Objective
The freezing point of water decreases when salts are dissolved in it. Using OLI Studio: Stream Analyzer, you can simulate this effect with precision. This guide outlines two approaches—a Temperature Survey and a Custom Calculation—to model freezing point depression effectively, generating equivalent predictions.
Disclaimer: The user interface, calculations, and results displayed in this article are from OLI Studio Version 12.0. Other software versions may appear different due to continual developments to the software.
Option 1: Temperature Survey
In this example, two salts—sodium chloride and calcium chloride—are added to 1kg of water. The effect of these salts on the freezing point of water is investigated using a temperature survey.
Step-by-Step Instructions
1. Create a Stream
- Label the stream as “NaCl-CaCl2-H2O” and select the MSE framework.
2. Input Stream Composition:
- Add the following inflows:
- 0.1 mol NaCl
- 0.1 mol CaCl2
3. Set Up a Temperature Survey:
- Open the Add Calculation dropdown and add a Survey > Survey by: Temperature.
4. Adjust Temperature Settings
- Go to “Specs…”
- Set the temperature range from -5 °C to 5 °C, with increments of 0.1 °C.
5. Run the Calculation
6. Visualize Results
- Navigate to the Plot tab
- Use the Variables button to remove default parameters on the Y1 axis. Add H2O – Sol from the Solid section
- View the freezing point. By clicking “View Data,” the data is displayed in a table. This information demonstrates that the freezing point is between -0.8 °C and -0.9 °C.
Tip: Increase the number of steps for finer resolution.
Option 2: Custom Calculation
This approach uses a Custom Calculation to determine freezing point depression.
Step-by-Step Instructions
-
Select the Stream
- Select the “NaCl-CaCl2-H2O” stream in the Navigator Panel.
-
Create a Custom Calculation
- Add a Single Point calculation > Custom.
- Add a Single Point calculation > Custom.
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Configure Variables
- In the “Specs…” window, set:
- Variable to Fix: H2O – Sol
- Variable to Free: Temperature
- Note: in a Custom Calculation, the number of “Variables to Fix” must equal the number of “Variables to Free.”
- In the “Specs…” window, set:
-
Set a Target
- Specify a small, fixed amount of ice (H2O – Sol) to represent initial precipitation:
- Enter 1e-6 mol of Target: H2O
- The “Adjusted: Temperature” parameter is an initial guess of 0 °C.
- Specify a small, fixed amount of ice (H2O – Sol) to represent initial precipitation:
- Run the Calculation
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Interpret Results
- The calculated freezing point will appear in the Summary box. The result is -0.804 °C.
- The calculated freezing point will appear in the Summary box. The result is -0.804 °C.
Conclusion
In this article, we outlined two ways to precisely calculate the freezing point depression of water by simulating the effects of dissolved salts using OLI Studio: Stream Analyzer. If you have any questions on this simulation, please submit a support ticket at support.olisystems.com.