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Author: Publisher: ISBN: Category : Languages : en Pages : 126
Book Description
In this report, we studied the local phasic characters of dispersed flow regime both at the entrance and at the fully developed regions. Since the dispersed phase is distributed randomly in the medium and enclosed in relatively small interfaces, the phasic measurement becomes difficult to obtain. Local probe must be made with a miniaturized sensor in order to reduce the interface distortion. The double-sensor resistivity probe has been widely used in local void fraction and interface velocity measurements because the are small in comparison with the interfaces. It has been tested and proved to be an accurate local phasic measurement tool. In these experiments, a double-sensor probe was employed to measure the local void fraction and interface velocity in an air-water system. The test section was flow regime can be determined by visualization. Furthermore, local phasic measurements can be verified by photographic studies. We concentrated our study on the bubbly flow regime only. The local measurements were conducted at two axial locations, L/D = 8 and 60, in which the first measurement represents the entrance region where the flow develops, and the second measurement represents the fully developed flow region where the radial profile does not change as the flow moves along the axial direction. Four liquid flow rates were chosen in combination with four different gas injection rates. The superficial liquid velocities were j{sub t} = 1.0, 0.6,0.4, and 0.1 m/s and superficial gas velocities were j{sub g} = 0.0965, 0.0696, 0.0384, and 0.0192 m/s. These combinations put the two-phase flow well in the bubbly flow regime. In this sequence of phenomenological studies, the local void fraction, interface area concentration, sauter mean diameter, bubble velocity and bubble frequency were measured.
Author: Publisher: ISBN: Category : Languages : en Pages : 126
Book Description
In this report, we studied the local phasic characters of dispersed flow regime both at the entrance and at the fully developed regions. Since the dispersed phase is distributed randomly in the medium and enclosed in relatively small interfaces, the phasic measurement becomes difficult to obtain. Local probe must be made with a miniaturized sensor in order to reduce the interface distortion. The double-sensor resistivity probe has been widely used in local void fraction and interface velocity measurements because the are small in comparison with the interfaces. It has been tested and proved to be an accurate local phasic measurement tool. In these experiments, a double-sensor probe was employed to measure the local void fraction and interface velocity in an air-water system. The test section was flow regime can be determined by visualization. Furthermore, local phasic measurements can be verified by photographic studies. We concentrated our study on the bubbly flow regime only. The local measurements were conducted at two axial locations, L/D = 8 and 60, in which the first measurement represents the entrance region where the flow develops, and the second measurement represents the fully developed flow region where the radial profile does not change as the flow moves along the axial direction. Four liquid flow rates were chosen in combination with four different gas injection rates. The superficial liquid velocities were j{sub t} = 1.0, 0.6,0.4, and 0.1 m/s and superficial gas velocities were j{sub g} = 0.0965, 0.0696, 0.0384, and 0.0192 m/s. These combinations put the two-phase flow well in the bubbly flow regime. In this sequence of phenomenological studies, the local void fraction, interface area concentration, sauter mean diameter, bubble velocity and bubble frequency were measured.
Author: Publisher: ISBN: Category : Languages : en Pages : 121
Book Description
The interfacial transfer terms and the importance of the interfacial area concentration are reviewed first with respect to the two-fluid model formulation of two-phase flow systems. Then the available measurement techniques for interfacial area are reviewed. At present, it appears that various methods such as the chemical, light attenuation, photographic, ultrasound attenuation and probe techniques have a number of limitations. Among these measurement techniques, however, the local probe method using one or more double sensors seems to have the greatest potential in terns of accuracy and wider applicability in various two-phase flow patterns. From the brief review of existing interfacial area modeling methods, it is concluded that the conventional approaches might not be sufficient, and new directions are indicated. Recent experimental results on local interfacial structural characteristics of horizontal bubbly two-phase flow and internal flow structure development are presented. More specifically, experimental results on local void fraction, interfacial area concentration, bubble size, bubble interface velocity and bubble frequency are documented in detail. Finally, a theoretical model predicting the mean bubble size and interfacial area concentration is proposed. The theoretically predicted bubble size and interfacial area concentration are found to agree reasonably well with those measured by using a double-sensor resistivity technique.
