On the influence of thermal hysteresis on the performance of thermomagnetic motors

Abstract

Although thermal hysteresis might be a problem in the magnetocaloric refrigeration, the same is not necessarily true for thermomagnetic motor applications. This work presents a comparison of the magnetocaloric properties of materials with first order magnetic transition (having large or narrow thermal hysteresis) to those with second order magnetic transition, assessing the application of these materials in thermomagnetic motors through a thermodynamic approach. Results show that the larger the thermal hysteresis, the higher the specific work produced in a thermal cycle. This allows operation at higher temperature differences with high efficiency relative to Carnot efficiency, when compared with systems using narrow hysteresis and second order transition materials.

Temperature-FORC analysis of a magnetocaloric Heusler alloy using a unified driving force approach (T*FORC)

“…However, there are alternative applications of magnetocaloric materials, such as thermomagnetic motors, for which there are theoretical studies, indicating that a moderate thermal hysteresis could be beneficial for the performance of the device. 11 Consequently, as in any other aspect of magnetic materials' research, we should not consider thermal hysteresis as an intrinsically bad characteristic. Let us just recall that for permanent magnet applications, coercivity is a required property, while it has to be avoided in the case of soft magnetic materials; the situation might be analogous with magnetocaloric materials, depending on the target application.…”

Development of a rotary thermomagnetic motor for thermal energy conversion.

“…"First-order" materials have a transition in which the magnetization changes discontinuously at T C , with a latent heat associated with the phase transition, and in most cases presenting a high thermal hysteresis in the thermomagnetic transition, meaning that the critical transition temperature will be different for the heating and cooling processes. While the thermal hysteresis is usually associated with a loss of energy, especially for the applications in magnetocaloric refrigeration, and therefore attempts have been made to reduce its magnitude , for thermomagnetic motors this effect could, in fact, represent an increase in the efficiency (BESSA et al, 2017).…”

Métodos analí­ticos para o cálculo de desempenho de motores termomagnéticos do tipo tesla.

“…[7], [8], [72], [81], [83], [93], [22], [36], [52], [55], [59], [61], [68], [71]. Fonte: Adaptado do artigo de Bessa et al [19]. (Artigo do autor).…”

“…(c) MnAs. (d) Eficiência relativa à eficiência de Carnot quando a temperatura da fonte fria está a 2 K abaixo de T ColdMax .Fonte: Adaptado do artigo de Bessa et al[19]. (Artigo do autor).A Figura 100 mostra as curvas de trabalho específico em função de  rel quando T Cold é igual à T ColdMax .…”

“…Para todos os trechos onde o motor operando com MnAs produz trabalho, para um mesmo valor de eficiência, o trabalho específico produzido por ciclo é muito maior do que para os outros materiais. Ao se desconsiderar o MnAs, o material que apresenta melhor desempenho no uso em motores termomagnéticos tipo Tesla é o LaFe 11,76 Mn 0,06 Si 1,18 H 1,65 , que é o material com a segunda maior histerese entre os estudados.Fonte: Adaptado do artigo de Bessa et al[19]. (Artigo do autor).Também foi observada uma diferença no perfil das curvas de trabalho específico em função de  rel , onde para os materiais de primeira ordem, a concavidade apresentada pelas curvas é negativa.…”