Filter resistance

Face dimensions, in Depth, less gaskets, in Design air-flow capacity at clean-filter resistance of 1.0 in water (standard ftVmin)... 

The pressure drop through the filter is a function of two separate effects. The clean filter has some initial pressure drop. This is a function of filter material, depth of the filter, the superficial gas velocity, which is the gas velocity perpendicular to the filter face, and the viscosity of the gas. Added to the clean filter resistance is the resistance that occurs when the adhering particles form a cake on the filter surface. This cake increases in thickness as approximately a linear function of time, and the pressure difference necessary to cause the same gas flow also becomes a linear function with time. Usually, the pressure available at the filter is limited so that as the cake builds up the flow decreases. Filter cleaning can be based, therefore, on (1) increased pressure drop across the filter, (2) decreased volume of gas flow, or (3) time elapsed since the last cleaning. 

Rf = initial filter resistance (resistance of filter plate and filter channels) (m" )... 

K l = specific dust/fabric filter resistance coefficient C, = inlet dust concentration (g/m- )... 

Design airflow capacity at clean filter resistance ... 

Rotary viscous A continuously rotating oil-coated roll of material. The filter resistance is kept low by a motor drive that ensures a clean surface is always presented to the airflow. 

Air filter resistance The pressure drop created between the upstream and downstream faces of a filter, increases as the dust burden. 

Air filter resistance, final The maximum pressure drop allowed across a filter to ensure that the design airflow rate is achieved. 

Since the filter resistance in the filter medium is neglected, the second part of equation (7.3.1.5) is neglected. Let us define a new constant, C, equal to the mass of solid deposited on the filter per volume of filtrate. 

Ro is some typical value of the filter resistance. Equations (6.2.2), (6.2.3) are reduced to the dimensionless form... 

Table 84—Filter-Resistance Coefficients, K t for Certain Industrial Dusts. (Industrial Cloth-Type Air Filters)...

Directly prior the experiment the quality, that is the tightness, of the PBCEC monolayer is assessed by determination of the transendothelial electrical resistance (TEER) of each filter. TEER measurements can be easily performed with the ENDOHM-24 chamber and the EVOHM voltometer (World Precision Instruments, Inc,). The resistance data, expressed in Q, are multiplied with the filter surface (4.52 cm2), corrected for blank filter resistance and expressed in L2 x cm2. 

Filter pressure gauges should be marked with the clean filter resistance and the change-out filter resistance. 

GMF FILTERS Resistant to weakening or disruption of the fibrous matrix by inorganic or organic solutions and has a broad chemical compatibility. Made of borosilicate glass microfibers. Presterilized by gamma irradiation. 

Efficiency 1. Commercial makes are fbnnd in a variety of efficiencies, these depending roughly on filter resistance for similar types of medium 2. Efficiency decreases with increased dust load and increases with increased velocity up to certain limits 1. In general, give higher efficiency than viscous typa, particularly on fine particles 2. Efficiency increases with increased dust lond and decreases with increased velocity ... 

The product of the specific filter resistance a and the liquid viscosity tj lies in the ranges between at] =10 mPa s for filterable suspensions and arj =10 mPa s for insufficiently filterable suspensions. 

In some cases, acid scavenging is not used to stop further reactions of the acid, but to shift an existing equilibrium to the favored side. This is true for elimination reactions or the formation of ylids that are further used in Wittig reactions. Hydrochloric acid (HCI) is the acid most commonly formed. Usually, tertiary amines such as triethylamine are added to scavenge the acid. With the acid, these substances form solid salts which turn the reaction mixture into a suspension. The solid byproduct must then be removed. This can be done via a filtration step which requires expensive equipment, especially for precipitates vrith high filter resistances or continous filtration. If the product is inert to and insoluble in water, one can dissolve the solid by adding water to the reaction mixture, and remove the organic phase by a simple liquid-liquid separation. If the product is sensitive to acids and moisture, until now only filtration was left as a suitable means. 

When short cycle times are used in continuous filtration and/or the filter medium resistance is relatively large, the filter resistance term B must be included, and Eq. (14.2-13) becomes... 

For suspensions with a low solid content, a thickening of the suspension, for example, in a hydrocydone, can be advantageous. Some centrifuges need high suspension densities to work properly. In cases where the filter resistance of a suspension is high, a thickening can reduce the filtration time considerably. 

Particle shape and particle size are often linked to the permeability of the filter. Figure 14.5 shows such a clear-cut example. However, cases of large plate-like crystals are known that still have an acceptable filterability. Thus, a determination of the filter resistance is highly recommended. 

A test method called the modified fouling index (MFI or MFI-0.45) is gaining popularity and has been used in Europe for 25 years. The test was developed based on Darcy s Taw that relates flux (dV/dt) to the thickness of the cake layer, which is the sum of the filter resistance (R ) and the cake resistance (R) ... 

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