Harnessing low-grade waste heat by a thermomagnetic engine in conjunction with a hybrid generator system

Conversion of low-grade thermal energy into electrical energy was explored with the application of a hybrid generator system driven by a thermomagnetic heat engine. The hybrid generator system consists of an electromagnetic generator (EMG) and flexible piezoelectric films, which was designed to draw electric power as much as possible from the rotating shaft of the thermomagnetic engine. The major components of the engine are Gadolinium (Gd) blocks and a bar shaped permanent magnet, where their interaction develops the rotational motion of the engine thanks to the magneto-caloric effect of Gadolinium (Gd). Gadolinium is one of the distinct materials whose transition temperature (Curie temperature) of magnetic property from ferromagnetic to paramagnetic takes place near room temperature facilitating the use of low–grade waste heat. The conventional electromagnetic generator (EMG) has an excellent performance with an open circuit voltage of 2 V, a short-circuit current of 6 mA under the rotational speed of 130 rpm, when the temperature difference between hot and cold water jets was around 6.5°C. Under the same conditions piezoelectric generator produced an open circuit voltage and short circuit current of 8 V and 8.2 μA, respectively.