the Tech Gas Blender project: a scientific approach
The best available models in thermodynamics
There has to be a Real Gas calculation model that makes a reliable connection between the quantity of gas and the measurement of their pressure.
This model must be capable of representing Oxygen – Helium – Nitrogen in a given range of pressures and temperatures and in all their different possible combinations and fractions.
Of all the available blending software, only few of them try an approach according to the Real Gas. They are done, instead with completely inadequate equations (usually van der Waals) and none of them manages the interactions between gases: they use common sense, with weighted averages arrangements, without any correspondence to the actual experimental data.
In a nutshell, the Real Gas model has to successfully manage two key points:
• Gas compressibility
• Molecular interactions
The first topic is usually represented with lack of precision, while the second one I think is not taken into account by any software: these are forces that occur in mixtures which are not present when the gases are alone.
The ability to correctly calculate these effects ensures the alignment between pressure and quantity.
Tech Gas Blender is based on a scientific approach that provides theoretical criteria to calculate by partial pressure Oxygen - Helium - Nitrogen mixtures in any possible combination and gas sequence, without the need of empirical adjustments like "Fudge Factors", "trials and errors" etc.
The model adopted by Tech Gas Blender is based on a very complex calculation, it considers both these points and is based on the most accurate equations of state for the calculation of pure gases (modified Benedict-Webb-Rubin equation of State and the Helmholtz Equations of State), integrated with an advanced equation of the molecular gas interaction (Helmholtz Energy equation) that defines the adequate "mixing rules".
The Helmholtz Energy equation includes all the specific binary interaction gas parameters, including Helium-Oxygen, which are not easy to find.
The objective in selecting these property calculation algorithms was to implement the most accurate models integrated with all the gas maths for advanced divers.
The accuracy of these formulae is reproduced in the diving range of pressures and temperatures (up to 300 bar and 0 - 80 °C temp) with negligible deviations in density:
Pure gas uncertainties in density:
Nitrogen 0.02 %
The Ideal Gas option was maintained solely for educational purposes !
• Extended functional features: all the features you want in mixing
• The best available models in thermodynamics
• A set of tools, some of them classic, others more advanced that would help to understand some issues and errors origin.
The Tech Gas Blender project was born with the ambition to create a software that would include:
Extended functional features
Some software in certain cases will respond in this way: "Mix impossible to fill .... "
So then you have to go by trial and error. Tech Gas Blender is structured so as to provide instructions as comprehensive as possible, finding alternatives when necessary.
In the past, I needed some requirements that were not present in the features of the available software, especially during off-shore expeditions, when logistics needs reduce available gas stock.
Regarding this point, the question is simple: if you have the need and the application does not support them, there is not much to comment on. You can only debate whether you really need it or if you can find another solution.
A few examples:
Example 1 - You need to fill one cylinder with a lot of residual mix and the software warns you that you need to vent the initial mix to a certain pressure.
What if there were other alternatives to draining, maybe by slightly changing the target pressure or the final composition of helium and nitrogen?
Example 2 - And how about if you want to do a top-off? Why not simulate a step by step sequence by checking what happens to the final mix for each step, perhaps with different gases and maybe choosing the value on the pressure intervals ?
Example 3 - Again, did you ever have a trimix that might be useful to mix another mix but that is in the wrong bottle?
If the application does not support a trimix as a bank source mix, then you cannot use it.
These were real needs experienced in expeditions, and now they are requirements satisfied by specific functionalities of the application, rigorously assisted by Real Gas model.
Some of them are basic like END and PO2 calculations, some are more advanced to go in-depth like the “what if analysis”, so that they also have a value in terms of learning to identify the source of possible errors in blending.
The software is extremely powerful and configurable in depth, offering a high capacity for personalization.
The GUI (Graphical User Interface), however, is designed according to the concept of a workflow with a sequence of questions/answers making use of intuitive application.
The result is that the program , once correctly customized, follows the strategy “Only show what I need when I need it”
Tech Gas Blender project ... Is it worth it ?
Obviously the answer is subjective and therefore I cannot honestly give a response with an absolute value .
As I have already mentioned before, there are experienced blenders who mix thousands of Trimix per year without any problem.
It is also true that there is no need for a maniacal precision in pursuing the exact composition of a mixture: breathing something "a bit different " than the target mix is not like touching high tension wires.
However, it is equally true that when blending Trimix without industrial apparatus, several components are involved which contribute, with different levels of uncertainty, to determine the accuracy of the final result.
The mere fact of being able to eliminate one of these factors - probably the most important - for me is “yes”.
Gas mixing is an expensive and time consuming process, and if we can avoid some frustrations and waste of money while increasing flexibility and functionality, it is a good thing.
Then there is an element of personal satisfaction: I cannot resign myself to the fact that such an advanced environment cannot rely on an application based on scientific foundations.
I have devoted over ten years of my free time looking for information about these topics; mainly in the Real Gas section.
The goal of the application is to combine the management of the most advanced models of thermodynamics with fast and simple usability.
In other words, the software has to act as a layer between the computational complexity and not cause any difficulties or problems for the user.
The software is, therefore, extremely powerful and configurable in depth , offering a high capacity for personalization.
The interface , however, is designed according to the concept of a workflow with a sequence of questions/answers making use of intuitive application.
The result is that the program, once correctly customized, follows the strategy “Only show what I need when I need it”. More in the section “functional features”.