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Moulay Youssef El Hafidi and Mohamed El Hafidi Laboratoire Modlisation et Instrumentation Facult des sciences Ben Msik - Dpartement de Physique Universit Hassan II Mohammedia-Casablanca ICNMRE, Safi Morocco08/07/20101

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Outline of this talk Introduction Model specifications Model design Magnetic cooling Nanofluids Conclusion & perspective ICNMRE, Safi Morocco08/07/20102

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Introduction ICNMRE, Safi Morocco Conventional techniques of cooling Gas compression and expansion: Chlorofluorocarbon (CFC) Hydrofluorocarbon (HFC) Hydrochlorofluorocarbon (HCFC) These greenhouse gases contribute to global warming. vs Magnetic cooling Ecology (Absence of greenhouse gas emissions) Energy efficiency (up to 60%) 08/07/20103

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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: 20C ICNMRE, Safi Morocco08/07/20104

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I- Model specifications Fluid flow rate: 1L/min = 60g/s Cycle time: 2 seconds Porous Gd caracteristics: 200g flat disc, 400m diameter Generated refrigeration power: 50-60W COP: about 26 T: 6 K ICNMRE, Safi Morocco08/07/20105

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II.Model design ICNMRE, Safi Morocco08/07/20106

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III.Magnetic cooling Magnetocaloric Effect (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. Material magnetic moments are oriented in the direction of magnetic field. ICNMRE, Safi Morocco08/07/20107

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MCE and thermodynamics Entropy is a state function that measures the degree of system disorder at microscopic level. Total entropy: Magnetic entropy 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 Morocco08/07/20108 III.Magnetic cooling

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MCE calculation Total entropy is given by: Adiabatic process: Isothermal process: ICNMRE, Safi Morocco08/07/20109 III.Magnetic cooling

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ICNMRE, Safi Morocco Molecular field theory (Weiss model) The applied magnetic field is increased by an additional magnetic field proportional to the induced magnetization. with: R: universal gas constant J: total angular momentum : Brillouin function 08/07/201010 III.Magnetic cooling

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MCE experimental results for Gd ICNMRE, Safi Morocco08/07/201011 III.Magnetic cooling

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Magnetic cooling cycles ICNMRE, Safi Morocco08/07/201012 III.Magnetic cooling

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Coefficient of performance (COP) It is the ratio of cold energy to the supplied work ICNMRE, Safi Morocco08/07/201013 III.Magnetic cooling

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A powerful magnetic refrigerator has the following characteristics: A giant magnetocaloric effect(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 Morocco08/07/201014

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What is a nanofluid? A fluid in which nanometer-sized particles (with typical length scales of 1 to 100nm) are suspended. ICNMRE, Safi Morocco08/07/201015 IV.Nanofluids

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Why nanofluids? 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). Why carbon nanotubes? The conductivity ratio goes up to 1,7 for volume concentration of 2% only. ICNMRE, Safi Morocco08/07/201016 IV.Nanofluids

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Base Liquids Water Ethylene glycol Light oils Nanoparticle materials 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 Morocco08/07/201017 IV.Nanofluids

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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 Morocco08/07/201018 IV.Nanofluids

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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 Morocco08/07/201019 IV.Nanofluids

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Nanofluid thermal conductivity enhancement parameters: Particle volume concentration Particle material Particle size Particle shape Base fluid material Temperature Additive Acidity (pH) ICNMRE, Safi Morocco08/07/201020 IV.Nanofluids

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Nanofluid Thermal conductivity Hamilton-Crosser formula: Nanofluid viscosity Brinkman formula: Nanofluid density Nanofluid specific heat ICNMRE, Safi Morocco08/07/201022

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Conclusion & perspective We proposed in this study a self magnetic refrigerator design. The originality of this work relates to the connection between magnetic cooling technology and Nanofluid technology. The design is mainly dedicated to air conditionning. We still need to perform experimental test to validate theory As perspective, we will try to replace porous Gd by Nanoporous Gd. ICNMRE, Safi Morocco08/07/201023

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Thank you for your attention 08/07/2010ICNMRE, Safi Morocco24