This paper describes an optical fiber droplet sizer which can measure 0.1∼12μm diameter particles.
The measuring principle of this sizes is the forward scattering method. First, laser light is irradiated on many particles, and the scattered light intensity pattern by the particles are measured. Second, the intensity pattern is inverted to the particle size distribution using Eq. (1),
I(θ)=∫i(D, θ)n(D)dD (1)
where
I(θ) is the measured light intensity pattern,
i(D, θ) is the light intensity scattered by one particle,
n(D) is the particle size distribution,
D is the particle diameter and θ is the scattering angle.
A conventional particle sizer based on this method could not measure particles smaller than 5μm diameter. The following improvements were made in the optical fiber droplet sizer.
(1)
i(D, θ) based on the Mie theory was used. The Mie theory is applicable to spherical particle of all sizes.
(2) The measuring range of the scattered light intensity pattern was extended using optical fibers.
The above two improvements extended the lower limit of the measurable particle size range.
(3) In the inversion from the scattered light intensity pattern to the particle size distribution, the Logarithmic Constrained Inversion Method proposed by the author was used. In this method, equation (2) is directly solved for
n(D).
log
I(θ)=log[∫
i(D, θ)n(D)dD] (2)
The feature of this method is that any form of distribution (even bimodal distribution) can be determined without a prior assumption of the size distribution form.
In order to test the performace of the optical fiber droplet sizer, 0.1∼12μm average diameter Polystyrene particles were measured. The test results showed close agreements between measured size distributions and actual size distributions.
Finally, it is shown that the scattered light intensity pattern can be measured accurately without the effect of multiscattering if the transmission ratio is larger than 50%.
抄録全体を表示