Fluids

In TP-Cloud, a "Fluid Package" refers to the combination of an Equation of State (EoS) with a set of components such as CO₂, nitrogen or argon. A fluid package is often just referred to as a "fluid". A fluid package always defines the thermodynamic model and component set. Some tools also store a composition on the fluid package, but processes handle composition a little differently.

More information is available on which EoS to choose. When performing process calculations, cubic EoS such as SRK or PR are usually good initial choices due to their computational robustness and speed.

Fluid Library

The Fluid Library is your centralized place to define and store fluids. Library fluids can be imported and reused across TP-Cloud:

A library fluid is a reusable template. When you import it into a process or phase diagram, TP-Cloud creates a local copy for that calculation. Editing the local copy does not change the library entry unless you explicitly save or export it back to the library.

Creating a fluid package

To create a library fluid, property-calculator fluid, or phase-diagram fluid, fill in:

Name: The name shown in selectors and lists.
Equation of state: The thermodynamic model used for the fluid.
Components: The substances included in the fluid.
Composition basis: Mole or mass fractions.
Composition: Component fractions. For a single-component fluid, the composition is set to 1 automatically.

Subscripts and superscripts in names

The Name field supports subscript and superscript characters, which is handy for chemical formulas and ion charges such as CO₂ or Ca²⁺. To convert characters, select them (or place the caret right after a single character) and then press the ↑ and ↓ arrow keys.

Each press moves the characters one step along the superscript → normal → subscript ladder, so pressing the opposite direction reverts them. Only digits and the + / - signs have script forms; other characters are left unchanged.

When you create a process fluid from the process Fluids dialog, you do not enter the composition there. You only define the shared model and component set:

Process fluid package = EoS + components
Feed stream composition = fractions for a specific stream

This is intentional. One process fluid can be used by several feed streams with different compositions.

The equation of state and the components narrow each other, and you can choose either first. Every component stays listed, with the ones the chosen EoS cannot model shown dimmed at the bottom of the list. Every EoS stays listed too, with the ones that do not cover your components dimmed and naming what they are missing instead of describing themselves.

A saved or imported fluid can still hold a combination that no longer agrees. Its unsupported components are called out, and the fluid cannot be saved until you remove or replace them.

Editing composition

Compositions can be specified as mole or mass fractions and should be normalized to sum to one.

You can modify the fluid composition wherever you select or edit a fluid, for example in the Fluid Library, Property Calculator, Phase Diagrams, and Processes. For multi-component fluids, the Normalize action scales the entered fractions so the total becomes one while preserving their relative sizes.

Example:

Before normalize: methane = 8, ethane = 2
After normalize:  methane = 0.8, ethane = 0.2

Fluid packages in processes

Processes have their own process-level fluid package list. Open it from the Fluids button in the process editor.

In a process, a fluid package can be used by several unit operations. This means one fluid definition can be shared by multiple input streams or other units with a Fluid package field.

The process fluid says which components are allowed. The feed stream says how much of each component enters that stream.

Example:

Process fluid: PR with methane and ethane

Feed A composition: methane = 0.8, ethane = 0.2
Feed B composition: methane = 0.4, ethane = 0.6

Both feeds can use the same process fluid because they use the same EoS and components. Their compositions can still be different.

Composition Manager

Use the Composition Manager when you need to edit process-fluid compositions. This is separate from creating the process fluid package itself. Creating the process fluid only chooses the EoS and components; the Composition Manager edits the default composition and the compositions used by feed-like units.

The table has one column for each composition:

Default: The reusable composition stored on the process fluid package.
Feed columns: The compositions stored on individual feed-like units such as Input Stream, Cycle Stream, and Recycle.

The default is useful when several feeds should start with the same values. Changing it does not overwrite every feed composition. A feed can copy the default, reset to it, or keep its own values.

When you edit a shared fluid, TP-Cloud asks whether you want to:

Update all units using this fluid: One shared fluid changes, and every linked unit sees the new model and component set. Existing feed compositions are preserved for components that still exist.
Create a copy for this unit: The current unit gets its own fluid package, and the other units keep using the old one.

The process fluid list also shows which units use each fluid. If you delete a process fluid that is still in use, those units have their fluid configuration cleared.