Dynamic Europa ocean shows transient Taylor columns and convection driven by ice melting and salinity

The deep (~100 km) ocean of Europa, Jupiter’s moon, covered by a thick icy shell, is one of the most probable places in the solar system to find extraterrestrial life. Yet, its ocean dynamics and its interaction with the ice cover have received little attention. Previous studies suggested that Europa’s ocean is turbulent using a global model and taking into account non-hydrostatic effects and the full Coriolis force. Here we add critical elements, including consistent top and bottom heating boundary conditions and the effects of icy shell melting and freezing on ocean salinity. We find weak stratification that is dominated by salinity variations. The ocean exhibits strong transient convection, eddies, and zonal jets. Transient motions organize in Taylor columns parallel to Europa’s axis of rotation, are static inside of the tangent cylinder and propagate equatorward outside the cylinder. The meridional oceanic heat transport is intense enough to result in a nearly uniform ice thickness, that is expected to be observable in future missions.

Numerical investigation of heat transfer and solidification in a cavity filled with molten metal alloys in the presence of thermodiffusion

The objective of this research was to study the solidification process of binary molten metals. This study was conducted in three phases. One was to estimate the thermodiffusion factor, two was to simulate the effect of natural convection and radiation on the velocity, temperature, and concentration distributions, and the third was to investigate the solidification process of binary molten metals using the proposed thermodiffusion factors. The proposed expression for the estimation of thermodiffusion factor was based on the physical properties of the mixture constituents. The estimated thermodiffusion factor was used to study thermosolutal convection in a quartz enclosure filled with molten Sn-Bi alloy. Two simulations were carried out: top heating and bottom heating. The sidewalls in both cases were exposed to convection and radiation. Numerical results show that in the case of top heating, the distribution of temperature and concentration are linear, but species segregation occurs due to the thermodiffusion effect. In the bottom heating case, boundary-driven convective flow develops with a large Rayleigh number (Ra) where an increase in the Ra number negates thermodiffusion due to the development of strong mixing. The results of these simulations showed that the effect of convection and radiation are negligible. In phase three, finite element method (FE) was employed to investigate the effect of thermodiffusion during vertical solidification of binary molten metal alloys with bottom cooling. The systems considered here are tin-bismuth (Sn-Bi), tin-cadmium (Sn-Cd), tin-zinc (Sn-Zn), tin-lead (Sn-Pb), tin-gallium (Sn-Ga), and bismuth-lead (Bi-Pb) binary molten metals. The geometry under study was a cylindrical cavity. The FE model was constructed using a 2D axisymmetric element to represent a 3D cyclindrical model. Two cases were studied: one without and one with the effect of thermodiffusion. The simulation including thermodiffusion showed slight variation from the simulation without thermodiffusion, in that thermodiffusion causes a slightly faster solidification and a more uniform concentration distribution if the thermodiffusion coefficient is greater than zero (DT > 0). The main object of this research is development of a more accurate thermodiffusion factor, and applying it in a numerical simulation to study its effects on radiation, natural convection, and solidification processes.

Numerical investigation of heat transfer and solidification in a cavity filled with molten metal alloys in the presence of thermodiffusion

The objective of this research was to study the solidification process of binary molten metals. This study was conducted in three phases. One was to estimate the thermodiffusion factor, two was to simulate the effect of natural convection and radiation on the velocity, temperature, and concentration distributions, and the third was to investigate the solidification process of binary molten metals using the proposed thermodiffusion factors. The proposed expression for the estimation of thermodiffusion factor was based on the physical properties of the mixture constituents. The estimated thermodiffusion factor was used to study thermosolutal convection in a quartz enclosure filled with molten Sn-Bi alloy. Two simulations were carried out: top heating and bottom heating. The sidewalls in both cases were exposed to convection and radiation. Numerical results show that in the case of top heating, the distribution of temperature and concentration are linear, but species segregation occurs due to the thermodiffusion effect. In the bottom heating case, boundary-driven convective flow develops with a large Rayleigh number (Ra) where an increase in the Ra number negates thermodiffusion due to the development of strong mixing. The results of these simulations showed that the effect of convection and radiation are negligible. In phase three, finite element method (FE) was employed to investigate the effect of thermodiffusion during vertical solidification of binary molten metal alloys with bottom cooling. The systems considered here are tin-bismuth (Sn-Bi), tin-cadmium (Sn-Cd), tin-zinc (Sn-Zn), tin-lead (Sn-Pb), tin-gallium (Sn-Ga), and bismuth-lead (Bi-Pb) binary molten metals. The geometry under study was a cylindrical cavity. The FE model was constructed using a 2D axisymmetric element to represent a 3D cyclindrical model. Two cases were studied: one without and one with the effect of thermodiffusion. The simulation including thermodiffusion showed slight variation from the simulation without thermodiffusion, in that thermodiffusion causes a slightly faster solidification and a more uniform concentration distribution if the thermodiffusion coefficient is greater than zero (DT > 0). The main object of this research is development of a more accurate thermodiffusion factor, and applying it in a numerical simulation to study its effects on radiation, natural convection, and solidification processes.

