Question

A monomedia anthracite filter has effective size 1.0 mm and a media density 1650 kg/m3. a) Calculate backwash rate to get a 25-percentage expansion at the design summer temperature of 25oC. b) Calculate the expansion that occurs at the backwash rate determined in part a) at the minimum winter temperature of 5oC.

Answer 1

Ans) Given,

Effective particle size (d)= 1 mm

Media density (_s)= 1650 kg/m³

We know,

L_e / L = 1 - e/(1-e')

where, Le = expended depth

L = average depth

e = porosity of loose bed

e' = porosity of expended bed

Given expansion of 25% so, Le = 1.25L

1.25 = (1 - e)/(1-e')

Porosity of anthracite = 0.40

1.25 = (1 - 0.40)/(1-e')

1 - e' =0.48

e' = 0.52

Now, at 5^oC , e = 0.20

Le/L = 0.8 / 0.48

Le/L = 1.667

Le= 1.667 L

Therefore % expansion = 0.667 x 100

= 66.7 %