Measurements Of Interfacial Area Concentration In Two Phase Flow With Two Point Conductivity Probe Brief Communication
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| Total Pages | : 16 |
| Release | : 1997 |
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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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| Release | : 2001 |
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Interfacial area concentration is an important parameter in the two-fluid model for two-phase flow analysis, which is defined as the total interface area per unit mixture volume and has the following local time-averaged expression:[bar a][sup t]= 1/[Delta]T[Sigma][sub j](1/[vert-bar]V[sub i][center-dot] n[sub i][vert-bar])[sub j], where j denotes the j-th interface that passes the point of interest in a time interval[Delta]T. V[sub i] and n[sub i] refer to the bubble interface velocity and surface normal vector, respectively. To measure this parameter, the double-sensor probe technique is commonly used. Due to the influences of the bubble lateral motions, however, the measurement results should be interpreted via a certain statistic approach. Recently, to take into account the effects of the probe spacing, Wu and Ishii provided the following new formula to correlate the measurable values to the interfacial area concentration:[bar a][sub i][sup t]= 2N[sub b]/[Delta]T ([Delta][bar t]/[Delta]s)[2+ (1.2[sigma][sub[Delta]t]/[Delta][bar t])[sup 2.25]], for D= 1.2[approximately] 2.8[Delta]s, where N[sub b] refers to the number of the bubbles that hit the probe front tip during time interval[Delta]T, [Delta]s denotes the distance between the two probe tips, D is the bubble diameter, [Delta][bar t] represents the measured average time interval for an interface to travel through the two probe tips, and[sigma][sub[Delta]t] is the standard deviation of[Delta]t. The theoretical accuracy of this formula is within[+-] 5% if the sample size is sufficiently large. The purpose of this study is to evaluate this method experimentally using an image processing method.
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| Total Pages | : 126 |
| Release | : 1992 |
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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 | : Isao Kataoka |
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| Total Pages | : 58 |
| Release | : 1984 |
| Genre | : Fluid mechanics |
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| Author | : Kent C. Abel |
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| Total Pages | : 232 |
| Release | : 2002 |
| Genre | : Two-phase flow |
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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.
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| Total Pages | : 121 |
| Release | : 1991 |
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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 | : David M. McCreary |
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| Total Pages | : 116 |
| Release | : 2000 |
| Genre | : Two-phase flow |
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This thesis examines two techniques for measuring two-phase flow parameters in an air/water system using intrusive conductivity probes. Specifically, the theoretical derivation for measuring void fraction and interfacial area using a two-sensor needle-type probe is derived, and a statistical analysis of the accuracy using the two-sensor probe for measuring interfacial area will be determined from a comprehensive literature review. The second technique used to measure void fraction in air/water flows is with a half-ring type conductivity probe. This half-ring type probe measures an area-averaged void fraction, while the needle-type probe measures local two-phase parameters. A single-sensor needle-type probe is used to experimentally measure void fraction in a test section, and is then benchmarked with another instrument as well as the drift-flux model. The half-ring type probe is then cross-calibrated with the needle-type probe. A complete system for measurement of local void fraction in an air/water two-phase mixture using two measurement techniques is presented. A detailed design procedure for a single-sensor conductivity probe as well as a half-ring type probe, and the corresponding circuits to power them are discussed. The two techniques discussed are accurate, simple, reliable, and inexpensive.
| Author | : Matthew Bernard |
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| Release | : 2014 |
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Correctly predicting the interfacial area concentration is vital to the overall accuracy of the two-fluid model because the interfacial area concentration describes the amount of surface area that exists between the two-phases, and is therefore directly related to interfacial mass, momentum and energy transfer. The conventional method for specifying the interfacial area concentration in the two-fluid model is through flow regime-based empirical correlations coupled with regime transition criteria. However, a more physically consistent approach to predicting the interfaciala area concentration is through the interfacial area transport equation (IATE), which can address the deficiencies of the flow regime-based approach. Some previous studies have been performed to demonstrate the feasibility of IATE in developmental versions of the nuclear reactor systems analysis code, TRACE. However, a full TRACE version capable of predicting boiling two-phase flows with the IATE has not been established.Therefore, the current work develops a version of TRACE that is capable of predicting boiling two-phase flows using the IATE. The development is carried out in stages. First, a version of TRACE which employs the two-group IATE for adiabatic, vertical upward, air-water conditions is developed. An in-depth assessment on the existing experimental database is performed to select reliable experimental data for code assessment. Then, the implementation is assessed against the qualified air-water two-phase flow experimental data. Good agreement is observed between the experimental data for and the TRACE code with an average error of 9% for all conditions. Following the initial development, one-group IATE models for vertical downward and horizontal two-phase flows are implemented and assessed against qualified data. Finally, IATE models capable of predicting subcooled boiling two-phase flows are implemented. An assessment of the models shows that TRACE is capable of generating interfacial area concentration in subcooled boiling two-phase flows with the IATE and that heat transfer effects dominate the evolution of in these flows.In parallel to developing a TRACE version with the IATE capability, an extensive study is performed to improve the capabilities of the four-sensor conductivity probe. These include improvements in both the signal processing software and processing schemes. Furthermore, experiments are performed in 14 additional test conditions. These test conditions are strategically chosen to establish database in flow conditions where specific bubble interaction mechanisms in the IATE are highlighted. The data established in the experiments are used to further assess and validate the IATE models available in TRACE.
| Author | : Julio M.* Dejesus |
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| Total Pages | : 452 |
| Release | : 1989 |
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| Author | : Mohan Singh Yadav |
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| Total Pages | : 193 |
| Release | : 2009 |
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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.
