Two-Phase Flow Regimes in Exchangers and Piping: Part 1

2015 ◽  
Author(s):  
Siddharth Talapatra ◽  
Kevin Farrell
Keyword(s):  
Flow Visualization ◽  
Flow Regime ◽  
Void Fraction ◽  
Heat Exchangers ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase Flows ◽  
Two Phase ◽  
Gas Phases ◽  
Shell And Tube

The ability to predict the liquid-gas two-phase flow regime and void fraction in exchangers and piping is a critical engineering requirement in the process industry. The distribution of the liquid and gas phases depend on many factors including flow conditions, physical properties of the two fluids, and geometry of the flow conduit. The problem of correctly predicting the two-phase distribution is of enormous complexity, and generalized correlations that adequately describe the flow regime and/or the void fraction have not been yet been developed even for the simplest of geometries. While Computational Fluid Dynamics codes that model two-phase flows exist, they are limited in their applicability and usually require a priori knowledge of the flow regime. In this part of a two paper series, we discuss the state-of-the-art in two-phase flow regime studies inside shell-and-tube heat exchangers, while in the second part, we will discuss two-phase flows inside piping. We have performed air-water tests inside a glass shell-and-tube exchanger at HTRI, and by systematically varying various geometrical parameters, compiled the largest flow visualization database inside such exchangers. We have evaluated the best available flow regime maps available in the open literature, and shown how our results help enhance understanding of liquid-gas distribution inside heat exchangers. We have shown how, for a given flow rate, increasing the baffle spacing and reducing baffle-cut enhances two-phase separation. While these results are expected, they have never been quantified before. However, the use of flow visualization limits the liquid and gas phases to water and air mixtures, which limits the range of applicability. Shellside studies using various industrially relevant fluids such as hydrocarbon mixtures, steam water are planned, where non-visual flow regime detection techniques need to be applied.

New void fraction equations for two-phase flow in helical heat exchangers using artificial neural networks

2018 ◽  
Vol 130 ◽  
pp. 149-160 ◽  
Author(s):  
A. Parrales ◽  
D. Colorado ◽  
J.A. Díaz-Gómez ◽  
A. Huicochea ◽  
A. Álvarez ◽  
...  
Keyword(s):  
Neural Networks ◽  
Artificial Neural Networks ◽  
Void Fraction ◽  
Heat Exchangers ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Artificial Neural

Numerical Investigation on Two-Phase Flow Characteristic in the Separated Structure Shell-and-Tube Waste Heat Boiler

2017 ◽  
Author(s):  
Huaishuang Shao ◽  
Yungang Wang ◽  
Haidong Ma ◽  
Qinxin Zhao
Keyword(s):  
Void Fraction ◽  
Flow Characteristic ◽  
Two Phase Flow ◽  
Waste Heat ◽  
Phase Flow ◽  
Waste Heat Boiler ◽  
Shell Side ◽  
Two Phase ◽  
Saturated Water ◽  
Shell And Tube

The shell-and-tube waste heat boiler is a common facility to recover and utilize the energy of flue gas in industries. To improve the ability and efficiency of the boiler, a steam dome is configured above the drum so as to arrange more heat exchange tubes. Simulation and analysis of vapor-liquid two-phase flow across tube bundles arranged in the drum are of vital importance to design and safety operation. Numerical simulation of boiling two-phase flow across tube bundles in the drum was carried out to analyze the shell side thermal-hydraulics. Commercial software ANSYS FLUENT 14.5 was adopted for modeling and computational calculations. The applied modeling approach was validated against experimental results with a good agreement. In order to analyze the vapor-liquid two-phase flow performance under various working conditions, the inlet velocity of downcomer tubes of 3m·s−1, 4m·s−1 as well 5m·s−1 for saturated water were simulated, respectively. The pressure field, flow characteristic, void fraction distribution and heat transfer characteristic were analyzed to have a good knowledge of the boiler operation. The following conclusions have been drawn through analyzing simulation results. (1)The total pressure drop on shell side increased with increasing the inlet velocity of downcomer tubes of saturated water. (2)The velocity of saturated water decreased after flowing into the drum less than z = 0.1m as the flow area increasing, and then increased rapidly as the volume of the mixture two-phase flow increasing. (3)The integral average void fraction of the drum decreased as the mass flow rate of inlet saturated water increasing. (4)The HTC (heat transfer coefficient) of the heat exchange tubes varied with the flow direction, which is related to the vapor-water void fraction. The conclusions obtained above can be used as a reference for the design of the separated structure shell-and-tube waste heat recovery boiler.

