Thermomagnetic Convection as a Tool for Heat and Mass Transfer Control in Nanosize Materials Under Microgravity Conditions

Magnetic colloids are relatively new man-made nanomaterials whose magnetic susceptibility is several orders of magnitude larger than that of natural substances. Experiments conducted in magnetic fluids show that strengthening or weakening of thermal convection in colloids is dictated by a competition between the gravitational and magnetic mechanisms as well as by the effect of the fluid density stratification due to gravitational sedimentation of magnetic particles and their aggregates. Therefore experiments in microgravity conditions are required to eliminate gravitational sedimentation. This will enable an accurate investigation of convection in magnetic fluids and unambiguous study of the interaction of a magnetic field with a magnetopolarized medium. Such experiments are also needed to perform an accurate measurement of fluid’s transport coefficients.     

Convective coherent structures in a Hele-Shaw cell

Convective processes related to the onset of chaotic flows in a Hele-Shaw cell have been theoretically and experimentally studied. The properties of various modifications of a specific pulsation regime, in which certain characteristics exhibit chaotization with increasing Rayleigh number while the flow pattern remains statistically reproducible and retains a regular character, have been determined for the cavities with various ratios of the dimensions of wide sides. An analogy is established that allows pulsating vortices in the flow to be treated as simple coherent structures of a convective nature.     

Separation of mixtures and heat and mass transfer in connected channels

The stationary and oscillatory regimes of thermal convection in a binary liquid mixture flowing in narrow connected channels under the action of positive and negative thermodiffusion have been studied. It is established that specific oscillatory flows develop in the case of positive thermodiffusion at a small supercriticality. A mechanism explaining the observed phenomena is proposed and confirmed by the results of numerical calculations. It is shown that connected channels can be used in technological processes for the separation of components in binary liquid mixtures.     

Active control of fluid equilibrium in a thermosyphon

We have theoretically and experimentally studied the problem of automated control over the mechanical equilibrium of an inhomogeneously heated fluid in a rectangular convection loop (thermosyphon), which comprises two coupled vertical channels with rectangular cross sections arranged in a unit made of a heat-conducting material. The equilibrium is maintained using a control feedback subsystem (controller) capable of responding to the onset of a convective motion by introducing small changes in the spatial orientation of the thermosyphon in the gravitational field. The effect of the dynamic stabilization of the equilibrium, which is unstable in the absence of control, is achieved in a broad range of parameters of the system. It is established that excess feedback leads to the excitation of oscillations in the system. An analysis of the theoretical model showed that these oscillations are related to a delay in the correction introduced by the controller into the state of the system under control. The experimental data are in perfect agreement with the results of analysis of the theoretical model.     

Convection and heat transfer experiments in supercritical fluid under microgravity: From MIR to ISS

The results of two series of space experiments carried out onboard the MIR in 1999–2000 are presented. The experiments were undertaken to study the effect of microgravity environment as well as specially excited vibration on heat spread from a point source inside a cell filled with SF₆ near its critical point. New space experiments are proposed to continue the series interrupted by the deorbiting of the MIR. These proposals are the central point of the CRIT project planned for the realization onboard the Russian Segment of the ISS.     

Logarithmic density dependence of viscosity and thermal conductivity of a dense gas

Polynomial and logarithmic dependences on density of the viscosity and thermal conductivity of a dense gas are compared with experimental data.     

Equation for calculating the thermal conductivity of a gas in the critical region

An equation that describes the experimental data on the thermal conductivity of a gas in the critical region ¦T/T_cr-1¦<0.03 and ¦ρ/ρ_cr-1¦<0.4, is presented.