Loss analysis of the thermodynamic cycle of magnetic heat pumps. Phase 1, Final report of thermal sciences research program on thermophysics of magnetocaloric energy conversion.

摘要

The needs for developing non-ozone-depleting, no-greenhouse-effect heat pump systems and for exploring the potential of new high-temperature superconducting materials have prompted a renewed interest in the study of magnetic heat pumps. The new materials can provide the high magnetic field that an effective superconducting magnetic heat pump requires, and magnetic heat pumps do not use freon for a working fluid. Traditionally, magnetic heat pump concepts have been successfully developed and used for refrigeration applications at temperatures near absolute zero degree. In these cases, a temperature lift of a few degrees in a cryogenic environment is sufficient and can be easily achieved by a simple magnetic heat pump cycle. The working media are usually the chemical compounds of gadolinium. To extend magnetic heat pumping to other temperature ranges and other types of applications in which the temperature lift is more than just a few degrees requires more involved cycle processes dependent upon the thermomagnetic properties of the working media and the availability of a high magnetic field. This report documents our efforts to study the thermophysics of magnetic heat pumps, including a survey of literature, a study of thermodynamic cycles and cycle thermal losses, and an analysis of pulse magnets. The regenerative cycle has been identified as the most efficient, with a maximum of 42% loss in coefficient of performance at 260 K cooling temperature and a maximum of 15% loss in capacity at 232 K cooling temperature for the constant field (magnetic Ericsson) cycle, between 200 K and 320 K, as compared with the ideal regenerative cycle with gadolinium as the core material. 71 refs., 19 figs., 2 tabs.