Depth filters are used in air-conditioning, cleanroom technology and exhaust gas aftertreatment to remove particles from gases. These removed particles form deposits in the porous structure of the filter media. Such deposits adhere to the filter media in most applications because high flow velocities are necessary for detachment, for instance velocities above 1 m/s for deposits of 10 µm glass spheres. Velocities in filtration processes are usually lower because of particle bounce and backpressure. New findings show that reaction of reactive components in deposited particle structures can enable re-arrangement and detachment of particulate structures even at low flow velocities. In the scope of this project first experimental results regarding re-arrangement and detachment of agglomerates, consisting of soot and glass spheres, on/from a single fibre exposed to hot air flow are presented and discussed.
In the experiments, particulate matter deposits were built by consecutive collection of soot and glass spheres on a single fiber. Two types of experiments were performed. One type at ambient temperature and therefore without reaction and the other type at high temperature with reaction. The mean velocity necessary for detachment of agglomerates without reaction was determined as 3.5 m/s. With reaction detachment occurred at velocities as low as 0.48 m/s. Detachment of agglomerates was recorded by a camera and investigated using image analysis.
The investigations show that even dense soot deposits can break up, re-arrange and detach from a single fibre at low flow velocities due to reaction of a deposited component. Based on these investigations a penetration of deposited material through filter media seems to be possible.