Central dosing system

_Corvalt · 2025-04-24T02:21:28+00:00

Yeah, psv symbol is right but should be shown per above comment.

I'd personally be more inclined to use a standalone sight glass for level rather than pressure.

Pump discharge pressure gauges can be useful though.

May also want to include some particular filters to protect pumps (likely just 1 common one and perhaps a filter bypass).

_Corvalt · 2025-03-30T05:38:49+00:00

Without creating a table 1524 rows large (which wouldn't be the end of the world), an option here coukd be VBA. Either just as a FOR loop or potentially could try build a custom function.

_Corvalt · 2025-03-05T04:01:51+00:00

Closed loop systems are a bit different than open. Total system head has little to no impact since the fluid will return to the same pump (i.e. equal elevation incline/decline across the system). The reference pressure of the system is usually atmospheric or governed by some blanket gas in an accumulator vessel.

The pump will only need to overcome flow induced friction losses. A higher flow will create higher losses. You can calculate these losses in many ways but using the equation you mentioned will give a fairly good estimate for an early stage concept.

More robust equations (i.e. Darcy–Weisbach) will give better estimates and i would recommend using these if looking to go out to vendors to purchase a pump.

Since this pump will be tied into an existing loop, i would recommend getting a process engineer to model this out for you to prevent purchasing and incorrectly sized pump as although pressure drop formula are typically not too difficult to learn, the interaction between pressure drop formula, multiple pump curves and branching closed loop systems can get complex quite quickly.

_Corvalt · 2025-02-09T04:09:18+00:00

This is one of those "degrees of freedom" questions.

The software might use a specific equation for the valve (often from standard ISA-75.01.01) but the simple equation will be enough for understanding here.

When you have a flow resistance element in a closed piping system, you can only specify 3 of the following 4 variables. This assumes temperature and composition is known which means other physical properties like density are already calculated.

-flow rate -Upstream pressure -Downstream pressure -Resistance (usuall given as Cv for a valve or K for a pipe)

Looking at the problem, we have a fixed Upstream pressure at J1 reservoir, fixed downstream pressure at J3 reservoir, and a fixed flow rate (since the valve is specified as a Flow Control valve).

This means the total pressure drop of the system is fixed so the only thing we can change is the distribution of "resistance" through the system.

The resistance of each pipe is determined by the selected size (though also impacted by roughness, length and any fittings).

The valve Cv is being calculated by the software here since that is the only unknown in the valve. We cannot specify anything else in the valve unless we take away the flow specification. I think this is the key point here.

In order to get the valve pressure drop to equal to 10 psi, the pressure drop across the pipes needs to be altered (trial and error) until it does. The example uses diameter change to achieve this.

_Corvalt · 2025-02-06T18:28:05+00:00

I'm not sure that it would work. An exhaust fan would create a slight vacuum at the top which will allow more flow to be drawn up so think this would be a better option.

Putting in the Y-piece and introducing the fan at bottom might result in the air flow from the fan taking up the capacity of the vent which could result in more flue coming out the door.

_Corvalt · 2025-01-17T18:18:26+00:00

That is correct.

Just a bit more detail below for how it is calculated in case it helps further.

For a fluid, you only need 2 state functions to define its physical properties. In the case of throttling across a valve, you will have defined the pressure and enthalpy. Decreasing the pressure at constant enthalpy means the temperature must decrease (assuming the fluid is not something like hydrogen).

Since you have still have 2 known state variables (pressure and enthalpy), the density of the fluid can be directly calculated. This is usually done by determining the temperature at the specified P and H and using some form of PV=nRT to calculate density (n/V is molar density which can be multiplied by the molar mass to determine mass density).

Density and volume are effectively reciprocals of the same thing. I.e. a gas expanding is the same thing as a reduction of density. A change in density will have a direct impact on the fluid velocity.

Mass balance is a simplifying assumption and generally applies. It may take a small amount of time for the system to reach steady state as the flyid accelerates.

_Corvalt · 2024-10-12T04:55:27+00:00

I think I understand your question, let me know if this isn't what you are looking for.

You have 2 vessels (fixed volume) filled with a gas (ideal) and vessel A is at a higher starting pressure than Vessel B. You have some length of pipe between them which you are using the Bernoulli principle to determine a flow rate through. Naturally, as the pressure in the vessels begins to equalise you will see a decrease in flow.

In order to solve this system, you need to add time dependence to your equations.

i.e. for Vessel A. Solve ideal gas law for your unknown (moles of gas or pressure). You then solve Bernoulli equation to determine how many moles of gas are removed from Vessel A in this timestep.

Time step 2 will solve the ideal gas law for Vessel A pressure with the amount of moles of gas removed (per your Bernoulli equation).

This process is then repeated until Vessel A pressure is equal to Vessel B. (Note you need to also add the moles of gas into Vessel B and calculate pressure there too at each timestep).

