Viscous panel filters

Viscous panel filters provide dust retention by the effective impingement of dust on a large area of oily surface. In this respect they can have a snperior performance to dry filters (particularly in heavily contaminated atmospheres). Their effectiveness, however, will also rely on adequate particle retention properties to eliminate subsequent re-entrainment of particles as the oil is dried up by collected sohds. In practice, the retention properties can be adjusted to give constant efficiency or falling (reducing) efficiency. 

Panel filters may use either viscous or dry filter media. Viscous filters are so called because the filter medium is coated with a tacky liquid of high viscosity (e.g., mineral oil and adhesives) to retain the dust. The filter pad consists of an assembly of coarse fibers (now usually metal, glass, or plastic). Because the fibers are coarse and the media are highlv porous, resistance to air flow is low and high filtration velocities can be used. 

Various media, woven and nonwoven fabrics, paper, wire mesh and even membranes may be employed for dry panel filters. The most favoured materials are synthetic fibres and glass fibre, in a pad or mat, in multi-layer or pleated form. It is becoming increasingly common practice to coat the media with a viscous agent to ensure high dust retention. 

This is controlled by the operating characteristics of the viscous panel. If wetting characteristics are adequately maintained, efficiency remains high and substantially constant. In certain circumstances, efficiency may increase, as with conventional dry filters, if the presence of oil on the element assists the formation of a porous bed of solids. If the degree of wetting decreases markedly with build-up of contaminants, the retention properties of the filter will fall, hence its efficiency will also fall. 

There are three main types of filter viscous, dry and HEPA. Viscous filters are normally a coarse weave of glass, plastic or metal strands coated with oil. As the air passes through the filter, particles impact against the material and are held in the oil. The panels are normally washable and can be re-used after re-oiling. Viscous filters provide good general filtration for air inlet to buildings. 

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