Molecular Flow Modelling for pressure determination by a new nanobalance system under zero gravity
The vapor pressure over a liquid or solid sample is an essential physical property. Fundamental thermodynamic data such as enthalpy, entropy and Gibbs Energy can be determined by temperature dependence of the vapor pressure. These data are essential to design the microstructure or either the complex metallurgical melting process for new alloys in the automotive and aerospace sector. Performing vapor pressure determination under zero gravity will give new insights into free vaporization without influence between sample and Knudsen Cell and gravity driven effects such as convection, sedimentation and natural drift.
We have modelled the vaporisation behaviour of a special designed Knudsen cell for levitation experiments using the COMSOL Multiphysics software environment.
A new experimental set up for measuring evaporation rates of metals and alloys under zero gravity is to be developed. The set up will determine vapor pressures of species effusing from a special designed Knudsen Cell using a high-resolution nanobalance system based on a piezoelectric langasite single crystals. The compatibility to the electromagnetic levitator system (EML) on board of the International Space Station (ISS) will be ensured and is demonstrated during DLR Parabolic Flight Campaigns (Novaspace, Bordeaux-Merignac).
Different boundary conditions are considered in the Simulation: sample temperatures, Knudsen Cell Geometries, condensation effects or thermal gradients. A critical evaluation of existing vapor pressure data will be given within the Ag-Cu System. The flux is simulated for a levitated sample made of Zn, Ag and the eutectic composition Ag-Cu (60-40 at.%). Finally, compared by measured values of DLR Parabolic Flight Campaigns.