Numerical study of collection efficiency and heat-transfer characteristics of packed granular filter
Junlin Chena,b, Xunfeng Lia,b,*, Xiulan Huaia,b,*, Yongwei Wanga,b, Jingzhi Zhoua,b
The collection mechanism and heat-transfer characteristics of a packed granular filter were investigated using a three-dimensional randomly packed granular filter model. The bridging method was introduced to optimize the grids of contact points between granules. The influences of granular bed depth, gas velocity, and gas temperature on grade collection efficiency were investigated. The results indicated that a decrease of temperature improved collection efficiency when the particle diameter was greater than 5 μm. The grade collection efficiency maintained a stable value when the Stokes number, St, was less than 0.009, but increased linearly with lg(St) when St ≥ 0.009. A logarithmic mean temperature difference method was used to obtain overall heat-transfer coefficients of gas–solid two-phase flow through the packed granular filter. The results showed that convective heat transfer was enhanced due to the introduction of solid particles in the bed. The overall heat-transfer coefficient increased approximately linearly with an increase in particle loading ratio. The Nusselt number was related to the Reynolds number, the Archimedes number, and the particle loading ratio.
Packed granular filter; Gas–solid two-phase flow; Grade collection efficiency; Heat transfer