The Effect of Inlet Tube Size on a Cone Shaped Flocculater

Shubha Bhar Taylor Britton

Purpose and GoalsPurpose: To study the effects of influent tube size

on the growth and stability of the sludge blanket in a cone flocculator.

Goals:• Build up sludge blanket• Take turbidity values above blanket• Conduct Dimensional Analysis• Determine ideal tube size

Velocity, Momentum, & Shear Velocity: too slow and the flocs settle,

too fast and they all wash out

Momentum: causes the interface between the sludge blanket and the overlying water to be unstable

Shear: Breaks up floc

Hypothesis

We expected that the largest tube size will be most effective in producing the most stable sludge blanket for a given flow rate.

Expected points of failure:velocity = 0.2 m/s

shear = 0.1 Pa

Set Up

Flow Rates and DosageDose Rate and Concentrations

Alum Dose 50 mg/L

Clay 100 NTU

     

Flow 1:    

Alum Concentration 12.5 g/L

Clay Concentration 12.2 g/L

     

Flow 2:    

Alum Concentration 25 g/L

Clay Concentration 24.4 g/L

Flow RatesSludge Blanket Pump 20 mL/min

     

Flow 1:    

Water Flow 100 mL/min

Alum Pump 0.46 mL/min

Clay Pump 1.65 mL/min

     

Flow 2:    

Water Flow 200 mL/min

Alum Pump 0.46 mL/min

Clay Pump 1.65 mL/min

f f

a a c c w w f f cc

Q CQ C Q C Q C Q c C

Q

Trials: Q = 100 mL/min

Trial 1: Pipe diameter = 0.635 cm (0.25 inch)Q = 100 mL/min

Trial 2: Pipe diameter = 0.953 cm (3/8 inch)Q = 100 mL/min

No sludge blanket formed!

Trials: Q = 200 mL/min Trial 3: Pipe diameter = 0.953 cm (3/8 inch)

Sludge Blanket: 27 cm

Trial 4: Pipe diameter = 0.635 cm (0.25 inch)Sludge Blanket failure

Trial 5: Pipe diameter = 0.953 cm (3/8 inch)Sludge Blanket: 15 cm

Trial 6: Trial 4: Pipe diameter = 0.635 cm (0.25 inch)Sludge Blanket failure

Turbidity Measurements: Trial 4Turbidity vs. Time: 1/2" pipe, 200 mL/min

0

1

2

3

4

5

6

7

8

9

0 5000 10000 15000 20000 25000 30000

Time (s)

Tu

rbid

ity

(NT

U)

Q = 200 mL/min, sludge blanket height = 27 cm,

pipe diameter = 0.953 cm

Turbidity: Trial 5

Turbidity vs. Time: Sludge Blanket Growth

40

60

80

100

120

140

160

0 5000 10000 15000 20000 25000 30000

Time (s)

Tu

rbid

ity

(NT

U)

Q = 200 mL/min, sludge blanket height = 15 cm, pipe diameter = 0.635 cm

Velocity CalculationsInner Tube Diameter (cm)

Q (mL/min)

Velocity out of pipe (m/s)

Velocity in Tank (m/s)

0.635 100 0.054 0.0083

0.953 100 0.024 0.0083

0.635 200 0.047 0.0166

0.935 200 0.105 0.0166

Mass balance used to determine velocity out of pipe and upward velocity in tank through the sludge blanket.

ShearShear Values

Q (mL/min) Pipe Diameter Shear (Pa)

100 0.635 0.066

100 0.953 0.019

200 0.635 0.132

200 0.953 0.039

4

4 3

128 4

128 32

L Lw

Lw

gh gh ddQ

l l

h Q Q

l d g d

Froude Number

Sludge Blanket Density = 1.00094 g/mL

Fr = 0.33

Froude number proportional to (inertial force) / (gravitational force)

Froude number is generally used to characterize flow,

• Fr numbers of less than 1 equal tranquil flow

• Fr numbers = 1 indicate critical flow

• Fr numbers greater than 1 indicate rapid flow.

Reynolds NumberFlow is non turbulent!

jetVd

Re

Q = 200 mL/min

Pipe Diameter = 0.635 cm

Re = 56.6

Pipe Diameter = 0.953 cm

Re = 40

Conclusions Our flow rates may have been too low Success may have been influenced by alum

spikes Building sludge blankets can be

unpredictable!