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Zafar Said - One of the best experts on this subject based on the ideXlab platform.
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Rheological behaviour and the Hysteresis Phenomenon of Al2O3 nanofluids
Materials Research Innovations, 2014Co-Authors: Zafar Said, M.h. Sajid, Rahman Saidur, Nasrudin Abdul Rahim, M.h.u. BhuiyanAbstract:The effects of temperature and low-volume concentration on the dynamic viscosity of the Al2O3/water and Al2O3/ethylene glycol/water nanofluids are investigated. Nanofluids were prepared and characterised. Data were collected for temperatures ranging from 25 to 80°C. The presence of aggregated Al2O3 nanoparticles in the fluid, with average diameter of 109 nm which is ∼8 times the primary diameter (13 nm) of Al2O3 nanoparticles was witnessed. Furthermore, only at temperature below 40°C water-based alumina nanofluid at 0·05% v/v showed Newtonian behaviour. On the other hand, Al2O3/ethylene glycol/water mixture exhibited Newtonian behaviour. Results clearly showed the presence of a critical temperature, beyond which the particle suspension properties were noticed to be radically changed, which results in activating the Hysteresis Phenomenon. The Hysteresis Phenomenon on viscosity measurement, which is believed to be the first observed for ethylene glycol/water-based nanofluids, has raised serious concerns reg...
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new thermophysical properties of water based tio2 nanofluid the Hysteresis Phenomenon revisited
International Communications in Heat and Mass Transfer, 2014Co-Authors: Zafar Said, Arif Hepbasli, R Saidur, N A RahimAbstract:Abstract Homogeneous stable suspensions acquired by dispersing dry Al2O3 and TiO2 nanoparticles in controlled pH solution and distilled water, respectively, were prepared and investigated in this study. First of all, the mean nanoparticle diameters were studied by dynamic light scattering (DLS) technique, and the nanofluid stability was analyzed by zeta potential measurements. The nano-crystalline structures were characterized by scanning electron microscope and transmission electron microscope. The rheological behavior was determined for both nanofluids at nanoparticle volume concentrations up to 0.3%. The effect of temperature for the heating and cooling phases was analyzed from 25 °C to 80 °C. Furthermore, the influence of temperature, pressure drop, pumping power, zeta potential, size and densities were analyzed for fresh prepared samples as well as for samples used in a flat plate solar collector over a period of 30 days. The thermal conductivity enhancement of the two nanofluids demonstrated a nonlinear relationship with respect to temperature and volume fraction, with increases in the volume fraction and temperature. All resulted in an increase in the measured enhancement. Existence of a critical temperature was observed beyond which the particle suspension properties altered drastically, which in turn triggered a Hysteresis Phenomenon. The Hysteresis Phenomenon on viscosity measurement, which is believed to be the first observed for Al2O3/water and TiO2/water-based nanofluids, has raised serious concerns about the use of nanofluids for heat transfer enhancement. The pressure drop and pumping power of the nanofluid flows are found to be very close to those of the base liquid for low volume concentration. It may be concluded that nanofluids can be utilized as a working medium with a negligible effect of enhanced viscosity and/or density. Our findings provide a view on the thermo physical properties of nanofluids that is compared with that in the literature, and new findings (such as viscosity, Hysteresis Phenomenon and pumping power) have been presented, which are not available in literature as yet.
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New thermophysical properties of water based TiO2 nanofluid—The Hysteresis Phenomenon revisited ☆
International Communications in Heat and Mass Transfer, 2014Co-Authors: Zafar Said, Rahman Saidur, Arif Hepbasli, Nasrudin Abdul RahimAbstract:Abstract Homogeneous stable suspensions acquired by dispersing dry Al2O3 and TiO2 nanoparticles in controlled pH solution and distilled water, respectively, were prepared and investigated in this study. First of all, the mean nanoparticle diameters were studied by dynamic light scattering (DLS) technique, and the nanofluid stability was analyzed by zeta potential measurements. The nano-crystalline structures were characterized by scanning electron microscope and transmission electron microscope. The rheological behavior was determined for both nanofluids at nanoparticle volume concentrations up to 0.3%. The effect of temperature for the heating and cooling phases was analyzed from 25 °C to 80 °C. Furthermore, the influence of temperature, pressure drop, pumping power, zeta potential, size and densities were analyzed for fresh prepared samples as well as for samples used in a flat plate solar collector over a period of 30 days. The thermal conductivity enhancement of the two nanofluids demonstrated a nonlinear relationship with respect to temperature and volume fraction, with increases in the volume fraction and temperature. All resulted in an increase in the measured enhancement. Existence of a critical temperature was observed beyond which the particle suspension properties altered drastically, which in turn triggered a Hysteresis Phenomenon. The Hysteresis Phenomenon on viscosity measurement, which is believed to be the first observed for Al2O3/water and TiO2/water-based nanofluids, has raised serious concerns about the use of nanofluids for heat transfer enhancement. The pressure drop and pumping power of the nanofluid flows are found to be very close to those of the base liquid for low volume concentration. It may be concluded that nanofluids can be utilized as a working medium with a negligible effect of enhanced viscosity and/or density. Our findings provide a view on the thermo physical properties of nanofluids that is compared with that in the literature, and new findings (such as viscosity, Hysteresis Phenomenon and pumping power) have been presented, which are not available in literature as yet.
