Development of Conductivity Sensors for Multi-Phase Flow Local Measurements at the Polytechnic University of Valencia (UPV) and University Jaume I of Castellon (UJI)

[EN] This paper describes all the procedures and methods currently used at UPV (Universitat Politécnica de Valencia) and UJI (University Jaume I) for the development and use of sensors for multi-phase flow analysis in vertical pipes. This paper also describes the methods that we use to obtain the values of the two-phase flow magnitudes from the sensor signals and the validation and cross-verification methods developed to check the consistency of the results obtained for these magnitudes with the sensors. First, we provide information about the procedures used to build the multi-sensor conductivity probes and some of the tests performed with different materials to avoid sensor degradation issues. In addition, we provide information about the characteristics of the electric circuits that feed the sensors. Then the data acquisition of the conductivity probe, the signal conditioning and the data processing including the device that have been designed to automatize all the measurement process of moving the sensors inside the channels by means of stepper electric motors controlled by computer are shown in operation. Then, we explain the methods used for bubble identification and categorization. Finally, we describe the methodology used to obtain the two-phase flow information from the sensor signals. This includes the following items: void fraction, gas velocity, Sauter mean diameter and interfacial area concentration. The last part of this paper is devoted to the conductance probes developed for the annular flow analysis, which includes the analysis of the interfacial waves produced in annular flow and that requires a different type of sensorThe authors are indebted to the support received from MINECO for the project MODEXFLAT ENE2013-48565-C2-1-P and ENE2013-48565-C2-2-P.Muñoz-Cobo, JL.; Chiva, S.; Mendez, S.; Monrós, G.; Escrivá, A.; Cuadros-Orón, JL. (2017). Development of Conductivity Sensors for Multi-Phase Flow Local Measurements at the Polytechnic University of Valencia (UPV) and University Jaume I of Castellon (UJI). Sensors. 17(5):1-35. https://doi.org/10.3390/s17051077S13517

Experimental Measurements and CFD Results of Liquid Film Thickness in Vertical Downward Air-Water Annular Flow

[EN] Annular gas¿liquid flows have been extensively studied over the years. However, the nonlinear behavior of the interface is still currently the subject of study by multiple researchers worldwide. The appearance of a liquid layer on the wall and its turbulent behavior support the heat exchange of multiple systems in the industrial field. Research in this area allows the optimization of these installations as well as the analysis of possible safety problems if the liquid film disappears. This study first shows some of the most important findings obtained in the GEPELON experimental facility (GEneración de PElícula ONdulatoria or Wavy Film Generator). The facility was built in order to analyze the behavior of the liquid film in annular downward air¿water flow. The experimental range of the inlet conditions is 800¿8000 for the ReL and 0¿110,000 for the Reg. Measurements for the mean film thickness show a fairly good agreement with the empirical correlations and the measurements of other authors. One of the most demanded applications of this type of measurements is the validation of computational dynamics or CFD codes. Therefore, the experiment has been modeled using Ansys CFX software, and the simulation results have been compared with the experimental ones. This article outlines some of the reasons why two-phase flow simulations are currently challenging and how the codes are able to overcome them. Simulation predictions are fairly close to the experimental measurements, and the mean film thickness evolution when changing the boundary conditions also shows a good agreement.The authors are indebted to the plan of I+D support of the EXMOTRANSIN project ENE2016-79489-C2-1-P.Rivera-Durán, Y.; J. L. Muñoz-Cobo; A. Escrivá; C. Berna; Y. Córdova (2022). Experimental Measurements and CFD Results of Liquid Film Thickness in Vertical Downward Air-Water Annular Flow. International Journal of Computational Methods and Experimental Measurements. 10(2):93-103. https://doi.org/10.2495/CMEM-V10-N2-93-1039310310

Ultrasonic Velocity Profiler for the Measurement of a Bubbly Flow Velocity Vector in Small Channels

