A slotwall panel storage system has a slotwall panel with a plurality of generally \u201cT\u201d shaped slots forming a plurality of generally \u201cT\u201d shaped slats and a hanger bracket for removably mounting a device on the slotwall panel. Various aspects involve treating a fluid with a porous body. Particularly, various embodiments of the present invention provide for a bio-oil having sufficient heating value and stability to be useful as heating oil without the need to hydrotreat the bio-oil or use a similar deoxygenating process. An effective sampling ratio from the sample pool size of the stream of packets in the time interval and the number of sample packets received over the time interval can be calculated. In accordance with the invention, the base plate has in its central region at least one lower tang bent down through 180 degrees whose lateral edges are supported at the inner lateral edges of tangs bent down through 180 degrees at the cover plate. A supplementary magnet is also used in a space that is enclosed in a circular trace of the magnetic sensor around the shaft for even distribution of the magnetic flux generated by the magnetic flux generation means.