Fiber collector

Filtration is a physical separation whereby particles are removed from the fluid and retained by the filters. Three basic collection mechanisms involving fibers are inertial impaction, interception, and diffusion. In collection by inertial impaction, the particles with large inertia deviate from the gas streamlines around the fiber collector and collide with the fiber collector. In collection by interception, the particles with small inertia nearly follow the streamline around the fiber collector and are partially or completely immersed in the boundary layer region. Subsequently, the particle velocity decreases and the particles graze the barrier and stop on the surface of the collector. Collection by diffusion is very important for fine particles. In this collection mechanism, particles with a zig-zag Brownian motion in the immediate vicinity of the collector are collected on the surface of the collector. The efficiency of collection by diffusion increases with decreasing size of particles and suspension flow rate. There are also several other collection mechanisms such as gravitational sedimentation, induced electrostatic precipitation, and van der Waals deposition their contributions in filtration may also be important in some processes. 

Unique fiber collector designs have been attempted to loosen the electrospun scaffold to improve cell infiltration. The principle of the collector design is to reduce the fiber intersections. For example, a half-ball collector containing pillars was designed to achieve cotton ball-like fibrous scaffolds by changing the fiber deposition space (Figure 19.5(a)) [22]. An ethanol bath was used as a collector to obtain low-density electrospun polycaprolactone scaffolds (Figure 19.5(b)) [23]. The ethanol quickly stabilizes the polymer fiber surface to reduce the intersections between fibers. 

Table 11. Chemical Compatibility of Fibers in Dust Collector Bags...

In the spunbond process (Fig. 10), an aspiratory is used to draw the fibers in spinning and directiy deposit them as a web of continuous, randomly oriented filaments onto a moving conveyor belt. In the meltblown process (Fig. 11), high velocity air is used to draw the extmded melt into fine-denier fibers that are laid down in a continuous web on a collector dmm. 

Fiber-reiaforced panels covered with PVF have been used for greenhouses. Transparent PVF film is used as the cover for flat-plate solar collectors (114) and photovoltaic cells (qv) (115). White PVF pigmented film is used as the bottom surface of photovoltaic cells. Nonadhering film is used as a release sheet ia plastics processiag, particularly ia high temperature pressing of epoxy resias for circuit boards (116—118) and aerospace parts. Dispersions of PVF are coated on the exterior of steel hydrauHc brake tubes and fuel lines for corrosion protection. 

No collector sHt is fitted, and the full width of the ion beam falls onto microchaimel plates which emit electrons. The emitted electrons strike a phosphor coating on the end of a fiber-optic cable (see Fiber optics). The phosphor emits photons which travel along the cable to the photodiode array. 

Solid particulates are captured as readily as hquids in fiber beds but can rapidly plug the bed if they are insoluble. Fiber beds have frequently been used for mixtures of liqmds and soluble sohds and with soluble solids in condensing situations. Sufficient solvent (usually water) is atomized into the gas stream entering the collector to irrigate the fiber elements and dissolve the collected particulate. Such nber beds have been used to collect fine fumes such as ammonium nitrate and ammonium chloride smokes, and oil mists from compressed air. 

Otner Collectors Tarry particulates and other difficult-to-handle hquids have been collected on a dry, expendable phenol formaldehyde-bonded glass-fiber mat (Goldfield, J. Air Pollut. Control A.SSOC., 20, 466 (1970)] in roll form which is advanced intermittently into a filter frame. Superficial gas velocities are 2.5 to 3.5 m/s (8.2 to 11.5 ft/s), and pressure drop is typically 41 to 46 cm (16 to 18 in) of water. CoUection efficiencies of 99 percent have been obtained on submicrometer particles. Brady [Chem. Eng. Prog., 73(8), 45 (1977)] has discussed a cleanable modification of this approach in which the gas is passed through a reticulated foam filter that is slowly rotated and solvent-cleaned. 

On approaching a collecting body (fiber or liquid droplet), 0 porticle corried along by the gas stream tends to follow the stream but may strike the obstruction because of its inertia. Solid lines represent the fluid streamlines oround a body of diameter Dt, and the dotted lines represent the paths of particles that initially followed the fluid streamlines. X is the distance between the limiting streamlines A and B The fraction of particles initially present in a volume swept by the body that is removed by inertiol interception is represented by the quantity X/Dt, for a cylindrical collector and (X/Dt,) for a sphericol collector... 

Interception A special case of impingement, in which a particle is trapped on a fiber due to the effect of Van der Waals forces rather than inertia. The interception of a particle in a particle collection device occurs when the particle follows a gas streamline round a collector at a distance less than the radius of the particle. 

In an in-bed filter (also known as deep filtration) the particles are separated throughout the whole depth of the filter. The filter is either made of fibers (filter mats) or of collector bodies, see Figure 3.2.1. Collector bodies are applied when the operating conditions are extreme as per the temperature (up to 1400 °C) and the nature of the entrained particles (sticky and abrasive). For separating sticky particles or droplets of high viscosity a moving bed filter can be applied. Movement... 

Due to their high electrical and thermal conductivity, materials made out of metal have been considered for fuel cells, especially for components such as current collectors, flow field bipolar plates, and diffusion layers. Only a very small amount of work has been presented on the use of metal materials as diffusion layers in PEM and DLFCs because most of the research has been focused on using metal plates as bipolar plates [24] and current collectors. The diffusion layers have to be thin and porous and have high thermal and electrical conductivity. They also have to be strong enough to be able to support the catalyst layers and the membrane. In addition, the fibers of these metal materials cannot puncture the thin proton electrolyte membrane. Thus, any possible metal materials to be considered for use as DLs must have an advantage over other conventional materials. 

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