High School What attribute makes some fluids more compressible than others?

[thetexan]

Are all fluids incompresible? If not, what is the attribute that allows any compressible fluid to do so while others, such as hydraulic fluid to not?

tex

 

[Dale]

Are all fluids incompresible?

No. Air is compressible.

 

[Chestermiller]

Are all fluids incompresible? If not, what is the attribute that allows any compressible fluid to do so while others, such as hydraulic fluid to not?

tex

The word fluid includes liquids and gases. All fluids have some level of compressibility. The term incompressibity is an ideal limit of small, but finite, compressibility, and is often an excellent approximation.

 

[thetexan]

So I should have used the work liquids. So, all liquids have "some" compressibility? Even hydraulic oil?

tex

 

[Chestermiller]

So I should have used the work liquids. So, all liquids have "some" compressibility? Even hydraulic oil?

tex

Sure

 

[Bandersnatch]

So I should have used the work liquids. So, all liquids have "some" compressibility? Even hydraulic oil?

tex

Look up tables showing the property called 'bulk modulus' for various liquids. It's the inverse of compressibility. While in mechanical applications higher bulk modulus means you're losing less power on compressing the liquid, it's not always worth the effort of going for exotic substances (I don't think anybody is using mercury in their hydraulics, despite its superior bulk modulus).
You'll find out that most hydraulic oils are not much different than water in terms of how compressible they are. But they do tend to have other desirable properties, such as higher boiling point, anti-corrosive or lubricative properties, etc.

 

[DrDu]

This is also a question of what you are interested in. When you are talking about calculating the aerodynamics of a boat, the assumption of water to be incompressible is certainly excellent. If you are doing chemical reactions in an autoclave at 100 kbar, it might turn out to be rather poor.

 

[Chestermiller]

This is also a question of what you are interested in. When you are talking about calculating the aerodynamics of a boat, the assumption of water to be incompressible is certainly excellent. If you are doing chemical reactions in an autoclave at 100 kbar, it might turn out to be rather poor.

Can you please give a specific reaction example where the fluid dynamics are affected in a liquid phase system?

 

[DrDu]

Not the fluid dynamics but the chemical reaction.
I had this article in mind (sorry, German only):
http://onlinelibrary.wiley.com/doi/10.1002/ciuz.19890230205/full

 

[Chestermiller]

Not the fluid dynamics but the chemical reaction.
I had this article in mind (sorry, German only):
http://onlinelibrary.wiley.com/doi/10.1002/ciuz.19890230205/full

I think the OP was referring specifically to fluid dynamic considerations.

 

[DrDu]

I think the OP was referring specifically to fluid dynamic considerations.

May be, I just wanted to indicate that the notion of whether a substance is compressible or not may be different between a naval engineer and a guy simulating nuclear bombs.

 

[Nidum]

The compressibility of some common fluids like water and hydraulic fluid can vary quite a lot in practical applications .

Air can get mixed in with these fluids very easily and the effect of the air is to make the fluids more compressible .

This effect can cause some serious problems in hydraulic systems and in work like boiler pressure testing .