08 TECHNICAL INFORMATION | PRODUCT-SPECIFIC SECTION
Flow rate
To determine the possible applications of glass filter disks and filtration apparatus, it is necessary to know not only the porosity, but also the flow rates of liquids and gases. These are given in Figures 9 and 10 for water and air. The data applies to 30mm diameter filter disks.
The flow rates for other disk diameters can be calculated by multiplying the value read off by the conversion factor given in Table the following table:
Filter disk diam. mm
Conversion factor
10 20 30 40 60 90
0.13 0.55
1
1.5 2.5 4.3 6.8 9.7
120 150 175
15
Example Suction filtration of an aqueous solution under vacuum using a suction filter with a 60mm disk diameter and porosity 4. Figure 9 gives a flow rate of 200mI/min for a pressure differential of about 900mbar. Table 8 gives a flow volume of 200 x 2.5 = 500ml/min for a 60mm disk diameter. As the flow rate is heavily dependent on the pore diameter (pore radius to the power of 4), deviations from the values indicated may occur. Flow can also be obstructed by the formation of a filter cake over the surface of the filter disk. Further changes to the flow rate occur if liquids are used whose viscosity differs from that of water. The resultant flow rate is then inversely proportional to the viscosity. Differences for gases result when using filter disks that are coated with water or other liquids (gas flow in washing processes). More detailed information can be found in the literature 1 .
1 Frank, W.: GIT (1967) Iss. 7 pp. 683 – 688
Water flow rate
Water flow rate through filter discs of various porosities as a function of pressure differential. For filter discs with Ø 30mm
214
Powered by FlippingBook