Method and apparatus for measuring diameter, distribution and so forth of micro gas bubbles and micro liquid droplets and optical system for measuring diameter, distribution and so forth of micro bubbles and micro liquid drop

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam;
• and
• measuring numbers of interference fringes in the respective out-of-focus images corresponding to the micro gas bubbles or the micro liquid droplets to determine diameters and distribution of the micro gas bubbles or the micro liquid droplets;
• wherein said out-of-focus images are captured with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said sheet-shaped parallel laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane.

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• and
• determining a center of each of said out-of-focus images, thereby determining a center position of the corresponding micro gas bubble or micro liquid droplet.

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• subjecting each of the out-of-focus images to Fourier transform to obtain a frequency;
• multiplying the obtained frequency by a length of the out-of-focus image to obtain the number of interference fringes in the out-of-focus image;
• and
• determining a diameter of the micro gas bubble or the micro liquid droplet on a basis of the number of interference fringes.

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing two image frames at a micro time interval Δt, the two image frames each containing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam, the linear out-of-focus images being captured from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• calculating cross correlation between the two captured image frames for each linear out-of-focus image in the two captured image frames to obtain a displacement Δsi of each linear out-of-focus image;
• and
• determining a velocity ui of each micro gas bubble or micro liquid droplet from the following relationship:
• ui=Δsi/Δt (6)

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• determining a center of each of said out-of-focus images, thereby determining a center position of the corresponding micro gas bubble or micro liquid droplet;
• subjecting each of the out-of-focus images to Fourier transform to obtain a frequency;
• multiplying the obtained frequency by a length of the out-of-focus image to obtain the number of interference fringes in the out-of-focus image;
• determining a diameter of the micro gas bubble or the micro liquid droplet on a basis of the number of interference fringes;
• capturing two image frames containing the linear out-of-focus images at a micro time interval Δt;
• calculating cross correlation between the two captured image frames for each linear out-of-focus image in the two captured image frames to obtain a displacement {si of each linear out-of-focus image;
• and
• determining a velocity ui of each micro gas bubble or micro liquid droplet from the following relationship:
• ui=Δsi/Δt (6)

An apparatus for measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said apparatus comprising:

• laser beam application means for applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• imaging means for capturing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam, which is applied by said laser beam application means, from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• center position measuring means for determining a center of each of said out-of-focus images to thereby determine a center position of the corresponding micro gas bubble or micro liquid droplet;
• diameter measuring means for subjecting each of the out-of-focus images to Fourier transform to obtain a frequency, multiplying the obtained frequency by a length of the out-of-focus image to obtain the number of interference fringes in the out-of-focus image, and determining a diameter of the micro gas bubble or the micro liquid droplet on a basis of the number of interference fringes;
• and
• velocity measuring means for capturing two image frames containing the linear out-of-focus images at a micro time interval Δt, calculating cross correlation between the two captured image frames for each linear out-of-focus image in the two captured image frames to obtain a displacement Δsi of each linear out-of-focus image, and determining a velocity ui of each micro gas bubble or micro liquid droplet from the following relationship:
• ui=Δsi/Δt (6)