the maximum radius of the tip;
η is the calculated viscosity;
t is the testing duration from the beginning of the droplet to fall on the substrate to the end of the test;
the surface tension is F=γR n ;
γ is the surface tension coefficient, which represents surface tension on a straight line segment of a unit length on a liquid surface;
obtaining a formula:
Δ
H
max
=
γ
R
n
2
t
η
3
(
4
)
by solving the formula (3),
obtaining
γ
=
η
C
2
R
n
2
by the formula (4);
where C 2 is the second calculation coefficient, where
C
2
=
Δ
H
max
3
t
.
7 . The method for measuring the liquid flow property of claim 5 , wherein the preset height is less than 8 cm, and the maximum radius of the tip is between 0.5 mm to 1 mm.
8 . The method for measuring the liquid flow property of claim 7 , wherein a calculation formula of the Weber number is:
W
e
=
ρ
v
0
2
γ
(
3
V
0
4
π
)
1
3
where W e is the Weber number;
ρ is the droplet density;
v 0 is a dripping speed of the droplet when it just drips on the substrate;
V 0 is a droplet volume;
γ is the surface tension coefficient, which represents the surface tension on the straight line segment of the unit length on the liquid surface;
acquiring the dripping speed v 0 and the droplet volume V 0 when the droplet just drips on the substrate, and adjusting a numerical range of the Weber number by controlling the dripping speed v 0 and the droplet volume V 0 .
9 . The method for measuring the liquid flow property of claim 1 , wherein controlling the droplet to drop from the preset height to the substrate further comprises:
acquiring a flowing duration of the droplet flowing in a container; wherein the container is configured to contain a liquid, and the liquid forms the droplet at an opening of the container;
acquiring a dripping duration from the beginning of the droplet to fall on the substrate;
determining that a sum of the flowing duration, the dripping duration and the testing duration is a total duration, and the testing duration is far less than the total duration.
10 . The method for measuring the liquid flow property of claim 1 , wherein determining the ratio of the tip height change value to the testing duration as the first calculation coefficient comprises:
acquiring the initial height of the tip and a plurality of the real-time heights of the tip within the testing duration, and obtaining a linear relationship between the first calculation coefficient, the testing duration and the tip height change value by fitting.