Documents disponibles écrits par cet auteur

Measurement and modeling of condensation heat transfer in non-circular microchannels / Akhil Agarwal in International journal of refrigeration, Vol. 33 N° 6 (Septembre 2010) 

Public ISBD [article]  in International journal of refrigeration > Vol. 33 N° 6 (Septembre 2010) . - pp. 1169-1179 Titre : Measurement and modeling of condensation heat transfer in non-circular microchannels Titre original : Transfert de chaleur lors de la condensation à l'intérieur des micro-canaux non circulaires: mesures et modélisation Type de document : texte imprimé Auteurs : Akhil Agarwal, Auteur ; Todd M. Bandhauer, Auteur ; Srinivas Garimella, Auteur Année de publication : 2010 Article en page(s) : pp. 1169-1179 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Condensation  Microchannel  Heat  transfer  Model  Measurement  Non-circular Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Heat transfer coefficients in six non-circular horizontal microchannels (0.424 < Dh < 0.839 mm) of different shapes during condensation of refrigerant R134a over the mass flux range 150 < G < 750 kg m−2 s−1 were measured in this study. The channels included barrel-shaped, N-shaped, rectangular, square, and triangular extruded tubes, and a channel with a W-shaped corrugated insert that yielded triangular microchannels. The thermal amplification technique developed and reported in earlier work by the authors is used to measure the heat transfer coefficients across the vapor-liquid dome in small increments of vapor quality. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The effect of tube shape was also considered in deciding the applicable flow regime. A modified version of the annular-flow-based heat transfer model proposed recently by the authors for circular microchannels, with the required shear stress being calculated from a non-circular microchannel pressure drop model also reported earlier was found to best correlate the present data for square, rectangular and barrel-shaped microchannels. For the other microchannel shapes with sharp acute-angle corners, a mist-flow-based model from the literature on larger tubes was found to suffice for the prediction of the heat transfer data. These models predict the data significantly better than the other available correlations in the literature. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710000149 [article] Measurement and modeling of condensation heat transfer in non-circular microchannels = Transfert de chaleur lors de la condensation à l'intérieur des micro-canaux non circulaires: mesures et modélisation [texte imprimé] / Akhil Agarwal, Auteur ; Todd M. Bandhauer, Auteur ; Srinivas Garimella, Auteur . - 2010 . - pp. 1169-1179. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 33 N° 6 (Septembre 2010) . - pp. 1169-1179 Mots-clés : Condensation  Microchannel  Heat  transfer  Model  Measurement  Non-circular Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Heat transfer coefficients in six non-circular horizontal microchannels (0.424 < Dh < 0.839 mm) of different shapes during condensation of refrigerant R134a over the mass flux range 150 < G < 750 kg m−2 s−1 were measured in this study. The channels included barrel-shaped, N-shaped, rectangular, square, and triangular extruded tubes, and a channel with a W-shaped corrugated insert that yielded triangular microchannels. The thermal amplification technique developed and reported in earlier work by the authors is used to measure the heat transfer coefficients across the vapor-liquid dome in small increments of vapor quality. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The effect of tube shape was also considered in deciding the applicable flow regime. A modified version of the annular-flow-based heat transfer model proposed recently by the authors for circular microchannels, with the required shear stress being calculated from a non-circular microchannel pressure drop model also reported earlier was found to best correlate the present data for square, rectangular and barrel-shaped microchannels. For the other microchannel shapes with sharp acute-angle corners, a mist-flow-based model from the literature on larger tubes was found to suffice for the prediction of the heat transfer data. These models predict the data significantly better than the other available correlations in the literature. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710000149

