A System for Measurement of Convection Aboard Space Station

A simple device for direct measurement of buoyancy driven fluid flows in a low-gravity environment is proposed. A system connecting spacecraft accelerometers data and results of thermal convection in enclosure measurements and numerical simulations is developed. This system will permit also to evaluate the low frequency microacceleration component. The goal of the paper is to present objectives and current results of ground-based experimental and numerical modeling of this convection detector

Thermo-magneto-convective instabilities in a vertical layer of ferro-magnetic fluid

We study convection in a vertical layer of ferro-magnetic fluid heated from the side and subject to a transverse magnetic field. It is found that the subsequent fluid motion is caused by interacting thermo-gravitational and thermo-magnetic mechanisms. Our experiments and computations show that the excitation of magneto-convection leads to the formation of vertically aligned stationary rolls, while gravitational convection results in horizontal rolls corresponding to a pair of counter-propagating thermal waves. The interaction of these instability modes leads to a wide spectrum of experimentally observed flow patterns including stationary rolls and standing waves of various spatial orientations. A comprehensive stability map is computed and compared with experimental flow visualisations. Disturbance energy is analysed to achieve a deeper insight into the physical mechanisms driving the fluid motion

Magneto-hydrodynamic interaction in a vertical slot filled with ferrofluid

Convection flow in a vertical layer of ferrofluid heated from a side and subject to the transverse magnetic field is studied. A stability map is computed and compared with experimental flow visualizations. It is shown that the excitation of magneto-convection leads to the formation of vertically aligned rolls. The interaction of thermo-gravitational and thermo-magnetic motions results in roll and wave patterns of various spatial orientations. A new thermo-magnetic wave instability mechanism is found to exist for sufficiently large values of magnetic Grashof number

Non-conducting magnetic fluids and their application for heat removal in micro-gravity conditions

We propose a comprehensive theoretical and experimental investigation (including ground-based studies and experiments conducted on board of the International Space Station) with the aim of understanding and quantifying transport properties of nonconducting ferrofluids and physics of their flows. The specific emphasis is on using such fluids for safe and reliable heat removal in micro-gravity conditions of a realistic spacecraft. Our preliminary investigation indicates that compact magneto-convection heat removal systems can operate in zero-gravity conditions and deliver better efficiency than their conventional convection-based counterparts operating at normal gravity

Thermomagnetic convective flows in a vertical layer of ferrocolloid: perturbation energy analysis and experimental study

Flow patterns arising in a vertical differentially heated layer of nonconducting ferromagnetic fluid placed in an external uniform transverse magnetic field are studied experimentally and discussed from the point of view of the perturbation energy balance. A quantitative criterion for detecting the parametric point where the dominant role in generating a flow instability is transferred between the thermogravitational and thermomagnetic mechanisms is suggested, based on the disturbance energy balance analysis. A comprehensive experimental study of various flow patterns is undertaken, and the existence is demonstrated of oblique thermomagnetic waves theoretically predicted by Suslov and superposed onto the stationary magnetoconvective pattern known previously. It is found that the wave number of the detected convection patterns depends sensitively on the temperature difference across the layer and on the applied magnetic field. In unsteady regimes its value varies periodically by a factor of almost 2, indicating the appearance of two different competing wave modes. The wave numbers and spatial orientation of the observed dominant flow patterns are found to be in good agreement with theoretical predictions

Intermittent flow regimes near the convection threshold in ferromagnetic nanofluids

The onset and decay of convection in a spherical cavity filled with ferromagnetic nanofluid and heated from below are investigated experimentally. It is found that, unlike in a single-component Newtonian fluid where stationary convection sets in as a result of supercritical bifurcation and where convection intensity increases continuously with the degree of supercriticality, convection in a multicomponent ferromagnetic nanofluid starts abruptly and has an oscillatory nature. The hysteresis is observed in the transition between conduction and convection states. In moderately supercritical regimes, the arising fluid motion observed at a fixed temperature difference intermittently transitions from quasiharmonic to essentially irregular oscillations that are followed by periods of a quasistationary convection. The observed oscillations are shown to result from the precession of the axis of a convection vortex in the equatorial plane. When the vertical temperature difference exceeds the convection onset value by a factor of 2.5, the initially oscillatory convection settles to a steady-state regime with no intermittent behavior detected afterward. The performed wavelet and Fourier analyses of thermocouple readings indicate the presence of various oscillatory modes with characteristic periods ranging from one hour to several days

Oscillatory instability of convection in ferromagnetic nanofluid and transformer oil

Experimental investigation of thermal convection in ferromagnetic nanofluid and transformer oil

New type of thermal waves in a vertical layer of magneto-polarizable nano-suspension: theory and experiment

Study of Boussinesq convection in a vertical differentially heated fluid layer is one of classical problems in hydrodynamics. It is well known that as the value of fluid's Grashof number increases the basic flow velocity profile becomes unstable with respect to stationary shear-driven disturbances (at Prandtl numbers Pr<12.5) or thermogravitational waves propagating vertically (at larger values of Prandtl number). However linear stability studies of a similar flow of magnetopolarizable nanosuspensions (ferrofluids) placed in a uniform magnetic field perpendicular to a fluid layer predicted the existence of a new type of instability, oblique waves, that arise due to the differential local magnetisation of a non-uniformly heated fluid. The existence of such (thermomagnetic) waves has now been confirmed experimentally using a kerosene-based ferrofluid with magnetite particles of the average size of 10 nm stabilized with oleic acid. The heat transfer rate measurements using thermocouples and flow visualization using a thermosensitive film and an infrared camera have been performed. Perturbation energy analysis has been used to determine the physical nature of various observed instability patterns and quantitatively distinguish between thermogravitational and thermomagnetic waves