Definition
A dry particle size meter is an instrument used to measure the particle size distribution of solid particles in a dry and dispersed state. It physically disperses particles in the air and keeps them suspended, and then detects and analyzes the physical properties of the particles to obtain particle size distribution data based on quantity, volume, or mass. The instrument is suitable for a variety of dry powder samples and has a wide range of applications in the fields of chemical, mineral, building materials, food and new material research and development.
Principle
The core principle of dry particle size is based on the correlation between the physical properties of particles and their particle size as they move in a gas stream. Common techniques include laser diffraction and dynamic image analysis. The laser diffraction method uses the scattering phenomenon of particles to laser, and calculates the particle size distribution by the inverse relationship between the scattering angle and the particle size (i.e., Flanghefer diffraction or Mie scattering theory). Its basic relationship can be expressed as:
d ∝ λ / θ
where d is the diameter of the particle, λ is the laser wavelength, and θ is the scattering angle. The dynamic image analysis method captures the moving image of particles in the air flow through a high-speed camera, and directly measures the projection size and morphology of each particle through the image processing algorithm.
Measurement method
Dry particle size measurement typically involves four steps: sample preparation, dispersion, detection, and data analysis. First, the sample is ensured to be dry and free of agglomeration, and the sample is introduced into the dispersion chamber via a vibrating feed or venturi nozzle. Inside the cavity, high-pressure airflow or mechanical force allows the particles to fully disperse and form a stable aerosol stream. The laser source then irradiates the particle stream, the detector collects the scattered light signal, or the high-speed camera acquires the particle image. Finally, the instrument's built-in software converts the signal into particle size distribution results based on optical models or image algorithms, which are often presented in the form of cumulative distribution or frequency distribution.
Influencing factors
The accuracy of the measurement results is influenced by several factors. Sample properties such as particle morphology, density, electrostatic properties, and hygroscopicity can interfere with dispersion uniformity. Instrument parameters include dispersion air pressure, feed rate, and optical window cleanliness, which may cause agglomeration if the air pressure is too low, and particle fragmentation may occur if it is too high. Environmental conditions such as humidity and vibration can also introduce errors. The operator needs to adjust the parameters according to the characteristics of the sample and calibrate it with a standard sample to verify the system status.
Application:
Dry particle size meters are suitable for powder analysis scenarios where the influence of liquid media is avoided. In the cement and ceramics industry, it is used to monitor the particle size of raw material powders to optimize the sintering process. Coatings and pigments use it to evaluate the dispersion properties of fillers and pigments. It can be used in the food industry to detect the particle size consistency of edible powders such as powdered sugar and flour. In addition, in the development of new materials such as metal powders, catalysts, and battery materials, dry measurement can quickly provide particle size data directly related to the drying process to assist in product performance optimization.
Selection
When selecting a dry particle size meter, consider the measurement range, repeatability, sample throughput and applicable standards. The measurement range needs to cover the expected particle size of the sample to be tested, with common instruments ranging from about 0.1 microns to several millimeters. Repeatability can be assessed by measuring bias from the same sample multiple times. For high-throughput needs, automated sample handling helps improve efficiency. In addition, whether the instrument complies with international standards such as ISO 13320 (laser diffraction method) or industry-specific specifications is also an important reference. Users should conduct comprehensive evaluations based on their own sample characteristics, testing environment and data requirements, and verify the suitability of the instrument through sample testing if necessary.