Characterization of the dissipation of elbow effects in bubbly two-phase flows
Introduction
The study of two-phase flow in straight pipes with different orientations and through various flow restrictions is very important for both practical applications and scientific advancement of the subject. Most energy systems, for example nuclear reactors, contain coolant channels that are arranged in varying orientations and that are interconnected by various flow restrictions such as elbows, valves, and tees. Flow restrictions can induce significant changes in the two-phase flow interfacial structures and their transport phenomena (Salcudean et al., 1983, Wang et al., 2004, Kim et al., 2007, Talley et al., 2009). Since the mass, momentum, and energy transfer in two-phase flow systems is governed by the interfacial structures, it is important to perform experiments and to develop models that capture the effects of flow restrictions on the interfacial structures. Most of the detailed studies on the interfacial structures have focused on two-phase flows in separate vertical-upward (Ishii and Kim, 2004), vertical-downward (Ishii et al., 2004), or horizontal (Talley et al., 2012) straight pipe geometries. However, flow restrictions such as vertical-upward elbows are essential to connect the vertical and horizontal pipes in practical two-phase flow systems.
Therefore, it is important to characterize the elbow-effects on two-phase flow parameters and develop a method to determine the length of the elbow-region. The elbow-region describes the section of the two-phase flow system where the elbow-effects are dominant. In general, the elbow-effects dissipate as the flow develops downstream of the elbow. A few studies in the literature have considered the dissipation of elbow-effects in single-phase flow conditions (Sudo et al., 1998, Mattingly and Yeh, 1991). Moreover, these studies characterize the elbow-effect in terms of the strength or intensity of the secondary flow generated by the elbow (Sudo et al., 1998), which can be utilized to predict the length of the elbow-region in single-phase flows.
However, there is a complete lack of studies that address the dissipation characteristics of the elbow-effects in two-phase flow conditions and model development for the elbow-region. In view of this, the objectives of the current study are: (1) to characterize the effects of a 90° vertical-upward elbow on two-phase flow parameters, (2) to define and identify the elbow-region in two-phase flow conditions, and (3) to develop a correlation to predict the length of the elbow-region in two-phase flow conditions.
The study is divided into three major sections. The first section describes the experimental studies on the geometric effects of a 90° vertical-upward elbow on two-phase flow parameters. The second section presents a modeling strategy for two-phase flow systems with elbows. Both the experimental study and modeling strategy form the basis for the development of a correlation for the dissipation length of the elbow-effects to define the elbow-region in vertical-upward-to-horizontal bubbly two-phase flows; this is presented in the third section.
Section snippets
Experimental studies
This section describes the experimental study that was performed to investigate the effects of a 90° vertical-upward elbow on local two-phase flow parameters in air–water bubbly two-phase flow. The experimental results are discussed to show the geometric effects of the elbow on the two-phase flow parameters, which are crucial toward the development of models for the elbow-region. A detailed discussion of the experimental study is given by Yadav et al. (2014).
Model development strategy
This section presents a modeling strategy for two-phase flow configurations with elbow restrictions. It also highlights the importance of characterizing the elbow-effects and the need for an accurate prediction of the elbow-region. The current discussion is presented in the context of the vertical-upward-to-horizontal two-phase flow configuration connected by a 90° vertical-upward elbow as described in the section on the experimental studies. However, one can easily extend the proposed modeling
Characterization of the elbow-region
As discussed, an accurate prediction of two-phase flows in systems with elbow restrictions requires an accurate prediction of the elbow-region. Since the elbow-effects on two-phase flow parameters are negligible in the upstream section, the elbow-region includes the length between the inlet of the elbow and a downstream location in the horizontal section where the elbow-effects are significantly dissipated. The objective of the present work is to establish a quantitative definition of the
Summary and conclusions
This study presents a method to characterize the elbow-region for vertical-upward-to-horizontal bubbly two-phase flows through a 90° vertical-upward elbow. Furthermore, a correlation is developed to predict the dissipation length to define the elbow-region. The correlation is developed based on experiments performed in an air–water two-phase flow facility. The facility has a loop configuration and consists of three vertical and two horizontal sections that are interconnected by four 90°
Acknowledgement
This work is supported by the United States Nuclear Regulatory Commission Office of Nuclear Regulatory Research.
This report was prepared as an account of work sponsored by an agency of the U.S. Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party’s use, or the results of such use, of any information, apparatus, product, or process disclosed in
References (16)
- et al.
Interfacial structures and interfacial area transport in downward two-phase bubbly flow
Int. J. Multiphase Flow
(2004) - et al.
Development of the miniaturized four-sensor conductivity probe and the signal processing scheme
Int. J. Heat Mass Transfer
(2000) - et al.
Geometric effects of 90° elbow in the development of interfacial structures in horizontal bubbly flow
Nucl. Eng. Des.
(2007) - et al.
Effects of pipe elbows and tube bundles on selected types of flowmeters
J. Flow Meas. Instrum.
(1991) - et al.
Effect of flow obstruction geometry on pressure drop in horizontal air-water flow
Int. J. Multiphase Flow
(1983) - et al.
Influence of horizontal return bend on two-phase flow pattern in small diameter tubes
Exp. Therm. Fluid Sci.
(2004) - et al.
Sensitivity study on double-sensor conductivity probe for the measurement of interfacial area concentration in bubbly flow
Int. J. Multiphase Flow
(1999) - et al.
Experiments on geometric effects of 90° vertical-upward elbow in air water two-phase flow
Int. J. Multiphase Flow
(2014)
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