Hi there,
I am looking at gravity flow for the attached system for the drain line from the upstream vessel (~atm pressure) to the downstream vessel (~atm pressure). For a given inlet liquid flow (say water at 15m3/h) to the upstream vessel I wish to calculate if the drain line to the downstream vessel has the capacity to prevent filling the upstream vessel above its high alarm set point. I understand this system will result in unstable flow, as described in the PD Hills article, whereby the liquid level in the upstream vessel will rise and fall as gas is entrained and then driven out by the higher liquid level.
My approach has been to:
- Calculate the liquid height in the upstream vessel required to avoid gas entrainment based on the upstream vessel inflow (based on the equation in the PD Hills article)
- Based on this calculate the single phase liquid flow of the drain line based on the frictional losses equal to the static head.
- Compare flow rate calculated in part 2 to the liquid flow rate into the upstream vessel and if the drain rate is higher then I assume that the level in the upstream vessel should not rise significantly above that calculated in part 1.
Does this approach seem reasonable? Perhaps there is a simpler way?