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Experimental analysis of microchannel entrance length characteristics using microparticle image velocimetry / Tariq Ahmad in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 13 p. Titre : Experimental analysis of microchannel entrance length characteristics using microparticle image velocimetry Type de document : texte imprimé Auteurs : Tariq Ahmad, Auteur ; Ibrahim Hassan, Auteur Année de publication : 2010 Article en page(s) : 13 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  channels  (hydraulic  engineering);  particulate  matter;  reservoirs;  Reynolds  number;  entrance  region;  experiment  analysis;  microchannels;  microparticles;  mechanisms Résumé : The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Experimental analysis of microchannel entrance length characteristics using microparticle image velocimetry [texte imprimé] / Tariq Ahmad, Auteur ; Ibrahim Hassan, Auteur . - 2010 . - 13 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 13 p. Mots-clés : flow  (dynamics);  channels  (hydraulic  engineering);  particulate  matter;  reservoirs;  Reynolds  number;  entrance  region;  experiment  analysis;  microchannels;  microparticles;  mechanisms Résumé : The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Experimental investigation of flow boiling instability in a single horizontal microtube with and without inlet restriction / YanFeng Fan in Journal of heat transfer, Vol. 134 N° 8 (special issue) (Août 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 8 (special issue) (Août 2012) . - 11 p. Titre : Experimental investigation of flow boiling instability in a single horizontal microtube with and without inlet restriction Type de document : texte imprimé Auteurs : YanFeng Fan, Auteur ; Ibrahim Hassan, Auteur Année de publication : 2012 Article en page(s) : 11 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : flow  boiling  instability;  orifice;  single  horizontal  microtube;  oscillation  frequency;  oscillation  amplitude;  pressure  drop Index. décimale : 536 Chaleur. Thermodynamique Résumé : An experimental study is conducted to investigate the effects of inlet restriction (orifice) on flow boiling instability in a single horizontal microtube. The test-section is composed of a stainless steel tube with an inner diameter of 889 µm, and a length of 150 mm. Experiments are performed for three different orifice configurations with 20%, 35%, and 50% area ratio. Mass flux is varied from 700 to 3000 kg/m2 · s, whereas the heat flux is varied from 6 to 27 W/cm2. The dielectric coolant FC-72 is selected as the working fluid. In the absence of an orifice at the inlet, four oscillation types are observed at the onset of flow instability; it is also noticed that the frequency of the oscillations increases with increasing heat flux, while the amplitude remains constant. The addition of an orifice at the inlet helps stabilizing the flow without generating significant pressure drop at the same operating condition as the microtube without orifice. The 20% area ratio orifice shows better performance at low mass fluxes (<1000 kg/m2 · s). Whereas, at high mass fluxes (>2000 kg/m2 · s), 50% and 35% area ratio orifices are efficient in stabilizing the flow or delaying the onset of flow instability. Therefore, selecting the area ratio of the orifice depends on the operating condition. A small area ratio orifice is preferably used at low mass fluxes, whereas a large area ratio orifice is more suitable for high mass fluxes. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000008 [...] [article] Experimental investigation of flow boiling instability in a single horizontal microtube with and without inlet restriction [texte imprimé] / YanFeng Fan, Auteur ; Ibrahim Hassan, Auteur . - 2012 . - 11 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 8 (special issue) (Août 2012) . - 11 p. Mots-clés : flow  boiling  instability;  orifice;  single  horizontal  microtube;  oscillation  frequency;  oscillation  amplitude;  pressure  drop Index. décimale : 536 Chaleur. Thermodynamique Résumé : An experimental study is conducted to investigate the effects of inlet restriction (orifice) on flow boiling instability in a single horizontal microtube. The test-section is composed of a stainless steel tube with an inner diameter of 889 µm, and a length of 150 mm. Experiments are performed for three different orifice configurations with 20%, 35%, and 50% area ratio. Mass flux is varied from 700 to 3000 kg/m2 · s, whereas the heat flux is varied from 6 to 27 W/cm2. The dielectric coolant FC-72 is selected as the working fluid. In the absence of an orifice at the inlet, four oscillation types are observed at the onset of flow instability; it is also noticed that the frequency of the oscillations increases with increasing heat flux, while the amplitude remains constant. The addition of an orifice at the inlet helps stabilizing the flow without generating significant pressure drop at the same operating condition as the microtube without orifice. The 20% area ratio orifice shows better performance at low mass fluxes (<1000 kg/m2 · s). Whereas, at high mass fluxes (>2000 kg/m2 · s), 50% and 35% area ratio orifices are efficient in stabilizing the flow or delaying the onset of flow instability. Therefore, selecting the area ratio of the orifice depends on the operating condition. A small area ratio orifice is preferably used at low mass fluxes, whereas a large area ratio orifice is more suitable for high mass fluxes. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000008 [...]

