Page 603 - Polymer-based Nanocomposites for Energy and Environmental Applications

556 Polymer-based Nanocomposites for Energy and Environmental Applications

Compared with randomly laid nanofibrous webs, filters composed of aligned nano-
fibers provided lower pressure drop [8].
Tehrani et al. [9] investigated aerosol movement and deposition through parallel
and gradual multifibrous membranes via finite-volume method (FVM). They
supposed that the particulate flows were transitory, incompressible, and laminated.
Aerosols have been sent uniformly to filter and simulated by Lagrangian method,
which is related to Saffman’s lift, drag, and Brownian forces [9]. The influence of
laminar particulate flows from laminar vortex shedding (Re¼100 and Re¼200) to
supercritical (Re¼1000) has been examined for the nanofiber diameter range of
100 and 500 nm [9]. Pressure drop and particle deposition have been affected by
the fiber alignment, solid volume fraction (SVF), and filter thickness. It was found
that regular structures are more suitable than irregular structures for airborne particles,
as the parallel-structured nanofiber filters have shown superior capture efficiency in
the range of 750–1000 nm. As a result, the parallel filter is found to be the best candi-
date with the characteristics of l/h¼1.143 (ratio of horizontal to vertical distances
between fibers), α¼0.687, I x ¼116.572 (the membrane thickness), and h/d f ¼1.0
(the ratio of vertical distances between fibers and fiber’s diameter) for aerosol
filtration [9].

20.2.3 Reuse and cleanability

Nanofibrous filters can more effectively capture nanoparticles than the conventional
glass fiber filters. However, the aerosols can be deposited on the filter surface and
form a cake, over time during filtration. Hau et al. [10] investigated backpulse and
backblow cleaning of nanofiber filter loaded with nanoparticles. Nylon 6 nanofibers
were fabricated using electrospinning technique, and then, these nanofibers were
loaded with particles that were produced with an aerosol generator. In order to clean
loaded filters, the air jets in the form of three modes—(a) backpulse, (b) backblow, and
(c) combined backpulse with backblow—were used. The results revealed that all
modes can effectively remove particles trapped in the filter. Also, it is found that back-
pulse is more effective in removing cake form from the filter surface than backblow.
However, the backblow mode has an advantage that removing by convection of the
detached aerosols away from the filter prevents recapture. Combined-mode cleaning
is found to be performing the most effective cleaning due to synergistic effect [10].
Recent developments in the production of synthetic fibers enable to fabricate fibers
with various cross sections such as trilobal, triangular, quatrefoil, ellipsoidal, rectan-
gular, and square. Wang and Zhao [11] investigated the influence of fiber geometry
and their orientation angle on filtration performance. For evaluation of filtration
performance, the pressure drop, the capture efficiency, and the QF due to three main
capture mechanisms (diffusion, interception, and inertial impaction) were calculated.
Results were analyzed by comparing the results with circular fibers and four
noncircular (triangular, quatrefoil, trilobal, and rectangular) fibers. The diffusional
capture efficiencies of all fibers were almost independent of the orientation angle
for small particles. When the interception mechanism is predominant, larger aspect
ratio would mostly lead to higher capture efficiency [11].