A PC-based fluid and heat transfer analyzer for two-phase flow in pipes

Stratified flow is one of the most basic flow pattern in the analysis of gas-liquid two-phase flow in pipes. In the present paper, different interfacial friction factor correlations were used to predict the liquid holdup and pressure gradients. The comparison of predictions with experimental observations shows that most existing correlations for the interfacial friction factor can lead to large deviations from measurements and that the standard method underestimates the liquid phase wall friction factors. New correlations for both the liquid phase wall friction factor and the interfacial friction factor were developed based on large amounts of available experimental data. The resulting correlations were used to predict liquid holdup and pressure gradient for different experiments. Considerable improvement in predictions was observed. Introduction Gas-liquid flow in pipes is of practical importance in petroleum, chemical, nuclear and geothermal industries, and has been the subject of intensive research for dozens of years. Theoretical analyses and experiments have been conducted to predict key factors, such as pressure drop, liquid holdup, gas-liquid interfacial area, heat and mass transfer and temperature distribution. In general, gas-liquid two-phase flow is much more complicated than single phase flow, due primarily to the existence of a phase interface and the spatial distribution of the phases. Some consequences of the complex nature of gas-liquid pipe flow are:–Pressure drop in transmission lines increases significantly even with the presence of very small quantities of condensate. Significant energy loss occurs as a result of acceleration and transportation of the liquid which wets the pipe wall and creates waves at the gas-liquid interface. The liquid film reduces the area of the pipe and increases the effective roughness.–Whereas in hilly terrain the pressure loss because of gravity head on the uphill side of a pipe would be recovered on the downhill side for single phase flow, this is often not the case for gas-liquid two-phase flow.–In hilly terrains and in submerged river crossings, energy is lost in lifting the liquid over natural obstacles. If the pressure is insufficient to overcome the obstacle, there may be flooding of the pipe, thus further reducing the area accessible for gas flow and therefore creating an even larger pressure drop.–In single phase flow, pressure drop decreases as pipe diameter increases, but this is not necessarily so in gas-liquid flow. Under certain conditions, pressure drop exhibits a minimum with pipe diameter. Due to the complex nature of gas-liquid two-phase flow, the problem was first approached through empirical or engineering methods. This approach is based on empirical or semi-empirical relations and has dominated practical design procedures. It leads to correlations that should be extrapolated with caution outside the range of parameters investigated in the experimental work. Most of the available correlations deal with air-water or steam-water systems, their reliability for other systems of industrial importance is questionable. Recently the trend has shifted towards the modeling approach, or mechanistic models. This approach is based on the fundamentals of multiphase flow and fluid dynamics. The fundamental postulate in this kind of approach is the existence of flow patterns or flow regimes and it has greatly contributed to the basic understanding of the nature of gas-liquid two-phase flow. P. 285

Correlation of heat transfer coefficient for two-component two-phase slug flow in a vertical pipe

Artificial neural networks (ANNs) are useful for the prediction and control of complex systems in which it is difficult or impossible to do so from first principles. This is particularly true for many thermal systems due to the presence of complex fluid mechanics like turbulence or two-phase flows, lack of knowledge of exact material properties, complex geometries, etc. The applications of ANNs to thermal systems in general has been reviewed before by the present authors (Sen and Yang, 1999). As a continuation of this, there is a growing body of recent work related to multiphase flow and heat transfer which is the subject of this review. There are several areas of applications in multiphase flow and heat transfer to which ANN techniques have been applied. Roughly speaking they may be classified in the following manner: two-phase flow in pipes including flow regime identification in pipes and heat transfer in two-phase flows; multiphase flows and heat transfer in columns, towers, packed beds and other fluid-particle systems; heat transfer in evaporators; boiling heat transfer in liquid mixtures; heat transfer in manufacturing processes; and thermal processing of food. There is a detailed list of references that can be used for further information.Copyright © 2003 by ASME

A fully implicit EOS based compositional two-phase transient flow simulator in wellbores

