Na modelu naknadnega krožnega usedalnika disertacija obravnava tipične tokovne strukture, ki se vzpostavijo pri dvanajstih različnih kombinacijah hidravlične obremenitve in koncentracije suspenzije na vtoku. Poleg že omenjenih so bili spremenljiv parameter tudi trdni delci, ki so služili kot suspendirana snov. Prva skupina uporabljenih delcev je bila mleta lešnikova lupina, ki je bila na voljo v dveh sestavih glede na strukturo velikosti zrn; drugo skupino so zastopali stekleni delci v treh različnih granulacijah. Trije kontrolni poskusi so se izvedli pri gostotno nevtralnih pogojih z vnosom barvila.
Vsi poskusi so bili snemani z digitalno kamero, iz posnetkov je bil s fotogrametričnim pristopom v vtočnem jašku in v neposredni bližini iztoka določen indikator koncentracije v suspenziji, s pomočjo računalniško podprte vizualizacije pa so bili pridobljeni podatki o tokovnem polju. Pri ponovitvi prve serije poskusov se je izvajalo še vzorčenje suspenzije na vtoku in iztoku.
Velik nabor eksperimentov s skrbno izbranimi parametri je omogočal sistematično obravnavo hidrodinamičnih fenomenov v usedalni komori. Ugotovilo se je, da sta tokovno polje in učinkovitost usedanja trdnih delcev tesno povezana z vrednostjo Froudovega densimetričnega števila Frd. Pri vseh poskusih je bil opažen trend naraščanja učinkovitosti s padanjem vrednosti Frd. Pri največjih izmed steklenih mikrokroglic in grobo mlete lešnikove lupine se troslojni tok ni pojavil; pri ostalih delcih pa je nizka vrednost Frd pogojevala vzpostavitev ugodne troslojne tokovne strukture, pri čemer je bila mejna vrednost Frd, nad katero se troslojni tok ne oblikuje več, neodvisna od tipa in velikosti delcev.
| Language: | English |
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| Title: | Influence of flow field on sedimentation efficiency in a settling tank with continuous operation |
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| Abstract: |
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On a model of a circular secondary settling tank the dissertation deals with typical flow structures that establish at twelve different combinations of hydraulic and solids loading. Another variable parameter beside the already mentioned were also solid particles that served as suspended matter. The first group of used particles was fine ground hazelnut shell that was available in two different compositions of grain size; the second group were glass microbeads in three different granulations. Three control experiments were conducted at neutral density conditions by introducing a dye.
All experiments were filmed with a digital camera. By processing video clips of experiments an indicator of concentration in the inflow and in the vicinity of the effluent was captured by photogrammetric approach and data on flow field was obtained by computer-aided flow visualization. A repetition of the first series was carried out in order to collect samples of inflow and outflow suspension.
A wide set of experiments with carefully chosen parameters enabled a systematic study of hydrodynamic phenomena in the sedimentation chamber. Flow field and clarification efficiency were found out to be closely related to the value of the densimetric Froude number Frd. All experiments exhibited trends of growing efficiency when values of the densimetric Froude number Frd were decreasing. A three-layer flow structure never occurred when the biggest particle granulation from glass microspheres and when coarse ground hazelnut shell was used. By the rest of the model particles a low value of Frd reflected in a formation of favourable three-layer flow structure, whereas the threshold value of Frd (when the value is exceeded, the three-layer flow does not develop) was independent from the type or size of the particles.
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| Keywords: | civil engineering, thesis, secondary settling tank, densimetric Froude number, density currents, continuous operation, wastewater treatment, efficiency, suspension, particle size, computer-aided flow visualization |
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