Documents disponibles écrits par cet auteur

A comprehensive parameter study of an active magnetic regenerator using a 2D numerical model / K.K. Nielsen in International journal of refrigeration, Vol. 33 N° 4 (Juin 2010) 

Public ISBD [article]  in International journal of refrigeration > Vol. 33 N° 4 (Juin 2010) . - pp. 753-764 Titre : A comprehensive parameter study of an active magnetic regenerator using a 2D numerical model Titre original : Etude approfondie sur les paramètres des régénérateurs magnétiques actifs à l'aide d'un modèle numérique bidimensionnel Type de document : texte imprimé Auteurs : K.K. Nielsen, Auteur ; C. R. H. Bahl, Auteur ; A. Smith, Auteur Année de publication : 2010 Article en page(s) : pp. 753-764 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Magnetic  refrigerator  Simulation  Performance  Heat  transfer  Heat  exchange  Regenerator  Gadolinium Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A two-dimensional numerical heat transfer model is used to investigate an active magnetic regenerator (AMR) based on parallel plates of magnetocaloric material. A large range of parameter variations are performed to study the optimal AMR. The parameters varied are the plate and channel thicknesses, cycle frequency and fluid movement. These are cast into the non-dimensional units utilization, porosity and number of transfer units (NTU). The cooling capacity vs. temperature span is mapped as a function of these parameters and each configuration is evaluated through the maximum temperature span and exergy. The results show that the optimal AMR should have a utilization in the range 0.2–1 and an NTU higher than 10 and not necessarily more than 30. It is concluded that parallel plate-based regenerators face significant challenges in terms of manufacturability. However, the benefit of parallel plate regenerators is a very low pressure drop, which is needed for high performance. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710000058 [article] A comprehensive parameter study of an active magnetic regenerator using a 2D numerical model = Etude approfondie sur les paramètres des régénérateurs magnétiques actifs à l'aide d'un modèle numérique bidimensionnel [texte imprimé] / K.K. Nielsen, Auteur ; C. R. H. Bahl, Auteur ; A. Smith, Auteur . - 2010 . - pp. 753-764. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 33 N° 4 (Juin 2010) . - pp. 753-764 Mots-clés : Magnetic  refrigerator  Simulation  Performance  Heat  transfer  Heat  exchange  Regenerator  Gadolinium Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A two-dimensional numerical heat transfer model is used to investigate an active magnetic regenerator (AMR) based on parallel plates of magnetocaloric material. A large range of parameter variations are performed to study the optimal AMR. The parameters varied are the plate and channel thicknesses, cycle frequency and fluid movement. These are cast into the non-dimensional units utilization, porosity and number of transfer units (NTU). The cooling capacity vs. temperature span is mapped as a function of these parameters and each configuration is evaluated through the maximum temperature span and exergy. The results show that the optimal AMR should have a utilization in the range 0.2–1 and an NTU higher than 10 and not necessarily more than 30. It is concluded that parallel plate-based regenerators face significant challenges in terms of manufacturability. However, the benefit of parallel plate regenerators is a very low pressure drop, which is needed for high performance. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710000058

Determining the minimum mass and cost of a magnetic refrigerator / R. Bjørk in International journal of refrigeration, Vol. 34 N° 8 (Décembre 2011) 

