Institute for Radiohydrometry of the Technical University Munich

Layout of a flow model for the imitation of installed screens under operational conditions

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Permeabilities and Hydraulic Properties

You will find the advantage of con-slot Screens in the large open area. However, since the free open area alone is not the criteria for the efficiency, a direct comparison of con-slot Screen open area with the open area of other screen media should never be made!

We note that in practical application very of­ten the width of the support structure “b2” is being omitted when investigating the open area of a profile wire screen structure. First it falsifies the open area and then it alters the results of the flow pattern calculation. The values of the specific properties of a con-slot Screen structure are to be found in the constants “a” and “b” - see the Forchheimer-Schnebelli law - (see formula)

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This means: even if the direct comparison between con-slot and other screen structu­res does look disadvantageous for con-slot the calculation of the flow-losses alone proves the advantages of the con-slot Screen! High flow rates with negligible pressure los­ses - the advantage of the V-form giving slot, comparable with a Venturi-nozzle!

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Hydraulic properties of filter tubes or filter plates are related to physical laws which de­fine the flow gradient (pressure loss) through the screen wall structure as a function of the velocity of flowing media. Experiments have shown that with the increasing flow velocity (filter velocity) “v” also the gradient “l” at the screen wall structure increases.

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The diffe­rence between laminar and turbulent flow as known in fluid dynamics is also valid for filtra­tion. However, the following difference must be noted: The transition between laminar and turbulent flow through con-slot Screen structures does not occur abruptly as deter­mined likewise for pipes and channels, but gradually. It is comparable to the behaviour of porous medias i.e. precoat filter medias, filtersand, filter of sintered metal, etc., or ion-exchange medias like resin, catalyst beds, etc. Experience has shown that the combination of both, con-slot Screens and above medi­as, develop advantageous flow characteri­stics for operation and efficiency.

Therefore, no mathematical equation can be formulated which only describes the resist­ance of a screen structure either for laminar or for turbulent flow. The best approach is to distinguish between “viscous” and “inert” flow of the media through the screen wall structure.

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Constants “a” and “b” are resistivity figures of the con-slot screen structure and are related to the viscous and inert flow characteristics.

Research conducted at the Institute for Radiohydrometrie at Munich, showed that the con-slot Screen structure permeability (flow capacity) can be defined by a “k”-factor:

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The larger the k-factor (and not the open area!), the larger is the filtration/flow effi­ciency.
Efficiency diagrams for standard screen structure are available for you, calculated for water with a temperature of 14 degrees Cel­sius. We are at your disposal with our programmes, if the determination of flow pattern for other conditions/for other media is re­quested.

con-slot Screens: High permeability combined with high mechanical strength.

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con-slot SCREENS | Industriegebiet Hafen | Graue Riethe 2 | D-29378 Wittingen
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