Flocculation small-bore tubes

Bearing in mind the problem that scale-up is not meaningful from the jar test apparatus, an alternative test method is to avoid paddle stirrers (although they appear superficially like the full-scale paddle flocculators) and use small-bore tubes. These can be related to practice in the sense that they are flow-through devices, and their mean velocity gradients (G) can be easily measured or calculated. 

It is claimed that small-bore tube flocculators have advantages over the conventional jar test because there is a rapid response to changes in chemical conditions and so optimum conditions can be established fairly quickly using quite small sample volumes, typically about 20% of the jar test requirements. 

The natural turbulence of flow through a pipe can create velocity gradients leading to flocculation. In the laboratory, small-bore tubes operate in laminar flow (section 4.9.2) with Reynolds numbers less than 2000. In practical pipe flow the situation is turbulent and head loss is given by the Darcy-Weisbach equation 4.66. 

In the case of fixed bed (deep bed granular filters) flocculators the power is dissipated as laminar flow through granular media, with local velocity gradients in the pores formed by quasi-parabolic velocity distributions. The system is analogous to small-bore tubes (section 4.9.2) bearing in mind the capillary model concept of the Kozeny-Carman equation 4.68 for head loss through a fixed bed,... 

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