specific gravity from molecular weight

[rQuestionEngineering]

I am trying to calculated power requirements from the below data.
However , I am not able to enter data specific gravity below 0.5
The gas molecular weight given to me is 11kg/kmol.
What is the specific gravity ?

https://catsolar.my.salesforce-sites.com/GasCompCalculator

 

[1503-44]

Air has 28.9656 grams/mole
You have 11 g/mole
Your specific gravity relative to air is 11/28.9656 =

Seems like Solar compressors are not designed for such a light gas.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[georgeverghese]

Looks like that spreadsheet is meant for gases methane and heavier.
Why not work it out manually then ? Use an isentropic eff of say 70-75% for high throughput streams. If you have a P-h diagram for this gas ( what is it btw?), results will be more accurate.

 

[JStephen]

I've never seen "specific gravity" used for anything other than with reference to water as the standard (which is obviously not the intent here). Is specific gravity relative to air a common measure that I just haven't seen? Maybe they mean relative to hydrogen or some other gas? Anyway, seems a poor way to have you specify density.

 

[1503-44]

Referencing to air is as common when working with gases as it is as referencing to water when working with liquids and solids. It's obviously much easier to use SG_gas referenced to air = 1 than its value of 0.0011 when referenced to water. That's especially true if you think about not so very long ago you would be using your slide rule to do your calculations and carrying the E+/- around in your head.

https://www.engineeringtoolbox.com/density-specific-weight-gravity-d_290.html

Of course when working with crude oils, you could opt for using API gravity, where
SG_api = (141.5 / SG_w) -131.5
So SG_api of water = 10

And when working with gases, always specify what your reference temperature and pressure are. That's the part that does not have a true international standard. Some use 59°F, or 15°C, others 0°C


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."