Experimental characterization of thermal conductance switching in magnetorheological fluids

We experimentally investigate thermal conductance switching in Fe-based magnetorheological fluids (MRFs). The transient hot-square technique is employed to directly measure enhancement in the thermal conductivity of bulk samples with volume concentrations up to 33% along the field direction. The ratio of the thermal conductivities of bulk MRFs under no and strong (similar to 290 kA/m) field is approximately 1.3, nearly independent of particle concentration. Significantly higher on-off conductance ratios can be achieved at a device level by exploiting the normal field instability to form columns of MRFs across an air gap. We experimentally demonstrate reversible switching in one implementation of this device concept. (C) 2010 American Institute of Physics. [doi:10.1063/1.3350906]