F. Aitken

Electrocoalescence Criterion for Two Close Anchored Water Drops and Estimate for Pairs of Drops in a Field

An investigation is presented of the deformation and coalescence of two closely spaced drops of conducting liquid suspended in an insulating fluid under the action of an electric field. After a recap of previous work on two identical drops, the equation governing the droplets deformation is derived in the asymptotic case of very close drops subjected to a potential difference. The critical conditions for the existence of a stationary solution are determined for a pair of droplets anchored on coaxial rings and on capillary tubes. In particular, electrocoalescence is predicted to occur when the interfaces distortions are such that the initial drops spacing has decreased by nearly 50%. The case of drops subjected to a uniform field is also considered, and an approximate expression for the critical field is proposed based on a semiempirical relation estimating the potential difference between two close spheres as a function of the applied field, of the spheres radius, and of their spacing.

Electrocoalescence Criterion for Two Close Water Drops

We investigate the deformation and coalescence of two closely spaced drops of conducting liquid suspended in an insulating fluid under the action of an electric field. After a recap of previous work on two identical drops, the equation governing the droplets deformation is derived in the asymptotic case of very close drops subjected to a potential difference. The critical conditions for existence of a stationary solution are determined for a pair of droplets anchored on coaxial rings; in particular, electrocoalescence is predicted to occur when the interfaces distortions are such that the initial drops spacing has decreased by nearly 50%. The case of drops subjected to a uniform field is also considered and an approximate expression for the critical field is proposed based on a semi-empirical relation giving the potential difference between two close spheres as a function of the applied field, of the spheres radius and of their spacing.

The mobility of positively charged `snowballs' in normal liquid helium

Positively charged helium clusters, also called snowballs, have been investigated within normal liquid helium. Thermodynamic state equations for ionic helium clusters in liquid helium have been developed, allowing us to discern the hydrodynamic radius for a wide range of hydrostatic pressures and temperatures. The mobilities derived from the cluster sizes using stokes law match experimental data with unsurpassed accuracy. For low pressures the compressibility of the cluster ions was found to be distinctly larger than the compressibility of solid helium suggesting that in this pressure range clusters are fully or partially liquid.

Molecular and atomic spectra emitted by normal liquid and supercritical 4 He excited by corona discharge

The properties of corona discharge were study by electro-physical and spectral methods in the supercritical phase at 6 K and 11 K as well as in normal liquid helium at 4.2K within the pressure range of 0.1-10 MPa. The electro-physical investigations (measurement of corona current as a function of the applied voltage) gave information about the mobility of charged particles in the medium. The observed corona current is very small, less than 10-7 A. The measured current-voltage characteristics allow for the calculation of the charged particle mobilities (i.e., electrons for negative corona and positive ions for positive corona). The observed charge mobilities decrease as a function of external pressure in both supercritical and liquid phases of helium. The light emitted from the ionization zone was analyzed and assigned to atomic and molecular lines. Distortion of the spectral lines due to the dense helium environment was analyzed. The observed P and R branch rotational line shifts of He2* are markedly different from the previous theoretical predictions. The observed atomic line shifts and widths depend strongly on the applied pressure in both the supercritical and the liquid phases, which can be understood in terms of a bubble formation around the emitters.

Mobility of positively charged ions in supercritical helium

The mobility of positively charged ions in supercritical helium at temperatures from 6 to 11 K and up to 20 bar was measured using corona discharges. Regions of increased and decreased hydrodynamic radius are interpreted in terms of growth, compression and solidification of ion clusters. Modelling of the mobility using a thermodynamic state equation for the ion-helium mixed system and a temperature dependent Cunningham correction provides best match with experimental data for a van der Waals helium-ion interaction term. Regions of large hydrodynamic radius and large compressibility are attributed to liquid-like behaviour.