mixing chemicals

[spaceman93308]

I have two chemicals when added together for 30 seconds, form a compound that is used for purifying water. tentatively i plan on using 6" pipe to mix, and 1/2" pipe to discharge. flow will be regulated with a throttling needle valve or gate on discharge, and a pressure regulator on the source. My question is how long, at what pressure, should i make the 6" pipe to maintain a 30 second pass, from source to discharge?

[admin]

You have two independent unknown values - pressure and length wit one equation to use. That means that you can combine as you like - if you have longer pipe - higher pressure will be required, if you have shorter pipe - lower pressure will be required. At the and I think that pipe length will not influence to much, but more flow restriction will be made by 1/2" discharge pipe.

For example, if you have 100 m long 6" pipe, it has internal volume of about 6x0.254 * 1000 = 1524 L and to have it flow in 30 s - flow rate is 1524/30=50.8 L/s.

Now to have flow of 50.8 L/s through 1/2" discharge pipe using orifice calculator you can calculate required pressure of 332 psi. This is very high and it is because of very high flow rate, which is required due to long pipe of 100 m. To make pressure lower, you should choose shorter pipe like 10m, to have smaller flow rate required as well as pressure.