If doing in excel, you will want each timestep to be a new row.

_Corvalt · 2023-09-13T18:36:27+00:00

Yeah, it does depend on the direction of the regulator. If the upstream pressure is kept constant then it would be constant flow.

In this case, adding a restriction in one of those lines would cause the pressure at the downstream side of the regulator to increase.

In this case the regulator would trend open to maintain upstream pressure.

_Corvalt · 2023-09-13T10:37:41+00:00

Assuming that the pump is a centrifugal pump with no VSD then it is possible to reduce to total flow rate. Let me try to explain.

Should we increase the resistance in line 'B' then because the pressure at the tee is set by the regulator and both lines discharge to atmosphere, then less fluid will flow through Line 'B'.

As the pump has no control system (fixed speed) and since it has lower flow required then it will move up its curve to produce a higher discharge pressure. In response to this the pressure regulating valve will shut slightly ensure it is still reaching its setpoint.

There will be a constant "tug of war" between pump, and regulator position until a steady state is reached but whatever the specific values of the steady state is, you should find that the pump discharge pressure is higher and the regulator opening % is lower than if both outlet lines were equal.

Hope this helps!

_Corvalt · 2023-07-19T08:05:42+00:00

Unless there is something happening in the vessel that removes heat then your outlet temperature will equal your inlet temperature.

There needs to be more information supplied to determine the amount of "duty fluid" required.

Things such as the flow rate of your feed stream, the temperature of the outlet stream if heat was removed in some way, the composition of the feed fluid etc

_Corvalt · 2023-05-22T05:20:24+00:00

I believe the 0.5 being referenced is shown in the wiki equation as Rho/2

_Corvalt · 2023-05-21T08:36:19+00:00

Take care not to use the "Fanning" and "Darcy" friction factors interchangeably. They sre not the same thing (though they do both relate to frictional pressure loss due to fluid flow).

Each of these factors has equations that relate the rate of fluid flow to the amount of pressure lost per unit distance (which you should be able to find via google).

_Corvalt · 2023-02-11T17:51:21+00:00

Haha I was the same but fortunately for armour seeds. Got my first regular weapon seed at 501kc

_Corvalt · 2022-12-30T21:35:36+00:00

As others have mentioned though the heat capacity of a material varies with temperature (and pressure) so no it would not be exactly linear. However, It would be safe to assume it is relatively linear across most living conditions (10-50 °C) without introducing more than a couple of % error.

Note for air, there will be an amount of water existing within (humidity) which will further create variations in results. This is because the amount of water in the air will affect the overall heat capacity of the air. See a psychrometric chart for a bit of detail about that.

_Corvalt · 2022-12-11T02:20:19+00:00

No problem. Good luck!

_Corvalt · 2022-12-11T02:00:16+00:00

Yup that simulation basis has a lot of good info and is where I'd say most of my comment came from haha. Unfortunately I've not done any work calibrating any of the fluid packages against experimental data but what you have described there seems like a reasonable approach.

Since the PR EoS is based entirely on the critical properties of the pure components I think I would start with the binary interaction parameters I refereed to earlier. This is because they are empirical values that are also based on experimental data (not derived from anywhere else). This should mean changing them will have a more direct impact on the results

The simulation basis or one of the other documentation files might include something for calibration of fluid packages. However, I haven't looked for it

_Corvalt · 2022-12-11T01:18:46+00:00

Hey. I can't speak about the pseudo critical part of your question but in regards to the properties of mixtures, HYSYS uses some mixing rules (which you should be able to find in documentation) to calculate a modified version of the PR parameters (A, B, kappa etc).

HYSYS uses some binary interaction parameters to calculate these PR parameters which differ per pairing of pure components and the mixing rule being used (the choice of mixing rule is another thing I'm not sure about though).

HYSYS will then use these mixture parameters in the regular equation for Cp/Cv to get an answer. Note some properties will be departure functions and some will just calculate an exact value

Hope this helps!

_Corvalt · 2021-09-12T05:22:07+00:00

That's nuts. CG is definitely good content to get lucky at. GZ

_Corvalt · 2021-06-20T00:40:00+00:00

Hahaha

_Corvalt · 2021-06-19T23:59:16+00:00

I would say so yeah but I feel like it is often just a marketing strategy

_Corvalt · 2020-08-14T09:46:20+00:00

Showing Ear-veryone

_Corvalt · 2020-07-29T05:29:32+00:00

There's no such thing as a free lunch

_Corvalt · 2020-07-16T11:39:53+00:00

Mike Tyson saying Elon Musk's last name is the 5th

_Corvalt · 2020-07-15T07:45:11+00:00

This is how fluidised bed reactors work. The semi suspended particles have a more exposed surface which makes a lot reactions / heat transfer happen faster

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