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Heat Transfer Enhancement Using Ferrofluids

In this paper we demonstrate how ferrofluids (magnetic nanofluids) can be used to significantly enhance heat transfer rates in microchannels to help meet the ever-growing demand for high heat flux removal. There are a few mechanisms that can be used to aid mixing and to enhance heat transfer in inherently low Reynold number flow in microchannels. Firstly, the addition of a small amount of the thermally conductive paramagnetic particles can increase the thermal conductivity of the base fluid. For example, a solution of 5% particles can increase the thermal conductivity by approximately 10%, with only a 4% increase in dynamic viscosity. With the application of a magnetic field, the effective thermal conductivity can be increased further in the direction of the field, due to the formation of particle chains. Heat transfer can be additionally enhanced by applying a magnetic field to disrupt the flow, but a non-uniform magnetic field is required. Two-phase slug flow using a plug of ferrofluid in an immiscible liquid can have a large and controllable effect on the heat transfer rate.