The multi-dimensional velocity distribution of coolant in bubbly flow within the fuel rod bundles of the reactor core in boiling water reactors (BWRs) is elucidated by experimental investigation in this study. Since a measurement technique is required for such an investigation, this paper proposes the development of an ultrasonic velocity profiler (UVP). The combination of special ultrasonic transducers and modified signal processing on the UVP is proposed to obtain a multi-dimensional velocity vector of the bubbles and liquid in bubbly flow. The ability of the proposed technique is demonstrated by performing an experiment in swirling bubbly flow and its applicability confirmed by comparing the results with another technique. The sound pressure distribution in the narrow channel of the rod bundle is then measured prior to the verification of the ultrasonic wave emitted through a small channel. The echo signal reflected from reflectors dispersed in the liquid, bubble, and tracer particles in the small channel of the rod bundle indicates that the proposed UVP can be applied in this application with a low level of multi-reflection. Finally, the UVP system is demonstrated to measure the velocity vector of bubbly flow in the narrow flow channel on the rod bundle, and the velocity vector of the bubble and liquid obtained simultaneously

Ultrasonic Velocity Profiler for the Measurement of a Bubbly Flow Velocity Vector in Small Channels

The multi-dimensional velocity distribution of coolant in bubbly flow within the fuel rod bundles of the reactor core in boiling water reactors (BWRs) is elucidated by experimental investigation in this study. Since a measurement technique is required for such an investigation, this paper proposes the development of an ultrasonic velocity profiler (UVP). The combination of special ultrasonic transducers and modified signal processing on the UVP is proposed to obtain a multi-dimensional velocity vector of the bubbles and liquid in bubbly flow. The ability of the proposed technique is demonstrated by performing an experiment in swirling bubbly flow and its applicability confirmed by comparing the results with another technique. The sound pressure distribution in the narrow channel of the rod bundle is then measured prior to the verification of the ultrasonic wave emitted through a small channel. The echo signal reflected from reflectors dispersed in the liquid, bubble, and tracer particles in the small channel of the rod bundle indicates that the proposed UVP can be applied in this application with a low level of multi-reflection. Finally, the UVP system is demonstrated to measure the velocity vector of bubbly flow in the narrow flow channel on the rod bundle, and the velocity vector of the bubble and liquid obtained simultaneously

Characterization of the gas-liquid interfacial waves in vertical upward co-current annular flows

[EN] For more than fifty years, hundreds of research works have focused on the study of annular flow because of its huge importance in many industrial processes, for instance, chemical, petroleum, etc., being of particular interest in nuclear industry. Specifically, interfacial waves play a vital role in the mass, momentum and energy transference processes between gas and liquid phases. This paper describes the new experimental measurements of vertical upward co-current two-phase gas-liquid flow carried out in a tube with an inner diameter of 44 mm. The liquid film thickness and the major characteristics of the interfacial waves have been measured using a non-intrusive instrument, a conductance probe. The physical phenomenon in which this device is based is the change in the electrical conductivity between air and water, i.e., the electrical signal collected in the sensor receiver depends on the thickness of the liquid film layer. The experimental measurements range from 2000 to 3500 l/min for the gas volumetric flow rate, and from 4 to 10 l/min for the liquid volumetric flow rate. Correlation of the experimental measurements of liquid film thickness and the major properties of the interfacial waves have been analyzed using non-dimensional numbers. An important part of the document focuses on the comparison of the experimental data and the fitting correlations against several of the most widely used expressions. Throughout this paper, in addition to present all the available correlations, the existing scattering found when comparing against other expressions have been also confirmed, underlining the existence of gaps of knowledge even today. Emphasize that the proposed correlations are the ones that better fit the data of all experimental series carried out under the present study for the analyzed variables, with almost all the experimental points covered by the +/- 10% error bands of the new correlations.The authors are indebted to the plan of I+D support of the EXMOTRANSIN project ENE2016-79489-C2-1-P.Cuadros-Orón, JL.; Rivera-Durán, Y.; Berna, C.; Escrivá, A.; Muñoz-Cobo, JL.; Monrós-Andreu, G.; Chiva, S. (2019). Characterization of the gas-liquid interfacial waves in vertical upward co-current annular flows. Nuclear Engineering and Design. 346:112-130. https://doi.org/10.1016/j.nucengdes.2019.03.008S11213034

Experiments in free falling and downward cocurrent annular flows-Characterization of liquid films and interfacial waves

