Two-phase Flow Applications Research Articles

Optimum Positioning of Ports in the Limaçon Gas Expanders

Positive displacement expanders are quickly gaining popularity in the fields of micropower generation and refrigeration engineering. Unlike turbomachines, expanders can handle two-phase flow applications at low speed and flow rate levels. This paper is concerned with a simple-design positive displacement expander based on the limaçon of Pascal. The paper offers an insight into the thermodynamic workings of the limaçon gas expander and presents a mathematical model to describe the manner in which the port locations affect the expander performance. A stochastic optimization technique is adopted to find the locations, for the expander ports, which produce best expander performance for given chamber dimensions. The operating speed and other parameters will be held constant during the optimization procedure. A case study is offered in this paper to prove the validity of the presented approach, and comments are given on how various operating parameters affect system performance in the limaçon design.

Microfluidic extraction using two phase laminar flow for chemical and biological applications

We review the state of the art in microfluidic separation technique based two-phase laminar flow with an application focus on chemical and biological sample. As we describe herein, two-phase laminar flow in the microfluidic extraction has several biological and engineering advantages over other methods including high reproducibility, biocompatibility, and selectivity. We review advances in applications of two-phase laminar flow and examine key parameters such as flow rate, phase composition, and surface charge property, how these can affect extract performance with the technology including microfluidic separation system. A special technology focus is given to emerging novel integrative microfluidic extraction, which aims to merge aqueous phase laminar flow and electric field technologies into simple packages. We conclude with a brief discussion of some of the emerging challenges in the field and some of the approaches that are likely to enhance their application.

Special issue dedicated to the Second Brazilian Conference on Boiling, Condensation and Multiphase Flow, São Carlos, Brazil, 03-07 May 2011

It gives us great pleasure to present this special issue highlighting some of the papers presented at the Second Brazilian Conference on Boiling, Condensation and Multiphase Flow held at the University of Sao Paulo (USP), in Sao Carlos, Brazil, May 03-07, 2011. The event was part of the First Multiphase Flow Brazilian Journey and was jointly cosponsored by PETROBRAS and Sao Paulo Research Foundation (FAPESP). The conference was built on the success of the previous meetings held in Florianopolis in the State of Santa Catarina, southern Brazil. As before, the objective of the conference was to give scientists, engineers and students from Brazil as well as from other countries, an opportunity to get together for the dissemination of the state-of-the-art and recent advances in the field and to enhance future collaborative research activities between them. More than 100 scientists participated in the event. The program of the First Multiphase Flow Brazilian Journey included seven invited keynotes, twelve lectures by Brazilian specialists and thirty four oral presentations of research papers. The invited keynotes were delivered by worldwide leading researchers in their field as Prof. Akio Tomyiama from Kobe University, Prof. Gretar Triggvasson from Worcester Polytechnique Institute, Prof. John R. Thome from Ecole Polytechnique Federale de Lausanne and Profs. Rene Oliemans and Luis M. Portela from Delft University. All research papers were reviewed on full manuscripts by external reviewers and collected together in a CD. Contributed papers have been sorted in sessions on measurement techniques, two-phase flow without phase change, boiling and condensation, multiphase flow fundamentals, CFD and two-phase flow applications. The twelve lectures on fundamental aspects of multiphase flows are published together in a book. This special issue of Journal of the Brazilian Society of Mechanical Sciences and Engineering presents a selection of eight papers presented in the conference. The topics covered include film fraction measurements in a Venturi scrubber, superficial void fraction measurements by using the wire-mesh technique, statistical characterization of the two-phase slug flow in a horizontal pipe, flow boiling in micro-scale channels, a comparison between numerical and experimental results for natural circulation in nuclear reactors and a discussion on the main criterion to determine the transition region from stratified flow to slug or roll-waves and a paper that presents a literature review on two-phase flow pressure drop and heat transfer during flow boiling in tubes containing twisted-tape inserts and the development of a new correlation to predict pressure drop in tubes containing such devices. The volume contains also a kind contribution of Prof. Rene Oliemans in which the author presents a comprehensive state-of-the-art review on two- and three-phase oil/water/gas flows in horizontal and inclined pipes addressing the relevant flow-pattern-dependent model capabilities to compute oil/water pressure loss and hold-up. This review concludes with an outlook on future research directions in this field. Finally, we thanks to all members of the organizing committee, conference delegates, keynote speakers, referees, and authors for their work in ensuring that the Second Brazilian Conference on Boiling, Condensation and Multiphase Flow and the First Multiphase Flow Brazilian Journey were a success. In particular we thank PETROBRAS and the Brazilian Society of Mechanical Sciences and Engineering who have sponsored this special issue.