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Viscosity data of al203/water and al2031 (eg/water) mixturenanofluids and the Hysteresis Phenomenon
2013Co-Authors: Zafar Said, M.h. Sajid, Alim, R SaidurAbstract:The effects of temperature and low particle volume concentration on the dynamic visosity of the Ah03/water and Ah03lEG/water-based nanofluids are investigated. Measurements of the nanofluid viscositres were accomplished using Brookfield viscometer (DV-II + Pro Programmable Viscometer) with a tempera~re controlled bath, supplied by Brookfield engineering laboratories of Malaysia. Viscosity of the stud led nanofluids are strongly depended on the Ah03 particle volume fractions in the base fluid. Data were collected for temperatures ranging from 25 to 80°C. The presence of aggregated Ah03 nanoparticles in the fluid, with average diameter of 109nm, which is -8 times the primary diameter (13nm) of Ah03 nanoparticles, have been confirmed by Dynamic Light Scattering (DLS) data. The results clearly showed the presence of a critical temperature, beyond which the particle suspension properties were noticed to be radically changed, which result in activating the Hysteresis Phenomenon. The Hysteresis Phenomenon on viscosity measurement, which IS believed to be the first observed for EG/water-based nanofluids, has raised serious concerns regarding the use of nanofluids for heat transfer enhancement purposes.
Fumitaka Tsukihashi - One of the best experts on this subject based on the ideXlab platform.
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Hysteresis Phenomenon and wetting characteristics of molten sn 3 0 wt ag 0 5 wt cu on different tilting substrates
Journal of Alloys and Compounds, 2009Co-Authors: Zhangfu Yuan, Hiroyuki Matsuura, Fumitaka TsukihashiAbstract:Abstract The Hysteresis Phenomenon and wetting characteristics of molten Sn–3.0 wt.%Ag–0.5 wt.%Cu on wetting and non-wetting tilting substrates at different temperatures were investigated. The viewpoint on negative interfacial tension was proposed in this paper to explain the spreading and wetting behaviors for sample on different tilted substrates. The critical sliding angle was defined as limited tilting angle of surface at which the molten drop slid down and the upper and lower contact angles of molten drop were measured as the advancing and receding contact angles, respectively. Wetting experiments were performed to determine how contact angle and contact Hysteresis on alumina and oxygen-free copper tilting substrates changed with temperature. Static, limited tilting, advancing and receding contact angles on two kinds of substrates were measured at different temperatures. In general, both negative interfacial tension and Hysteresis for sample on copper were much larger than that on alumina over the range of temperatures studied, indicating better wettability but worse motion characteristics for the former. It was due to the larger adhesion between solid and liquid than the cohesion of liquid, the negative interfacial tension and the acute contact angle.
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Hysteresis Phenomenon and wetting characteristics of molten Sn-3.0 wt.%Ag-0.5 wt.%Cu on different tilting substrates
Journal of Alloys and Compounds, 2009Co-Authors: Zhangfu Yuan, Hiroyuki Matsuura, Fumitaka TsukihashiAbstract:Abstract The Hysteresis Phenomenon and wetting characteristics of molten Sn–3.0 wt.%Ag–0.5 wt.%Cu on wetting and non-wetting tilting substrates at different temperatures were investigated. The viewpoint on negative interfacial tension was proposed in this paper to explain the spreading and wetting behaviors for sample on different tilted substrates. The critical sliding angle was defined as limited tilting angle of surface at which the molten drop slid down and the upper and lower contact angles of molten drop were measured as the advancing and receding contact angles, respectively. Wetting experiments were performed to determine how contact angle and contact Hysteresis on alumina and oxygen-free copper tilting substrates changed with temperature. Static, limited tilting, advancing and receding contact angles on two kinds of substrates were measured at different temperatures. In general, both negative interfacial tension and Hysteresis for sample on copper were much larger than that on alumina over the range of temperatures studied, indicating better wettability but worse motion characteristics for the former. It was due to the larger adhesion between solid and liquid than the cohesion of liquid, the negative interfacial tension and the acute contact angle.
