No abstract

In 1974, reference correlations for the viscosity of molten LiF-NaF-KF, LiF-BeF2, and Li2CO3-Na2CO3-K2CO3 were proposed by Janz and have been extensively used since then. However, in the last 45 years, many additional measurements have been published. This is why in this paper, new reference correlations for the viscosity of these salts are proposed. All available experimental data for the viscosity of these three molten salts have been critically examined with the intention of establishing improved or new reference viscosity correlations. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. The reference correlation proposed for LiF-NaF-KF, with an uncertainty of 2.9% at the 95% confidence level, expands the temperature range of the previous correlation from (770–970) K to (732–1163) K and retains its uncertainty. The correlation proposed for LiF-BeF2, with an uncertainty of 4.9% at the 95% confidence level, expands the high temperature range of the previous correlation from (740–870) K to (793–1573) K, with a slight loss in its uncertainty. It is, however, a much better correlation as it is based upon measurements not available at the time of the previous one. Finally, the reference correlation for Li2CO3-Na2CO3-K2CO3, with an uncertainty of 3%, also expands the temperature range of the previous correlation from (920–1170) K to (738–1170) K and retains its uncertainty.

To better characterize the lifetime and performance of electrospray thrusters, electron emission due to electrode impingement by the propellant cation 1-ethyl-3-methylimidazolium (EMI+) has been evaluated with semi-empirical modeling techniques. Results demonstrate that electron emission due to grid impingement by EMI+ cations becomes significant once EMI+ attains a threshold velocity of ∼9×105cm  s−1. The mean secondary electron yield, γ¯, exhibits strong linearity with respect to EMI+ velocity for typical electrospray operating regimes, and we present a simple linear fit equation corresponding to thruster potentials greater than 1 kV. The model chosen for our analysis was shown to be the most appropriate for molecular ion bombardments and is a useful tool in estimating IIEE yields in electrospray devices for molecular ion masses less than ∼1000 u and velocities greater than ∼106cm  s−1. Droplet-induced electron emission (DIEE) in electrospray thrusters was considered by treating a droplet as a macro-ion, with low charge-to-mass ratio, impacting a solid surface. This approach appears to oversimplify back-spray phenomena, meaning a more complex analysis is required. While semi-empirical models of IIEE, and the decades of solid state theory they are based upon, represent an invaluable advance in understanding secondary electron emission in electrospray devices, further progress would be gained by investigating the complex surfaces the electrodes acquire over their lifetimes and considering other possible emission processes.