Adding a Compound to The Database

[nrgeng]

I could not locate Dowtherm A in the chemical database. I want to use it as a heat transfer fluid in certain heat exchange units and in a distillation.

Dowtherm A is an mixture of biphenyl and diphenyl oxide of unspecified ratio. The Dow Website provides liquid and vapor thermochemical data, i.e., heat capacity, enthalpy and entropy as well as some physical and critical properties.

I found biphenyl in TEA and I found Dowtherm E (O-dichlorobenzene) in TEA. I located PCD Manager in TEA but where to start is the question since Dowtherm A is a mixture of pure components.

If it is possible to add it, please explain how I can add it or provide a link to an online explanation of how to add it to the chemical database.

[jasper]

The compound you are adding is not a real compound, but rather a mixture. This is possible, but the automated functionality to get the properties from the NIST web site will not work. So you will have to add all required properties by hand.

- start the PCD manager
- make a new PCD file
- Hit Add New to make a new compound
- enter the name
- enter properties that you have available, such as the CAS registry number (8004-13-5)
- enter the critical properties. If you do not have them, estimate them, most models require them
- enter chemical formula, molecular weight...
- on the T-correlations page, you can fit vapor and liquid correlations to data. To do so, you can import the data

You will need the ideal gas heat capacity, which you may not have. I suggest you put in a dummy correlation (e.g. copy that from one of the two compounds), save the PCD file, load it in TEA, calculate enthalpy in TEA from your model at condition at which you have enthalpy available, and then back-calculate the actual ideal gas heat capacity from the difference between the model calculations and the actual enthalpy (e.g. of vapor and liquid on the saturation line). Put the back-calculated ideal gas heat capacity data in and fit a correlation.

[nrgeng]

Last month I completed a simulation to determine the amount of space heating created by dissipating the thermal energy from the condenser of a vapor compression machine. For that simulation, I created a mixture of four pure components: nitrogen, oxygen, argon, and carbon dioxide, having a mixture molecular weight of 28.9 g/mol. In other words, I made up my own air. While researching this latest question, I noticed in PCDman that air is available in the chemical database. I thought that I looked for air in the past but apparently I missed it. The air that is in the chemical database is a mixture of pure components and may have been set up using the method that you described to add Dowtherm A, which is also a mixture of pure components.

As an alternative method to the one that you suggested, since biphenyl is already in the chemical database, if I added the other component of Dowtherm A, which is diphenyl ether, and chose an appropriate ratio of the two, would that have the same effect as making a new entry simulating the mixture as a pure component with PCDman? If that is true, how do I enter diphenyl ether as you alluded to in your last response in the second sentence, “This is possible, but the automated functionality to get the properties from the NIST web site will not work.” Do you mind explaining how the automated functionality to get the properties from the NIST web site works, in order to avoid my adding the properties manually? Diphenyl ether (101-84-8) is in the NIST database.

[jasper]

Adding a mixture of the two compounds is not exactly equivalent. If both compounds are present, you may be able to separate them with a separator. Which is not the case of course if they are defined as a single compound. Also the calculation is a bit more demanding if you add more compounds.

To get a known component in loaded in the PCD Manager, use Web Import.

However, trying it I run into some trouble. It appears to have a problem. I will contact the authors.