Adventitious rooting in stem and rhizome cuttings of Tuscan (Italy) Vaccinium myrtillus L. under different environmental conditions

BACKGROUND: There is no mention in the literature of vegetative propagation of Vaccinium myrtillus. OBJECTIVE: The aim of the study was to evaluate the rooting potential of bilberry rhizome and stem cuttings. METHODS: Rhizome and stem cuttings collected in early Autumn were dipped in different IBA solutions (0 – 2000 – 4000 mgL–1) and rooted in non-sterilized V. myrtillus soil and expanded perlite under controlled growth chamber environment or under mist with basal heating in a greenhouse for 12 weeks. RESULTS: Rhizome cuttings showed high rooting potential in plant growth regulator (PGR) free substrates. Conversely, stem cuttings took advantage from IBA treatments; this positive effect on rooting percentage was synergistically increased when rooted in agriperlite. A higher rooting capacity was achieved when rhizome and stem cuttings were placed in agriperlite, however number of developed roots and shoots were much higher when V. myrtillus turf was used as substrate. Mist and bottom heating did not improve rooting significantly. CONCLUSIONS: V. myrtillus can be successfully propagated both by rhizome and stem cuttings. With an overall rooting success of 56–68% and with a reasonably good growth rate, production of planting material from stem cuttings of V. myrtillus offers opportunities for a cheaper, practically feasible and technically less demanding alternative means of propagation.

Europa's dynamic ocean: Taylor columns, eddies, convection, ice melting and salinity

<p class="p1">The deep ocean (~100 km) of Europa, Jupiter’s moon, is covered by a thick (tens of km) icy shell, and is one of the most probable places in the solar sys- tem to find extraterrestrial life. Yet, its ocean dynamics and its interaction with the ice cover have so far received little attention. Previous studies sug- gested that Europa’s ocean is turbulent, yet neglected to take into account the effects of ocean salinity and appropriate boundary conditions for the ocean’s temperature. Here, the ocean dynamics of Europa is studied using global ocean models that include non-hydrostatic effects, a full Coriolis force, con- sistent top and bottom heating boundary conditions, and including the effects of melting and freezing of ice on salinity. The density is found to be dominated by salinity effects and the ocean is very weakly stratified. The ocean exhibits strong transient vertical convection, eddies, low latitude zonal jets and Tay- lor columns parallel to Europa’s axis of rotation. In the equatorial region, the Taylor columns do not intersect the ocean bottom and propagate equatorward, while off the equator, the Taylor columns are static. The meridional oceanic heat transport is intense enough to result in a nearly uniform ice thickness, that is expected to be observable in future missions.</p>

Experimental Investigations on the Thermal Performance of a Single Closed Loop Pulsating Heat Pipe Using TiO2 Nanofluid

This paper describes the experimental investigations conducted on a closed loop pulsating heat pipe (CLPHP) for assessing the thermal performance. The pulsating heat pipe has a single closed loop made of copper. The working fluids used are water and titanium dioxide nanofluids with varying concentrations of TiO2 nanoparticles (1.5% and 1%) on weight basis. The TiO2 particles are mixed in water to form a stable suspension using a sonicator. The heat input is varied between 40 W and 100 W in steps of 20 W. All experiments are conducted in the bottom heating mode (evaporator at the top) in the vertical and horizontal orientations. The parameters considered for evaluating the thermal performance are the temperature difference between evaporator and condenser, thermal resistance, heat transfer coefficient, and thermal conductivity. The results of the investigation reveal that the vertical orientation and increase in nanoparticle concentration favors better heat transfer performance of the single closed loop pulsating heat pipe.