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.
|Control showing the detailed results of the estimation.
|Column of data values.
|Column of estimated values.
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.
The accuracy/applicability code for several estimation techniques are shown here:
These example accuracy/applicability codes show 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 estimation techniques for the liquid vapor pressure require values for the critical temperature. Cranium and Synapse will use the same technique selection procedure described previously in a recursive manner, selecting the best estimation technique for each dependent property.
For example, the Estimation Results shown below show how the application tried to estimate the vapor pressure using several techniques including the Ambrose + Walton Method. This method requires a value for the critical temperature. The application thus recursively tried to estimate the critical temperature using several techniques including the Joback's Method. This technique requires a value for the boiling point which is again estimated using this recursive method.
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.
To estimate properties dependent upon temperature, pressure or composition, you must first enter values for these state variables. Values can be entered individually or as a series. For examples, see the documentation for Temperature Dependent Section and Temperature and Pressure Dependent Section.
The Command Menu's Estimate Multiple Chemicals command enables you to estimate a property for several chemicals at a time.
For temperature and pressure dependent properties, the dialog enables you to enter values for these state variables. Once these values are entered and one or more chemicals selected, pressing the dialog's Start button will generate estimates.
See documentation for the Estimate Multiple Chemicals Dialog for more details.
A chemical design is often done on a limited set of physical property constraints. For example, in the design of a new refrigerant, we might design for constraints on vapor pressures, heat capacities and various thermodynamic derivatives. Once candidates have been designed, you can use the multiple chemical 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.