**Jacek Piekarski **

Koszalin University of Technology, Poland

corresponding author’s e-mail:

**Abstract**

Gravitational filtration process velocity is directly proportional to the pressure difference occurring on both sides of the filtrating layer and inversely proportional to the resistance that the medium meets during its flow through filtering layer pores. Velocity of filtration increases at a smaller rate than the pressure difference increase because in the case of the pressure difference increasing, filtrating layer porosity decreases and resistance increases. Therefore, correct selection of the porous layer has impact on the filtration device efficiency and filtrate parameters, so, it should stop suspended solids and generate insignificant hydraulic resistance to the filtrate stream. Often an assumption is made in practical analyses that granular porous beds do not get compressed during filtration process. However, due to action of various factors, thickness of the filtrating layer reduces resulting in increase of compression and bed total resistance. Bed porosity and filtration, as well as permeability coefficients values, decrease. Change of bed porosity value can be determined through mathematical approach depending on, among other things, bed compression change as gravitational filtration process distorting factor.

**Keywords **

gravitational filtration, bed porosity, bed compression, mathematical modelling

**Full text**

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