Documents disponibles écrits par cet auteur

Experimental study on flow boiling heat transfer of multiport tubes with R245fa and R1234ze(E) / F. Vakili-Farahani 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. 335–352 Titre : Experimental study on flow boiling heat transfer of multiport tubes with R245fa and R1234ze(E) Titre original : Etude expérimentale sur le transfert de chaleur lors de l’ébullition du R245fa et du R1234ze(E) à l’intérieur de tubes à plusieurs orifices Type de document : texte imprimé Auteurs : F. Vakili-Farahani, Auteur ; B. Agostini, Auteur ; J. R. Thome, Auteur Année de publication : 2013 Article en page(s) : pp. 335–352 Note générale : Refrigeration Langues : Anglais (eng) Mots-clés : Two-phase  flow;  Multiport  tube;  Heat  transfer;  Flow  boiling;  Microchannel;  R245fa;  R1234ze(E) Résumé : The upward flow boiling experiments were carried out in a flat aluminum extruded multiport tube, which is composed of 7 parallel rectangular channels (1.1 mm × 2.1 mm) with hydraulic diameter of 1.4 mm. Two refrigerants, R245fa and R1234ze, the latter a recent environmentally safe refrigerant proposed as a potential replacement for R134a, were tested. A new hot water heating technique that accounts for either uniform or non-uniform local heat flux distribution along the channel was developed to obtain and reduce the data. Effects of heat flux, mass flux, vapor quality, and saturation temperature on flow boiling heat transfer in multiport tubes were considered. Finally, the experimental results were compared with some well-known correlations to evaluate the capabilities of existing prediction methods. The analysis shows that the three-zone model for slug flows works well for that subset of test results, utilizing the apparent surface roughness in place of the dryout thickness in the model, as has been previously done for silicon, stainless steel and copper microchannels with measured surface roughnesses. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700712003507 [article] Experimental study on flow boiling heat transfer of multiport tubes with R245fa and R1234ze(E) = Etude expérimentale sur le transfert de chaleur lors de l’ébullition du R245fa et du R1234ze(E) à l’intérieur de tubes à plusieurs orifices [texte imprimé] / F. Vakili-Farahani, Auteur ; B. Agostini, Auteur ; J. R. Thome, Auteur . - 2013 . - pp. 335–352. Refrigeration Langues : Anglais (eng) in International journal of refrigeration > Vol. 36 N° 2 (N° spécial) (Mars 2013) . - pp. 335–352 Mots-clés : Two-phase  flow;  Multiport  tube;  Heat  transfer;  Flow  boiling;  Microchannel;  R245fa;  R1234ze(E) Résumé : The upward flow boiling experiments were carried out in a flat aluminum extruded multiport tube, which is composed of 7 parallel rectangular channels (1.1 mm × 2.1 mm) with hydraulic diameter of 1.4 mm. Two refrigerants, R245fa and R1234ze, the latter a recent environmentally safe refrigerant proposed as a potential replacement for R134a, were tested. A new hot water heating technique that accounts for either uniform or non-uniform local heat flux distribution along the channel was developed to obtain and reduce the data. Effects of heat flux, mass flux, vapor quality, and saturation temperature on flow boiling heat transfer in multiport tubes were considered. Finally, the experimental results were compared with some well-known correlations to evaluate the capabilities of existing prediction methods. The analysis shows that the three-zone model for slug flows works well for that subset of test results, utilizing the apparent surface roughness in place of the dryout thickness in the model, as has been previously done for silicon, stainless steel and copper microchannels with measured surface roughnesses. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700712003507

Pool boiling data and prediction method for enhanced boiling tubes with R-134a, R-236fa and R-1234ze(E) / E. Van Rooyen 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. 