The Experts below are selected from a list of 11367 Experts worldwide ranked by ideXlab platform
Yassin A Hassan - One of the best experts on this subject based on the ideXlab platform.
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experimental study on bubble dynamics and wall heat transfer arising from a single Nucleation Site at subcooled flow boiling conditions part 1 experimental methods and data quality verification
International Journal of Multiphase Flow, 2016Co-Authors: Carlos E Estradaperez, Yassin A HassanAbstract:Abstract A novel experimental method and data acquisition/analysis strategy that ensures reliable measurements of various subcooled flow boiling parameters is discussed. In this study, all experiments were performed by keeping a single active Nucleation Site within the entire heated area in a square upward flow channel. This approach greatly facilitated the observation of bubble and wall heat transfer features in subcooled boiling flow. Vapor bubbles originating from the Nucleation Site were observed with both micro- and macroscopic views from high-speed cameras while corresponding wall temperature was measured by an infrared camera. This allowed simultaneously capturing various bubbles characteristics with multiple scales (both space and time) as well as their impact on wall heat transfer. In addition, efforts were made to characterize the observed boiling behavior with high statistical accuracy by analyzing numerous images taken at each test condition. This study proves that by taking the current strategy excellent repeatability and thus reliability can be achieved for a wide range of flow boiling parameters such as bubble size, bubble velocity, statistical distribution of bubble size and time-averaged wall heat transfer coefficients. Also, the major sources of uncertainty for each measurement are thoroughly investigated, from which the final uncertainties are determined. Overall, the present study suggests what we must concern to achieve truly reliable and useful data from any boiling experiments.
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experimental study on bubble dynamics and wall heat transfer arising from a single Nucleation Site at subcooled flow boiling conditions part 2 data analysis on sliding bubble characteristics and associated wall heat transfer
International Journal of Multiphase Flow, 2016Co-Authors: Carlos E Estradaperez, Yassin A HassanAbstract:This second of two companion papers presents an analysis of sliding bubble and wall heat transfer parameters measured during subcooled boiling in a square, vertical, upward flow channel. Bubbles were generated only from a single Nucleation Site for better observation of both the sliding bubble characteristics and their impact on wall heat transfer through optical measurement techniques. Specific interests include: (i) bubbles departure and subsequent growth while sliding, (ii) bubbles release frequency, (iii) coalescence of sliding bubbles, (iv) sliding bubbles velocity, (v) bubbles size distribution and (vi) wall heat transfer influenced by sliding bubbles. The results showed that sliding bubbles involve two distinct growth behaviors: (i) at low mass fluxes, sliding bubbles grew fast near the Nucleation Site, subsequently shrank, and then grew again, (ii) as mass flux increased, however, sliding bubbles grew more steadily. The bubbles originating from the single Nucleation Site coalesced frequently while sliding, which showed close relation with bubbles release frequency. The sliding bubble velocity near the Nucleation Site consistently decreased by increasing mass flux, while the observation often became reversed as the bubbles slid downstream due to the effect of interfacial drag. The sliding bubbles moved faster than the local liquid (i.e., ur < 0) at low mass flux conditions, but it became reversed as the mass flux increased. The size distribution of sliding bubbles followed Gaussian distribution well both near and far from the Nucleation Site. The standard deviation of bubble size varied insignificantly through sliding compared to the changes in mean bubble size. Lastly, the sliding bubbles enhanced the wall heat transfer and the effect became more noticeable as inlet subcooling/mass flux decreased or wall heat flux increased. In particular, the sliding bubble characteristics such as bubble growth behavior observed near the Nucleation Site played a dominant role in determining the ultimate level of wall heat transfer enhancement within the test channel.
Carlos E Estradaperez - One of the best experts on this subject based on the ideXlab platform.
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experimental study on bubble dynamics and wall heat transfer arising from a single Nucleation Site at subcooled flow boiling conditions part 1 experimental methods and data quality verification
International Journal of Multiphase Flow, 2016Co-Authors: Carlos E Estradaperez, Yassin A HassanAbstract:Abstract A novel experimental method and data acquisition/analysis strategy that ensures reliable measurements of various subcooled flow boiling parameters is discussed. In this study, all experiments were performed by keeping a single active Nucleation Site within the entire heated area in a square upward flow channel. This approach greatly facilitated the observation of bubble and wall heat transfer features in subcooled boiling flow. Vapor bubbles originating from the Nucleation Site were observed with both micro- and macroscopic views from high-speed cameras while corresponding wall temperature was measured by an infrared camera. This allowed simultaneously capturing various bubbles characteristics with multiple scales (both space and time) as well as their impact on wall heat transfer. In addition, efforts were made to characterize the observed boiling behavior with high statistical accuracy by analyzing numerous images taken at each test condition. This study proves that by taking the current strategy excellent repeatability and thus reliability can be achieved for a wide range of flow boiling parameters such as bubble size, bubble velocity, statistical distribution of bubble size and time-averaged wall heat transfer coefficients. Also, the major sources of uncertainty for each measurement are thoroughly investigated, from which the final uncertainties are determined. Overall, the present study suggests what we must concern to achieve truly reliable and useful data from any boiling experiments.
