Magnetocaloric effect: From materials research to refrigeration devices

Magnetic refrigeration, heating and power conversion technologies are interesting alternatives to the conventional refrigeration, heat pumping and different conventional energy conversion technologies. At present they all show a realistic potential to enter conventional markets, respectively to be applied in a few years. In this review paper, mainly magnetic refrigeration and magnetic heating are addressed and from these two technologies the main part is dedicated to magnetic refrigeration at room temperature. This article covers the demand of giving a complete list and description of existing magnetic heating and cooling prototypes up to the year 2010. Forty-one machines, their components and operation principles are presented in detail.

A review of magnetic refrigerator and heat pump prototypes built before the year 2010

In recent years, several emerging technologies in the domain of solid-state physics have been investigated as serious alternatives for future refrigeration, heat pumping, air conditioning, or even power generation applications. These technologies relate to what is called caloric energy conversion, i.e., barocalorics, electrocalorics, magnetocalorics, and elastocalorics. Of these technologies, the greatest progress has been observed in the domain of magnetic refrigeration. However, in the recent few years, significant research efforts have also been made in the field of electrocaloric and elastocaloric refrigeration. Many of these technologies suggest the possibility for improvements in energy efficiency, compactness, noise level, as well as a reduction in environmental impacts, so it seems very probable that they will start to fill particular market niches as a replacement for vapor-compression technology in the future.

Present and future caloric refrigeration and heat-pump technologies

The active magnetic regenerator (AMR) is an alternative refrigeration cycle with a potential gain of energy efficiency compared to conventional refrigeration techniques. The AMR poses a complex problem of heat transfer, fluid dynamics and magnetic field, which requires detailed and robust modeling. This paper reviews the existing numerical modeling of room temperature AMR to date. The governing equations, implementation of the magnetocaloric effect (MCE), fluid flow and magnetic field profiles, thermal conduction etc. are discussed in detail as is their impact on the AMR cycle. Flow channeling effects, hysteresis, thermal losses and demagnetizing fields are discussed and it is concluded that more detailed modeling of these phenomena is required to obtain a better understanding of the AMR cycle.

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Review on numerical modeling of active magnetic regenerators for room temperature applications

Exploring La(Fe,Si)13-based magnetic refrigerants towards application

In the present paper we consider the problem of optimizing the cooling of a magnetocaloric refrigerator. In this work we first theoretically and then experimentally study the performance of a single material regenerator under different operating conditions. The basic principles of the design and implementation of our magnetic refrigerator prototype are presented as well as a new magnetic assembly of NdFeB permanent magnets. The design of the equipment uses a movement of relative displacement optimized for the phases of activation and inactivation of the magnetic field. Each part of the equipment is implemented in order to be controlled separately and to allow a large variety of the tests: gear pumps with individual control, sequence of programmable magnetocaloric cycle, unit control by programmable controller and application programming interface by color LCD touch screen, real-time processing data acquisition using a National Instruments System implemented on Independent PC, expelled heat using different standard heat exchangers.

Innovative design of a magnetocaloric system

This paper presents a numerical model conceived for a multi-physics evaluation of a magnetic refrigeration system. The model takes into account the variable magnetic field, the characteristics of the magnetocaloric materials (MCM) as well as the efficiency of the fluid flow heat transfer between the hot and the cold sources via the MCM. This model allows us to optimize these elements and to determine their impact on the overall performance of a magnetocaloric device. We present here a finite-difference model of AMRR cycles for a sub-unit of MCM crossed by micro-channels of fluid connected to cold and hot regenerative receivers. Thus, the calculation of the output parameters such as the temperature span, and thermal power passing from the cold receiver to the hot receiver has been performed. The influence of the geometry of the MCM and the fluid flow were investigated over the working domain highlighting the current technological achievements and indicating possible improvements.

Numerical simulation of magnetocaloric system behaviour for an industrial application

Numerical analysis of a reciprocating active magnetic regenerator

The simulation of magnetocaloric refrigerator behaviour needs a good description of the material properties. Magnetocaloric material data are often given as a function of few values of the external magnetic field applied on a sample, but active material reacts to its internal field. The simulating of the magnetocaloric effect using experimental data can then create some artefacts. In this paper we present an alternative way to obtain material data expressed as a function of the internal magnetic field. This characterization is built on the knowledge of the zero magnetic field heat capacity of second-order phase transition materials such as gadolinium, as well as on the direct measurements of magnetocaloric data. An inverse approach is performed to calculate the data as a function of the internal magnetic field with an improved level of detail. The obtained data allow a better modelling of the magnetocaloric effect in an active magnetic regenerator.

Construction of consistent magnetocaloric materials data for modelling magnetic refrigerators

Magnetocaloric systems are interesting from the point of view of energy efficiency and could be environment-friendly products. Numerous prototypes have demonstrated the feasibility of such systems for applications around room temperature, but there is still room for improvement. The research of an optimal configuration only by an experimental approach is a complex and difficult task due to numerous building parameters and driving parameters. Therefore we propose here a methodology based on a numerical approach. A numerical model calibrated with respect to experimental tests is used to make a parametric analysis of a magnetocaloric system. The design of the system is made according to given functional specifications, targeting different design strategies such as the power density, the energy efficiency, the maximizing of the temperature span, etc. This work is a step forward to the increase of the efficiency in the design of our future systems.

C. Vasile

Papers

Innovative design of a magnetocaloric system

Numerical simulation of magnetocaloric system behaviour for an industrial application

Numerical analysis of a reciprocating active magnetic regenerator

Construction of consistent magnetocaloric materials data for modelling magnetic refrigerators

Improvement and application of a numerical model for optimizing the design of magnetic refrigerators