Analysis and Development of a Magnetocaloric Pump for Electronic Cooling Applications Using a Mn-Zn Ferrite Ferrofluid

Abstract

A device able to pump a fluid with no moving mechanical parts represents a very encouraging alternative since such device would be practically maintenance free. A magnetocaloric pump could achieve this purpose by providing a magnetic pressure gradient to a ferrofluid placed inside a magnetic field while experiencing a temperature change. If the temperature change is produced by extracting heat out of an element that needs refrigeration, coupling this generated heat with the magnetocaloric pump will result in a passive cooling system. For applications near ambient temperature the ferrofluid must have specific characteristics such as low “Curie temperature”, high pyromagnetic coefficient, high thermal conductivity and low viscosity. This work presents an analysis of the ferrohydrodynamic governing equations, emphasizing the importance of the Kelvin force in the magnetocaloric pump analysis. The general equations are simplified and scaled to show which parameters are important in the generation of the magnetic pressure gradient. Based on the scaling analysis, a variable magnetic field and a higher saturation magnetization is needed to generate a higher magnetic pressure gradient. The working fluid used is an aqueous Mn0.5Zn0.5Fe2O4 ferrite ferrofluid synthesized by the co-precipitation technique. This ferrite shows lower “Curie temperature” than commercially available magnetite. Important issues in the design of a magnetocaloric pump prototype with a variable magnetic field source are also discussed.