Modeling of a room temperature magnetic refrigerator based on nanofluid

1. Moulay Youssef El Hafidi and Mohamed El Hafidi Laboratoire “Modélisation et Instrumentation” Faculté des sciences Ben M’sik - Département de Physique Université Hassan II Mohammedia-Casablanca Modeling of a room temperaturemagneticrefrigeratorbased on nanofluid ICNMRE, Safi Morocco

2. Outline of this talk • Introduction • Model specifications • Model design • Magnetic cooling • Nanofluids • Conclusion & perspective ICNMRE, Safi Morocco

3. Introduction • Conventional techniques of cooling Gas compression and expansion: • Chlorofluorocarbon (CFC) • Hydrofluorocarbon (HFC) • Hydrochlorofluorocarbon (HCFC) Thesegreenhousegasescontribute to global warming. vs • Magneticcooling • Ecology (Absence of greenhousegasemissions) • Energyefficiency (up to 60%) ICNMRE, Safi Morocco

4. I- Model specifications • Magnetism source: NdFeB permanent magnets • Magnetic field: 1.3 Tesla • Magnetocaloric material: Porous Gadolinium • Base liquid: Water • Nanoparticles: Carbon nanotubes (CNT) • Temperature: 20°C ICNMRE, Safi Morocco

5. I- Model specifications • Fluid flow rate: 1L/min = 60g/s • Cycle time: 2 seconds • Porous Gdcaracteristics: 200g flat disc, 400µm diameter • Generated refrigeration power: 50-60W • COP: about 26 • ΔT: 6 K ICNMRE, Safi Morocco

6. Model design ICNMRE, Safi Morocco

7. Magneticcooling • MagnetocaloricEffect (MCE) It is an intrinsic property of certain materials resulting in a change in temperature (hot / cold) during the change of magnetic state (magnetized / demagnetized) induced by an external magnetic field. Materialmagnetic moments are oriented in the direction of magneticfield. ICNMRE, Safi Morocco

8. Magneticcooling • MCE and thermodynamics Entropy is a state function that measures the degree of system disorder at microscopic level. Total entropy: Magneticentropy Structure entropy Electrons entropy (negligible) Under the action of a magnetic field, the magnetic moments are aligned and lead to the reduction of the magnetic entropy. If this process is adiabatic and reversible, this increases the temperature of the material [Tura 2002]. This effect is maximum around the phase transition temperature of magnetic material (Curie temperature). ICNMRE, Safi Morocco

9. Magneticcooling • MCE calculation Total entropyisgiven by: • Adiabaticprocess: • Isothermalprocess: ICNMRE, Safi Morocco

10. Magneticcooling • Molecularfieldtheory (Weiss model) • The applied magnetic field is increased by an additional magnetic field proportional to the induced magnetization. • with: • R: universalgas constant • J:total angularmomentum • : Brillouin function ICNMRE, Safi Morocco

11. Magneticcooling • MCE experimentalresults for Gd ICNMRE, Safi Morocco

12. Magneticcooling • Magneticcooling cycles ICNMRE, Safi Morocco

13. Magneticcooling • Coefficient of performance (COP) It is the ratio of cold energy to the suppliedwork ICNMRE, Safi Morocco

14. Magneticcooling A powerful magnetic refrigerator has the following characteristics: • A giantmagnetocaloriceffect(MCE). • A Curie temperature near the cold source. • A high heat capacity of fluid • A high thermal conductivity in the direction of the exchanges with the fluid and low in other directions to reduce losses by diffusion. •  A low viscosity fluid to reduce losses of the flow. •  A high coefficient of heat exchange to have the maximum possible exchange between the magnetic material and the fluid. ICNMRE, Safi Morocco

15. Nanofluids • Whatis a nanofluid? A fluid in which nanometer-sized particles (with typical length scales of 1 to 100nm) are suspended. ICNMRE, Safi Morocco

16. Nanofluids • Whynanofluids? • Nanofluids have the potential to reduce thermal resistances • They have been shown to enhance the thermal conductivity and convective heat transfer performance of the base liquids. • Significant increase of thermal performance. • For example, the addition of a small amount (less than 1 percent by volume) of nanoparticles to conventional heat transfer liquids increased the thermal conductivity of the fluids up to approximately two times (Choi, et al. 2001). • Whycarbon nanotubes? The conductivity ratiogoes up to 1,7 for volume concentration of 2% only. ICNMRE, Safi Morocco

17. Nanofluids • Base Liquids • Water • Ethylene glycol • Light oils • Nanoparticlematerials • Oxide ceramics (AlO3, CuO) • Nitride ceramics (AlN, SiN) • Carbide ceramics (SiC, TiC) • Metals (Ag, Au, Cu, Fe) • Semiconductors (TiO2) • Single-, double- or multi-walled carbon nanotubes (SWCNT, DWCNT, MWCNT) ICNMRE, Safi Morocco

18. Nanofluids • Nanoparticles production methods • Physical methods • Mechanical grinding • Inert-gas-condensation • Chemical methods • Chemical precipitation • Chemical vapor deposition • Micro-emulsions • Spray pyrolysis • Thermal spraying ICNMRE, Safi Morocco

19. Nanofluids • Nanofluids production techniques • Two-step technique It starts with nanoparticles produced by one of the physical or chemical methods and proceeds to disperse them into a base fluid. • Single-step technique It makes and disperses simultaneously the nanoparticles into a base fluid.  Most of nanofluids containing carbon nanotubes are produced by the two-step technique. ICNMRE, Safi Morocco

20. Nanofluids • Nanofluid thermal conductivity enhancement parameters: • Particle volume concentration • Particle material • Particle size • Particle shape • Base fluid material • Temperature • Additive • Acidity (pH) ICNMRE, Safi Morocco

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22. Nanofluid Thermal conductivity Hamilton-Crosser formula: • Nanofluidviscosity Brinkman formula: • Nanofluiddensity • Nanofluidspecificheat ICNMRE, Safi Morocco

23. Conclusion & perspective • Weproposed in thisstudy a self magneticrefrigerator design. • The originality of thiswork relates to the connectionbetweenmagneticcoolingtechnology and Nanofluidtechnology. • The design ismainlydedicated to air conditionning. • Westillneed to performexperimental test to validatetheory • As perspective, wewilltry to replace porous Gd by Nanoporous Gd. ICNMRE, Safi Morocco

24. Thank you for your attention ICNMRE, Safi Morocco