Adjust

Overview

An Adjust automatically varies one input specification until a chosen property elsewhere in the flowsheet reaches a value you set. It does the iterating an engineer would otherwise do by hand: change a value, recalculate, check the result, repeat. Thus, you can state the result you want and let the solver find the input that produces it.

For example, to find the heater outlet temperature that leaves a downstream stream exactly half vaporised, let Adjust vary the heater's outlet temperature (the adjustable) until that stream's vapour fraction (the target) reaches 0.5.

Each Adjust manipulates one adjustable specification to meet one target. The target can be a property of a stream or of another component.

Inputs

• adjustable_node / adjustable_prop: The specification the Adjust is allowed to manipulate. To assign, drag the Adjustable port (on the left of the Adjust symbol) onto the component whose specification you want to adjust, then pick the property in the "Adjustable" tab.
• target_stream / target_node / target_prop: The measured property used as the control target. To assign, drag the Target port (on the right of the Adjust symbol) onto a stream or a component — the target type is inferred from what you drop on — then pick the property in the "Target" tab.
• target_value: Desired value for the target property.

Outputs

• If the solver converges, the target property will have reached the desired value, and the adjustable property will have changed from its initial value.

Details

Seeing the current values. If you add an Adjust after the process has already been solved, the "Target" and "Adjustable" tabs show the current solved values. This lets you see the conditions before the Adjust takes effect, and helps you pick a sensible target.

Helping convergence. When a calculation runs, the value currently set on the adjustable specification is used as the starting point for the iteration. If an Adjust fails to converge, setting that value closer to the expected answer gives the solver a better start and often resolves it.