Fabric filters bridging

Nanofluidic Altering is based on an electrokinetic trapping mechanism enabled by recent advances in nanochannel fabrication. A nanofluidic filter consists of two microfluidic channels bridged by buffer-filled nanochannels which act hke an ion-selective membrane. The technique is a relatively new technique which has a demonstrated potential for sample enrichment. A schematic chip layout of a nanofluidic Alter is given in Figure 50.36. 

Cake filtration this is undoubtedly the most widely encountered mechanism in industrial filtration and involves the accnmulation of particles that bridge together in a porous structure on the surface of the fabric. It follows from this that, once formed, the cake effectively becomes the filter medium, with the fabric thereafter acting simply as a support. In cases where it is difficult for the particles to form a naturally porous cake, the use of a special precoat or body feed may be employed to assist in this task. 

Problems are usually encountered when pressure systems designed to operate at reasonable levels of particulate concentration are fed with dilute suspensions at the start of filtration. Low concentrations of sohds prevent the bridging effect which ensues when concentrated swarms of sohds are directed towards the pores in the filter medium. This effect is discussed quantitatively elsewhere in this Chapter. Failure to bridge the cloth pores will lead to deposition of particles inside the fabric. 

Most models currently available for blood filtration are based on empirical models/ Bruil proposed a mathematical model for leucocyte filtration process and could explain the filtration law in the plain membrane filter. However, the effect of direct interception in blood filtration is not clearly understood, and the particle capture efficiency may be modelled based on an empirical model proposed by Khilar and Fogler"" for Newtonian liquid flow. With the consideration of the further particle capture due to the reduction of the pore sizes and the porosity of filter fabric by particle bridging, pore blockage, and pore closure, a modified Khilar—Fogler model of the particle capture efficiency by Gruesbeck and Collins" may be applied in blood filtration. 

In the past decade a technology known as micromachining has developed out of IC technology ll. It uses the same techniques, but instead of fabricating electronic circuits on a chip, three dimensional physical structures on a micrometer scale can be made. Intriguing devices such as 100 micrometer electrostatic motors, tweezers, bridges and oscillating beams, 10 nm filters, micropumps and valves have all l n made in silicon and other IC compatible materitds. 

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