All:
Update: I took a control valve engineering course at Fisher Controls just last week, and I asked the question regarding gas specific gravity. The instructor stated that gas specific gravity is normalized for air at standard conditions, regardless of inlet conditions. I referred him to the...
katmar,
That is the same definition as in the 4th ed of the handbook. Now that I think about it, I think he did say both at standard conditions, I just didn't catch it, because my attention was so focused on the air requirements. Thanks for taking the time to look it up in the handbook. They...
katmar,
I took your advice and spoke to a Fisher rep on this subject, since I am referencing Fisher equations. He said that specific gravity is the ratio of the densities of your fluid to air or water depending on your fluid's state. He then stated that the density of air is at standard...
athomas:
Thanks for the specific definition and referencing your source of information.
Is your interpretation, the same as quarks directly above? Meaning, you don't think that the specific gravity is going to change under different pressure and temperature conditions?
quark:
"Gas SG can't be the ratio of gas density at actual conditions to air density at standard condition. In that case gas SG closely follows its actual density as the air density at standard conditions is about 1.2 bar."
I am assuming you meant 1.2 kg/m³, and not 1.2 bars for the density of...
jmw:
I don't really have a choice on using specific gravity. I am trying to calculate the maximum flow through a regulator at wide-open conditions. Fisher controls has a website full of equations dedicated to this...
Thanks to all that posted a reply, this helps a lot. I wouldn't have put two and two together about the molecular weight and density being directly proportional. I would have thought that the density would be affected by pressure on compressible fluids, and molecular weight would not be...
I thought it was the density of the vapor versus the density of air, is this not the case? Either way, I would assume dry air at standard conditions, correct? If so, what IS the appropriate value of dry air at standard conditions, in USC units?
Okay, good. It sounds like critical flow is the same as choked flow. I was guessing that was the case, from the of the terms "choked" and "critical" used interchangeably in various texts.
From what I see on the threads you speak of, the difference is that choked flow is when no more flow will go through your valve when decreasing the downstream pressure, with fixed inlet conditions, and critical flow is attributed with a pressure drop ratio (dP/P1) of 0.5 or higher.
Correct?