THERMODYNAMIC ANALYSIS OF A CLOSED BRAYTON/ERICSSON CYCLE ENGINE WITH SCROLL MACHINES

Stirling and Ericsson engines have great potential for many applications, including micro-cogeneration, solar power, and biomass. However, ideal cycles of both types of engines are difficult to achieve in practice because neither isothermal compression nor isothermal expansion is practical with reciprocating piston engines or with turbomachinery. On the other hand, scroll compressor and expander can be very suitable for effective cooling and heating because of the high area-to-volume ratio of scroll geometry or the application of two-phase flow. To achieve quasi-isothermal compression, either a large amount of liquid is injected into the inlet of the compressor or the compressor is externally cooled by liquid. Similarly, for quasi-isothermal expansion, either hot liquid, such as thermal oil, is injected into the inlet of the expander or the expander is externally heated by a heat source. In this current study, we have undertaken a theoretical investigation of thermodynamic analyses of several kinds of scroll-type engines, in particular with regard to associated compression and expansion processes, adiabatic or quasi-isothermal processes, and the highest cycle temperature. We selected power density, or thermal efficiency, as an objective function, and then deduced optimal design parameters for the scroll-type engine.

A study of the effect of flow maldistribution on heat transfer performance in evaporators

AbstractThe performance of a heat exchanger with parallel channels can be seriously affected by flow maldistribution. In two-phase flow applications, such as evaporators, this situation may lead to local dryout and off-specification products. However, due to the complexity of describing this effect, it is normally not considered in the design process.Two models are proposed in this work for predicting the effect of maldistribution on performance. The first model neglects the interaction between channels, while the second one incorporates an equal pressure drop constraint. Both models analyze the geometry (shell-and-tube) in terms of radial layers. Here, the number of layers considered is irrelevant for the first model, while it affects the results of the second one.All results were compared to a homogeneous reference case, and reduction of performance was noticed in all cases. The first model predicts unrealistic pressure differences at the outlet. This situation is controlled by the second model, which predicts a secondary maldistribution to fit the constraint that further reduces the performance. When both models are compared, the first one underestimates the reduction in performance roughly by half.

Density estimation of two-phase flow with multiscale and randomly perturbed data

In this paper, we describe an efficient approach for quantifying uncertainty in two-phase flow applications due to perturbations of the permeability in a multiscale heterogeneous porous medium. The method is based on the application of the multiscale finite element method within the framework of Monte Carlo simulation and an efficient preprocessing construction of the multiscale basis functions. The quantities of interest for our applications are the Darcy velocity and breakthrough time and we quantify their uncertainty by constructing the respective cumulative distribution functions. For the Darcy velocity we use the multiscale finite element method, but due to lack of conservation, we apply the multiscale finite volume element method as an alternative for use with the two-phase flow problem. We provide a number of numerical examples to illustrate the performance of the method.

Two–Phase Pressure Drops in Adiabatic Horizontal Circular Smooth U-Bends and Contiguous Straight Pipes (RP-1444)

Curved channels in the form of bends are encountered in many industrial two-phase flow applications, such as U-bends in air-conditioning and refrigeration evaporators and condensers. For engineering design purposes, the evaluation of the pressure loss in two-phase flows is necessary. Basically, for the same flow conditions the pressure loss is higher in a U-bend than in a straight pipe with an equal cross-flow section and mean length. Moreover, the curved tube causes a perturbation that propagates up- and downstream of the U-bend itself. Many studies have been made on two-phase flows in bent tubes, but none have yet focused on the axial evolution of the pressure gradients before and after the U-bend or on the peripheral pressure differences that may be created. Therefore, this study reports new data obtained for R-134a at saturation temperatures ranging from 3°C to 5°C (37°F to 41°F), flowing at mass velocities ranging from 155 to 533 kg·s−1·m−2 (114·103 to 393·103 lb·h−1·ft−2) through a horizontal U-bend tube with internal tube and bend centerline diameters of 13.4 mm (0.52 in.) and 66.1 mm (2.6 in.), respectively, over a wide range of vapor qualities. The experimental results show that the differences between the peripheral inner and outer pressures up- and downstream of the bend are negligible, even very close to the bend (at 4 internal diameters). The frictional pressure gradients in the U-bend were found experimentally to be about two times that in a straight pipe. Close to the bend, up- and downstream, the pressure gradients are highly affected. For lower and medium mass velocities the perturbation caused by the U-bend does not propagate further than 6 internal diameters upstream from the bend. For the higher mass velocity, that perturbation seems to propagate further. Downstream of the U-bend the perturbed length extends over 100 internal diameters.