Public ISBD [article]  in International journal of refrigeration > Vol. 34 N° 8 (Décembre 2011) . - pp. 1805–1816 Titre : Determining the minimum mass and cost of a magnetic refrigerator Titre original : Détermination de la masse minimale et du coût d'un réfrigérateur magnétique Type de document : texte imprimé Auteurs : R. Bjørk, Auteur ; A. Smith, Auteur ; C. R. H. Bahl, Auteur Année de publication : 2012 Article en page(s) : pp. 1805–1816 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Magnetic  refrigerator  Regenerator  Magnetic  fieldModeling Résumé : An expression is determined for the mass of the magnet and magnetocaloric material needed for a magnetic refrigerator and these are determined using numerical modeling for both parallel plate and packed sphere bed regenerators as function of temperature span and cooling power. As magnetocaloric material Gd or a model material with a constant adiabatic temperature change, representing an infinitely linearly graded refrigeration device, is used. For the magnet a maximum figure of merit magnet or a Halbach cylinder is used. For a cost of $40 and $20 per kg for the magnet and magnetocaloric material, respectively, the cheapest 100 W parallel plate refrigerator with a temperature span of 20 K using Gd and a Halbach magnet has 0.8 kg of magnet, 0.3 kg of Gd and a cost of $35. Using the constant material reduces this cost to $25. A packed sphere bed refrigerator with the constant material costs $7. It is also shown that increasing the operation frequency reduces the cost. Finally, the lowest cost is also found as a function of the cost of the magnet and magnetocaloric material. ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S014070071100140X [article] Determining the minimum mass and cost of a magnetic refrigerator = Détermination de la masse minimale et du coût d'un réfrigérateur magnétique [texte imprimé] / R. Bjørk, Auteur ; A. Smith, Auteur ; C. R. H. Bahl, Auteur . - 2012 . - pp. 1805–1816. Génie mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 34 N° 8 (Décembre 2011) . - pp. 1805–1816 Mots-clés : Magnetic  refrigerator  Regenerator  Magnetic  fieldModeling Résumé : An expression is determined for the mass of the magnet and magnetocaloric material needed for a magnetic refrigerator and these are determined using numerical modeling for both parallel plate and packed sphere bed regenerators as function of temperature span and cooling power. As magnetocaloric material Gd or a model material with a constant adiabatic temperature change, representing an infinitely linearly graded refrigeration device, is used. For the magnet a maximum figure of merit magnet or a Halbach cylinder is used. For a cost of $40 and $20 per kg for the magnet and magnetocaloric material, respectively, the cheapest 100 W parallel plate refrigerator with a temperature span of 20 K using Gd and a Halbach magnet has 0.8 kg of magnet, 0.3 kg of Gd and a cost of $35. Using the constant material reduces this cost to $25. A packed sphere bed refrigerator with the constant material costs $7. It is also shown that increasing the operation frequency reduces the cost. Finally, the lowest cost is also found as a function of the cost of the magnet and magnetocaloric material. ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S014070071100140X

Review and comparison of magnet designs for magnetic refrigeration / R. Bjørk in International journal of refrigeration, Vol. 33 N° 3 (Mai 2010) 

Public ISBD [article]  in International journal of refrigeration > Vol. 33 N° 3 (Mai 2010) . - pp. 437-448 Titre : Review and comparison of magnet designs for magnetic refrigeration Titre original : Tour d'horizon et comparaison des conceptions d'aimants pour le froid magnétique Type de document : texte imprimé Auteurs : R. Bjørk, Auteur ; C. R. H. Bahl, Auteur ; A. Smith, Auteur Année de publication : 2010 Article en page(s) : pp. 437-448 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Magnetic  refrigerator  Review  Design  Technology  Magnetic Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : One of the key issues in magnetic refrigeration is generating the magnetic field that the magnetocaloric material must be subjected to. The magnet constitutes a major part of the expense of a complete magnetic refrigeration system and a large effort should therefore be invested in improving the magnet design. A detailed analysis of the efficiency of different published permanent magnet designs used in magnetic refrigeration applications is presented in this paper. Each design is analyzed based on the generated magnetic flux density, the volume of the region where this flux is generated and the amount of magnet material used. This is done by characterizing each design by a figure of merit magnet design efficiency parameter, Λcool. The designs are then compared and the best design found. Finally recommendations for designing the ideal magnet design are presented based on the analysis of the reviewed designs. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700709002898 [article] Review and comparison of magnet designs for magnetic refrigeration = Tour d'horizon et comparaison des conceptions d'aimants pour le froid magnétique [texte imprimé] / R. Bjørk, Auteur ; C. R. H. Bahl, Auteur ; A. Smith, Auteur . - 2010 . - pp. 437-448. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 33 N° 3 (Mai 2010) . - pp. 437-448 Mots-clés : Magnetic  refrigerator  Review  Design  Technology  Magnetic Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : One of the key issues in magnetic refrigeration is generating the magnetic field that the magnetocaloric material must be subjected to. The magnet constitutes a major part of the expense of a complete magnetic refrigeration system and a large effort should therefore be invested in improving the magnet design. A detailed analysis of the efficiency of different published permanent magnet designs used in magnetic refrigeration applications is presented in this paper. Each design is analyzed based on the generated magnetic flux density, the volume of the region where this flux is generated and the amount of magnet material used. This is done by characterizing each design by a figure of merit magnet design efficiency parameter, Λcool. The designs are then compared and the best design found. Finally recommendations for designing the ideal magnet design are presented based on the analysis of the reviewed designs. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700709002898