This paper uses a large amount of available data for liquid holdup in horizontal, two-phase flow to compare and evaluate 12 different correlations and models. In a proposed two-step holdup prediction method, an expected flow pattern is predicted on the basis of the system variables. The correlation recommended for use with that flow regime then is used to predict the holdup. Introduction The complexity of the different flow regimes involved in the flow of gas and liquid mixtures in pipes has greatly hindered the development of theoretical mechanistic flow models. However, because of the industrial importance of these systems, there has been a substantial buildup of knowledge and experience, largely in the form of empirical correlations. As a result, from the pipeline designer's point of view, the task of selecting the "best" or most point of view, the task of selecting the "best" or most appropriate correlations has become rather formidable. A need clearly exists for a periodic critical evaluation of available prediction methods. This paper presents the results of a detailed comparison of correlations and models for holdup in horizontal two-phase flow. The results of other evaluations of flow-pattern maps and pressure-drop prediction methods for two-phase flow pressure-drop prediction methods for two-phase flow in horizontal pipes, and holdup for two-phase flow in inclined pipes are reported elsewhere. The term "liquid holdup" is used in this paper to mean "in-situ liquid volume fraction." Other definitions or measures are often used in the literature to describe the amount of liquid actually contained in a pipe under twophase flow conditions. Previous Evaluations Previous Evaluations In 1964, Dukler et al. published a critical comparison of a number of holdup prediction methods. The correlations of Hoogendoorn, Hughmark, and Lockhart and Martinelli were tested against culled holdup data contained in the AGA/API data bank. On the basis of three statistical parameters, the Hughmark correlation was found to be best parameters, the Hughmark correlation was found to be best over all, but the agreement with the data was generally poor for all the correlations. The parameters used by poor for all the correlations. The parameters used by Dukler et al. were based on percentage errors and thus were very sensitive to incorrect predictions for low measured values of holdup. A recent study by Vohra et al. used the data of Beggs and Eaton to compare the correlations of Beggs and Brill, Dukler, Eaton et al., Guzhov et al., Hughmark, and Lockhart and Martinelli. Perhaps not too surprisingly, they reported that the Eaton et al. correlation was in best agreement with the Eaton data, and the Beggs and Brill correlation was in best agreement with the Beggs data. Over all, the Eaton et al. correlation was found to be in best agreement with the test data, followed by the Beggs and Brill correlation. It should be noted that there were 238 data points from Eaton and only 58 from Beggs used in the study. Approach Followed in This Study In the early stages of this study, it was apparent that there were several aspects of the proposed comparison that should be considered in some detail. The first point concerned the question of bias in the analysis resulting from the test data. Clearly, if a given correlation is based directly on a substantial portion of the test data being used in the comparison, it is given an unfair advantage over the other correlations being tested. JPT P. 1017

The characteristics of two-phase flow in a vertical pipe are investigated to gain a better understanding of vibration excitation mechanisms. An analytical model for two-phase flow in a pipe was developed by Sim et al. (2005), based on a power law for the distributions of flow parameters across the pipe diameter, such as gas velocity, liquid velocity and void fraction. An experimental study was undertaken to verify the model. The unsteady momentum flux impinging on a ‘turning tee’ (or a ‘circular plate’) has been measured at the exit of the pipe, using a force sensor. From the measured data, especially for slug flow, the predominant frequency and the RMS value of the unsteady momentum flux have been evaluated. It is found that the analytical method, given by Sim et al. for slug flow, can be used to predict the momentum flux.

Two-phase slug flow exhibits intrinsically stochastic and statistically periodic flow behaviors. Understanding the mechanisms of flow and heat transfer of upward two-phase slug flow is important. This paper develops a mechanistic model of flow and heat transfer for upward two-phase slug flow in vertical pipes. First, a hydrodynamic model of two-phase slug flow in regular-sized channels is developed based on the hypothesis of the slug unit cell. Each slug unit cell is hypothesized to be composed of a liquid slug and a Taylor bubble region. Second, a mechanistic heat transfer model is derived based on the hydrodynamic model. The overall heat transfer coefficient is integrated by using the local heat transfer coefficients of liquid slug and the Taylor bubble region. Third, the proposed mechanistic model is validated by the experimental void fraction, pressure drop, and two-phase heat transfer coefficient from different sources. Finally, the effect of flow geometry and parameters—such as superficial gas and liquid velocities, void fraction, slug frequency, pressure drop, and the ratio of slug length to unit cell length—on heat transfer in two-phase slug flow is comprehensively investigated. The enhancement in heat transfer in two-phase slug flow compared with that of single-phase flow can be attributed to an increase in the turbulence of the liquid due to the injection of air and a reduction in the thermal boundary layer owing to the frequent alternation between liquid slug and the Taylor bubble.

