The electronic air filter has a pair of pads between which a grid is sandwiched. The vertical multitubular heat exchanger of the present invention introduces a process fluid containing an easily-polymerizable substance into heat exchanger tubes to perform heat exchange. Data is output that corresponds to a particular address in the selected storer. A third step involves forming a interior cavity in at least one of the segments. The second contact device is arcuate in shape and has at least one deformation at the beginning and at the end of the arc, wherein, as a result of the deformations of the second contact device co-operating with the two stop elements of the pressure member, the connection element is prestressed.