Measurement and simulation of the magnetocaloric effect induced by demagnetizing fields

• Autor(a) principal: Oliveira, Rodrigo Kiefe Soares de
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/39747
• topic: Magnetocaloric effect; Demagnetizing; Refrigeration; Finite elements

The magnetocaloric effect (MCE) allows for the refrigeration of systems using solid materials rather than gases harmful to the environment. The effect can be induced by geometric effects – the demagnetizing field – possibly being a more efficient process than the conventional method of inducing the magnetocaloric effect. Yet, this method has not been explored by the scientific community. A fully automated device was developed from scratch capable of measuring the magnetocaloric effect induced by this non-conventional method, for temperatures between - 6 and 35 ºC. Automatization of the measurement process involved controlling the temperature of the system, rotation of the refrigerant, data acquisition and subsequent treatment for the extrapolation of the MCE. Furthermore, an implementation of the Finite Element method was constructed completely from scratch, capable of simulating both the non-conventional magnetocaloric effect and the conventional one, and capable of describing the impact of the demagnetizing field on the conventional effect. The Finite Element method is used to solve the Laplace equation which governs the system, allowing for the calculation of the MCE individually for each element. The MCE induced by the demagnetizing fields was observed to have a flatter temperature profile in comparison to the conventional method, and the maximum temperature change observed was around 1.1 ºC, for temperatures between 7 and 15 ºC. The experimental measurements and the numerical predictions were compared and the profile of the measured magnetocaloric effect corresponds with the computational calculations, the numerical predictions being of higher intensity by 0.5 ºC. Also, the implementation of the Finite Element method proved capable of describing the impact of the demagnetizing field on the conventional process of inducing the MCE.