scholarly journals On the use of area-averaged void fraction and local bubble chord length entropies as two-phase flow regime indicators

2010 ◽  
Vol 49 (5) ◽  
pp. 1147-1160
Author(s):  
Leonor Hernández ◽  
J. Enrique Juliá ◽  
Sidharth Paranjape ◽  
Takashi Hibiki ◽  
Mamoru Ishii
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Two Phase Flow ◽  
Chord Length ◽  
Phase Flow ◽  
Two Phase ◽  
Local Bubble

Impedance-Based Void Fraction Measurement and Flow Regime Identification in Microchannel Flows

2011 ◽  
Author(s):  
Sidharth Paranjape ◽  
Susan N. Ritchey ◽  
Suresh V. Garimella
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
High Speed ◽  
Electrical Impedance ◽  
Two Phase Flow ◽  
Phase Distribution ◽  
Electrical Conductance ◽  
Statistical Characteristics ◽  
Phase Flow ◽  
Two Phase

Electrical impedance of a two-phase mixture is a function of void fraction and phase distribution. The difference in the electrical conductance and permittivity of the two phases can be exploited to measure electrical impedance for obtaining void fraction and flow regime characteristics. An electrical impedance meter is constructed for the measurement of void fraction in microchannel two-phase flow. The experiments are conducted in air-water two-phase flow under adiabatic conditions. A transparent acrylic test section of hydraulic diameter 780 micrometer is used in the experimental investigation. The impedance void meter is calibrated against the void fraction measured using analysis of images obtained with a high-speed camera. Based on these measurements, a methodology utilizing the statistical characteristics of the void fraction signals is employed for identification of microchannel flow regimes.

On the Damping in Tube Arrays Subjected to Two-Phase Cross-Flow

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
J. E. Moran ◽  
D. S. Weaver
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Two Phase Flow ◽  
Cross Flow ◽  
Working Fluid ◽  
Exponential Fitting ◽  
Phase Flow ◽  
Two Phase ◽  
Tube Arrays ◽  
Half Power

An experimental study was conducted to investigate the mechanism of damping in tube arrays subjected to two-phase cross-flow, mainly focusing on the influence of void fraction and flow regime. The model tube bundle had a parallel-triangular configuration, with a pitch ratio of 1.49. The two-phase flow loop used in this research utilized Refrigerant 11 as the working fluid, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the homogeneous equilibrium model (HEM). Three different damping measurement methodologies were implemented and compared in order to obtain a more reliable damping estimate: the traditionally used half-power bandwidth, the logarithmic decrement and an exponential fitting to the tube decay response. The experiments showed that the half-power bandwidth produces higher damping values than the other two methods, due to the tube frequency shifting triggered by fluctuations in the added mass and coupling between the tubes, which depend on void fraction and flow regime. The exponential fitting proved to be the more consistent and reliable approach to estimating damping. A dimensional analysis was carried out to investigate the relationship between damping and two-phase flow related parameters. As a result, the inclusion of surface tension in the form of the capillary number appears to be useful when combined with the two-phase component of the damping ratio (interfacial damping). A strong dependence of damping on flow regime was observed when plotting the interfacial damping versus the void fraction, introducing an improvement over the previous results obtained by normalizing the two-phase damping, which does not exhibit this behavior.

