Abstract
This paper investigates the characteristics of a nitrogen jet (the thermodynamic conditions ranging from subcritical to supercritical) ejected into a supercritical nitrogen environment using the molecular dynamics (MD) simulation method. The thermodynamic properties of nitrogen obtained by molecular dynamics show good agreement with the Soave-Redlich-Kwong (SRK) equation of state (EOS). The agreement provides validation for this nitrogen molecular model. The molecular dynamics simulation of homogeneous nitrogen spray is carried out in different thermodynamic conditions from subcritical to supercritical, and a spatio-temporal evolution of the nitrogen spray is obtained. The interface of the nitrogen spray is determined at the point where the concentration of ejected fluid component reaches 50%, since the supercritical jet has no obvious vapor-liquid interface. A stability analysis of the transcritical jets shows that the disturbance growth rate of the shear layer coincides very well with the classical theoretical result at subcritical region. In the supercritical region, however, the growth rate obtained by molecular dynamics deviates from the theoretical result.
Highlights
Supercritical fluid injections have many applications ranging from internal combustion engines to supercritical fluid extraction [1,2]
We simulated the thermodynamic properties of nitrogen using the molecular dynamics method and compared the result with the SRK equation of state
It is obvious that the state equations obtained by molecular dynamics simulation are perfectly in line with the SRK equation of state, both at a low temperature (Figure 3a) and a high temperature (Figure 3b)
Summary
Supercritical fluid injections have many applications ranging from internal combustion engines to supercritical fluid extraction [1,2]. It is well-known that the critical point is a singularity in thermodynamics. Fluids in supercritical conditions have distinct properties from subcritical conditions. The interface between the liquid and the gas phases no longer exists, as the liquid surface tension and the latent heat of evaporation tend towards zero. There is no longer a distinction between liquid and gas, but it is collectively referred to as a homogeneous supercritical fluid. Its density is close to that of the liquid and its transport characteristics are close to those of the gas
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