One of Cranium’s and Synapse's key capabilities is to estimate physical properties quickly, easily and accurately. To estimate a property the application first collects all applicable techniques, sorts them by accuracy, and then tries each one until an estimate is generated.
This example is a continuation of the previous example so please first complete those steps.
|The Properties control displays all properties that are functions of both composition and temperature.
|The Values Type control shows the types of values that can be displayed in the field's table.
|The component whose composition will be varied to generate the series.
|The component whose composition will be calculated as the remainder after all other component compositions are totaled.
|The constant temperature that will be used for each series entry.
|The starting value for the variable composition.
|The ending value or increment used to calculate the series of compositions.
|State variables generated by the Composition Series dialog.
Cranium and Synapse store estimation techniques as entities just like chemicals, mixtures and references. Estimation techniques are stored in the Techniques Chapter of knowledge bases. (For details see documentation on the Techniques Chapter and Knowledge Base Documents.)
Every estimation technique contains two types of code: 1) accuracy/applicability code; 2) model code. When executed, the accuracy/applicability code returns two values: 1) a boolean true/false value indicating if the technique is applicable; 2) a numerical value denoting the technique's accuracy.
Often, for estimation techniques applicable to mixtures, the accuracy/applicability code will check for the presence of specific component chemicals. For example, several mixture techniques are not applicable if the mixture contains water. The accuracy/applicability code for these techniques usually contains the following lines:
The above code checks if one of the mixture's components is water. If it is, then the code return FALSE indicating that the technique is not applicable.
This example accuracy/applicability code shows how Cranium and Synapse decide which estimation technique should be used to estimate a particular property, of a particular chemical or mixture at a particular temperature, pressure and composition.
Before Cranium and Synapse perform an estimation, they first collect all estimation techniques for the property and execute each technique's accuracy/applicability code. Techniques whose codes return "false" are removed from consideration - those techniques are not applicable. The numerical result of each code represents the technique's accuracy. Techniques are sorted by this accuracy and the most accurate code is tried first. If this most accurate technique fails to generate and estimate, due to a missing parameter for example, the second most accurate technique is tried and so on.
Very often, Cranium and Synapse will need to estimate a dependent property during an estimation. For example, many mixture estimation techniques require physical property values of their component chemicals. Cranium and Synapse will use the same technique selection procedure described previously in a recursive manner, selecting the best estimation technique for the property of each component chemical.
Cranium and Synapse will automatically select the best applicable estimation technique. At times you may wish to manually specify which technique should be used for a particular property.
Your selected manual techniques are stored within the current knowledge base. Thus, you may have two open knowledge bases that estimate the critical temperature by two different techniques. To check which techniques have been manually set, change to the Techniques chapter and run the Specify Manual Techniques command. (See documentation on the Set Manual Techniques Dialog for details.)
The Command Menu's Estimate Multiple Mixtures command enables you to estimate a property for several mixtures at a time.
For temperature, pressure and composition dependent properties, the dialog enables you to enter values for these state variables. Once these values are entered and one or more mixtures selected, pressing the dialog's Start button will generate estimates.
See documentation for the Estimate Multiple Mixtures Dialog for more details.
A mixture design is often done on a limited set of physical property constraints. For example, in the design of a new refrigerant mixture, we might design for constraints on bubble points, dew points, heat capacities and various thermodynamic derivatives. Once candidates have been designed, you can use the multiple mixture estimation capability to generate other properties, e.g., thermal conductivity, for each candidate at a series of temperatures for further evaluation.
|Estimating Chemical Properties
|a short video demonstrating how to estimate physical properties using either Synapse or Cranium.
|Getting Started using Cranium
|provides a quick tour of Cranium's capabilities including a discussion of structure editing.
|the chemicals chapter contains numerous sections for entering and displaying data and estimates including the chemical structure section.