The influence of non-magnetocaloric properties on the performance in parallel-plate AMRs / K.K. Nielsen in International journal of refrigeration, Vol. 37 N° 1 (Janvier 2014) 

Public ISBD [article]  in International journal of refrigeration > Vol. 37 N° 1 (Janvier 2014) . - pp. 127–134 Titre : The influence of non-magnetocaloric properties on the performance in parallel-plate AMRs Titre original : Influence des propriétés non magnétocaloriques sur la performance des plaques parallèles de réfrigérateurs magnétiques actifs Type de document : texte imprimé Auteurs : K.K. Nielsen, Auteur ; C. R. H. Bahl, Auteur ; A. Smith, Auteur Année de publication : 2014 Article en page(s) : pp. 127–134 Note générale : Refrigeration Langues : Anglais (eng) Mots-clés : Modelling;  flow  maldistribution;  demagnetizing  effects;  magnetic  refrigeration Résumé : The performance of Active Magnetic Regenerators (AMR) does not depend solely on the magnetocaloric effect of their constituents. Rather, it depends on several additional parameters, including, magnetic field, geometry (hydraulic diameter, cross-sectional area, regenerator length etc.), thermal properties (conductivity, specific heat and mass density) and operating parameters (utilization, frequency, number of transfer units etc.). In this paper we focus on the influence of three parameters on regenerator performance: 1) Solid thermal conductivity, 2) magnetostatic demagnetization and 3) flow maldistribution due to geometrically non-uniform regenerators. It is shown that the AMR performance is optimal at an intermediate value of the solid thermal conductivity for many operating conditions. The magnetostatic demagnetization is shown to have a significant influence on the AMR performance, giving a strong dependence on the orientation of the applied field and the regenerator geometry. Finally, the flow maldistribution of non-uniform regenerator geometries is found to degrade the AMR performance even at minor deviations from perfectly homogeneous regenerator matrices. This paper reflects a summary of various recently published results. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700713002569 [article] The influence of non-magnetocaloric properties on the performance in parallel-plate AMRs = Influence des propriétés non magnétocaloriques sur la performance des plaques parallèles de réfrigérateurs magnétiques actifs [texte imprimé] / K.K. Nielsen, Auteur ; C. R. H. Bahl, Auteur ; A. Smith, Auteur . - 2014 . - pp. 127–134. Refrigeration Langues : Anglais (eng) in International journal of refrigeration > Vol. 37 N° 1 (Janvier 2014) . - pp. 127–134 Mots-clés : Modelling;  flow  maldistribution;  demagnetizing  effects;  magnetic  refrigeration Résumé : The performance of Active Magnetic Regenerators (AMR) does not depend solely on the magnetocaloric effect of their constituents. Rather, it depends on several additional parameters, including, magnetic field, geometry (hydraulic diameter, cross-sectional area, regenerator length etc.), thermal properties (conductivity, specific heat and mass density) and operating parameters (utilization, frequency, number of transfer units etc.). In this paper we focus on the influence of three parameters on regenerator performance: 1) Solid thermal conductivity, 2) magnetostatic demagnetization and 3) flow maldistribution due to geometrically non-uniform regenerators. It is shown that the AMR performance is optimal at an intermediate value of the solid thermal conductivity for many operating conditions. The magnetostatic demagnetization is shown to have a significant influence on the AMR performance, giving a strong dependence on the orientation of the applied field and the regenerator geometry. Finally, the flow maldistribution of non-uniform regenerator geometries is found to degrade the AMR performance even at minor deviations from perfectly homogeneous regenerator matrices. This paper reflects a summary of various recently published results. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700713002569