The coupled momenta induced by thermal effects near interfaces cause complex three-dimensional flow structures, called thermocapillary flow or Marangoni convection. Thermocapillary convection is crucial for crystal growth quality, and the mainstream method used to study thermocapillary convection is the half-zone liquid bridge model. This paper designs a gas–liquid two-phase system and reports the numerical results on the instability and associated roll structures of thermocapillary convection in half-zone liquid bridge under microgravity environment. The gas and liquid transferred momentum and energy through the free surface. The geometry of interest is high aspect ratio (AR) silicone oil suspended between coaxial disks heated differentially. It was found that with the increase in AR, the vortex of thermocapillary convection gradually moves to the upper disk at the steady state. In the range of 2 < AR < 2.5, the vortex cell splits from 1 to 2, and the distance between the vortex center increases with the increase in AR. The flow field after the onset of instability exhibits a traveling wave with wave number m = 1 when AR ≤ 3 and exhibits a standing wave with wave number m = 1 when AR ≥ 3.5.

The effect of the temperature gradient on the Soret coefficient in n-pentane/n-decane (n-C₅/n-C₁₀) mixtures was investigated using non-equilibrium molecular dynamics (NEMD) with the heat exchange (eHEX) algorithm. n-Pentane/n-decane mixtures with three different compositions (0.25, 0.5, and 0.75 mole fractions, respectively) and the TraPPE-UA force field were used in computing the Soret coefficient ( S T {S_{T}} ) at 300 K and 1 atm. Added/removed heat quantities (ΔQ) of 0.002, 0.004, 0.006, 0.008, and 0.01 kcal/mol were employed in eHEX processes in order to study the effect of different thermal gradients on the Soret coefficient. Moreover, a phenomenological description was applied to discuss the mechanism of this effect. Present results show that the Soret coefficient values firstly fluctuate violently and then become increasingly stable with increasing ΔQ (especially in the mixture with a mole fraction of 0.75), which means that ΔQ has a smaller effect on the Soret coefficient when the temperature gradient is higher than a certain thermal gradient. Thus, a high temperature gradient is recommended for calculating the Soret coefficient under the conditions that a linear response and constant phase are ensured in the system. In addition, the simulated Soret coefficient obtained at the highest ΔQ within three different compositions is in great agreement with experimental data.

The effect of the instability of the interface morphology due to mechanical disturbances and acceleration changes (or gravity flutter) on Marangoni convective stability has been confirmed via space experiments. However, compared with the research on Marangoni convection with an axisymmetric liquid bridge, research on the transition and interface flow behavior of Marangoni convection with a non-axisymmetric liquid bridge is not sufficiently deep. Based on the thermal-buoyant capillary convection (TBCC) experiment of the conventional liquid bridge, in this study, the influence of the interfacial energy instability triggered by the gravitational tilt angle (GTA) on the spatiotemporal evolution of the flow pattern and velocity distribution of the thermal-buoyant capillary convection is examined by applying the GTA to form the non-axisymmetric liquid bridge model. The results show that the non-equilibrium change in the interface curvature due to GTA leads to a non-axisymmetric liquid bridge morphology. With increasing GTA, the cell-flow morphology during the development process is restricted, transverse/longitudinal velocity component is suppressed, and velocity peak value position gradually approaches the interface. In the oscillating TBCC stage, the deviation of cell flow vortex cores from the intermediate height intensifies with the increasing GTA, resulting in the expansion of the alternating flow zone in the center. Furthermore, the longitudinal velocity component distribution is transformed into the “two peaks and one valley” morphology (“M”-type) from the original multi-peak morphology. The interfacial energy instability due to the GTA can increase the critical temperature difference of the oscillating TBCC, maintain its stability, and delay the onset of the oscillating flow. Simultaneously, the oscillation frequency of the oscillating TBCC is reduced and the development of the oscillating TBCC is suppressed.