447–455 Titre : Pool boiling data and prediction method for enhanced boiling tubes with R-134a, R-236fa and R-1234ze(E) Titre original : Données sur l'ébullition libre et une méthode de prévision pour des tubes d'ébullition améliorés utilisés pour le R-134a, le R-236fa et le R-1234ze(E) Type de document : texte imprimé Auteurs : E. Van Rooyen, Auteur ; J. R. Thome, Auteur Année de publication : 2013 Article en page(s) : pp. 447–455 Note générale : Refrigeration Langues : Anglais (eng) Mots-clés : Pool  boiling;  Enhancement;  Prediction;  Heat  transfer;  Two-phase  flow;  GWP Résumé : The phase-change process of enhanced surface pool boiling is an effective mode of heat transfer requiring on-going investigation with new refrigerants. Two of the latest generation Wolverine Tube Inc. (Turbo-B5) and Wieland Werke (Gewa-B5) enhanced boiling tubes have been studied under pool boiling conditions with refrigerants R-134a, R-236fa and R-1234ze(E). A 1.027 m length of tube with semi-local heat flux and heat transfer coefficient measurements was tested in each case. The Wilson plot method was validated and used to characterise the inside heat transfer coefficient of the heating water. Pool boiling tests were carried out for saturation temperatures of 5–25 °C and heat fluxes from 15 to 70 kW m−2, based on the outer tube diameter. It was found that heat flux and refrigerant type had the dominant effect on heat transfer. A new enhanced tube pool boiling correlation was proposed, based on a boiling heat transfer mechanism in the near-wall region. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700712003313 [article] Pool boiling data and prediction method for enhanced boiling tubes with R-134a, R-236fa and R-1234ze(E) = Données sur l'ébullition libre et une méthode de prévision pour des tubes d'ébullition améliorés utilisés pour le R-134a, le R-236fa et le R-1234ze(E) [texte imprimé] / E. Van Rooyen, Auteur ; J. R. Thome, Auteur . - 2013 . - pp. 447–455. Refrigeration Langues : Anglais (eng) in International journal of refrigeration > Vol. 36 N° 2 (N° spécial) (Mars 2013) . - pp. 447–455 Mots-clés : Pool  boiling;  Enhancement;  Prediction;  Heat  transfer;  Two-phase  flow;  GWP Résumé : The phase-change process of enhanced surface pool boiling is an effective mode of heat transfer requiring on-going investigation with new refrigerants. Two of the latest generation Wolverine Tube Inc. (Turbo-B5) and Wieland Werke (Gewa-B5) enhanced boiling tubes have been studied under pool boiling conditions with refrigerants R-134a, R-236fa and R-1234ze(E). A 1.027 m length of tube with semi-local heat flux and heat transfer coefficient measurements was tested in each case. The Wilson plot method was validated and used to characterise the inside heat transfer coefficient of the heating water. Pool boiling tests were carried out for saturation temperatures of 5–25 °C and heat fluxes from 15 to 70 kW m−2, based on the outer tube diameter. It was found that heat flux and refrigerant type had the dominant effect on heat transfer. A new enhanced tube pool boiling correlation was proposed, based on a boiling heat transfer mechanism in the near-wall region. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700712003313

Transition of bubbly flow in vertical tubes / A. K. Das in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 9 (Septembre 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 9 (Septembre 2009) . - 06 p. Titre : Transition of bubbly flow in vertical tubes : effect of bubble size and tube diameter Type de document : texte imprimé Auteurs : A. K. Das, Auteur ; J. R. Thome, Auteur ; P. K. Das, Auteur Année de publication : 2009 Article en page(s) : 06 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  bubbles;  bubbly  flow;  slug;  porosity Résumé : In a companion paper (“Modelling Bubbly Flow by Population Balance Technique Part I: Axial Flow Development and Its Transitions,” ASME J. Fluids Eng), a two fluid model along with a multiclass population balance technique has been used to find out comprehensive criteria for the transition from bubbly to slug flow, primarily through a study of axial flow development. Using the same basic model the transition mechanism has been investigated in the present paper covering a wide range of process parameters. Though the dominating rate of bubble coalescence during the axial development of the flow acts as the main cause for the transition to slug flow, the simultaneous transformation of the radial voidage pattern cannot be overlooked. Appearance of core, intermediate, wall, and two peaks are observed in the radial voidage distribution depending on the phase superficial velocities. A map has been developed indicating the boundaries of the above subregimes. It has been observed that not only the size of the bubbles entering the inlet plane but also the size distribution (monodispersion or bidispersion) changes the voidage peak and shifts the transition boundary. It is interesting to note that the bubbly flow only with a core peak void distribution transforms into slug flow with a change in the operating parameters. Transition boundary is also observed to shift with a change in the tube diameter. The simulation results have been compared with experimental data taken from different sources and very good agreements have been noted. