Temperature Dependent Goal Seek Dialog
Applicability: Cranium, Synapse (core versions 0315+)

Typically you first enter state variable values and then request Cranium or Synapse to generate an estimated property value. Sometimes, the opposite process is desired - you specify a desired property value and ask the application to estimate the state variable values that would generate that estimate.

For example, the estimated vapor pressures shown below are all 15 kPa apart. Each vapor pressure was entered as a goal value and the temperature was varied until the goal value was matched.

Dialog Controls

The Goal Seek dialog has controls for entering an initial temperature value, a goal value, and for performing the goal seek operation.

Initial Temperature Control: enables you to enter an initial guess for the temperature.
Property Control: displays the property being estimated.
Goal Control: enables you to enter your goal physical property value.
Value Control: displays the value estimated given the current temperature. This value should start approaching the goal value as the solution process proceeds.
Delta Control: displays the difference between the goal value and the current estimated value. This value should approach zero as the solution process proceeds.
Start Seek Button: pressing this button starts the solution process.
Example: Seeking a goal vapor pressure
  1. Open the MKS Sample Knowledge Base document. (Open a "working" copy or create a copy of the document (see here) if you are just experimenting with this functionality.)
  2. Make sure the current units are: kPa for pressure, C for temperature. (See documentation on the Property Units Dialog for details on changing units.)
  3. Change to the Chemicals Chapter and navigate to 'Benzyl alcohol'. (See the Navigation Overview documentation for details on navigating chapters and pages.)
  4. Scroll down to the Temperature Dependent Section and click the left mouse button on the property control. (See the section's documentation for additional details.)
  5. The Properties Dialog is activated. Select 'Vapor Pressure, Liquid - f(T)' as the property and 'Estimates' as the values type.
  6. Now click the left mouse button on the Section's large table control. The application activates the Estimates dialog. (See documentation on the Temperature Dependent Estimates Dialog for additional information.
  7. Click the left mouse button on the dialog table's first row and press the Goal Seek button. The application activates the Goal Seek Dialog.
  8. Enter a temperature guess of 150 C and a goal value of 15 kPa.
  9. Press the dialog's Start Seek button. Pressing the Start Seek button begins the solution process. During the process, the application will update the temperature, estimate the property value, and compute the difference between this estimate and the goal value. For example, after the first iteration the temperature will have changed and the Goal Value controls will have been updated.
  10. After the second iteration, the estimated value will be closer to the goal value.
  11. Finally the iterations will converge onto a solution.
  12. Pressing the Goal Seek Dialog's OK button will store the temperature and estimated value into the Estimates dialog.
  13. Pressing the Estimates dialog's Save button will store this estimated value into the current document.
Tip: Estimate some values first

It is sometimes necessary to have a very good initial guess in order to find a successful goal seek solution. One way you can often get a good initial is by estimating some values at temperature values near those you expect for goal value.

You can use these estimated values as your initial guess by simply selecting them in the Estimates Dialog and pressing the Goal Seek button. The selected temperature will be assign to the Goal Seek dialog's controls.

Related Documentation
Topic Description
Getting Started using Synapse provides a quick tour of Synapse's capabilities including examples of chemical product design.
Getting Started using Cranium provides a quick tour of Cranium's capabilities including a discussion of structure editing.
Estimating Chemical Properties a short video demonstrating how to estimate the physical properties of chemicals using either Synapse or Cranium.
Estimating Mixture Properties a short video demonstrating how to estimate the physical properties of mixtures using either Synapse or Cranium.