Settling is the process by which particulates settle to the bottom of a liquid and form a sediment.

Settling velocity or fall velocity or terminal velocity (ws) of a (sediment) particle is the rate at which the sediment settles in still fluid. It is diagnostic of grain size, but is also sensitive to the shape (roundness and sphericity) and density of the grains as well as to the viscosity and density of the fluid. It integrates all of these into a key transport parameter.

For dilute suspensions, Stokes' Law predicts the settling velocity of small spheres in fluid, either air or water. Stokes' Law finds many applications in the natural sciences, and is given by:

 
where w is the settling velocity, ρ is density (the subscripts p and f indicate particle and fluid respectively), g is the acceleration due to gravity, r is the radius of the particle and μ is the dynamic viscosity of the fluid.

Stokes' law applies when the Reynolds number is less than 0.1.

Settleable solids are the particulates that settle out of a still fluid. Settleable solids can be quantified for a suspension using an Imhoff tank or cone.
 
沉淀是微粒沉降到液體底部并形成沉淀物的過(guò)程。

一種(沉淀物)微粒的沉淀速率或者叫下降速率或未速是微粒在靜止液體內(nèi)的沉淀速率。它可以診斷微粒大小，但也敏感于微粒形狀(圓度和球度)、密度以及液體的密度和粘度。它將所有這些綜合為一個(gè)關(guān)鍵的 運(yùn)移參數(shù)。

對(duì)于稀懸浮液，斯托克斯定律可預(yù)測(cè)小球在液體中、水中或空氣中的沉降速率。斯托克斯定律在自然科學(xué)中有許多用途，它是這樣表示的：

式中，W是沉淀速率；p是密度(下標(biāo)p和f分別代表微粒和液體)；g是重力加速度；r是微粒半徑；μ是液體的運(yùn)動(dòng)粘度。

雷諾數(shù)小于0.1時(shí)，斯托克斯定律適用。

沉淀性固體是從靜止液體中沉淀出來(lái)的微粒。

懸浮液中的沉淀性固體可用雙層沉淀池或錐形沉淀池定量測(cè)定。