[EN] Falling liquid films and downward cocurrent flows in rounded shape pipes have been experimentally studied during the last decades, estimating the evolution of its major characteristics. The most important variables during the formation and growth of surface waves in falling downward flows have been measured using conductance probes. The main objective of the current research paper is to study the dependency of the characteristics of the thin liquid layer for downward cocurrent annular flows. The GEPELON experimental facility consists of a vertical pipe with 3.8 m of useful test length. Two pipe diameters have been analysed in this experimental study, 42 and 30 mm, in which the range covered by the liquid Reynolds number varies between 570 and 8500 and 800-7900 respectively, while the gas Reynolds numbers vary from 0 to 7.9.10(4) and from 0 to 1.1.10(5) respectively for the mentioned pipe diameters. Up to five conductance probes have been placed along the pipes test sections to capture the liquid film thickness fluctuations along time at different distances of the pipe entrance for both developing and fully developed regions. After the study and analysis of the experimental data, the central point of this paper has been the development of new correlations for the liquid film thicknesses and the two major properties of the interfacial waves. Their adjustment procedure has been carried out in terms of dimensionless numbers, aiming to provide more general relationships. In particular, the magnitudes that characterise the interface behavior have been measured, particularly film thicknesses, average disturbance wave amplitudes, and disturbance wave frequencies for each boundary condition. An additional part of the document contains an extensive comparison between the results obtained in this study and the data and expressions of other authors. It has been confirmed the significant dispersion existing among different researchers, especially when analysing variables related to the interfacial waves. This highlights the lack of knowledge in some aspects even today. The different correlations proposed have been calculated based on the best fit of the data from all the series of experiments carried out in this study. Comparisons of the behaviour of these correlations with data from other researchers have also been included.This research is supported by the EXMOTRANSIN project ENE2016-79489-C2-1-P included in the I + D Spanish plan. Funding for open access charge: CRUE-Universitat Politècnica de València.Rivera-Durán, Y.; Berna, C.; Muñoz-Cobo, JL.; Escrivá, A.; Córdova, Y. (2022). Experiments in free falling and downward cocurrent annular flows-Characterization of liquid films and interfacial waves. Nuclear Engineering and Design. 392:1-23. https://doi.org/10.1016/j.nucengdes.2022.11176912339

Air entrainment and air-water separation in hydraulic air compressors

A hydraulic air compressor (HAC) is an isothermal gas compressor that uses hydropower to compress air, originally developed by Charles Taylor in the 1890s to supply industry with compressed air. In the modern revival of this technology, the hydropower will be provided by pumps rather than natural sources. As such, energy efficiency is an important driver of component design; all of the hydropower is consumed either to overcome irreversibility or to compress air. The compressor relies on the increasing pressure of water flowing downward in a downcomer to compress air in the form of bubbles being dragged along with the flow. The air entrainment process at the top of the downcomer is facilitated by a mixing head. At the bottom of the downcomer, the bubbles are separated from the flow in a separator vessel. The objective of this thesis is to develop the design methodology for the air entrainment and air-water separation components on either end of the downcomer process. Several mixing heads were tested on a small (4.5 m height) prototype HAC. The test without a mixing head successfully entrained air, confirming that air entrainment is a system effect. Two heads with dissimilar geometry were associated with the lowest irreversibility, leading to the conclusion that the best design at that scale is a mixing head incorporating some form of vortex breaker. Air entrainment is driven by a system energy balance and not exclusively by a local Venturi geometry. The fraction of the air successfully captured in the plenum of the separator is called the separator effectiveness. Mechanistic models have been created to characterize both the irreversibility and separator effectiveness of two types of gravity separator (horizontal and vertical orientation) for iv the design of separators for future commercial-scale compressors. The separator effectiveness models require as input the flow field information from computational fluid dynamics analysis and the bubble size distribution at inlet. The bubble size distribution was measured on the small prototype and used to select a bubble size prediction model for testing on a much larger scale (29 m height) demonstrator HAC. The displacement model for horizontal separators matched the actual performance at the prototype scale well, particularly at high flow rate. The vertical velocity model produced a good match for the separator on the demonstrator HAC, but not for the same bubble size model identified on the small prototype.Doctor of Philosophy (PhD) in Natural Resources Engineerin