Online measuring method of concentration and diameter of particles in multiphase system

An online measuring method of concentration and diameter of particles in multiphase system, based on an immersion-type online multiphase measuring instrument comprising:

• a package tube;
• a viewport, sealedly installed at a front end of the package tube;
• an illumination system for illuminating multiphase flow, including LED lamps and a brightness-adjustable light source connected with the LED lamps, which comprises a power supply, a signal generator and an oscilloscope;
• a photographic system for taking pictures, including a telecentric lens and an image sensor;
• a controller connected with the signal generator and the image sensor;
• a signal processing and outputting system connected with the image sensor;
• a display system connected with the signal processing and outputting system;
• the LED lamps, the telecentric lens and the image sensor are located in the package tube and the exposure period of the image sensor is less than the pulse period of the signal generator, controlled by the controller;
• wherein, the measuring method comprises the following steps:
• (1) the immersion-type online multiphase measuring instrument is arranged in a multiphase system, and an image of particles in the multiphase system is obtained;
• (2) valid particles are determined using the following steps:
• first, the focal plane position of the telecentric lens is determined;
• then, an object to be measured is respectively arranged on the front of the package tube, the l/2 positions ahead of or behind the focal plane, where l is the telecentric lens depth of field in mm;
• the object to be measured is photographed by the online multiphase measuring instrument, and the image of the object is obtained and a gray gradient Grad(Φl/2) around the boundary of the object is determined, where Φl/2 is a gray value at the ±l/2 positions ahead of or behind the focal plane;
• if Grad(Φ) is greater than or equal to Grad(Φl/2), the particle is labeled as a valid one;
• (3) the actual length of individual pixel is determined and the number of pixels occupied by the valid particle is measured, so the diameter of the valid particle di is a product of the number of pixels occupied by the valid particle and the actual length of individual pixel;
• according to the equation
• α
• =
• V
• c
• V
• =
• ∑
• i
• n
• ⁢
• 1
• 6
• ⁢
• π
• ⁢
• ⁢
• d
• i
• 3
• S
• ×
• l
• ,
• the concentration of the valid particles is calculated, where S is the effective area of the photosensitive area of the image sensor in (mm2;
• l is the telecentric lens depth of field in mm;
• di is the particle diameter in mm;
• Vc is the total volume of the valid particles, V is the volume of the measured area;
• n is the number of the valid particles.