Adiabatic Flow Boiling in Fractal-Like Microchannels

Fractal-like branching channels are proposed for a number of microscale applications, including heat sinks, heat exchangers, absorbers, desorbers, and micro-mixers. Based on model predictions, the benefit of fractal-like channel designs is a lower pressure drop than parallel straight channels for a given flow rate, when compared to an equal channel surface area basis with the terminal channel cross-section of the fractal-like network used to define the parallel channel geometry. The fractal-like flow networks are a unique geometry that follows fractal bifurcation patterns, in this case mimicking the flow patterns found in nature. Two-phase flow applications require an understanding of how the geometric constraints impact the flow characteristics during multiphase flow. One-dimensional modeling predictions are used in this study to asses the relative impact of flow network designs on pressure drop and void fraction distributions for adiabatic flow boiling. The characterization of the flow networks includes a specified branching ratio of channel length and channel width (or diameter) and also the number of branching levels, or bifurcations, in a given length. The goal of the present study is to identify the adiabatic boiling characteristics within the fractal-like flow network and compare results to straight parallel channels. The model used is a compilation of two-phase flow models presented in the literature but modified to include a local two-phase flow parameter, flow re-development, as well as variable property effects. Results are compared with straight channels based on flow boiling conditions, pressure drop, and vapor quality distributions for a range of flow rates and subcooling.

Innovative Application of Two-Phase Flow Yields Low Energy, Side-Stream Membrane Bioreactor Process

Innovative Application of Two-Phase Flow Yields Low Energy, Side-Stream Membrane Bioreactor Process

Boiling and two-phase flow in channels with extremely small dimensions: a review of Japanese research

Research concerning micro-actuators utilizing vapor–liquid interfacial phenomena has been carried out extensively to develop thermal devices applied to micromachines. On the other hand, the application of two-phase flow is useful for the removal of waste heat from the semiconductor chips with highly increased heat generation density to be integrated in notebook PCs. In the present paper, the latest Japanese research on boiling and two-phase flow in minichannels is reviewed, covering the topics for the fundamental phenomena and practical applications. Boiling in a narrow channel between parallel plates is an ideal system for the development of high-performance heat exchangers with extremely small sizes. The promising approaches to increasing the critical heat flux (CHF) are introduced, including those by the present author, to compensate for the disadvantages inherent in this system.

Two-phase phase distribution in a vertical large diameter pipe

In view of the practical importance of the application of two-phase flow in a large diameter pipe to various fields of engineering, the characteristics and phase distribution patterns of two-phase flow in a vertical large diameter pipe have been experimentally and theoretically studied for various flow conditions. The local measurements for the interfacial parameters (void fraction, Sauter mean diameter and pressure loss) in a vertical upward air–water two-phase flow in a pipe with 0.2 m in inner diameter and 24 m in height have been performed by using the optical probes and differential pressure transducers. The two-phase flow characteristics have been analyzed with experimental data, which shows that the phase distribution patterns in the vertical large diameter pipe can be divided into two basic patterns, namely, wall peak and core peak. With the application of the concept of skewness, the two-phase distribution patterns have been quantitatively distinguished by establishing a phase distribution pattern transition criterion. An empirical relation for the phase distribution transition from wall peak to core peak was fitted by using the phase distribution pattern transition criterion and the present experimental data and verified by other researchers’ experimental data. This study also showed that there existed the flow plugging phenomena in the low region of the test section at high superficial gas velocity conditions in the vertical large diameter pipe.

