Ultra pure water.Because the onset of convection depends on the difference in density and viscosity, there can be no other liquid with similarity in convection current
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The onset of natural convection is determined by the Rayleigh number (Ra). This dimensionless number is given by
Ra=ΔρgL^3/Dμ
where
Δρ is the difference in density between the two parcels of material that are mixing
g is the local gravitational acceleration
L is the characteristic length-scale of convection: the depth of the boiling pot, for example
D is the diffusivity of the characteristic that is causing the convection, and
μ is the dynamic viscosity