Author: Mohan Singh Yadav Publisher: ISBN: Category : Languages : en Pages : 193
Book Description
This study investigates the geometric effects of flow restrictions and flow configurations on two-phase flow parameters. Experiments are conducted in two distinct experimental setups employing different flow configurations and flow restrictions. In the first experiment, comparison of the effects of 90-degree and 45-degree elbows on interfacial structures and their transport characteristics in horizontal two-phase bubbly flow is investigated. The setup is made out of 50.3 mm inner diameter glass tubes and a double-sensor conductivity probe is used to collect time averaged local data. Experimental results show that both elbows have significant effect on the development of interfacial structures as well as the bubble interaction mechanisms. Furthermore, there are characteristic similarities and differences between the effects of two elbows. While the effect of the 45-degree elbow is evident immediately after the elbow, the 90-degree elbow effect is propagated further downstream of the elbow. Moreover, it is shown that both the elbows induce oscillations in the interfacial structures and two-phase flow parameters, but the degree and the nature of oscillation differ. Comparison of the elbow effect on the axial transport of two-phase flow parameters is also investigated. The second set of experiments is performed in combinatorial two-phase flow facility to study the effects of 90-degree vertical elbow and geometric configuration on two-phase bubbly flow. The elbow has a significant effect on two-phase flow regime transition boundaries at measurement locations downstream of the elbow. Modified two-phase flow regime maps based on the extensive flow visualization studies are suggested for both vertical and horizontal test sections. A four-sensor conductivity probe is employed to measure time averaged two-phase local parameters as the flow develops along vertical upward to horizontal section across the 90-degree vertical elbow. The elbow causes the bubbles to align along the horizontal radius of the pipe cross-section, creating a bi-peaked profile in void fraction and interfacial area concentration. One dimensional transport of area averaged two-phase flow parameters shows that the elbow promotes bubble interaction mechanism.
Author: Kent C. Abel Publisher: ISBN: Category : Two-phase flow Languages : en Pages : 232
Book Description
The next generation of nuclear safety analysis computer codes will include detailed modeling of the interfacial area concentration. The interfacial area concentration is the essence of the two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links the two phases together with six conservation equations. The interfacial area concentration, along with a driving potential, determines the energy, momentum and mass transfer between the two phases. The importance of this research lies in obtaining a greater understanding of the developing nature of two-phase flows and the application of the two-fluid model. With proper characterization of two-phase flow, the next generation of nuclear safety analysis computer codes will be able to incorporate this information to predict parameters during an accident scenario with greater precision. This research will provide a first order look into the developing nature of two-phase flow. As part of this research, the development of two-phase flow in a vertical column was analyzed using double sensor impedance probes. The resident vapor and liquid times were recorded along with the velocity of the vapor phase. By creating distributions of the bubble residence times, liquid residence times, velocities, and sizes, one can characterize the developing nature of the two-phase flow. Data was taken at four different axial locations for six different flow rates. The resulting data show clear trends in how the standard deviation and mean values for the measured parameters change as a function of flow rate and axial position. The void fraction contribution from the spherical/distorted bubble group as well as the cap/slug bubble group was also recorded to determine the net transfer rate of vapor between the two bubble groups. Interfacial area concentration was not included in the measurement since the probes that were used can only determine interfacial area concentration for spherical bubbles. Further research will be conducted with the inclusion of interfacial area concentration at a later time.
Author: A. Serizawa Publisher: Newnes ISBN: 0444600124 Category : Technology & Engineering Languages : en Pages : 820
Book Description
There is increasing world-wide interest in obtaining an understanding of various multiphase flow phenomena and problems in terms of a common language of multiphase flow. This volume contains state-of-the-art papers which have been contributed from all over the world by experts working on all aspects of multiphase flows. The volume also highlights international technology-sharing in the fields of energy, environment and public health, in order to create a brighter and sustainable future for man and for all life in the next century. It is intended that this volume will serve as a major source of literature for the advancement of multiphase flow and allied fields.
Author: Publisher: ISBN: Category : Languages : en Pages : 16
Book Description
Kataoka, Ishii and Serizawa analyzed the measurements of the local time-averaged interfacial area concentration in two-phase flow with a two-point conductivity probe. They considered the influence of the bubble velocity fluctuation on the measurement and directly transferred the mathematics concept of the local time-averaged interfacial area concentration into the measurable parameters. In the end of the derivation, however, the expression of the interfacial area concentration was inappropriate due to the over-simplification to the integration limits of the probability distributions. Consequently, the resultant interfacial area concentration may be significantly lower than the actual value. Since the formula is very important for the interpretation of experimental data, we feel it is necessary to provide a correction to the original work.
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Author: Mohan Singh Yadav
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Author: Kent C. Abel
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