The application potential of Capacitively Coupled Contactless Conductivity Detection (C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> D) technique to the velocity measurement of gas-liquid two-phase flow in millimeter-scale pipe is investigated. Combining C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> D technique and cross-correlation velocity measurement technique, a new velocity measurement method is proposed. The research work includes three parts. First, a three-electrode C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> D sensor, which is suitable for the velocity measurement of gas-liquid two-phase flow in millimeter-scale pipe, is developed. Second, with the two independent conductivity signals of fluid obtained by the developed sensor, the velocity measurement of gas-liquid two-phase flow is implemented by the cross-correlation velocity measurement technique. Finally, velocity measurement experiments are carried out to verify the effectiveness of the proposed method. The research results indicate that the proposed velocity measurement method is effective and the developed sensor is successful. C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> D technique may provide a useful approach for parameter measurement of gas-liquid two-phase flow in millimeter-scale pipe.

Fluid flow monitoring is essential in many industrial processes. However, some flow measurement methods may not be feasible in a few applications such as the ones in potentially explosive atmospheres or under presence of intense electromagnetic fields. In this study, we present the construction and evaluation of an optical fiber transducer, which is suitable for flow monitoring in industrial environments pipes. Besides single-phase flow, which has been already monitored by similar techniques in the past, we also present in this paper the measurement of two-phase gas-liquid flows. Working principle is based on the measurement of the force induced by the streaming fluid into a cantilever whose deformation is indirectly and optically monitored by means of fiber Bragg gratings. Static and dynamic tests were performed for transducer calibration and validation. In static calibration, sensor sensitivity to force corresponded to 2.34 nm/N. The transducer was successfully applied to measure single-phase flow rate in the range of 0 $\text{m}^{{3}}$ /h to 6.68 $\text{m}^{{3}}$ /h, presenting maximal uncertainty of 0.3 $\text{m}^{{3}}$ /h. Finally, the transducer was applied in two-phase gas-liquid flow, being able to correctly identify gaseous and liquid phases since the cantilever is exposed to different forces during the passage of the gas and liquid. In this way, the developed transducer may be well applied to two-phase flow monitoring.

Two-phase gas-liquid systems have wide applications both on Earth and in space. On Earth, they occur in a variety of process equipment, such as petroleum production facilities, condensers and re-boilers, power systems and core cooling of nuclear power plants during emergency operation. The potential space applications include active thermal control system, power cycle, storage and transfer of cryogenic fluids, and so on. Reliable design of such systems requires a thorough understanding of the mechanism of two-phase flow, such as the phase distributions (flow patterns), pressure drops and heat transfer coefficients at different gas and liquid flow rates. Among them, flow patterns will play an important role because of strong influence of the phase distributions on pressure drops and heat transfer coefficients and thus attract more attentions of the academic and technical communities all over the world. With the aid of numerous meticulous experiments, our present knowledge on two-phase gas-liquid systems has been built. It is, however, far from complete due to the complicate influence of gravity which is a dominant factor in normal gravity. Gravity strongly affects many phenomena of two-phase gas-liquid systems by creating forces in the systems that drive motions, shape boundaries, and compress fluids. Furthermore, the presence of gravity can mask effects that ever present but comparatively small. Depending on the flow orientation and the phase velocities, gravity can significantly alter the flow patterns, and hence the pressure drops and heat transfer rates associated the flow. Advances in the understanding of two-phase flow have been greatly hindered by masking effect of gravity on the flow. Therefore, the microgravity researches will be conductive to revealing of the mechanism underlying the phenomena, and then developing of more mechanistic models for the two-phase flow and heat transfer both on Earth and in space. Research on two-phase gas-liquid flow in microgravity has a history of more than 50 years with a short pause in the 1970s and has been advanced with the development of various microgravity facilities and with increased experimental opportunities, especially in the last two decades. Due to much strict restriction on flight chance, weight and size of the test facility, power supply, and so on, studies on two-phase gas-liquid flow in microgravity are

