Page 601 - Polymer-based Nanocomposites for Energy and Environmental Applications

554 Polymer-based Nanocomposites for Energy and Environmental Applications

V=0 Vπ0

Fiber Fiber
cross cross
section section

Nonslip flow Slip flow
Fig. 20.1 Velocity profiles at the fiber surface for nonslip flow and slip flow [2].

polyacrylonitrile-DMF solutions to produce bead-free fibers. The produced webs
were challenged with aerosol particles with 100 nm diameter, where pressure drop
and filtration efficiency were analyzed. The average pore size of nanofibrous filter
sample was found to be around 100 nm. When the fiber diameter increases, the
averagepore sizealsogetslarger. However, thepressuredropdecreases with
the increase of the fiber diameter. The filtration efficiency increases with a
decrease in the fiber diameter. Furthermore, thicker samples (higher basis weights)
provided better filtration efficiency at an expense of increase in the pressure drop.
Finally, webs composed of straight nanofibers exhibited higher efficiency as filter
media [3].
Dehghan et al. produced composite PAN-MgO nanofibers using electrospinning.
Fifteen experiments (different PAN-MgO concentration, applied voltage, and tip-to-
collector distance) were conducted to determine the optimized filtration performance,
which is related to web properties such as porosity and fiber diameter. They showed
that the fiber diameter increased with an increase of concentration, which means
higher viscosity. On the other hand, the fiber diameter had inverse correlation with
the applied voltage and the tip-to-collector distance. The optimum spinning conditions
were reported to be 12 wt% concentration, at a potential of 15 kV from a spinning
distance 13 cm for 10 min. HEPA filter efficiency (H13, 99%–97% for 0.3 μm
particles) was obtained at an expense of 132 Pa for flow rate of 20 L/min, which is
less than half of the commercial filters [4].

20.2.1 Quality factor

Not only the filter capture efficiency but also lifecycle and operational cost of a filter
are important performance parameters. Those can be estimated approximately from
the pressure drop through filters. The lower the pressure drop, the lower the energy
consumption of a filtration unit. As a consequence, the filter has longer operational
life. Filters with higher efficiency and lower pressure drop have promising potential
for high-performance applications. The term named as the quality factor (QF) is used