Documents disponibles écrits par cet auteur

Air-side heat transfer and pressure drop characteristics of accelerated flow evaporators / Paulo J. Waltrich in International journal of refrigeration, Vol. 34 N° 2 (Mars 2011) 

Public ISBD [article]  in International journal of refrigeration > Vol. 34 N° 2 (Mars 2011) . - pp. 484-497 Titre : Air-side heat transfer and pressure drop characteristics of accelerated flow evaporators Titre original : Evaporateurs à écoulement accéléré: transfert de chaleur côté air et caractéristiques de la chute de pression Type de document : texte imprimé Auteurs : Paulo J. Waltrich, Auteur ; Jader R. Barbosa Jr., Auteur ; Christian J.L. Hermes, Auteur Année de publication : 2011 Article en page(s) : pp. 484-497 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Evaporator  Heat  exchanger  Heat  transfer  coefficient  Enhancement  Household  refrigerator  Modeling  Experimentation Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : We investigate an alternative tube-fin evaporator design (accelerated flow evaporator, AFE) in which the air-side local heat transfer coefficient is increased due to a progressive reduction of the free-flow area. For a given heat transfer rate, this enhancement is expected to partially compensate the decrease in surface area, which reduces the evaporator material cost. The air-side thermal-hydraulic behavior of nine AFEs was determined experimentally, and a calculation method that relies on j and f correlations for plain tube-fin heat exchangers and on mass and momentum balances has been proposed. The method enables the calculation of the by-pass fraction associated with the air stream through the clearance between the tube bank and the outer edge of the fins. The agreement between the model, which introduces no additional fitting parameters, and the experiments is within ±10% for all heat transfer data and ±15% for the majority of the pressure drop data. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S014070071000201X [article] Air-side heat transfer and pressure drop characteristics of accelerated flow evaporators = Evaporateurs à écoulement accéléré: transfert de chaleur côté air et caractéristiques de la chute de pression [texte imprimé] / Paulo J. Waltrich, Auteur ; Jader R. Barbosa Jr., Auteur ; Christian J.L. Hermes, Auteur . - 2011 . - pp. 484-497. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 34 N° 2 (Mars 2011) . - pp. 484-497 Mots-clés : Evaporator  Heat  exchanger  Heat  transfer  coefficient  Enhancement  Household  refrigerator  Modeling  Experimentation Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : We investigate an alternative tube-fin evaporator design (accelerated flow evaporator, AFE) in which the air-side local heat transfer coefficient is increased due to a progressive reduction of the free-flow area. For a given heat transfer rate, this enhancement is expected to partially compensate the decrease in surface area, which reduces the evaporator material cost. The air-side thermal-hydraulic behavior of nine AFEs was determined experimentally, and a calculation method that relies on j and f correlations for plain tube-fin heat exchangers and on mass and momentum balances has been proposed. The method enables the calculation of the by-pass fraction associated with the air stream through the clearance between the tube bank and the outer edge of the fins. The agreement between the model, which introduces no additional fitting parameters, and the experiments is within ±10% for all heat transfer data and ±15% for the majority of the pressure drop data. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S014070071000201X

Alternative evaluation of liquid-to-suction heat exchange in the refrigeration cycle / Christian J.L. Hermes in International journal of refrigeration, Vol. 36 N° 8 (Décembre 2013) 