Modeling of pressure drop during condensation in circular and noncircular microchannels / Akhil Agarwal in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 1 (Janvier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 1 (Janvier 2009) . - 08 p. Titre : Modeling of pressure drop during condensation in circular and noncircular microchannels Type de document : texte imprimé Auteurs : Akhil Agarwal, Auteur ; Srinivas Garimella, Auteur Année de publication : 2009 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : multiple  flow-regime  model;  drop  during  condensation Résumé : This paper presents a multiple flow-regime model for pressure drop during condensation of refrigerant R134a in horizontal microchannels. Condensation pressure drops measured in two circular and six noncircular channels ranging in hydraulic diameter from 0.42mmto0.8mm are considered here. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from 100% vapor to 100% liquid for five different refrigerant mass fluxes between 150kg∕m2s and 750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to assign the applicable flow regime to the data points. (2005, “ Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3) pp. 1–8) reported a comprehensive model for circular tubes that addresses the progression of the condensation process from the vapor phase to the liquid phase by modifying and combining the pressure drop models for intermittent (, 2002, “ An Experimentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Circular Microchannels,” ASME J. Fluids Eng., 124(1), pp. 205–214) and annular (, 2003, “ Two-Phase Pressure Drops in the Annular Flow Regime in Circular Microchannels,” 21st IIR International Congress of Refrigeration, International Institute of Refrigeration, p. ICR0360) flows reported earlier by them. This paper presents new condensation pressure drop data on six noncircular channels over the same flow conditions as the previous work on circular channels. In addition, a multiple flow-regime model similar to that developed earlier by Garimella et al. for circular microchannels is developed here for these new cross sections. This combined model accurately predicts condensation pressure drops in the annular, disperse-wave, mist, discrete-wave, and intermittent flow regimes for both circular and noncircular microchannels of similar hydraulic diameters. Overlap and transition regions between the respective regimes are also addressed to yield relatively smooth transitions between the predicted pressure drops. The resulting model predicts 80% of the data within ±25%. The effect of tube shape on pressure drop is also demonstrated. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Modeling of pressure drop during condensation in circular and noncircular microchannels [texte imprimé] / Akhil Agarwal, Auteur ; Srinivas Garimella, Auteur . - 2009 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 1 (Janvier 2009) . - 08 p. Mots-clés : multiple  flow-regime  model;  drop  during  condensation Résumé : This paper presents a multiple flow-regime model for pressure drop during condensation of refrigerant R134a in horizontal microchannels. Condensation pressure drops measured in two circular and six noncircular channels ranging in hydraulic diameter from 0.42mmto0.8mm are considered here. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from 100% vapor to 100% liquid for five different refrigerant mass fluxes between 150kg∕m2s and 750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to assign the applicable flow regime to the data points. (2005, “ Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3) pp. 1–8) reported a comprehensive model for circular tubes that addresses the progression of the condensation process from the vapor phase to the liquid phase by modifying and combining the pressure drop models for intermittent (, 2002, “ An Experimentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Circular Microchannels,” ASME J. Fluids Eng., 124(1), pp. 205–214) and annular (, 2003, “ Two-Phase Pressure Drops in the Annular Flow Regime in Circular Microchannels,” 21st IIR International Congress of Refrigeration, International Institute of Refrigeration, p. ICR0360) flows reported earlier by them. This paper presents new condensation pressure drop data on six noncircular channels over the same flow conditions as the previous work on circular channels. In addition, a multiple flow-regime model similar to that developed earlier by Garimella et al. for circular microchannels is developed here for these new cross sections. This combined model accurately predicts condensation pressure drops in the annular, disperse-wave, mist, discrete-wave, and intermittent flow regimes for both circular and noncircular microchannels of similar hydraulic diameters. Overlap and transition regions between the respective regimes are also addressed to yield relatively smooth transitions between the predicted pressure drops. The resulting model predicts 80% of the data within ±25%. The effect of tube shape on pressure drop is also demonstrated. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Representative results for condensation measurements at hydraulic diameters ~100 microns / Akhil Agarwal in Journal of heat transfer, Vol. 132 N° 4 (n° spécial) (Avril 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 4 (n° spécial) (Avril 2010) . - pp. [041010-1/12] Titre : Representative results for condensation measurements at hydraulic diameters ~100 microns Type de document : texte imprimé Auteurs : Akhil Agarwal, Auteur ; Srinivas Garimella, Auteur Article en page(s) : pp. [041010-1/12] Note générale : Physique Langues : Anglais (eng) Mots-clés : Condensation  Microchannels  Measurement  Heat  transfer  Pressure  drop  refrigerants Index. décimale : 536 Chaleur. Thermodynamique Résumé : Condensation pressure drops and heat transfer coefficients for refrigerant R134a flowing through rectangular microchannels with hydraulic diameters ranging from 100 µm to 200 µm are measured in small quality increments. The channels are fabricated on a copper substrate by electroforming copper onto a mask patterned by X-ray lithography and sealed by diffusion bonding. Subcooled liquid is electrically heated to the desired quality, followed by condensation in the test section. Downstream of the test section, another electric heater is used to heat the refrigerant to a superheated state. Energy balances on the preheaters and postheaters establish the refrigerant inlet and outlet states at the test section. Water at a high flow rate serves as the test-section coolant to ensure that the condensation side presents the governing thermal resistance. Heat transfer coefficients are measured for mass fluxes ranging from 200 kg/m2 s to 800 kg/m2 s for 0< quality <1 at several different saturation temperatures. Conjugate heat transfer analyses are conducted in conjunction with local pressure drop profiles to obtain accurate driving temperature differences and heat transfer coefficients. The effects of quality, mass flux, and saturation temperature on condensation pressure drops and heat transfer coefficients are illustrated through these experiments. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Representative results for condensation measurements at hydraulic diameters ~100 microns [texte imprimé] / Akhil Agarwal, Auteur ; Srinivas Garimella, Auteur . - pp. [041010-1/12]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 4 (n° spécial) (Avril 2010) . - pp. [041010-1/12] Mots-clés : Condensation  Microchannels  Measurement  Heat  transfer  Pressure  drop  refrigerants Index. décimale : 536 Chaleur. Thermodynamique Résumé : Condensation pressure drops and heat transfer coefficients for refrigerant R134a flowing through rectangular microchannels with hydraulic diameters ranging from 100 µm to 200 µm are measured in small quality increments. The channels are fabricated on a copper substrate by electroforming copper onto a mask patterned by X-ray lithography and sealed by diffusion bonding. Subcooled liquid is electrically heated to the desired quality, followed by condensation in the test section. Downstream of the test section, another electric heater is used to heat the refrigerant to a superheated state. Energy balances on the preheaters and postheaters establish the refrigerant inlet and outlet states at the test section. Water at a high flow rate serves as the test-section coolant to ensure that the condensation side presents the governing thermal resistance. Heat transfer coefficients are measured for mass fluxes ranging from 200 kg/m2 s to 800 kg/m2 s for 0< quality <1 at several different saturation temperatures. Conjugate heat transfer analyses are conducted in conjunction with local pressure drop profiles to obtain accurate driving temperature differences and heat transfer coefficients. The effects of quality, mass flux, and saturation temperature on condensation pressure drops and heat transfer coefficients are illustrated through these experiments. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]