Successful calculations

Once a process has been simulated, a button to open the calculation log will appear at the top-right of the screen.

If this button has any color other than grey, it indicates possible safety hazards, simulation errors, or other issues with the process.

For example, a calculation can finish while still warning that liquid is entering a compressor. In that case, the affected compressor is marked on the flowsheet, and the same warning appears in the compressor's Safety Checks tab.

Failed calculations

The calculation log is perhaps most useful for calculations that fail. Streams affected by errors are marked on the flowsheet, and the log button turns red to show that something is wrong.

When we open the calculation log, we see that the calculation failed at the validation step. There is a fluid-package conflict because the fuel feed and air feed use incompatible fluid packages. Specifically, they use different equations of state and different components, making it impossible for the solver to determine which specification to use.

We also see that some nodes are "unreachable", and that a cycle is missing a Cycle Stream unit. Without a Cycle Stream unit, the mass flow of the upper loop is not determined, so there is a validation error.

If we fix the fluid package conflict and click Calculate again, the flowsheet changes.

We now only have errors affecting the top loop. Inserting a Cycle Stream in the loop to specify the mass flow and composition fixes the last error, and we can run the calculation.

After running a calculation, you may still get a red calculation log due to a calculation failure.

This tells us that something went wrong while the condenser in our cycle was being simulated. We can click different streams in the process to view the status of the streams at the moment when the calculation failed.

If the inlet stream to the condenser is 116.1 K, for example, that is very low. We can inspect the condenser more closely and find that we made the removed heat far too low.

Once we fix this, the process solves successfully.