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

There is a rising interest in electric vehicle׳s climate control system including cooling and heating Electric vehicles (EVs, including hybrid electric vehicles and full electric vehicles) have inadequate waste heat to warm up the cabin and the climate control system has a very significant effect on the energy consumption efficiency and operating mileage Heat pump (HP) is one approach for energy consumption efficiency improvement in EVs which can supply cooling and heating capacity A literature review was performed on the vapor compression HP cycle design, performance characteristics, and challenges for variable working fluids for electric vehicles The non-vapor compressor HP systems were also analyzed including the applications of magnetocaloric effect and thermoelectric effect It seems heat pump system is a reasonable and feasible option in EV׳s climate control system if some essential issues could be solved The mobile climate control systems based on magnetocaloric effect and thermoelectric effect could be the supplementary methods in future applications

Advances on air conditioning and heat pump system in electric vehicles – A review

The air conditioning (AC) system provides cool, heating and ventilation in the cabin of the electric vehicles (EVs). It is necessary to control the interior thermal environments of the vehicle and ensure safety in visibility. Because AC systems are electrically powered, vehicle range is reduced drastically when the AC system is operating. EVs present a particular challenge to the development of more efficient AC systems for automotive applications. In this paper, the state of the art for various AC system solutions to EVs was critically reviewed. The investigations of alternative solutions are continuing along many parallel routes, e.g. vapor compression refrigeration-dedicated heater AC systems, reversible vapor compression heat pump AC systems, non-vapor compression AC systems and integrated thermal management system combined AC and battery pack. The characteristics and particular applications of each solution have been extensively discussed. Finally, a comparison listing the various pros and cons of the different available solutions was presented.

The solutions to electric vehicle air conditioning systems: A review

The paper presents the numerical optimization of a packed-bed and a parallel-plate AMR with gadolinium as the magnetocaloric material. The diameter of the spheres and the length of the packed-bed AMR, and the plate thickness, the spacing between the plates (porosity) and the length of the parallel-plate AMR, were varied and optimized. The results reveal that for the considered conditions the optimum length of the packed-bed AMR should be 20 mm or less at higher operating frequency (3 Hz) and 40 mm at lower operating frequency (0.5 Hz) and the corresponding optimum sphere diameter should be between 0.07 mm (with regard to the cooling load) and 0.17 mm (with regard to the COP). The parallel-plate AMR should consist of plates that are as thin as possible, with a spacing between the plates of 0.035 mm (with regard to the cooling load) and 0.075 mm (with regard to the COP).

Geometrical optimization of packed-bed and parallel-plate active magnetic regenerators

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

As any innovative development program, magnetic refrigeration still faces many challenges before being widely accepted as an actual replacement technology for cooling. In the last years, more than 50 different types of prototypes of magnetocaloric refrigerators have been presented in literature, with limited cooling power values and/or limited temperature span. This paper presents several assembly details and experimental results of a new proof-of-concept magnetic refrigeration prototype having both a temperature span of more than 20 K and a cooling capacity designed for around 15 kW. It has been made as a part of a pilot project for a large industrial partner to be used for an industrial process. The obtained experimental results have been measured and validated by an exterior independent body. This performance achievement, that we believe to be as the largest rotary magnetic refrigerator ever created, could be a milestone for the future of magnetocaloric chillers.

A 15kW magnetocaloric proof-of-concept unit: Initial development and first experimental results

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

Recently, a lot of progress has been made by the community to optimize the properties of LaFeSi-based alloys in order to enable their integration into prototypes for different magnetocaloric applications. In this paper we present a set of experimental results obtained with a specific layering of materials having different Curie temperatures integrated into a rotating R&D prototype. The prototype was tested under different operating conditions and the results are presented here. Furthermore, two types of endurance tests were performed on those materials using a separate experimental test bench. The obtained results are promising and present the basis for a possible replacement of Gd-based alloys with first order LaFeSi-based alloys to be used in our ready-to-be-deployed magnetic refrigeration systems. LaFeSi-based alloys have the potential to increase the cooling power and reduce the cost of our units due to reduced raw material costs. This is a critical factor, which will make the technology more accessible for large-scale production.

LaFeSi-based magnetocaloric material analysis: Cyclic endurance and thermal performance results

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.

Michel Risser

Papers

Numerical simulation of magnetocaloric system behaviour for an industrial application

A 15kW magnetocaloric proof-of-concept unit: Initial development and first experimental results

Construction of consistent magnetocaloric materials data for modelling magnetic refrigerators

LaFeSi-based magnetocaloric material analysis: Cyclic endurance and thermal performance results

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