Documents disponibles écrits par cet auteur

Design concepts for a continuously rotating active magnetic regenerator / C. R. H. Bahl 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. 1792–1796 Titre : Design concepts for a continuously rotating active magnetic regenerator Titre original : Concepts appliqués dans la conception d'un régénérateur actif magnétique en rotation continue Type de document : texte imprimé Auteurs : C. R. H. Bahl, Auteur ; K. Engelbrecht, Auteur ; R. Bjørk, Auteur Année de publication : 2012 Article en page(s) : pp. 1792–1796 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Magnetic  refrigerator  Magnet  Design  Optimization  Model Résumé : Design considerations for a prototype magnetic refrigeration device with a continuously rotating AMR are presented. Building the active magnetic regenerator (AMR) from stacks of elongated plates of the perovskite oxide material La0.67Ca0.33−xSrxMn1.05O3, gives both a low pressure drop and allows grading of the Curie temperature along the plates. This may be accomplished by a novel technique where a compositionally-graded material is tape cast in one piece. The magnet assembly is based on a novel design strategy, to create alternating high- and low magnetic field regions within a magnet assembly. Focus is on maximising the magnetic field in the high field regions but also, importantly, minimising the flux in the low field regions. The design is iteratively optimised through 3D finite element magnetostatic modelling. ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700711001873 [article] Design concepts for a continuously rotating active magnetic regenerator = Concepts appliqués dans la conception d'un régénérateur actif magnétique en rotation continue [texte imprimé] / C. R. H. Bahl, Auteur ; K. Engelbrecht, Auteur ; R. Bjørk, Auteur . - 2012 . - pp. 1792–1796. Génie mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 34 N° 8 (Décembre 2011) . - pp. 1792–1796 Mots-clés : Magnetic  refrigerator  Magnet  Design  Optimization  Model Résumé : Design considerations for a prototype magnetic refrigeration device with a continuously rotating AMR are presented. Building the active magnetic regenerator (AMR) from stacks of elongated plates of the perovskite oxide material La0.67Ca0.33−xSrxMn1.05O3, gives both a low pressure drop and allows grading of the Curie temperature along the plates. This may be accomplished by a novel technique where a compositionally-graded material is tape cast in one piece. The magnet assembly is based on a novel design strategy, to create alternating high- and low magnetic field regions within a magnet assembly. Focus is on maximising the magnetic field in the high field regions but also, importantly, minimising the flux in the low field regions. The design is iteratively optimised through 3D finite element magnetostatic modelling. ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700711001873

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 the magnetic field on the performance of an active magnetic regenerator (AMR) / R. Bjørk in International journal of refrigeration, Vol. 34 N° 1 (Janvier 2011) 

Public ISBD [article]  in International journal of refrigeration > Vol. 34 N° 1 (Janvier 2011) . - pp. 192-203 Titre : The influence of the magnetic field on the performance of an active magnetic regenerator (AMR) Titre original : Influence du champ magnétique actif sur la performance d'un régénérateur magnétique actif Type de document : texte imprimé Auteurs : R. Bjørk, Auteur ; K. Engelbrecht, Auteur Année de publication : 2011 Article en page(s) : pp. 192-203 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Magnetic  refrigerator  Magnetic  field  Simulation  Modelling  Performance  Variation Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The influence of the time variation of the magnetic field, termed the magnetic field profile, on the performance of a magnetocaloric refrigeration device using the active magnetic regeneration (AMR) cycle is studied for a number of process parameters for both a parallel plate and packed bed regenerator using a numerical model. The cooling curve of the AMR is shown to be almost linear far from the Curie temperature of the magnetocaloric material. It is shown that a magnetic field profile that is 10% of the cycle time out of sync with the flow profile leads to a drop in both the maximum temperature span and the maximum cooling capacity of 20–40% for both parallel plate and packed bed regenerators. The maximum cooling capacity is shown to depend very weakly on the ramp rate of the magnetic field. Reducing the temporal width of the high field portion of the magnetic field profile by 10% leads to a drop in maximum temperature span and maximum cooling capacity of 5–20%. An increase of the magnetic field from 1 T to 1.5 T increases the maximum cooling capacity by 30–50% but the maximum temperature span by only 20–30%. Finally, it was seen that the influence of changing the magnetic field was more or less the same for the different regenerator geometries and operating parameters studied here. This means that the design of the magnet can be done independently of the regenerator geometry. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710001507 [article] The influence of the magnetic field on the performance of an active magnetic regenerator (AMR) = Influence du champ magnétique actif sur la performance d'un régénérateur magnétique actif [texte imprimé] / R. Bjørk, Auteur ; K. Engelbrecht, Auteur . - 2011 . - pp. 192-203. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 34 N° 1 (Janvier 2011) . - pp. 192-203 Mots-clés : Magnetic  refrigerator  Magnetic  field  Simulation  Modelling  Performance  Variation Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The influence of the time variation of the magnetic field, termed the magnetic field profile, on the performance of a magnetocaloric refrigeration device using the active magnetic regeneration (AMR) cycle is studied for a number of process parameters for both a parallel plate and packed bed regenerator using a numerical model. The cooling curve of the AMR is shown to be almost linear far from the Curie temperature of the magnetocaloric material. It is shown that a magnetic field profile that is 10% of the cycle time out of sync with the flow profile leads to a drop in both the maximum temperature span and the maximum cooling capacity of 20–40% for both parallel plate and packed bed regenerators. The maximum cooling capacity is shown to depend very weakly on the ramp rate of the magnetic field. Reducing the temporal width of the high field portion of the magnetic field profile by 10% leads to a drop in maximum temperature span and maximum cooling capacity of 5–20%. An increase of the magnetic field from 1 T to 1.5 T increases the maximum cooling capacity by 30–50% but the maximum temperature span by only 20–30%. Finally, it was seen that the influence of changing the magnetic field was more or less the same for the different regenerator geometries and operating parameters studied here. This means that the design of the magnet can be done independently of the regenerator geometry. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710001507