3 replies to this topic

[DANA-IF]

HELLO friends ;

I have gas specific gravity at 38°C and 14 barsG and it's equal to 0.812

As we know gas specific gravity is the ration between gas molecular weight and air molecular weight (29)

I was wondering if the molecular weight of gas in these conditions is   0.812 * 29=23.54 ?

does the specific gravity formula is applied on all temperature and pressure conditions ?

 

[shan]

The ratio of gas molecular weight is not a variable of temperature and pressure.  Therefore, the gas specific gravity is a constant at any temperature and pressure conditions.

[MrShorty]

As we know gas specific gravity is the ration between gas molecular weight and air molecular weight (29)

This is only partially true. Specific gravity is defined as the ratio of two densities: the density of the fluid divided by the density of a reference fluid (almost always air for gases). You should be able to show that, if we assume that our gases are ideal, that the ratio of the densities reduces to the ratio of the molecular weights. If you have forgotten or have never done this derivation, you should perform the derivation to convince yourself that it is true.

 

So, your specific gravity=MW/MW(air) is true, if we are assuming that our fluids and air are ideal gases. The question behind your question is, "can you assume that your test fluid and air are both ideal gases?"

[ahmadikh]

 DANA-IF,

 

The ratio of densities is equal to the ratio of molecular weights for two gases (or gaseous mixtures) only if they have no non-ideality. You need to incorporate the ratio of compressibility factors to the ratio of molecular weights as your pressure is far from the atmospheric pressure which tempts the gas to behave non-ideally (however, I do not know the nature of your gas). As such, your molecular weight might be different from 23.54.

 

Hope this helps.

 

Best,

Milad