Slip Factor for Centrifugal Impellers Under Single and Two-Phase Flow Conditions

Throughout the history of turbomachines investigators have tried to develop reliable methods for prediction of centrifugal pump behavior. Among the parameters available to estimate the performance of this kind of machine is the slip factor. In spite of being regarded as a variable of great significance in the analysis of turbomachinery, there seem to be a misconception regarding its concept and application. Indeed, empirical correlations have been widely used to estimate the slip factor, even in the case of two-phase flow applications, where it has not been investigated. Moreover, these correlations provide a constant value of the slip factor for a given impeller only at the best efficiency point, which is an important restriction to the pump performance prediction, considering that slip factor varies with the pump flow rate. In this study, three-dimensional computational fluid dynamics simulations were carried out on an impeller of known geometry (NS=1960) from which values of slip factor were calculated for both single- and two-phase flow (water and water-air). These results include curves of the slip factor as a function of the specific capacity and the gas-void fraction. Additionally, results for the slip factor in the case of single-phase flow (water) are given for various centrifugal impellers (NS=1157, 1447, 1612, and 3513) in order to illustrate the influence of the flow rate on this parameter. Finally, based on the numerical results, a methodology for prediction of the pump head is presented. Excellent agreement with experimental results has been found. This paper attempts to contribute to a better understanding of the fluid dynamics within centrifugal pump impellers and to shed more light on the path that prediction models should follow in the future.

Downward two-phase flow applications for a non-conventional heat pump

A non-conventional heat pump working by a difference in density between two branches of a hydraulic vertical loop has been described. This system called thermogravimetric heat pump, TGHP, operates with a non-conventional regenerative thermodynamic cycle which remarkably improves COP values. The lower density in the ‘downward branch’ is obtained by a liquid–vapour two-phase flow. Performances and main geometrical characteristic trends, such as plant height Z and two-phase column diameter D T–PD have been drawn, varying the minimum cycle temperature between 15 and 25 °C and the user temperature, T max, in the range 60–70 °C. The carrier fluid is demineralized water; according to the peculiar working fluid—PP 50, HFC 134a and HFC 338cca—different solutions can be obtained, such as for 10–12 storey buildings or for skyscrapers. Yet, the results obtained with HFC 338cca must be accepted with some cautions while waiting for a better characterisation of such fluid. Chemical compatibility, thermal stability, environmental impact have been also taken into account in the choice of the operating couple, carrier fluid—working fluid. While the thermodynamic conversion process is non-conventional, the TGHP can be assembled by standardised technology. The compressor of a conventional plant is here replaced by a feeding pump and COP values obtained through a regenerative TGHP are globally larger than those of a common heat pump.

Bubble transport in three-dimensional laminar gravity-driven flow – mathematical formulation

This paper presents a complete set of coupled equations that govern the bubble transport in three-dimensional gravity-driven flow. The model accounts for bubble growth or shrinkage due to pressure and temperature changes as well as for multiple gas diffusion in and out of the bubbles but neglects bubble coalescence, break-up, and nucleation. The model applies to glass melting furnaces but it could be extended to other two-phase flow applications such as metal and polymer processing, passive cooling systems, and two-phase flow around naval surface ships. Governing equations are given for the key variables which are, in the present case, (1) the refining agent concentration, (2) the gas species dissolved in the liquid phase, and (3) the bubble radius, gas molar fraction, and density function. The method of solution based on the backward method of characteristics is briefly discussed.

Determination of film thickness and flooding during reflux condensation in a small, inclined tube with an ultrasonic transducer

The fundamental mechanisms of heat and mass transfer as well as of two-phase flow in compact condensers are not well understood. In this experimental investigation a single sub-channel of a compact plate heat exchanger is simulated by using a small diameter inclined aluminium tube. The inner diameter of the tube is 7 mm and the length is 500 mm. Film thicknesses and flooding points during reflux condensation of steam in this tube are determined by using an ultrasonic technique. Measurements are carried out with a 15 MHz ultrasonic transducer attached to the outer tube wall. The emitted ultrasonic signal is reflected at each interface. The condensate film thickness can be determined by measuring the time difference between the reflections of the signal at the inner tube wall and at the liquid–vapour interface. The results for the liquid film thickness obtained by the pulse-echo technique are compared with those obtained by a needle-probe technique. As the measured film thicknesses were found to be in good agreement, the accuracy of the pulse-echo technique could be verified. The results demonstrate that the ultrasonic pulse-echo technique offers a feasible alternative for two-phase flow applications. With the pulse-echo technique the thickness of the condensate film was measured at the lowermost point of the tube. The film thickness measurements were carried out before the onset of flooding at inclination angles of 30, 60 and 90° to the horizontal. It was found that the inclination angle has only a minor effect on the film thickness. Shear stress and surface tension have in small diameter tubes apparently a more obvious effect than the gravitational force. The flooding experiments are carried out at a pressure of 10 kPa and at inclination angles of 30, 60 and 90° to the horizontal. The results show that the inclination angle has no significant effect on the onset of flooding in the small diameter tube. A modified form of a flooding correlation proposed by McQuillan and Whalley is presented. This correlation predicts well the experimental data. Copyright © 2003 John Wiley & Sons, Ltd.

