Vapor pressure in open container

[jbriggs444]

It doesn't have to be violent. Also, what is this about the pressure going negative? I can see the gauge pressure going negative, but not the absolute pressure (at least not in the kind of situations you are describing).

That was a statement with a condition -- if the fluid is to remain continuous, local pressure could be required to go negative. Under most conditions, local pressure cannot go negative. Voids will form and boiling will take place. However, in the absence of nucleation sites, negative absolute pressures become plausible.

 

[Chestermiller]

That was a statement with a condition -- if the fluid is to remain continuous, local pressure could be required to go negative. Under most conditions, local pressure cannot go negative. Voids will form and boiling will take place. However, in the absence of nucleation sites, negative absolute pressures become plausible.

Wow. I never heard of that before. Any references?

 

[jbriggs444]

Wow. I never heard of that before. Any references?

The statement was couched as "plausible" because I have no acceptable references. What I had in mind was capillary action.

 

[Chestermiller]

The statement was couched as "plausible" because I have no acceptable references. What I had in mind was capillary action.

I've, of course, heard of elastic solids being able to support negative absolute pressure, but I've never heard of purely viscous fluids being able to do this. The possibility of negative absolute pressure is not a feature of the rheological constitutive equation for an ideal viscous Newtonian fluid, or of the thermodynamic equation of state for a fluid. Maybe, for viscoelastic fluids, negative pressures might be possible.

 

[jbriggs444]

I've, of course, heard of elastic solids being able to support negative absolute pressure, but I've never heard of purely viscous fluids being able to do this. The possibility of negative absolute pressure is not a feature of the rheological constitutive equation for an ideal viscous Newtonian fluid, or of the thermodynamic equation of state for a fluid. Maybe, for viscoelastic fluids, negative pressures might be possible.

There is a good deal of relevant discussion in https://www.physicsforums.com/threads/negative-pressure.428998/

In that thread Andy Resnick provides a reference to http://www.nature.com/nature/journal/v278/n5700/abs/278148a0.html which discusses the tensile strength of water.

 

[Chestermiller]

There is a good deal of relevant discussion in https://www.physicsforums.com/threads/negative-pressure.428998/

In that thread Andy Resnick provides a reference to http://www.nature.com/nature/journal/v278/n5700/abs/278148a0.html which discusses the tensile strength of water.

Oh yeah. I remember this thing now. I never bought into the explanation related to assuming that there is a negative pressure to get the fluid to rise in the pores above a hydrostatic column. I felt that there were some other more likely explanations, such as peristaltic pumping of the pore fluid by the walls of the pores (so that the system is not hydrostatic) or viscoelasticity of the pore fluid (beyond the "tensile strength" of water; actually tensile stiffness). Has anyone ever measured the rheological (viscoelastic) characteristics of the (biological) pore fluid in the laboratory? (Biological fluids are notoriously viscoelastic)

In any event, our excursion into the esoteric subject of the possible existence of negative absolute pressure has gone far afield of the intent of the OP's original questions. Irrespective of whether negative absolute pressure can actually exist, the formation of bubbles and the occurrence of cavitation are realities that we have adequately explained in our previous responses.

Chet