Natural convection mass transfer behavior of fixed bed of spheres in relation to catalytic and electrochemical reactor design / Ibrahim Hassan in Industrial & engineering chemistry research, Vol. 48 N° 7 (Avril 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 7 (Avril 2009) . - pp. 3692–3695 Titre : Natural convection mass transfer behavior of fixed bed of spheres in relation to catalytic and electrochemical reactor design Type de document : texte imprimé Auteurs : Ibrahim Hassan, Auteur ; Inderjit Nirdosh, Auteur ; Gomaa H. Sedahmed, Auteur Année de publication : 2009 Article en page(s) : pp. 3692–3695 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Convection  mass  transfer  Spheres  Electrochemical  reactor Résumé : The free convection mass transfer behavior of a fixed bed of spheres has been studied experimentally using an electrochemical technique which involved measuring the limiting current of the cathodic deposition of copper from acidified copper sulfate solution. Variables studied were sphere diameter, bed height, and physical properties of the solution. The mass transfer coefficient was found to decrease slightly with increasing bed height and independent of sphere diameter. The data were correlated for the conditions 5 × 106 < Sc·Gr < 5.4 × 108 by the equation Sh = 0.28(Sc·Gr)0.32. A comparison between the present and some previous data at other packing geometries shows that the rate of natural convection mass transfer at a bed of spheres is higher than that at beds of Raschig rings and at cylinders. The importance of the present results for the design and operation of catalytic and electrochemical reactors used to conduct diffusion controlled liquid−solid reactions is highlighted. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801195b [article] Natural convection mass transfer behavior of fixed bed of spheres in relation to catalytic and electrochemical reactor design [texte imprimé] / Ibrahim Hassan, Auteur ; Inderjit Nirdosh, Auteur ; Gomaa H. Sedahmed, Auteur . - 2009 . - pp. 3692–3695. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 7 (Avril 2009) . - pp. 3692–3695 Mots-clés : Convection  mass  transfer  Spheres  Electrochemical  reactor Résumé : The free convection mass transfer behavior of a fixed bed of spheres has been studied experimentally using an electrochemical technique which involved measuring the limiting current of the cathodic deposition of copper from acidified copper sulfate solution. Variables studied were sphere diameter, bed height, and physical properties of the solution. The mass transfer coefficient was found to decrease slightly with increasing bed height and independent of sphere diameter. The data were correlated for the conditions 5 × 106 < Sc·Gr < 5.4 × 108 by the equation Sh = 0.28(Sc·Gr)0.32. A comparison between the present and some previous data at other packing geometries shows that the rate of natural convection mass transfer at a bed of spheres is higher than that at beds of Raschig rings and at cylinders. The importance of the present results for the design and operation of catalytic and electrochemical reactors used to conduct diffusion controlled liquid−solid reactions is highlighted. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801195b

Numerically investigating the effects of cross-links in scaled microchannel heat sinks / Minh Dang in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 13 p. Titre : Numerically investigating the effects of cross-links in scaled microchannel heat sinks Type de document : texte imprimé Auteurs : Minh Dang, Auteur ; Ibrahim Hassan, Auteur ; Sung In Kim, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Two-phase  flow;  heat  sinks;  pressure  drop;  microchannels;  flow  (Dynamics);  channels  (Hydraulic  engineering);  design;  computational  fluid  dynamics Résumé : Thermal management as a method of heightening performance in miniaturized electronic devices using microchannel heat sinks has recently become of interest to researchers and the industry. One of the current challenges is to design heat sinks with uniform flow distribution. A number of experimental studies have been conducted to seek appropriate designs for microchannel heat sinks. However, pursuing this goal experimentally can be an expensive endeavor. The present work investigates the effect of cross-links on adiabatic two-phase flow in an array of parallel channels. It is carried out using the three-dimensional mixture model from the computational fluid dynamics software, FLUENT 6.3 . A straight channel and two cross-linked channel models were simulated. The cross-links were located at 1/3 and 2/3 of the channel length, and their widths were one and two times larger than the channel width. All test models had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm. The results showed that the trend of flow distribution agrees with experimental results. A new design, with cross-links incorporated, was proposed and the results showed a significant improvement of up to 55% on flow distribution compared with the standard straight channel configuration without a penalty in the pressure drop. Further discussion about the effect of cross-links on flow distribution, flow structure, and pressure drop was also documented. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Numerically investigating the effects of cross-links in scaled microchannel heat sinks [texte imprimé] / Minh Dang, Auteur ; Ibrahim Hassan, Auteur ; Sung In Kim, Auteur . - 2009 . - 13 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 13 p. Mots-clés : Two-phase  flow;  heat  sinks;  pressure  drop;  microchannels;  flow  (Dynamics);  channels  (Hydraulic  engineering);  design;  computational  fluid  dynamics Résumé : Thermal management as a method of heightening performance in miniaturized electronic devices using microchannel heat sinks has recently become of interest to researchers and the industry. One of the current challenges is to design heat sinks with uniform flow distribution. A number of experimental studies have been conducted to seek appropriate designs for microchannel heat sinks. However, pursuing this goal experimentally can be an expensive endeavor. The present work investigates the effect of cross-links on adiabatic two-phase flow in an array of parallel channels. It is carried out using the three-dimensional mixture model from the computational fluid dynamics software, FLUENT 6.3 . A straight channel and two cross-linked channel models were simulated. The cross-links were located at 1/3 and 2/3 of the channel length, and their widths were one and two times larger than the channel width. All test models had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm. The results showed that the trend of flow distribution agrees with experimental results. A new design, with cross-links incorporated, was proposed and the results showed a significant improvement of up to 55% on flow distribution compared with the standard straight channel configuration without a penalty in the pressure drop. Further discussion about the effect of cross-links on flow distribution, flow structure, and pressure drop was also documented. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]