Hello all,

I have a very basic question regarding the presence of interface ( presence of surface tension to be precise) between liquid or gas phase with supercritical phase.

For instance, consider oxygen (Tc ~ 150 K, Pc ~ 50 bar).

Let us consider:

1. Case 1 wherein liquid oxygen (T and P > Tc, Pc, say 100 K and 45 bar) is injected into a chamber filled with gaseous oxygen ( say T = 130 K, P = 45 bar). Then if I understand well, then there will be phase change and we will have surface tension present between these phases.

2. Case 2: Oxygen above the critical point (say T = 160 K, 55 bar) injected into supercritical oxygen say T = 180 K and 55 Bar), Both are in supercritical phase. In such case there will be just diffusion ( which I understand is due to difference in concentration/density and thus self diffusion). No interface or effects of surface tension will be present.

3. Now let us take a case, say liquid oxygen is injected into supercritical oxygen.

For sake of convenience, say initial T = 120 K and P = 60 bar ( i.e above Pc but below Tc), and injected into supercrtical phase of oxygen. ( T = 180 K, P = bar).

Is this case similar to case 2 or case 1 described above.

My main concern was will there be surface tension present or will there be just diffusion.

( I am assuming here that at no local point, the T and P will fall below Tc,Pc to avoid any liquid --> gas conversion)

More precisely, will it be reasonable to consider surface tension in analytical/numerical computations?

To my understanding, we incorporate surface tension to account for increase in energy due to interfacial energy/latent heat.But here we don't have anything of this sort but as we have liquid and Supercritical state, it's slightly confusing.

How will things change when instead of liquid injection, we do same case with gas state ( say T = 190 K, P = 40 bar i.e. T> Tc , P < Pc)

Thanks