Yuanzineng kexue jishu (Nov 2023)
Experimental Study on Gas Flow and Aerosol Deposition Characteristics in Micro-channel
Abstract
Aerosol retention occurs when it penetrates through micro-leakage paths within the containment after nuclear reactor accidents. Aerosol particles are deposited by mechanisms such as gravity sedimentation, Brownian diffusion, entrance effect, and turbulence deposition, and the deposition efficiency is affected by the carrier gas flow conditions. Therefore, it is necessary to study aerosol deposition characteristics within micro-leakage paths under laminar and turbulent flow regimes. In this work, an experimental facility consisting of two circuits was established for investigating the flow characteristics and aerosol deposition behaviors. In the flow test circuit, the flow resistance characteristics of air within the Re range of 40 to 3 600 are obtained by measuring the pressure differential and volume flow rate. In the aerosol test circuit, the penetration of aerosols is obtained by measuring the particle size distribution and concentration at the inlet and outlet of the micro-leakage paths. The experimental configuration encompassed the use of capillaries with diameters of 350, 550, 800, and 1 000 μm and length of 52 mm, as well as a rectangular micro-channel with dimensions of 26 μm×30 mm×52 mm to simulate micro-leakage paths. The aerosol comprises polydisperse TiO2 dust particles with a mass median diameter of less than 1 μm. The results of the flow testing reveal that, in both capillaries and rectangular micro-channel, the variation curve of the Cd·Re (Cd is Darcy resistance coefficient) with Re significantly deviates from the traditional laminar characteristic curve within a range of ±5% when the Re reaches 700, indicating that the gas flow has transitioned into turbulent flow. Under laminar flow conditions, it is observed that within capillaries with diameters of 800 and 1 000 μm, aerosol deposition is not evident at Re ranging from 380 to 600. The particle size distributions at the inlet and outlet are similar, with the penetration exceeding 90%. However, within rectangular micro-channels at Re between 40 and 130, as the Re increases, the aerosol penetration increases from 12% to 50%. During to the differences in size and structure feature, rectangular micro-channel has an obvious entrance effect compared with thin wall capillary. With the increase of the Re, the lift force of particles generated by the entrance gas velocity gradient leads to a reduction in entrance deposition, so the penetration is enhanced. Under turbulent flow condition, it is observed that within capillaries with diameters of 350, 550, and 800 μm, the aerosol penetration shows a decreasing trend as Re increases from 800 to 3 600. In the test with capillary diameter of 550 μm and Re of 2 100, the proportion of larger particles shows significantly reduced. Aerosol deposition predominantly occurs within the vortex diffusion-impaction region and the inertia-dominated region, with the effect of turbulent eddies, the fluctuating velocity of particles towards the wall intensifies, accelerating the deposition of aerosols.
Keywords