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Transition of bubbly flow in vertical tubes : effect of bubble size and tube diameter [texte imprimé] / A. K. Das, Auteur ; J. R. Thome, Auteur ; P. K. Das, Auteur . - 2009 . - 06 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 9 (Septembre 2009) . - 06 p. Mots-clés : flow  (dynamics);  bubbles;  bubbly  flow;  slug;  porosity Résumé : In a companion paper (“Modelling Bubbly Flow by Population Balance Technique Part I: Axial Flow Development and Its Transitions,” ASME J. Fluids Eng), a two fluid model along with a multiclass population balance technique has been used to find out comprehensive criteria for the transition from bubbly to slug flow, primarily through a study of axial flow development. Using the same basic model the transition mechanism has been investigated in the present paper covering a wide range of process parameters. Though the dominating rate of bubble coalescence during the axial development of the flow acts as the main cause for the transition to slug flow, the simultaneous transformation of the radial voidage pattern cannot be overlooked. Appearance of core, intermediate, wall, and two peaks are observed in the radial voidage distribution depending on the phase superficial velocities. A map has been developed indicating the boundaries of the above subregimes. It has been observed that not only the size of the bubbles entering the inlet plane but also the size distribution (monodispersion or bidispersion) changes the voidage peak and shifts the transition boundary. It is interesting to note that the bubbly flow only with a core peak void distribution transforms into slug flow with a change in the operating parameters. Transition boundary is also observed to shift with a change in the tube diameter. The simulation results have been compared with experimental data taken from different sources and very good agreements have been noted. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Transition of bubbly flow in vertical tubes / A. K. Das in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 9 (Septembre 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 9 (Septembre 2009) . - 12 p. Titre : Transition of bubbly flow in vertical tubes : new criteria through CFD simulation Type de document : texte imprimé Auteurs : A. K. Das, Auteur ; J. R. Thome, Auteur ; P. K. Das, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  bubbles;  bubbly  flow;  simulation Résumé : The two fluid model is used to simulate upward gas-liquid bubbly flow through a vertical conduit. Coalescence and breakup of bubbles have been accounted for by embedding the population balance technique in the two fluid model. The simulation enables one to track the axial development of the voidage pattern and the distribution of the bubbles. Thereby it has been possible to propose a new criterion for the transition from bubbly to slug flow regime. The transition criteria depend on (i) the breakage and coalescence frequency, (ii) the bubble volume count below and above the bubble size introduced at the inlet, and (iii) the bubble count histogram. The prediction based on the present criteria exhibits excellent agreement with the experimental data. It has also been possible to simulate the transition from bubbly to dispersed bubbly flow at a high liquid flow rate using the same model. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Transition of bubbly flow in vertical tubes : new criteria through CFD simulation [texte imprimé] / A. K. Das, Auteur ; J. R. Thome, Auteur ; P. K. Das, Auteur . - 2009 . - 12 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 9 (Septembre 2009) . - 12 p. Mots-clés : flow  (dynamics);  bubbles;  bubbly  flow;  simulation Résumé : The two fluid model is used to simulate upward gas-liquid bubbly flow through a vertical conduit. Coalescence and breakup of bubbles have been accounted for by embedding the population balance technique in the two fluid model. The simulation enables one to track the axial development of the voidage pattern and the distribution of the bubbles. Thereby it has been possible to propose a new criterion for the transition from bubbly to slug flow regime. The transition criteria depend on (i) the breakage and coalescence frequency, (ii) the bubble volume count below and above the bubble size introduced at the inlet, and (iii) the bubble count histogram. The prediction based on the present criteria exhibits excellent agreement with the experimental data. It has also been possible to simulate the transition from bubbly to dispersed bubbly flow at a high liquid flow rate using the same model. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]