Refrigeration is used daily for the preservation of food or medicine (vaccine), for the reliability of electronic devices, as well as for the well-being of people. Based on the compression-expansion cycle of a gas, it presents some disadvantages: difficult integration in embedded systems and strong environmental impact. It is therefore necessary to develop alternative technologies in the field of solid state physics.
The objective of the ECPOR project is to contribute to this subject by evaluating the effectiveness of the elastocaloric effect in polymers for refrigeration applications and realizing, as proof of concept of the demonstrators. A multidisciplinary approach, combining experiments and modeling is used to better understand the mechanisms of the elastocaloric effect in order to improve it, to characterize with precision the transfer of heat between the surface of the polymer and its environment and to build prototypes of thermal machines to quantify their performances and therefore to gain experience on this new refrigeration technique. This project is part of the «clean, safe and efficient energy« challenge and more particularly in its «fundamental, exploratory and breakthrough concepts« line.
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 s
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"
Monsieur Laurent LEBRUN (Laboratoire de Génie Electrique et Ferroélectricité)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
CETHIL Centre d'Energétique et de Thermique de Lyon
MATEIS Matériaux : Ingénierie et Science
LTEN (ex LTN) Laboratoire de Thermique et Energie de Nantes (ex. Laboratoire de Thermocinétique)
LGEF Laboratoire de Génie Electrique et Ferroélectricité
Help of the ANR 549,102 euros
Beginning and duration of the scientific project: January 2018 - 36 Months