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experimental study on bubble dynamics and wall heat transfer arising from a single Nucleation Site at subcooled flow boiling conditions part 2 data analysis on sliding bubble characteristics and associated wall heat transfer
International Journal of Multiphase Flow, 2016Co-Authors: Carlos E Estradaperez, Yassin A HassanAbstract:This second of two companion papers presents an analysis of sliding bubble and wall heat transfer parameters measured during subcooled boiling in a square, vertical, upward flow channel. Bubbles were generated only from a single Nucleation Site for better observation of both the sliding bubble characteristics and their impact on wall heat transfer through optical measurement techniques. Specific interests include: (i) bubbles departure and subsequent growth while sliding, (ii) bubbles release frequency, (iii) coalescence of sliding bubbles, (iv) sliding bubbles velocity, (v) bubbles size distribution and (vi) wall heat transfer influenced by sliding bubbles. The results showed that sliding bubbles involve two distinct growth behaviors: (i) at low mass fluxes, sliding bubbles grew fast near the Nucleation Site, subsequently shrank, and then grew again, (ii) as mass flux increased, however, sliding bubbles grew more steadily. The bubbles originating from the single Nucleation Site coalesced frequently while sliding, which showed close relation with bubbles release frequency. The sliding bubble velocity near the Nucleation Site consistently decreased by increasing mass flux, while the observation often became reversed as the bubbles slid downstream due to the effect of interfacial drag. The sliding bubbles moved faster than the local liquid (i.e., ur < 0) at low mass flux conditions, but it became reversed as the mass flux increased. The size distribution of sliding bubbles followed Gaussian distribution well both near and far from the Nucleation Site. The standard deviation of bubble size varied insignificantly through sliding compared to the changes in mean bubble size. Lastly, the sliding bubbles enhanced the wall heat transfer and the effect became more noticeable as inlet subcooling/mass flux decreased or wall heat flux increased. In particular, the sliding bubble characteristics such as bubble growth behavior observed near the Nucleation Site played a dominant role in determining the ultimate level of wall heat transfer enhancement within the test channel.
Zhongqin Lin - One of the best experts on this subject based on the ideXlab platform.
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a model for strain induced martensitic transformation of trip steel with strain rate
Computational Materials Science, 2007Co-Authors: W J Dan, W.g. Zhang, Zhongqin LinAbstract:Pre-strain is one of the key factors which can influence metal sheet mechanical properties during material multi-step deformation process. In this study, a constitutive model, which can describe the transformation-induced plasticity (TRIP) accompanying the strain-induced martensitic transformation in TRIP steel under pre-strain, is developed. The increase of Nucleation Site in the austenite due to the plastic deformation is formulated as the increase of the shear-band intersection. The Nucleation Site probability and shear-band intersection are derived not only by stress state, plasticity strain and temperature, but also by pre-strain to simulate the transformation-induced plasticity characteristic for TRIP steel. Anisotropic yield function is used to describe the sheet anisotropic property. A mixture hardening law, which is based on the pre-strain, with four phases is developed. The constitutive model is implemented into ABAQUS/UMAT to analyze the material deforming processes. Mixture hardening law of four phases with pre-strain is verified by experiment. The martensitic volume fraction is tested by X-ray to describe the comparison between experiment data and simulation. All the results are agreeable.