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Hysteresis Phenomenon and wetting characteristics of molten Sn–3.0wt.%Ag–0.5wt.%Cu on different tilting substrates
Journal of Alloys and Compounds, 2009Co-Authors: Zhangfu Yuan, Hiroyuki Matsuura, Fumitaka TsukihashiAbstract:The Hysteresis Phenomenon and wetting characteristics of molten Sn-3.0 wt.%Ag-0.5 wt.%Cu on wetting and non-wetting tilting substrates at different temperatures were investigated. The viewpoint on negative interfacial tension was proposed in this paper to explain the spreading and wetting behaviors for sample on different tilted substrates. The critical sliding angle was defined as limited tilting angle of surface at which the molten drop slid down and the upper and lower contact angles of molten drop were measured as the advancing and receding contact angles, respectively. Wetting experiments were performed to determine how contact angle and contact Hysteresis on alumina and oxygen-free copper tilting substrates changed with temperature. Static, limited tilting, advancing and receding contact angles on two kinds of substrates were measured at different temperatures. In general, both negative interfacial tension and Hysteresis for sample on copper were much larger than that on alumina over the range of temperatures studied, indicating better wettability but worse motion characteristics for the former. It was due to the larger adhesion between solid and liquid than the cohesion of liquid, the negative interfacial tension and the acute contact angle. (C) 2009 Elsevier B.V. All rights reserved
Zhangfu Yuan - One of the best experts on this subject based on the ideXlab platform.
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Hysteresis Phenomenon and wetting characteristics of molten sn 3 0 wt ag 0 5 wt cu on different tilting substrates
Journal of Alloys and Compounds, 2009Co-Authors: Zhangfu Yuan, Hiroyuki Matsuura, Fumitaka TsukihashiAbstract:Abstract The Hysteresis Phenomenon and wetting characteristics of molten Sn–3.0 wt.%Ag–0.5 wt.%Cu on wetting and non-wetting tilting substrates at different temperatures were investigated. The viewpoint on negative interfacial tension was proposed in this paper to explain the spreading and wetting behaviors for sample on different tilted substrates. The critical sliding angle was defined as limited tilting angle of surface at which the molten drop slid down and the upper and lower contact angles of molten drop were measured as the advancing and receding contact angles, respectively. Wetting experiments were performed to determine how contact angle and contact Hysteresis on alumina and oxygen-free copper tilting substrates changed with temperature. Static, limited tilting, advancing and receding contact angles on two kinds of substrates were measured at different temperatures. In general, both negative interfacial tension and Hysteresis for sample on copper were much larger than that on alumina over the range of temperatures studied, indicating better wettability but worse motion characteristics for the former. It was due to the larger adhesion between solid and liquid than the cohesion of liquid, the negative interfacial tension and the acute contact angle.
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Hysteresis Phenomenon and wetting characteristics of molten Sn-3.0 wt.%Ag-0.5 wt.%Cu on different tilting substrates
Journal of Alloys and Compounds, 2009Co-Authors: Zhangfu Yuan, Hiroyuki Matsuura, Fumitaka TsukihashiAbstract:Abstract The Hysteresis Phenomenon and wetting characteristics of molten Sn–3.0 wt.%Ag–0.5 wt.%Cu on wetting and non-wetting tilting substrates at different temperatures were investigated. The viewpoint on negative interfacial tension was proposed in this paper to explain the spreading and wetting behaviors for sample on different tilted substrates. The critical sliding angle was defined as limited tilting angle of surface at which the molten drop slid down and the upper and lower contact angles of molten drop were measured as the advancing and receding contact angles, respectively. Wetting experiments were performed to determine how contact angle and contact Hysteresis on alumina and oxygen-free copper tilting substrates changed with temperature. Static, limited tilting, advancing and receding contact angles on two kinds of substrates were measured at different temperatures. In general, both negative interfacial tension and Hysteresis for sample on copper were much larger than that on alumina over the range of temperatures studied, indicating better wettability but worse motion characteristics for the former. It was due to the larger adhesion between solid and liquid than the cohesion of liquid, the negative interfacial tension and the acute contact angle.
