How to Maintain Continuous Flow with Fixed Delay Using Fluid Processor?

[jenny_chungVEV4M]

Hello,

I am trying to use the Fluid Processor in FlexSim to model a continuous fluid process with a processing delay.

In the documentation, I found the following description:

“The amount of time that material spends in the Processor is based on the Processor's maximum output rate and its maximum capacity.”

However, I would like to:

Maintain a continuous flow (input equals output)
Define a fixed residence time (processing delay) for the fluid inside the processor

For comparison, I noticed that FluidMixer allows setting a fixed processing time, but it only works in batches, while Fluid Processor is not batch-based but does not seem to support a fixed residence time.

Could you please advise whether this behavior can be achieved using the Fluid Processor, or if there is a recommended alternative approach?

Thank you very much for your help.

@tienchengwu8ETUZ 

[FelixMoehlmann]

You already quote the answer to your question: “The amount of time that material spends in the Processor is based on the Processor's maximum output rate and its maximum capacity.”

More precisely, the 'process time' is the result of diving the capacity by the output rate.

[jenny_chungVEV4M]

Hello,

I see, thank you for the clarification.

So for a process where fluid remains in a continuous process for three days without limiting the maximum content (i.e., without a batching concept), would the recommended approach be to simply reduce the flow rate to achieve the desired residence time?

Or is there another best-practice approach for modeling this kind of continuous delay process?

Thank you very much.

[FelixMoehlmann]

You would still use the maximum content setting to control the staytime, since, I assume, the output rate is the more important factor and shouldn't slow the downstream processes. You can think of the fluid processor as a pipe. The maximum capacity is the length multiplied by the cross section. In terms of the simulation the cross section is the output rate and the length is proportional to the time it takes the fluid to reach the end (the processing time). With a constant input at the same rate as the maximum output rate, the 'pipe' will be full when the first of liquid reaches the end and from there on stay completely filled.

If you require a buffer, for example because the next object might not always be able to take in all of the fluid, increase the maximum output rate to raise the capacity and instead limit the output flow by having a lower maximum input rate in the next object.

[jenny_chungVEV4M]

Hello,

Thank you for the explanation. I think my confusion comes from the modeling purpose itself.

My goal is to abstract a long and complex continuous process without modeling its internal details. In this process:

• The upstream fluid should always be accepted continuously
• No blocking or congestion is expected
• I only want to represent that the fluid remains in the process for a long residence time before reaching the downstream stage(ideally simplified into a single object for easier statistics tracking)

In this case, should I still use Maximum Content to indirectly control the residence time?

I am a bit confused because Maximum Content sounds more like a storage/capacity limitation, while my intention is mainly to model a pure continuous delay process.

Thank you very much for your clarification.

[FelixMoehlmann]

I understand that this can be confusing. But I think the pipe analogy (in fact the Fluid Pipe object operates in the exact same way) can help to understand why the object was designed this way. Assuming a constant speed (which is what you want, a fixed time until the fluid reaches the output), the pipe/processor working at its maximum throughput rate means that the fluid is taking up the full cross section. When the fluid reaches the end, the object pipe will be entirely filled. As such it makes sense to let the user define two of the three interconnected values (rate, capacity, time) and calculate the third based on it. 

[jenny_chungVEV4M]

I think I understand it better now.

However, I noticed that the Fluid Processor documentation mentions:
“The actual output rate is based on the rate that material came in.”

In that case, if the upstream input flow is not steady (for example, periods with little or no incoming material), would the fluid residence time still remain constant when using Maximum Content to define it?

Or does the residence time only remain stable under steady-state flow conditions?

Thank you very much.

[FelixMoehlmann]

The staytime is constant. The output rate will be equal to the input rate from X minutes ago.