Damping and Hydrodynamic Mass of a Cylinder in Simulated Two-Phase Flow

1980 ◽  
Vol 102 (3) ◽  
pp. 597-602 ◽  
Author(s):  
L. N. Carlucci
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Single Phase ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Mixture Density ◽  
Void Fractions ◽  
Fixed Cylinder

This paper describes the results of experiments conducted to determine the damping and hydrodynamic mass characteristics of a fixed-fixed cylinder both in liquid and in simulated two-phase flows. It was observed that damping was significantly higher in two-phase flow than in single phase flow, and that, depending on the flow regime, it exhibited a maximum or maxima at void fractions of 30% to 60%. The hydrodynamic mass was observed to decrease with increasing void fraction but at a higher rate than that of the mixture density.

Study of Behavior of Two Phase Flow in Vertical Large Diameter Pipe

2010 ◽  
Author(s):  
Mohammad Hassan Kebriayi ◽  
Hadi Karrabi ◽  
Mohsen Rezasoltani ◽  
M. H. Saidi
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Large Diameter ◽  
Petroleum Industry ◽  
Phase Flow ◽  
Empirical Correlations ◽  
Two Phase Flows ◽  
Two Phase ◽  
Cross Sectional

Knowledge of Air-water two phase flows is significant to different engineering systems such as chemical reactors and power plant and petrochemical and petroleum industry. One of the most industrial cases of two phase flow is two phase flow in vertical large pipes. In this paper in order to find two phase flow behavior along vertical large diameter pipes we simulate air inlets with different number of holes and different hole diameters in the same flow rate of air. In addition, flow characteristics such as cross-sectional void fraction and velocity and pressure were considered. To achieve this aim, main equations of flow have been developed for investigation of flow behavior in air-water two phase flows. 3-D numerical analyses were performed by a designed and written CFD package which is based on volume of fluid (VOF) approach. Geometries, which have been studied in this article, are round tubes with diameter of 5 cm and with length of 1 and 5 m. The fluid is assumed to be viscous and incompressible. The pressure-velocity coupling is obtained using the SIMPLEC algorithm. The results showed that at the entrance of the pipe the effect of air inlet geometry is significant while at the whole pipe this effect suppressed. Furthermore increasing the velocity at the inlet can increase average void fraction and decrease pressure loses along the pipe axis. Numerical results were compared with available empirical correlations and this comparison shows good agreement between this work and empirical correlations.

Research on the Air-Water Flow Regime and Characteristics in Rectangular Channel

2021 ◽  
Author(s):  
Qingche He ◽  
Liangming Pan ◽  
Luteng Zhang ◽  
Meiyue Yan ◽  
Wangtao Xu
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Slug Flow ◽  
Clustering Algorithm ◽  
Two Phase Flow ◽  
Rectangular Channel ◽  
Interfacial Structure ◽  
Phase Flow ◽  
Two Phase ◽  
Rectangular Channels

Abstract Two-phase Flow is widely involved in reactor design and is directly relevant to reactor safety. However, the flow regime in narrow rectangular channels still needs further study because it has a considerable difference from tube and bundle channels. To investigate the two-phase flow regime and interfacial structure characteristics, the air-water experiment with an adiabatic vertical channel of 4 × 66 × 1800, 6 × 66 × 1800 mm have been conducted under atmosphere pressure condition. The impedance void meter was used to measure the global void fraction in narrow rectangular channels. A high-speed camera was used to record the profiles of the flow regime. The flow regime was identified by the random forest clustering algorithm based on a training sample. The profiles of different parameters, including void fraction, pressure loss at Z/D = 150, were analyzed in this paper. Furthermore, based on the parameters’ distribution, the regime transition criteria in narrow rectangular channels were discussed. It is shown that the transition from bubble to slug flow always occurred when the average void fraction is 0.17–0.2. The transition value is 0.57–0.62 when the slug Flow changes to the churn-turbulent Flow and 0.78–0.8 from churn-turbulent to annular Flow. The constant used in the Lockhart-Martinelli correlation is found to calculate the frictional pressure drop in a rectangular channel. Furthermore, the drift-model applied to the rectangular channel is verified.

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