Fundamental performance of the disc-type thermomagnetic engine

This paper describes the fundamental performance of the disc-type thermomagnetic engine. The disc-type engine has been designed in order to decrease the eddy current braking loss. Performance characteristics such as power, torque, and loss have been measured and compared with those of the cylindrical engine under the condition of the same volume of temperature-sensitive magnetic material. The eddy current braking loss is 0.04 W, which corresponds to 1/30 the loss in the cylindrical engine at a rotation speed of 0.4 rps with maximum power output. The total loss including partial losses due to friction, the hydraulic effect, and the eddy current braking is 0.9 W in the disc-type engine and is 1.8 W in the cylindrical engine. The total loss in the disc-type engine is reduced to 50% of that in the cylindrical engine under the same conditions mentioned above. The maximum output power is 6.0 W at the rotation speed of 0.4 rps in the disc-type engine, which is about 1.6 times greater than that of the cylindrical engine. The eddy current braking loss in the disc-type engine is 0.7% of the value of the maximum output power, which is a negligible effect in this engine. The power per unit volume of the disc reaches a maximum value at a disc width of 40 mm. The clearance between discs was determined to be 1 mm in order to keep the working fluid flow conditions constant. The rotor thickness includes the clearance and the disc thickness. The power per unit rotor thickness also has a maximum value at a disc thickness of 0.5 mm. A thermomagnetic engine with the optimum conditions can be designed by using these results. When the permanent magnet fixes the size constant, the disc-type engine generates high output power in comparison with the cylindrical engine at the point of effective use of a magnetic field. (C) 2004 Wiley Periodicals, Inc.