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Hysteresis Phenomenon and wetting characteristics of molten Sn–3.0wt.%Ag–0.5wt.%Cu on different tilting substrates
Journal of Alloys and Compounds, 2009Co-Authors: Zhangfu Yuan, Hiroyuki Matsuura, Fumitaka TsukihashiAbstract:The Hysteresis Phenomenon and wetting characteristics of molten Sn-3.0 wt.%Ag-0.5 wt.%Cu on wetting and non-wetting tilting substrates at different temperatures were investigated. The viewpoint on negative interfacial tension was proposed in this paper to explain the spreading and wetting behaviors for sample on different tilted substrates. The critical sliding angle was defined as limited tilting angle of surface at which the molten drop slid down and the upper and lower contact angles of molten drop were measured as the advancing and receding contact angles, respectively. Wetting experiments were performed to determine how contact angle and contact Hysteresis on alumina and oxygen-free copper tilting substrates changed with temperature. Static, limited tilting, advancing and receding contact angles on two kinds of substrates were measured at different temperatures. In general, both negative interfacial tension and Hysteresis for sample on copper were much larger than that on alumina over the range of temperatures studied, indicating better wettability but worse motion characteristics for the former. It was due to the larger adhesion between solid and liquid than the cohesion of liquid, the negative interfacial tension and the acute contact angle. (C) 2009 Elsevier B.V. All rights reserved
Sébastien Candel - One of the best experts on this subject based on the ideXlab platform.
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A Hysteresis Phenomenon leading to spinning or standing azimuthal instabilities in an annular combustor
Combustion and Flame, 2017Co-Authors: Kevin Prieur, Thierry Schuller, D. Durox, Sébastien CandelAbstract:Thermo-acoustic instabilities in annular combustors equipped with swirling turbulent injectors are most often coupled by azimuthal modes with a spinning or a standing structure. Experiments, and recent large eddy simulations, indicate that switching takes place between these two types of modes while in other cases a single mode type prevails. Why and how one type arises is a subject of ongoing discussions in recent theoretical and numerical investigations. The present article considers this intriguing issue by malting use of well controlled experiments carried out in an annular combustion system comprising 16 identical matrix injectors operating in a laminar premixed mode and allowing full optical access to the flame region. This setup is used in a first stage to determine regions of instability as a function of equivalence ratio and injection velocity. It is shown that regions corresponding to spinning and standing azimuthal modes are well separated in this diagram, but with some overlap giving rise to a "dual mode" domain. For the same operating conditions, this annular system thus exhibits self-sustained instabilities with stable limit cycles coupled by a spinning or a standing mode. It is next shown that the mode which appears in that region depends on the path followed to reach the operating point. Starting from a lean operating condition, the system first develops a chugging instability with a broad frequency spectrum, which then gives rise to a well-established spinning oscillation with a narrow peak frequency in the dual mode region. When operation begins under rich conditions one first observes another chugging mode that finally yields a standing mode when the equivalence ratio is diminished. Away from these regimes, well defined slanted modes and longitudinal modes can also be triggered. In the dual mode region, the type of instability is controlled by an Hysteresis Phenomenon and the respective chugging modes act as precursors to these established azimuthal modes. It is found that the trajectories in a state space map contain indications on the kind of azimuthal oscillation that will be observed when the target operating point is reached. Beyond the various theoretical explanations of the prevalence of one type of mode on the other, the present observations indicate that spinning or standing modes may also appear in annular combustors as a result of the path used to enter the region of azimuthal instability. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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A Hysteresis Phenomenon leading to spinning or standing azimuthal instabilities in an annular combustor
Combustion and Flame, 2017Co-Authors: Kevin Prieur, Thierry Schuller, D. Durox, Sébastien CandelAbstract:Abstract Thermo-acoustic instabilities in annular combustors equipped with swirling turbulent injectors are most often coupled by azimuthal modes with a spinning or a standing structure. Experiments, and recent large eddy simulations, indicate that switching takes place between these two types of modes while in other cases a single mode type prevails. Why and how one type arises is a subject of ongoing discussions in recent theoretical and numerical investigations. The present article considers this intriguing issue by making use of well controlled experiments carried out in an annular combustion system comprising 16 identical matrix injectors operating in a laminar premixed mode and allowing full optical access to the flame region. This setup is used in a first stage to determine regions of instability as a function of equivalence ratio and injection velocity. It is shown that regions corresponding to spinning and standing azimuthal modes are well separated in this diagram, but with some overlap giving rise to a “dual mode” domain. For the same operating conditions, this annular system thus exhibits self-sustained instabilities with stable limit cycles coupled by a spinning or a standing mode. It is next shown that the mode which appears in that region depends on the path followed to reach the operating point. Starting from a lean operating condition, the system first develops a chugging instability with a broad frequency spectrum, which then gives rise to a well-established spinning oscillation with a narrow peak frequency in the dual mode region. When operation begins under rich conditions one first observes another chugging mode that finally yields a standing mode when the equivalence ratio is diminished. Away from these regimes, well defined slanted modes and longitudinal modes can also be triggered. In the dual mode region, the type of instability is controlled by an Hysteresis Phenomenon and the respective chugging modes act as precursors to these established azimuthal modes. It is found that the trajectories in a state space map contain indications on the kind of azimuthal oscillation that will be observed when the target operating point is reached. Beyond the various theoretical explanations of the prevalence of one type of mode on the other, the present observations indicate that spinning or standing modes may also appear in annular combustors as a result of the path used to enter the region of azimuthal instability.
