Pressure gradient basics

[ceramic57]

Suppose we have fluid in a vessel (Vessel A) with inside Pressure 120 bar (achieved by a pump)… When we open the valve, the fluid starts to flow into another vessel (vessel B) that was hitherto empty... Due to the Pressure gradient, the fluid flows with a certain velocity into vessel B. But the pressure difference would gradually decrease as the system tries to maintain equilibrium, hence the velocity would also decrease.
1. Is there a way in which when I open the valve, the fluid will flow with a constant velocity into the other tank for a specified period of time?
2. When I open the valve, the temperature drops suddenly, due to Joule Thomson effect… How can I calculate and control that?
3. What can I do if I want to maintain the Pressure in Vessel A above 100 bar at all times, while the Pressure in vessel B should not exceed 40 bar. I also want to maintain temperatures in both vessels at a specified value.
4. The fluid flowing from Vessel A to B is super critical CO2 that is carrying oil with it. The intention is to bring the Pressure and Temperature in vessel B, anywhere below critical of CO2 (i.e. 31 C and 74 bar)… How should I design that separator? Should Vessel B be a two phase flash separator or should it be a hydro cyclone separator? Any idea, which one would be better?

[Q_Goest]

1. If you want a constant flow rate, one way to do it is provide a pressure regulator with a choked restriction downstream. This requires a fairly sizable dP so it doesn't always work.

2. The temperature drops going through the flow restriction because of the JT affect. That's an isenthalpic process. Enthalpy in = Enthalpy out.

The temperature drops in the supply vessel as well, but that's because it is expanding. Assuming that expansion is adiabatic (which it really isn't) the cooling in the supply vessel is equal to an isentropic process. To be more accurate, you can add heat transfer from the vessel walls.

3. A back pressure regulator can prevent the supply from going below 100 bar and a downstream pressure regulator can prevent pressure rise in the receiver from exceeding 40 bar.

The only way to make this isothermal is to add/remove heat where needed. A heat sink at that temperature is one way but you also need lots of surface area.

4. Contact manufacturers of separators. Sorry, but I can't help much with that last one.

[ceramic57]

Thank you very much Mr. Q_Goest... I have a few more questions, I would be glad if you could help:
1. Is it correct that Pressure is inversely proportional to velocity of a flowing fluid? If we decrease the flow area of the fluid, its velocity increases and its Pressure decreases, as happens in a nozzle (is this correct?)... If the nozzle's exit is a pipe, what will be the behavior? And if the nozzle's exit is an entrance to a tank, what will be the behavior then?
2. I want to ask about knock-out drums used for flash distillation, they have an inlet diverter. What does it do? How can one calculate the right shape and dimensions of an inlet diverter for a particular requirement? (The intention is to drop the Pressure below critical of supercritical CO2, with essential oil mixed in it, so that CO2 becomes gas and liquid oil is settled at the bottom.)
3. You mentioned about a heat sink to maintain Temperature of a system experiencing Joule Thomson effect? How can I control the temperature in a vessel with more than 1 inch thick walls?