GIADA microbalance measurements on board Rosetta: submicrometer- to micrometer-sized dust particle flux in the coma of comet 67P/Churyumov-Gerasimenko

Context. From August 2014 to September 2016, Rosetta escorted comet 67P/Churyumov-Gerasimenko (67P) during its journey around the Sun. One of the aims of Rosetta was to characterize cometary activity and the consequent formation of dust flux structures in cometary comae. Aims. We characterize and quantify the submicrometer- to micrometer-sized dust flux that may be shaped in privileged directions within the coma of 67P inbound to and outbound from perihelion. Methods. The in situ dust-measuring instrument GIADA, part of the Rosetta/ESA payload, consisted of three subsystems, one of which was the Micro Balance Subsystem (MBS), composed of five quartz crystal microbalances. From May 2014 to September 2016, MBS measured the submicrometer- to micrometer-sized deposited dust mass every 5 min. Results. We characterized the submicrometer- to micrometer-sized dust mass flux in the coma of 67P. The anti-sunward and the radial direction are preferred, and the flux is higher in the anti-sunward direction. The measured cumulative dust mass in the anti-sunward direction is 2.38 ± 0.04 × 10−7 kg, and in the radial direction, it is 1.18 ± 0.02 × 10−7 kg. We explain the anti-sunward dust flux as the effect of nonuniform gas emission between the night- and dayside of the nucleus, which acts in combination with the solar radiation pressure. We compared the cumulated dust mass of particles ≤5 μm with particles ≥100 μm. The retrieved ratio of ≈2% implies a differential size distribution index of ≈−3.0, which confirms that particles of size ≥0.1 mm dominate the dust coma cross-section of 67P during the entire orbit. Conclusions. Submicrometer- to micrometer-sized dust mass flux measurements were made for the first time from the arising of cometary activity until its extinction. They indicate that these particles do not provide a substantial optical scattering in the coma of 67P with respect to the scattering caused by millimeter-sized particles. In addition, MBS data reveal that the measured dust flux is highly anisotropic: anti-sunward plus radial.

Numerical Approach to Study Nonuniform Gas–Liquid Distribution in the Refrigerant Distributor in an Air Conditioner

Factors that influence the nonuniform gas–liquid distribution in refrigerant distributors in air conditioners were studied. Gas–liquid flows in two-pass and multipass distributors were numerically simulated with a particle/grid hybrid method; droplets and liquid films were mainly simulated using a particle method, and gas flows were simulated using a grid method. Complex behaviors of multiscale gas–liquid interfaces in the multipass distributor were simulated because droplets that were smaller than the grid size could be simulated without numerical diffusion through the gas–liquid interfaces. The effect of the connecting angle of the bend pipe was studied in the two-pass distributor, whereas the effect of the tube's position relative to the distributor inflow and the effect of gravity were investigated in the multipass distributor. The model was validated against multiple experimental data taken from an at-scale physical model. We found that the direction of gravity plays a role in ensuring a uniform distribution of liquid in the multipass distributor for ensuring a uniform distribution.