Abstract
Given the great importance of renewable energies in our society, we identify the need of a device able to efficiently transform solar energy or industrial thermal rejects into mechanical or electrical energies. From our study of magnetic materials with first order transitions in relation to the magnetocaloric effect, we observed that some materials present a high magnetization variation in a short temperature interval around the transition. On assembling a magnetic refrigerator prototype, we observed the high magnetic torques. Putting together both observations, it is clear the possibility of using these features for the assembly of thermomagnetic motors, using the concept of Tesla motors working with materials with transition temperatures slightly above room temperature. Simulations point out to a morphology of the magnetic materials and permanent magnets called magnetic piston, able to provide large forces and torques. We built two motors prototypes, one reciprocative and the other rotating type variable reluctance, and both have been tested, and the results indicate the viability of their use as converter of low quality thermal energies into mechanical or electrical energy, even though the operating frequency of both motors were low, of the order of 0,1 Hz, and the obtained power also was low, as a consequence of the low operating frequency, which is connected to the heat transfer mechanism between the hot and cold fluids and the magnetic plates.Calculations indicate that these motors can operate with thermodynamic efficiencies that are an appreciable fraction of the Carnot efficiency. This proposal has as objectives: 1) re-design both motors to have magnetic plates with dead volumes of the heat transfer fluids minimized, with new shapes of the fluid channels, as variable cross section, and the use of variable hydraulic resistances to obtain homogeneous fluid flux in the plates, and also introduce flow of the fluids simultaneosly in the two senses of the plates, and this will lead to a decrease of the time for the temperature variation of the plates; 2) test the reciprocative motor with the new materials of first and second order to be developed in this proposal; 3) re-design the rotating motor with two approaches. The first corresponds to use only one magnetic piston, and control the temperature of the 6 plates so that their temperature difference is always small, leading to a decrease of the time to promote the magnetic transition, increasing the motor frequency. The second approach corresponds to design the rotating motor with three magnetic pistons working simultaneously, which will lead to increase of the torque; 4) for both approaches, re-design the stator of the motor, using an insulating material in order to minimize the eddy currents, and also re-design the channels of the magnetic plates in order to minimize the dead volume of fluids and to homogenize the temperature distribution in the magnetic plates, aiming the increase of the frequency of the motor. For both motors we will develop the following materials: 1) compounds from the MnFeSn system, which present high saturation magnetization, second order transitions and TC tunable by composition, and these materials can be applied to motors working at temperatures slightly above room temperature, or up to ~200oC. 2) compounds from the Mn2-xFexSiyP1-y system, x [0,9 , 1,5], y [0,4 , 0,6], which are first order materials with small thermal hysteresis and with TC slightly above room temperature. These compounds will be prepared using a chemical route. 3) the compound Fe2Zr, whose Tc is tunable by composition, and is aimed to motors to work at high temperatures (up to 300oC), and with Al addition to obtain higher Tc variation. 4) MnSb compound, which also presents TC tunable by composition, and that will be applied to motors working at high temperatures. We will also study compounds diluted with Fe - Mn1-xFexSb. (AU)
Scientific publications
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(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)