3 research outputs found
Injection of photoelectrons into dense argon gas
The injection of photoelectrons in a gaseous or liquid sample is a widespread
technique to produce a cold plasma in a weakly--ionized system in order to
study the transport properties of electrons in a dense gas or liquid. We report
here the experimental results of photoelectron injection into dense argon gas
at the temperatureT=142.6 K as a function of the externally applied electric
field and gas density. We show that the experimental data can be interpreted in
terms of the so called Young-Bradbury model only if multiple scattering effects
due to the dense environment are taken into account when computing the
scattering properties and the energetics of the electrons.Comment: 18 pages, 10 figures, figure nr. 10 has been redrawn, to be submitted
to Plasma Sources Science and Technolog
Supercritical Pseudo-Boiling and its Relevance for Transcritical Injection
In this paper, a new interpretation of cryogenic jet break-up in supercritical environments is introduced. It is firmly established that under these conditions a pure
fluid will exhibit neither latent heat of vaporization nor surface tension. The jet undergoes a transition from a dense cryogenic fluid to an ideal gas as it mixes and blends with the surrounding warmer gas. Regarding the thermodynamic process, this transition is characterized
by large changes in density and very small changes in temperature as energy is supplied. The state where density changes and the heat capacity are maximal is sometimes called `pseudo-boiling' in the literature. However, no clear definition of this process is available, its very existence debated. In this paper, the first quantitative pseudo-boiling analysis is presented. It can be shown that pseudo-boiling exists along a line which effectively structures supercritical
uid states. An equation for this continuation of the coexistence line is given. Across this line, a continuous state transition can be identfied. The temperature
at pseudo-boiling replaces the critical temperature as relevant parameter at supercritical pressures. By introducing a suitable definition for a supercritical
uid boundary, supercritical jet break-up can be quantified thermodynamically. This suggests a novel, thermal,
jet break-up mechanism. Experimental evidence from the literature is shown, further supported by CFD simulations. The pseudo-boiling effect is found to play a role for injection
conditions of reduced pressures smaller than 3, and reduced temperatures lower than 1.2