An improved semi-empirical friction model for gas-liquid two-phase flow in horizontal and near horizontal pipes

This chapter considers overall methods for pressure drop in gas liquid two-phase flow in pipes. The various elements of pressure drop are identified. Empirical methods are presented. The performance of these equations against available data are reported. Pressure drop in two-phase flow on the shell side of tube bundles is then considered. Geometries other than pipes are then considered. Firstly, pressure drop across fittings such and expansions and contractions are examined. Secondly, other aspects of two-phase flow at fittings are reviewed. Finally, the division of phase split at T-junctions is studied.KeywordsPressure DropVoid FractionLiquid Flow RateAnnular FlowOrifice PlateThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

This paper presents the heat transfer coefficient, pressure gradient, and flow pattern of R1234yf in a microchannel tube. Both heat transfer coefficient and pressure gradient are presented against real saturation pressure, while flow pattern captures at the exit of data points are presented in the same plot. The experiment was conducted on a 24-port microchannel tube with an average hydraulic diameter of 0.643 mm. The experiment covers mass flux from 100 to 200 kg m−2s−1, heat flux from 0 to 6 kW m−2, vapor quality from 0 to 1, and inlet saturation temperature from 10 to 30 °C. Comparing the correlations to the HTC measurements at very low quality (about 0.1), Gorenflo, D., and Kenning, D. (2010, Pool Boiling, in: VDI Heat Atlas, 2nd ed, Springer, pp. 757–788) agree with the results. As vapor quality increases, pressure gradient increases. The adiabatic pressure gradient is a strong function of mass flux and saturation pressure (temperature). Flow patterns of R1234yf are also affected by mass flux and saturation pressure. The heat transfer coefficient is a strong function of mass flux and heat flux. The saturation temperature has a smaller effect on HTC in the condition range (10 – 30 °C). Under the test range, the accelerating pressure drop is insignificant compared to friction. Comparing to the results, Mishima, K., and Hibiki, T. (1996, “Some Characteristics of Air-Water Two-Phase Flow in Small Diameter Vertical Tubes,” Int. J. Multiph. Flow, 22(4), pp. 703–712) and Muller-Steinhagen, H., and Heck, K. (1986, “A Simple Friction Pressure Drop Correlation for Two-Phase Flow in Pipes,” Accessed March 1, 2018)., 20, pp. 297–308.) have small mean absolute error (MAE) to predict local pressure gradient. For the heat transfer coefficient, Sun, L., and Mishima, K. (2009, “An Evaluation of Prediction Methods for Saturated Flow Boiling Heat Transfer in Mini-Channels,” Int. J. Heat Mass Transf, 52(23–24), pp. 5323–5329) and Gungor, K. E., and Winterton, R. H. S. (1986, “A General Correlation for Flow Boiling in Tubes and Annuli,” Int. J. Heat Mass Transf, 29(3), pp. 351–358) have an MAE less than 30%.

Influence of gravity on gas–liquid two-phase flow in horizontal pipes

The interfacial wave characteristics of stratified air-water two-phase flow in a horizontal pipe were experimentally investigated by using the flush-mounted constant electric current method (CECM) sensors. The experiments were conducted in a horizontal two-phase flow loop 9.5 m long (L) consisting of transparent acrylic pipe of 26 mm i.d. (D). To obtain the stratified flow pattern, the superficial gas and liquid velocities were set to 1.02 – 3.77 m/s and 0.016 – 0.92 m/s, respectively. Several interfacial wave patterns as described by several investigators were identified. The common parameters such as liquid hold-up, probability distribution function, wave velocity and wave frequency were investigated as the function of the liquid and gas flow rates. The interfacial curvature was calculated on the basis of the liquid hold-up data from the CECM sensors and the liquid film thickness data from the image processing technique in the previous work. As a result, it was found that the mean liquid hold-up decreases with the increase of the superficial gas velocity. In the same sub flow pattern, the wave velocity increases as the superficial gas velocity increases. On the other hand, in the two-dimensional wave region, the dominant frequency decreases with the increase of the superficial liquid velocity.