Showing papers by "Gerald V. Brown published in 1981"
TL;DR: In this article, the magnetocaloric effect in polycrystalline Gd was measured at temperatures from 190 to 370 K in applied fields from 1 to 7 T. The maximum ΔT with applied field was about 14 K at 7 tesla, and maxima in all applied fiels occurred near 292 K.
Abstract: The magnetocaloric effect in polycrystalline Gd was measured at temperatures from 190 to 370 K in applied fields from 1 to 7 T. The magnetocaloric temperature changes were combined with existing zero‐field specific heat data to construct a T‐S diagram for Gd near the Curie point. Experimental values of ΔT were also compared with values calculated from a simple mean field theory, which predicts rather well both the general shape of the magnetocaloric curve and the relative magnitudes of the temperature changes in various measuring fields. The maximum ΔT with applied field was about 14 K at 7 tesla, and maxima in all applied fiels occurred near 292 K. The relatively large magnetocaloric effect in Gd near room temperature is attractive for potential magnetic refrigeration applications, and the experimental T‐S diagram may now be used to refine estimates of the performance of Gd as a solid magnetic refrigerant.
143 citations
Patent•
19 Feb 1981TL;DR: In this article, the state of the element as represented on a temperature-magnetic entropy diagram repeatedly traverses a loop was represented by a regenerator, and the regenerator was employed to enhance desired cooling or heating effects.
Abstract: The method of the invention employs ferromagnetic or ferrimagnetic elements, preferably of rare-earth based material, for example gadolinium, and preferably employs a regenerator. The steps of the method comprise controlling the temperature and applied magnetic field of the element to cause the state of the element as represented on a temperature-magnetic entropy diagram repeatedly to traverse a loop. The loop may have a first portion of concurrent substantially isothermal or constant temperature and increasing applied magnetic field, a second portion of lowering temperature and constant applied magnetic field, a third portion of isothermal and decreasing applied magnetic field, and a fourth portion of increasing temperature and constant applied magnetic field. Other loops may be four-sided, with, for example, two isotherms and two adiabats (constant entropy portions). Preferably, a regenerator may be employed to enhance desired cooling or heating effects, with varied magnetic fields or varying temperatures including three-sided figures traversed by the representative point.
42 citations