Development of tesla thermomagnetic motors running on solar energy or industrial heat rejects: part II

Abstract

Given the ever greater importance of the renewable energies in our society, we identify the need of a device able to efficiently transform solar energy or industrial thermal energy rejects into mechanical or electrical energies. From our study of magnetic materials with first order magnetic transitions in relation to the magnetocaloric effect, aiming their application in magnetic refrigerators, 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 present in these machines. 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. Preliminary simulations point out to a morphology of the magnetic materials and permanent magnets that we called magnetic piston, able to provide large forces. These tractor sets can be easily multiplied through parallel association, providing high levels of forces. We also designed rotating systems, able to provide high torques. We built two prototypes of motors, one reciprocative and the other rotating type variable reluctance. The reciprocative motor has been tested, and the results indicate the viability of its use as converter of low quality thermal energies into mechanical or electrical energy.Observations concerning the behavior of the reciprocative prototype showed the importance of the heat transfer mechanism in the limitation of the operating frequency of the motors, and this led us to search for new agglomeration methods of the magnetic materials, aiming the maximization of the heat exchanges and so of the operating frequency and of the power to be obtained from these motors. These observations also showed the importance of the use of the first order magnetic materials to maximize the efficiency of the motors.It is expected that these motors can operate with thermodynamic efficiencies that are an appreciable fraction of the Carnot efficiency. This proposal has as objectives: 1) to test a theoretical model of the Kelvin force, to have means for a reliable calculation of the efficiency of the motors using measurements of the magnetic properties of the materials used in them, comparing the calculated efficiencies with the measured ones; 2) to obtain several materials presenting first order magnetic transitions in "large amounts" to be used in the thermomagnetic motors; 3) test of the reciprocating motor with the new materials of the item 2; 4) finish the assembly of the rotating motor, and test it with the materials of item 2; 5) build and test three new motors, one type Curie wheel, another based on ferrofluids and the third a pendulum type.The first order magnetic materials will be obtained in a scale of kilograms using methods based in the processes developed during the study of the magnetocaloric materials. The different models of thermomagnetic motors will be completely characterized in terms of performance, paying particular attention to the thermodynamic efficiency. Because of this, we need that the motors work at maximum frequency, and this means maximize the heat exchanges between the magnetic materials and the heat exchange fluids. As the functioning of the motors is reminiscent of the regenerator type of heat exchangers, for which the maximum efficiency is reached when the heat capacity of the matrix is similar to the heat capacity of the heat exchange fluid, we will test the motors with several different heat exchange fluids, aiming the maximization of the operating frequency, and so the maximization of the power of the motors. (AU)