Parallel fibers nonuniform

Hartwick (17) aligned uniformly sized fibers into a densely packed hexagonal array. The interstices between the fibers represented the flow channels. There was no transport between the channels. The performance of the device was low relative to its permeability. This is not unexpected A key property of a packed bed is the radial mass transfer, which evens out flow nonuniformities. Tto is not possible in a device consisting of parallel independent flow paths. In an array of circular parallel channels, the breakthrough time for an unretained sample is inversely proportional to the square of the diameter of the channel. To obtain a plate count of 10,000 plates, it would be necessary that the relative standard deviation of the channel diameter is under 0.5% (see also the footnote in Section 2.1.4). This is clearly a tall order. For retained peaks, similar demands would need to be placed on the uniformity of the stationary phase from channel to channel. 

Fig. 5.64 SEM of Izod impact fractured, glass fiber filled thermoplastic test specimens show nonuniform distribution of fibers in the two different specimens (A, C, D and B, D, F). The fibers (A) appear aligned parallel to the skin and the matrix exhibits brittle failure as hackle marks (arrows) are seen. The fibers (B) protruding appear long and poorly wetted with the resin. Hackle or ridged patterns (arrows) are observed (C). Resin is also seen on the fiber surfaces in some regions (D and F) whereas cleaner fiber surfaces and less well bonded regions are also observed (E).

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