Public ISBD [article]  in International journal of refrigeration > Vol. 36 N° 8 (Décembre 2013) . - pp. 2119–2127 Titre : Alternative evaluation of liquid-to-suction heat exchange in the refrigeration cycle Titre original : Évaluation alternative de l'echangeur liquide-vapeur dans le cycle frigorifique Type de document : texte imprimé Auteurs : Christian J.L. Hermes, Auteur Année de publication : 2014 Article en page(s) : pp. 2119–2127 Note générale : Refrigeration Langues : Anglais (eng) Mots-clés : Liquid–vapor  exchanger;  mechanical  vapor  compression;  thermodynamic  cycle;  COP Résumé : This paper advances a thermodynamic study of the effects of the liquid-to-suction heat exchange in vapor compression refrigeration cycles. The analysis was carried out for refrigerants of current interest, such as R134a, R22, R290, R410A, R600a and R717 assuming the cooling capacity as a constraint so that the evaporating pressure is free to vary. It is shown that the coefficient of performance may either increase or decrease when an internal heat exchanger is introduced into the cycle, depending not only on the working pressures, the heat exchanger effectiveness, the specific heat ratio, and the available latent heat to produce additional refrigerating effect, but also on the change experienced by the evaporating pressure. The thermodynamic conditions required for performance improvement are also discussed. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700713001540 [article] Alternative evaluation of liquid-to-suction heat exchange in the refrigeration cycle = Évaluation alternative de l'echangeur liquide-vapeur dans le cycle frigorifique [texte imprimé] / Christian J.L. Hermes, Auteur . - 2014 . - pp. 2119–2127. Refrigeration Langues : Anglais (eng) in International journal of refrigeration > Vol. 36 N° 8 (Décembre 2013) . - pp. 2119–2127 Mots-clés : Liquid–vapor  exchanger;  mechanical  vapor  compression;  thermodynamic  cycle;  COP Résumé : This paper advances a thermodynamic study of the effects of the liquid-to-suction heat exchange in vapor compression refrigeration cycles. The analysis was carried out for refrigerants of current interest, such as R134a, R22, R290, R410A, R600a and R717 assuming the cooling capacity as a constraint so that the evaporating pressure is free to vary. It is shown that the coefficient of performance may either increase or decrease when an internal heat exchanger is introduced into the cycle, depending not only on the working pressures, the heat exchanger effectiveness, the specific heat ratio, and the available latent heat to produce additional refrigerating effect, but also on the change experienced by the evaporating pressure. The thermodynamic conditions required for performance improvement are also discussed. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700713001540

In-situ study of frosting and defrosting processes in tube-fin evaporators of household refrigerating appliances / Fernando T. Knabben 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. 2031–2041 Titre : In-situ study of frosting and defrosting processes in tube-fin evaporators of household refrigerating appliances Titre original : Etude sur les processus de givrage et de dégivrage des évaporateurs à tubes ailetés des appareils frigorifiques domestiques Type de document : texte imprimé Auteurs : Fernando T. Knabben, Auteur ; Christian J.L. Hermes, Auteur ; Cláudio Melo, Auteur Année de publication : 2012 Article en page(s) : pp. 2031–2041 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Frosting  Defrosting  Evaporator  Refrigerator Résumé : The present paper advances an in-situ study of frosting and defrosting processes in tube-fin evaporators of household refrigerators and freezers. Frost growth experiments were carried out using a purpose-built test facility comprised of a refrigerated cabinet placed inside a climatized chamber, and a vapor compression refrigeration loop that controls both the evaporating temperature and the evaporator superheating. A first-principles two-dimensional simulation model was put forward to predict the evaporator blocking over time, and also the heat and mass transfer rates. The model validation exercise has shown that the model follows well the experimental trends of pressure drop, frost mass, cooling capacity and air flow rate, with all predictions falling inside ±10% error bounds. The model was then used to assess the impact of several design parameters on both the evaporator blockage and defrost efficiency. It was found that a nearly ideal defrost efficiency is achieved when the defrosting process is performed by two simultaneous heaters. ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700711001800 [article] In-situ study of frosting and defrosting processes in tube-fin evaporators of household refrigerating appliances = Etude sur les processus de givrage et de dégivrage des évaporateurs à tubes ailetés des appareils frigorifiques domestiques [texte imprimé] / Fernando T. Knabben, Auteur ; Christian J.L. Hermes, Auteur ; Cláudio Melo, Auteur . - 2012 . - pp. 2031–2041. Génie mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 34 N° 8 (Décembre 2011) . - pp. 2031–2041 Mots-clés : Frosting  Defrosting  Evaporator  Refrigerator Résumé : The present paper advances an in-situ study of frosting and defrosting processes in tube-fin evaporators of household refrigerators and freezers. Frost growth experiments were carried out using a purpose-built test facility comprised of a refrigerated cabinet placed inside a climatized chamber, and a vapor compression refrigeration loop that controls both the evaporating temperature and the evaporator superheating. A first-principles two-dimensional simulation model was put forward to predict the evaporator blocking over time, and also the heat and mass transfer rates. The model validation exercise has shown that the model follows well the experimental trends of pressure drop, frost mass, cooling capacity and air flow rate, with all predictions falling inside ±10% error bounds. The model was then used to assess the impact of several design parameters on both the evaporator blockage and defrost efficiency. It was found that a nearly ideal defrost efficiency is achieved when the defrosting process is performed by two simultaneous heaters. ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700711001800

