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Reynold

Reynolds flow classification in sedimentation tanks determines the flow type (laminar, transitional, turbulent) affecting particle settling and tank design. The classification is based on the Reynolds number calculated from water flow velocity and tank depth, with laminar flow preferred for efficient sedimentation. Additionally, settling velocity classification (Stokes' Law, transition, Newton's Law) helps understand particle motion in fluids, guiding design for effective sedimentation based on particle size.

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24 views2 pages

Reynold

Reynolds flow classification in sedimentation tanks determines the flow type (laminar, transitional, turbulent) affecting particle settling and tank design. The classification is based on the Reynolds number calculated from water flow velocity and tank depth, with laminar flow preferred for efficient sedimentation. Additionally, settling velocity classification (Stokes' Law, transition, Newton's Law) helps understand particle motion in fluids, guiding design for effective sedimentation based on particle size.

Uploaded by

Nagendra Kola
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reynolds flow classification for sedimentation tank

ChatGPT said:

Reynolds flow classification in a sedimentation tank is used to determine whether the flow is
laminar, transitional, or turbulent. This classification helps in understanding how particles
settle in the tank and affects the design and efficiency of sedimentation.

Reynolds Number (Re) Formula:

Re=VdνRe = \frac{V d}{\nu}Re=νVd

where:

 VVV = Velocity of water flow in the tank (m/s)


 ddd = Characteristic length (often taken as the depth of the tank) (m)
 ν\nuν = Kinematic viscosity of water (m²/s)

Classification of Flow:

1. Laminar Flow (Re<500Re < 500Re<500):


o Smooth and orderly flow.
o Preferred for sedimentation tanks because particles can settle easily without
excessive turbulence.
2. Transitional Flow (500<Re<2000500 < Re < 2000500<Re<2000):
o Flow begins to develop turbulence.
o May cause some disturbance in sedimentation.
3. Turbulent Flow (Re>2000Re > 2000Re>2000):
o Chaotic flow with strong mixing.
o Not desirable for sedimentation as particles may resuspend.

In sedimentation tanks, the aim is to maintain laminar or near-laminar conditions to enhance


settling efficiency. Design considerations like baffles, flow distribution, and appropriate tank
dimensions help in achieving this.

4o

You said:

reynolds flow classification for settling velocity


ChatGPT said:

Reynolds flow classification for settling velocity helps in understanding the nature of a
particle's motion as it settles in a fluid, such as water in a sedimentation tank. It is based on
the Reynolds number (Re) calculated using the particle's settling velocity.

Reynolds Number for Settling Velocity:

Re=VsdνRe = \frac{V_s d}{\nu}Re=νVsd


where:

 VsV_sVs = Settling velocity of the particle (m/s)


 ddd = Diameter of the particle (m)
 ν\nuν = Kinematic viscosity of the fluid (m²/s)

Classification of Settling:

1. Stokes’ Law (Laminar Settling) – Re<1Re < 1Re<1


o The flow around the particle is smooth and viscous forces dominate.
o The particle settles slowly and uniformly.
o Settling velocity (VsV_sVs) follows Stokes’ Law:

Vs=g(ρs−ρ)d218μV_s = \frac{g (\rho_s - \rho) d^2}{18\mu}Vs=18μg(ρs


−ρ)d2

oExample: Fine clay and small silt particles.


2. Transition Settling – 1<Re<10001 < Re < 10001<Re<1000
o Both viscous and inertial forces influence particle movement.
o Settling velocity does not strictly follow Stokes’ Law.
o Example: Medium-sized sand particles.
3. Newton’s Law (Turbulent Settling) – Re>1000Re > 1000Re>1000
o The flow around the particle is turbulent and dominated by inertial forces.
o The particle settles quickly.
o Settling velocity follows Newton’s Law:

Vs=4g(ρs−ρ)d3CdρV_s = \sqrt{\frac{4g (\rho_s - \rho) d}{3C_d \rho}}Vs


=3Cdρ4g(ρs−ρ)d

o Example: Gravel and large sand particles.

Practical Importance in Sedimentation Tanks:

 Fine particles (Re < 1) need long detention times or coagulants to enhance settling.
 Medium particles (1 < Re < 1000) settle effectively in well-designed tanks.
 Large particles (Re > 1000) settle rapidly and are easily removed.

Proper design ensures that the flow regime promotes effective sedimentation for different
particle sizes.

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