Planar particle/droplet size measurement technique using digital particle image velocimetry image data
View Patent ↗A method for determining a mass flux of an entrained phase in a planar two-phase flow records images of particles in the two-phase flow. Respective sizes of the particles (the entrained phase) are determined as a function of a separation between spots identified on the particle images. Respective velocities of the particles are determined. The mass flux of the entrained phase is determined as a function of the size and velocity of the particles.
1. A method for determining a mass flux of a particle, comprising:
recording an image of the particle entrained in a two-phase flow, using a camera; and
using a processor for determining a size of the particle as a function of a separation between spots identified on the particle, determining a velocity of the particle, and determining the mass flux of the particle as a function of the size and velocity, wherein the spots are glare spots and the separation between the glare spots is determined as:
x
o
=
-
a
M
cos
θ
o
2
;
x
1
=
n
a
M
sin
θ
o
2
[
n
2
+
1
-
2
n
cos
θ
o
2
]
1
2
;
and
d
p
=
2
Δɛ
p
-
M
cos
θ
0
2
+
n
M
sin
θ
0
2
n
2
+
1
-
2
n
cos
θ
0
2
,
where d p is an estimate of the particle diameter, n is a ratio of an index of refraction of a material of the particle to an index of refraction of a medium, a is a radius of the particle, M is an optical system magnification, Δ is a number of pixels separating the glare spots on a surface of a CCD, ε p is a size of the pixels in the CCD, and θ o is an observation angle.
2. The method for determining a mass flux of a particle as set forth in claim 1 , wherein the recording step includes:
recording an image of a transparent particle.
3. The method for determining a mass flux of a particle as set forth in claim 1 , further including:
identifying glare spots on the particle, the particle size being determined as a function of a separation between the glare spots.
4. The method for determining a mass flux of a particle as set forth in claim 1 , wherein the step of determining the velocity includes:
determining the velocity as a function of a velocimetry of the particles within the images.
5. The method for determining a mass flux of a particle as set forth in claim 4 , wherein the step of determining the velocity as a function of the velocimetry includes:
obtaining two exposures of the respective glare spots of the particles entrained in the fluid; and
measuring a displacement between the two exposures during a specified time interval.
6. The method for determining a mass flux of a particle as set forth in claim 4 , wherein the step of determining the velocity as a function of the velocimetry includes:
detecting a Doppler shift of light.
7. An optical flow meter for determining a mass flux of a particle, comprising:
a camera for recording an image of the particle entrained in a two-phase flow; and
a processor for determining a size of the particle as a function of a separation between spots identified on the particle, determining a velocity of the particle, and determining the mass flux of the particle as a function of the size and velocity, wherein the spots are glare spots and the separation between the glare spots is determined as:
x
o
=
-
a
M
cos
θ
o
2
;
x
1
=
n
a
M
sin
θ
o
2
[
n
2
+
1
-
2
n
cos
θ
o
2
]
1
2
;
and
d
p
=
2
Δɛ
p
-
M
cos
θ
0
2
+
n
M
sin
θ
0
2
n
2
+
1
-
2
n
cos
θ
0
2
,
where d p is an estimate of the particle diameter, n is a ratio of an index of refraction of a material of the particle to an index of refraction of a medium, a is a radius of the particle, M is an optical system magnification, Δ is a number of pixels separating the glare spots on a surface of a CCD, ε p is a size of the pixels in the CCD, and θ o is an observation angle.
8. The optical flow meter for determining a mass flux of a particle as set forth in claim 7 , wherein a Gaussian peak location estimate is used for determining a location of respective peaks of the glare spots, the separation between the glare spots being determined as a function of the locations of the peaks.
9. The optical flow meter for determining a mass flux of a particle as set forth in claim 7 , wherein the camera is a CCD camera.
10. The optical flow meter for determining a mass flux of a particle as set forth in claim 7 , wherein the particles are transparent.
11. A method for determining a size of a particle, the method comprising:
receiving an image of the particle entrained in a two-phase flow into a processor;
reducing background noise within the image;
grouping the pixels having non-zero values into respective particle image arrays;
identifying glare spots within the image as a function of the particle image arrays; and
determining the size of the particle as a function of a separation between the glare spots, wherein the separation between the glare spots is determined as:
x
o
=
-
a
M
cos
θ
o
2
;
x
1
=
n
a
M
sin
θ
o
2
[
n
2
+
1
-
2
n
cos
θ
o
2
]
1
2
;
and
d
p
=
2
Δɛ
p
-
M
cos
θ
0
2
+
n
M
sin
θ
0
2
n
2
+
1
-
2
n
cos
θ
0
2
,
where d p is an estimate of the particle diameter, n is a ratio of an index of refraction of a material of the particle to an index of refraction of a medium, a is a radius of the particle, M is an optical system magnification, Δ is a number of pixels separating the glare spots on a surface of a CCD, ε p is a size of the pixels in the CCD, and θ o is an observation angle.
12. The method for determining a size and a velocity of a particle as set forth in claim 11 , wherein the reducing step includes:
limiting non-zero intensity values of pixels within the image.
13. The method for determining a size and a velocity of a particle as set forth in claim 12 , wherein the limiting step includes:
determining a global threshold intensity value for the pixels within the image; and
setting intensity values of pixels below the global threshold to zero.
14. The method for determining a size and a velocity of a particle as set forth in claim 13 , further including:
determining a local threshold for discriminating the particle within the image.
15. The method for determining a size and a velocity of a particle as set forth in claim 11 , wherein the grouping step includes:
scanning the image for the pixels having the non-zero values;
identifying one of the pixels as having the non-zero value;
identifying pixels adjacent to the pixel having the non-zero value;
grouping any of the adjacent pixels having the non-zero values into the particle image array;
identifying subsequent pixels adjacent to each of the adjacent pixels having the non-zero value; and
grouping any of the subsequent pixels into the particle image array.
16. The method for determining a size and a velocity of a particle as set forth in claim 11 , further including:
rejecting ones of the particle image arrays that are saturated.