# Chemical engineering...

• Feb 12th 2009, 01:44 PM
Haris
Chemical engineering...
20million litres per day (MLD) of a conservative substance, with a concentration of 10mg/L is released into a stream having an upstream flow of 50 MLD and a substance concentration of 3mg/L. Assumin g complete mixing:

what is the concentration in ppm just downstream?
what is the mass flow rate of the substance in kg/day passing just downstream?
• Feb 13th 2009, 09:13 PM
Rincewind
Quote:

Originally Posted by Haris
20million litres per day (MLD) of a conservative substance, with a concentration of 10mg/L is released into a stream having an upstream flow of 50 MLD and a substance concentration of 3mg/L. Assumin g complete mixing:

what is the concentration in ppm just downstream?
what is the mass flow rate of the substance in kg/day passing just downstream?

The concentration just down stream is a weighted average of the two flows (upstream and released)

$c = \frac{20\times 10 + 50\times 3}{70} = 5$ mg/L

For part 2 you just need to multiply flow by concentration

$m = (50 + 20) \times 10^6 \times 5 = 350 \times 10^6$ mg/day

Now there are 10^6 mg in a kg so the mass flow just downstream is 350 kg per day.

Hope this helps.