Experimental determination of the critical Rayleigh number for thermomagnetic convection with focus on fluid composition


Abstract

Thermomagnetic convection has been investigated for two kerosene-based magnetic fluids (EMG905 and NF4000C) with a focus on the determination of the critical Rayleigh numbers for the onset of convective instability in a fluid layer. A comparison with published data for the ester-based APG513A-fluid and theoretical predictions yield similar critical magnetic Rayleigh numbers for the EMG and APG-fluids around Ram,c≈ 2500, which is near the expected value, but Ram,c=856 for the NF-fluid. As the latter differs from the other two fluids mainly in the particle size distribution, it is assumed that the size of the particles has an important and yet uninvestigated impact on the convective behavior of magnetic fluids.


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