In Aspen Plus, modifying the density and dynamic viscosity of a molten salt mixture can be done using several approaches depending on the available data and the property models required. Here’s how you can do it:

1. Using Built-in Property Models

Aspen Plus has various property methods that estimate density and viscosity. For molten salts, common methods include:

• PENG-ROB (Peng-Robinson)
• RK-SOAVE (Redlich-Kwong Soave)
• ELECNRTL (Electrolyte Non-Random Two-Liquid model) – Best for ionic mixtures.
• PC-SAFT (for complex fluids)

Steps:

2. Using Experimental Data (Property Input Method)

If Aspen Plus does not have accurate predictions for your molten salt, you can manually input experimental data for density and dynamic viscosity.

Steps:

3. Using Aspen’s Property Estimation (Regression)

If you have tabulated experimental data, you can fit a regression model in Aspen.

Steps:

4. Modifying Properties in Aspen Plus Simulation

Once properties are set, you can modify them in the simulation as follows:

• In a Stream: Go to Stream Results → Edit.
• Using FORTRAN Subroutines: For advanced property modifications, write a FORTRAN User Subroutine.

Conclusion

• Use ELECNRTL or PC-SAFT for better ionic system predictions.
• Manually input experimental density and viscosity correlations if Aspen lacks accurate models.
• Perform property regression if you have tabulated data.

Moses Chai Thank you for your response. However, since it is a mixture, I cannot use regression or experimental data directly. Aspen does not recognize the mass fractions in the properties environment, as they are specified in one of the streams within the simulation environment.

I can make slight adjustments to the density by modifying the properties of the individual components, but I cannot directly define it as a mixture. However, when I tweak certain values to align with the experimental data, I encounter an issue: when running a simple heat exchanger model, no heat exchange occurs, which is incorrect. Clearly, something is going wrong.

I have tabular data and temperature dependent relations for density and viscosity as a mixture, but not for the individual nitrate components.

Would you be able to provide some screenshots to guide me through the steps? The composition is 43 mass% potassium nitrate, 42 mass% calcium nitrate, and 15 mass% sodium nitrate. The density follows a linear equation, while the viscosity follows an exponential equation.