Characteristics of Thermogravimetric Plants

A nonconventional thermodynamic converter, called thermogravimetric system, capable of generating mechanical-electric energy is described in the present work. Such plant is basically an interesting application of a liquid-vapor two-phase flow, evolving in elevated vertical ducts of a large diameter. The most significant plants—those working with liquid lead/steam and liquid lead/PP 50 C5F12—have been analyzed in more detail. Plant height Z, power W (0.5–4 MW), and overall efficiency ηo have been evaluated through an appropriate calculus code, particularly regarding the two-phase flow behavior.

Evaluation of two-phase flow models for flashing flow in nozzles

A variety of methods and models have been proposed in the literature for sizing relief valves for two-phase flow applications. A typical application involves liquids which flash during discharge as the pressure drops. The predictions from these various methods can vary greatly under such circumstances, and can also deviate as much as 300% from measured values. This paper compares predictions from several versions of the homogeneous equilibrium and non-equilibrium models with data from the literature for flashing of initially subcooled and low quality steam-water mixtures through nozzles of various lengths. The results indicate that the homogeneous equilibrium model gives reasonable results for nozzle lengths greater than about six inches, but non-equilibrium effects must be taken into account for shorter nozzles. Both the Fauske model with no adjustable parameters and the TPHEM model with appropriate values of the non-equilibrium parameter (kne) are shown to give good results for short nozzles and subcooled or low quality inlet conditions.

Fin efficiency of extended surfaces in two-phase flow

Abstract Compact plane-fin heat exchangers and other extended surface heat exchanges are used in several two-phase flow applications, such as condensation, boiling, or moist-air cooling. Because of simplicity and lack of better information, designers often use fin efficiency formulas for two-phase flows that are derived based on uniform heat transfer coefficient. However, the heat transfer coefficient h on the fin surface under condensation or boiling may vary significantly compared to the single-phase forced convection attributable to the possible existence of different two-phase flow regimes on the fin surface, including the condition of partial dryout. Thus, the use of constant h fin efficiency formulas (of single-phase flow) for two-phase flow situation may result in serious errors. A critical assessment is made in this paper of the various methods available for calculating fin efficiency in practical fin configurations with condensation, moist air cooling, and boiling on the extended surfaces. Conditions under which the use of constant h can be made are identified. Based on the literature review, some specific design recommendations are made for the determination of the fin efficiency for two-phase flow heat exchanger applications.

Dynamics of growing interfaces from the simulation of unstable flow in random media.

Viscous fingering in random porous media is encountered in many applications of two-phase flow, where the interface is unstable because the ratio of the viscosity of the displaced fluid to that of the injected fluid is large. In these applications, including enhanced oil recovery, characterization of the width of the interface is an important concern. In the limit of stable flow, the interfacial width had been found to grow as w\ensuremath{\approxeq}${\mathit{t}}^{\mathrm{\ensuremath{\beta}}}$, where \ensuremath{\beta}\ensuremath{\approxeq}0.66, approximately independent of capillary number. To study the same behavior for the unstable case, we have simulated flow in two-dimensional random porous media using a standard model with different viscosity ratios and zero capillary pressure. When the injected fluid has zero viscosity, viscosity ratio M=\ensuremath{\infty}, the interfacial width has the expected self-similar diffusion-limited-aggregation-like behavior. For smaller viscosity ratios, the flow is self-affine with \ensuremath{\beta}=0.66\ifmmode\pm\else\textpm\fi{}0.04, which is the same value that had been observed in studies of stable flow. Furthermore, the crossover from self-similar fractal flow to self-affine fractal flow is observed to scale with the same ``characteristic'' time, \ensuremath{\tau}=${\mathit{M}}^{0.17}$, that had been found to scale the average interface position. This ``fractal'' scaling of the crossover leads to definite predictions about the viscosity-ratio dependence of the amplitudes associated with interfacial position and interfacial width.

Application of Gas-Liquid Two-Phase Flow to Whirlpool Bathtub and Subjects for Further Research

In recent years, as people have become more and more health conscious, they have taken a greater interest in bathroom amenities. As a result, whirllpool baths have become increasingly popular, because consumers believe that whirlpool baths are effective for relieving fatigue. This report introduces TOTO's applied technique, which controls the jet stream mixed air (gas-liquid two-phase flow) according to somatic sensations, and in addition, submits subjects for further research.