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a model for strain induced martensitic transformation of trip steel with pre strain
Computational Materials Science, 2007Co-Authors: W J Dan, W Zhang, Zhongqin LinAbstract:Pre-strain is one of the key factors which can influence metal sheet mechanical properties during material multi-step deformation process. In this study, a constitutive model, which can describe the transformation-induced plasticity (TRIP) accompanying the strain-induced martensitic transformation in TRIP steel under pre-strain, is developed. The increase of Nucleation Site in the austenite due to the plastic deformation is formulated as the increase of the shear-band intersection. The Nucleation Site probability and shear-band intersection are derived not only by stress state, plasticity strain and temperature, but also by pre-strain to simulate the transformation-induced plasticity characteristic for TRIP steel. Anisotropic yield function is used to describe the sheet anisotropic property. A mixture hardening law, which is based on the pre-strain, with four phases is developed. The constitutive model is implemented into ABAQUS/UMAT to analyze the material deforming processes. Mixture hardening law of four phases with pre-strain is verified by experiment. The martensitic volume fraction is tested by X-ray to describe the comparison between experiment data and simulation. All the results are agreeable.
J. T. Wang - One of the best experts on this subject based on the ideXlab platform.
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negative temperature dependence of recrystallized grain size formulation and experimental confirmation on copper
Materials, 2017Co-Authors: Mohamed Elmasry, Y Jiang, J. T. WangAbstract:The catalyzing effect on Nucleation of recrystallization from existing grains resulting from previous lower temperature deformation is analyzed, analogous to the size effect of foreign nucleus in heterogeneous Nucleation. Analytical formulation of the effective Nucleation Site for recrystallization leads to a negative temperature dependence of recrystallized grain size of metals. Non-isochronal annealing—where annealing time is set just enough for the completion of recrystallization at different temperatures—is conducted on pure copper after severe plastic deformation. More homogeneous and smaller grains are obtained at higher annealing temperature. The good fit between analytical and experimental results unveils the intrinsic feature of this negative temperature dependence of recrystallized grain size.
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negative temperature dependence of recrystallized grain size analytical formulation and experimental confirmation
IOP Conference Series: Materials Science and Engineering, 2017Co-Authors: Mohamed Elmasry, Y Jiang, J. T. WangAbstract:The catalyzing effect on Nucleation of recrystallization from pre-existing grains is analyzed, analogy to the foreign nucleus size effect in heterogeneous Nucleation. Analytical formulation of the effective Nucleation Site for recrystallization leads to a negative temperature dependence of recrystallized grain size. Non-isochronal annealing, where annealing time is set just enough for the completion of recrystallization at different temperature, is conducted on pure copper after severe plastic deformation. More homogeneous and smaller grains are obtained at higher annealing temperature. The good fitting between analytical and experimental results unveils the intrinsic feature of this negative temperature dependence of recrystallized grain size.
Masao Iwamatsu - One of the best experts on this subject based on the ideXlab platform.
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Line-tension effects on heterogeneous Nucleation on a spherical substrate and in a spherical cavity.
Langmuir, 2015Co-Authors: Masao IwamatsuAbstract:The line-tension effects on heterogeneous Nucleation are considered when a spherical lens-shaped nucleus is nucleated on top of a spherical substrate and on the bottom of the wall of a spherical cavity. The effect of line tension on the Nucleation barrier can be separated from the usual volume term. As the radius of the substrate increases, the Nucleation barrier decreases and approaches that of a flat substrate. However, as the radius of the cavity increases, the Nucleation barrier increases and approaches that of a flat substrate. A small spherical substrate is a less active Nucleation Site than a flat substrate, and a small spherical cavity is a more active Nucleation Site than a flat substrate. In contrast, the line-tension effect on the Nucleation barrier is maximum when the radii of the nucleus and the substrate or cavity become comparable. Therefore, by tuning the size of the spherical substrate or spherical cavity, the effect of the line tension can be optimized. These results will be useful in br...
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Line-tension effects on heterogeneous Nucleation on a spherical substrate and in a spherical cavity
arXiv: Soft Condensed Matter, 2015Co-Authors: Masao IwamatsuAbstract:The line-tension effects on heterogeneous Nucleation are considered when a spherical lens-shaped nucleus is nucleated on top of a spherical substrate and on the bottom of the wall of a spherical cavity. The effect of line tension on the Nucleation barrier can be separated from the usual volume term. As the radius of the substrate increases, the Nucleation barrier decreases and approaches that of a flat substrate. However, as the radius of the cavity increases, the Nucleation barrier increases and approaches that of a flat substrate. A small spherical substrate is a less active Nucleation Site than a flat substrate, and a small spherical cavity is a more active Nucleation Site than a flat substrate. In contrast, the line-tension effect on the Nucleation barrier is maximum when the radii of the nucleus and the substrate or cavity become comparable. Therefore, by tuning the size of the spherical substrate or spherical cavity, the effect of the line tension can be optimized. These results will be useful in broad range of applications from material processing to understanding of global climate, where the heterogeneous Nucleation plays a vital role.
