By Josh Perry, Editor
[email protected]

Scientists from the Siberian Federal University (SUF) and the Institute of Computational Modeling from the Siberian Branch of the Russian Academy of Sciences have developed a calculation to describe the structure of fluid flow and evaporation in two-layer systems with liquid-gas mixtures.

Structures on the surface of the evaporating liquids driven by co-current gas flow observed in the experiments. Now, the formation of the patterns can be predicted with the help of the new theoretical approaches developed by Siberian scientists.
(Prof. Kabov/Siberian Federal University)

According to a report from SUF, the calculations focused on the impact of gravity and the thickness of the liquid layer and a better understanding of how this flow works will enhance micro-level cooling devices for satellites and other aerospace applications.

In convection heat transfer, there is a permanent motion in the fluid. The upper layers cool, get heavier, and drop, while the lower levels get hotter and rise. Heat loss at the border between fluid and gas is related to evaporation in that molecules with higher energy break bonds and are released from the surface.

“The presented mathematical model describes convective processes in the two-layer liquid and gas-vapor system,” the report explained. “It is based on the most important equations of fluid dynamics (the Navier - Stokes equations) and takes into account several additional factors.”

The report continued, “For example, the thermodiffusion effect can lead to the formation of zones with different concentrations of molecules depending on the temperature. Under the influence of various factors a liquid can be stratified into warm and cold layers, whereby some physical properties of the medium (density, superficial tension, and so on) can be changed.”

Convection can be suppressed by changing the thickness of the fluid layers, according to the researchers. Reducing the height of the liquid layer can increase the influence of the thermocapillary effect that moves hot liquid along the liquid-gas interface.

The research was recently published in Microgravity Science and Technology. The abstract stated:

“The characteristics of convective regimes in a two-layer system have been investigated in the framework of the Boussinesq approximation of the Navier–Stokes equations. An exact invariant solution of the convection equations is used to describe a joint stationary flow of an evaporating liquid and a gas-vapor mixture in a horizontal channel. Thermodiffusion effects in the gas-vapor phase are additionally taken into account in the governing equations and interface conditions.

“The influence of gravity and thickness of the liquid layer on the hydrodynamical, thermal and concentration characteristics of the regimes has been investigated. Flows of the pure thermocapillary, mixed and Poiseuille’s types are specified for different values of the problem parameters. The linear stability of the evaporative convection regimes has been studied.

“The types and properties of the arising perturbations have been investigated and the critical characteristics of the stability have been obtained. Disturbances can lead to the formation of deformed convective cells, vortex and thermocapillary structures. The change of the instability types and threshold thermal loads occurs with the increasing thickness of the liquid layer and gravity action.”