Elastocaloric Coupling in Polymers for Solid State Refrigeration – ECPOR

Three effects in materials have been studied to replace the compression-expansion cycle of a gas. They are based on the same principle: vary the entropy of the system by using a reversible transition between an ordered state and a disordered state of the material driven by external excitation. In the case of the magnetocaloric effect, it is the application of an external magnetic field which imposes a variation of the magnetization in a magnetic material. In the case of the electrocaloric effect, it is the application of an external electric field which imposes a variation of the polarization in a dielectric material. Finally, in the mechanocaloric effect, a distinction is made between the barocaloric effect where the material is subjected to isostatic pressure and the elastocaloric effect where it is subjected to uniaxial deformation. The transition to the ordered state causes an increase of the temperature whereas that towards a disordered state leads to its decrease. While magnetocaloric and electrocaloric effects have been studied extensively and there is already, at least at the laboratory scale, prototypes of refrigeration systems, the elastocaloric effect, while it is just as promising as the two previous ones , has not been the subject of such intensive work.

The project has enabled the development of an analytical model to size a cooling system using a heat transfer fluid and natural rubber as elastocaloric material. This model has been validated by a laboratory demonstrator.
The project has equipped the partners with various original experimental benches for measuring the thermal characteristics (thermal conductivity, heat capacity, thermal effect of the induced crystallization) of the material under elongation and that of elastocaloric coupling at different frequencies and under different cycles of loading.

The next steps of the project will focus on optimizing the material by modeling and characterizing its properties, at various scales (microscopic, mesoscopic and macroscopic), under stress, but also on improving the first regenerative type demonstrator and on developing a second one-stage model.

Oral Communication :

E-MRS Fall Meeting 2019, Warsaw,

SymposiumE:Caloric materials for efficient heat management applications: advances and challenges,

Main key points for developing environmental friendly solid state cooling system based on the elastocaloric effect in rubber

Gael Sebald1, Atsuki Komiya1,2, Jean-Marc Chenal3, Laurent Chazeau3, Florent Dalmas3, Mathieu Vigouroux4, François Rousset4, M'hamed Boutaous4, Jacques Jay4, Bertrand Garnier5, Mohammad Rammal5, Ahmed Ould El Moctar5, Hiba Haissoune6, Gildas Coativy6, Laurence Seveyrat6, Kaori Yuse6, Laurent Lebrun6

1 ELyTMaX UMI 3757, CNRS - Université de Lyon - Tohoku University, International Joint Unit, Sendai, Japan 2 Institute of Fluid Science, Tohoku University, Sendai, Japan 3 Univ Lyon, CNRS, INSA-Lyon, Université Claude Bernard Lyon 1, MATEIS UMR5510, F-69621, Villeurbanne, France 4 Univ Lyon, CNRS, INSA-Lyon, Université Claude Bernard Lyon 1, CETHIL UMR5008, F-69621, Villeurbanne, France 5 LTeN Laboratoire de Thermique et Energie, CNRS, Université de Nantes, France ; 6 Univ Lyon, INSA Lyon, LGEF, EA682, Villeurbanne, France

The cooling applications belong to our daily life for the perishable food conservation, drug conservation (vaccine), for the reliability of the electronic devices as well as for the welfare of people. The most popular technique for cooling down is the cyclical compression and expansion of a gaz. Based on this principle, the widely used machines present several drawbacks: a limited potential for integration, complicated in embedded systems and environmental impact when using harmful volatile materials. Consequently, efforts have been put on the development of alternative technologies in the domain of the solid-state physic.

Three effects have been studied in materials to replace the vapor compression of a gas refrigerant. All of them are based on the same principle: a variation of the entropy caused by the reversible transition between an ordered state and a non-ordered state induced by external excitations.
In the case of the magnetocaloric effect (MC), an external magnetic field imposes a variation of the magnetization within a magnetic material. In the case of the electrocaloric effect (EC), an external electrical field imposes a variation of the polarization within a dielectric material. In the case of the mechano caloric effect, a distinction is done between the barocaloric effect for which the material is driven by a hydrostatic pressure and the elastocaloric effect for which the material is driven by uniaxial stress. The transition to the ordered state provokes an increase of the temperature whereas the return to the non-ordered state induces a decrease of temperature, which must be exploited to cool down the charge. If the magnetocaloric and electrocaloric effects have been widely studied and if there is already, at least on a laboratory scale, prototypes of refrigeration systems, the elastocaloric effect, while it is just as promising as the two previous ones , has not been so deeply studied.

The aim of the ECPOR project is to contribute to this topic by evaluating the efficiency of the elastocaloric effect within polymers for refrigeration applications. A multidisciplinary approach, combining experiences and modeling will be used to better understand the mechanisms which are at the origin of the elastocaloric effect in order to enhance it, to accurately characterize the heat transfer between the polymer surface and its surrounding and to build some laboratory prototypes of thermal machines to gain in experiences on this novel technique. This project is in good agreement with the societal challenge "Clean, Safe and Efficient Energy" and in particular its research axis "Fundamental and. Exploratory Research and breakthrought"