Depth filters are used, for instance, in air-conditioning and cleanroom technology for removal of particles from gases. In such applications, the particles deposit and accumulate inside the fibrous filter medium causing an increase in separation efficiency, pressure drop and hence energy consumption. In conventional depth filter systems operating flow velocities are below 1 m/s. At velocities well above 1 m/s particles are likely to bounce off or being blown off from the fibre. To detach particles of 10 μm from filter fibres high flow velocities above 1 m/s are needed (Löffler 1972). All the findings of Löffler are valid for stiff fibres. For this type of fibres, there is a huge expertise based on well-founded investigations. However, at present there is no knowledge about the detachment behaviour of particles and agglomerate structures from an elastic fibre, which is stretched and exposed to an airflow at velocities below 1 m/s. The detachment process will be the focus of subsequent investigations using elastic fibres and well defined glass particles, first findings using a simple professional set-up showed that glass particles and agglomerates detach from the fibre at velocities below 1 m/s, when an elastic filter fibre is stretched after loading with particles. For deeper investigations on re-arrangement and detachment of deposited particle structures from an elastic fibre, a new measurement system and new fibre mounting are designed. This device will be used during the loading process with particles and the stretching process of the fibre afterwards. During the loading process, the size and number of deposited particles will be determined by optical particle counters. During the stretching process, detached agglomerates will be characterised by a laser light sheet measurement system. The stretching of the fibre will be realised by piezo- actuators for a controlled manipulation/change of the fibre length. Experiments with different stretching rates and number of stretching cycles are planned.
Finally, the application of such elastic fibres in a filter medium could be an enabler for self-adaption or actively-controlled adjustment of filters. This application will have the aim to delay increasing filter backpressure while maintaining a high level of separation efficiency. Consequently, this would extend the life span of the filter.
This project is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) − 427981860.