Nasrudin Abdul Rahim - One of the best experts on this subject based on the ideXlab platform.
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Rheological behaviour and the Hysteresis Phenomenon of Al2O3 nanofluids
Materials Research Innovations, 2014Co-Authors: Zafar Said, M.h. Sajid, Rahman Saidur, Nasrudin Abdul Rahim, M.h.u. BhuiyanAbstract:The effects of temperature and low-volume concentration on the dynamic viscosity of the Al2O3/water and Al2O3/ethylene glycol/water nanofluids are investigated. Nanofluids were prepared and characterised. Data were collected for temperatures ranging from 25 to 80°C. The presence of aggregated Al2O3 nanoparticles in the fluid, with average diameter of 109 nm which is ∼8 times the primary diameter (13 nm) of Al2O3 nanoparticles was witnessed. Furthermore, only at temperature below 40°C water-based alumina nanofluid at 0·05% v/v showed Newtonian behaviour. On the other hand, Al2O3/ethylene glycol/water mixture exhibited Newtonian behaviour. Results clearly showed the presence of a critical temperature, beyond which the particle suspension properties were noticed to be radically changed, which results in activating the Hysteresis Phenomenon. The Hysteresis Phenomenon on viscosity measurement, which is believed to be the first observed for ethylene glycol/water-based nanofluids, has raised serious concerns reg...
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New thermophysical properties of water based TiO2 nanofluid—The Hysteresis Phenomenon revisited ☆
International Communications in Heat and Mass Transfer, 2014Co-Authors: Zafar Said, Rahman Saidur, Arif Hepbasli, Nasrudin Abdul RahimAbstract:Abstract Homogeneous stable suspensions acquired by dispersing dry Al2O3 and TiO2 nanoparticles in controlled pH solution and distilled water, respectively, were prepared and investigated in this study. First of all, the mean nanoparticle diameters were studied by dynamic light scattering (DLS) technique, and the nanofluid stability was analyzed by zeta potential measurements. The nano-crystalline structures were characterized by scanning electron microscope and transmission electron microscope. The rheological behavior was determined for both nanofluids at nanoparticle volume concentrations up to 0.3%. The effect of temperature for the heating and cooling phases was analyzed from 25 °C to 80 °C. Furthermore, the influence of temperature, pressure drop, pumping power, zeta potential, size and densities were analyzed for fresh prepared samples as well as for samples used in a flat plate solar collector over a period of 30 days. The thermal conductivity enhancement of the two nanofluids demonstrated a nonlinear relationship with respect to temperature and volume fraction, with increases in the volume fraction and temperature. All resulted in an increase in the measured enhancement. Existence of a critical temperature was observed beyond which the particle suspension properties altered drastically, which in turn triggered a Hysteresis Phenomenon. The Hysteresis Phenomenon on viscosity measurement, which is believed to be the first observed for Al2O3/water and TiO2/water-based nanofluids, has raised serious concerns about the use of nanofluids for heat transfer enhancement. The pressure drop and pumping power of the nanofluid flows are found to be very close to those of the base liquid for low volume concentration. It may be concluded that nanofluids can be utilized as a working medium with a negligible effect of enhanced viscosity and/or density. Our findings provide a view on the thermo physical properties of nanofluids that is compared with that in the literature, and new findings (such as viscosity, Hysteresis Phenomenon and pumping power) have been presented, which are not available in literature as yet.