Thermodynamic design of condensers and evaporators / Christian J.L. Hermes in International journal of refrigeration, Vol. 36 N° 2 (N° spécial) (Mars 2013) 

Public ISBD [article]  in International journal of refrigeration > Vol. 36 N° 2 (N° spécial) (Mars 2013) . - pp. 633–640 Titre : Thermodynamic design of condensers and evaporators : Formulation and applications Titre original : Conception thermodynamique des condenseurs et des évaporateurs: formulation et applications Type de document : texte imprimé Auteurs : Christian J.L. Hermes, Auteur Année de publication : 2013 Article en page(s) : pp. 633–640 Note générale : Refrigeration Langues : Anglais (eng) Mots-clés : Condenser;  Evaporator;  Design;  Optimization Résumé : This paper assesses the thermo-hydraulic design approach introduced in a previous publication (Hermes, 2012) for condensers and evaporators aimed at minimum entropy generation. An algebraic model which expresses the dimensionless rate of entropy generation as a function of the number of transfer units, the fluid properties, the thermal-hydraulic characteristics, and the operating conditions is derived. Case studies are carried out with different heat exchanger configurations for small-capacity refrigeration applications. The theoretical analysis led to the conclusion that a high effectiveness heat exchanger does not necessarily provide the best thermal-hydraulic design for condenser and evaporator coils, when the rates of entropy generation due to heat transfer and fluid friction are of the same order of magnitude. The analysis also indicated that a high aspect ratio heat exchanger produces a lower amount of entropy than a low aspect ratio one. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700712002927 [article] Thermodynamic design of condensers and evaporators = Conception thermodynamique des condenseurs et des évaporateurs: formulation et applications : Formulation and applications [texte imprimé] / Christian J.L. Hermes, Auteur . - 2013 . - pp. 633–640. Refrigeration Langues : Anglais (eng) in International journal of refrigeration > Vol. 36 N° 2 (N° spécial) (Mars 2013) . - pp. 633–640 Mots-clés : Condenser;  Evaporator;  Design;  Optimization Résumé : This paper assesses the thermo-hydraulic design approach introduced in a previous publication (Hermes, 2012) for condensers and evaporators aimed at minimum entropy generation. An algebraic model which expresses the dimensionless rate of entropy generation as a function of the number of transfer units, the fluid properties, the thermal-hydraulic characteristics, and the operating conditions is derived. Case studies are carried out with different heat exchanger configurations for small-capacity refrigeration applications. The theoretical analysis led to the conclusion that a high effectiveness heat exchanger does not necessarily provide the best thermal-hydraulic design for condenser and evaporator coils, when the rates of entropy generation due to heat transfer and fluid friction are of the same order of magnitude. The analysis also indicated that a high aspect ratio heat exchanger produces a lower amount of entropy than a low aspect ratio one. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700712002927