Design of self-cleaning pipe segment for concentration measurement of cooking fume particulate matter and analysis of influencing factors

For the on-line concentration measurement of cooking fume particles with light scattering method, considering the vulnerability of oil fume pollution on the measurement system, a rectangular pipe with the across-section size of 450 mm×400 mm was taken as an example to design a self-cleaning cooking fume particulate matter concentration measurement section by ejecting clean air to protect the optical components with Venturi effect. By using computational fluid dynamics (CFD) method, the pressure distribution characteristics and throat negative pressure levels of four types of measuring sections including linear, VitoHinsch, bicubic and quintic curves were compared and analyzed. It was found that the pressure loss of the VitoHinsch section was the smallest, which was 41% and 35% lower than that of the linear and quintic curve under the same conditions. Experimental measurement system was constructed based on the VitoHinsch profile, and the experimental data of the throat pressure under different working conditions were used to verify the simulation model. The experimental and simulation data of the composition distribution in the pipe segment were compared. The results showed that the error between experiment data and simulation data of the pressure near the measuring element was within 20%. Under the lowest flow rate, the throat negative pressure met the requirements,and the best measurement position was the mainstream area 20 mm away from the wall.