Thermal convection in a layer of magnetic colloid based on a single-component fluid

•Experimentally studying thermal convection in a horizontal magnetic colloid layer.•A new convection regime has been revealed just beyond the stability threshold.•Aggregates of magnetite particles effect on convective structures in the regime.•The Rayleigh number range for the regime shrinks as an average temperature grows.•Indirectly confirming that aggregate sizes reduce as the average temperature rises. Experiments on studying thermal gravitational convection in an undecane-based magnetic colloid layer are carried out. Undecane is a single-component carrier fluid. We use a cylindrical cavity with a diameter of 58mm and a height of 2.4mm to model a horizontal plane layer. Convection in the magnetic colloid layer heated from below is observed by means of a thermocouple system and a thermal imager. Several series of thermocouple measurements for a heat flux through the layer and thermal imaging survey for temperature fields at the magnetic colloid surface are performed at various average colloid temperatures. The average temperature increases from 20 to 55°C in increments of 5°C. A regime in the form of convective patterns consisting of stable downward flows in their centers and unstable upward flows along the edges is found in experiments. The Rayleigh number range for the regime shrinks as the average temperature increases. It can be seen from the convection regime map constructed in our study. We propose the hypothesis, according to which shrinkage of the Rayleigh number range and the instability of upward flows for this regime is due to the effect of aggregate sedimentation on convection in a horizontal magnetic colloid layer. Aggregate sizes decrease as the average colloid temperature rises.