The initial operation of the refrigerator/heat engine is very encouraging. The analysis indicates that the magnetic field profile and inefficient water pump are the main reasons for the limited ..delta..T. The next experiments will be performed with soft iron shielding to increase ..delta..H and also with a more efficient pump to reduce the heat load. The prognosis is very good. The basic advantages of magnetic refrigerators/heat engines are that the energy density in the working material is very high, 25 kJ/l of Gd at 300 K; the heat exchange is between a solid and a liquid which makes the regenerative stages of the cycle more efficient; and in some cases the expensive external heat exchangers could be eliminated. The disadvantage of magnetic refrigeration is that a superconducting magnet is required. An example of an application at room temperature is a magnetic heat pump for utilization of low-grade waste heat such as in nuclear power plants. For applications such as this, where external heat exchangers may be eliminated, the economics look attractive. The prospects for magnetic refrigeration at low temperatures (< 77K) look much better than at room temperature because the ratio of magnetic entropy to lattice entropy increases rapidly as the temperature decreases
