The Experts below are selected from a list of 90 Experts worldwide ranked by ideXlab platform

J. Ducree - One of the best experts on this subject based on the ideXlab platform.

  • centrifugo magnetic pump for Gas to liquid sampling
    Sensors and Actuators A-physical, 2007
    Co-Authors: S. Haeberle, N. Schmitt, R. Zengerle, J. Ducree
    Abstract:

    Abstract This paper describes a novel Gas micropump realized on a centrifugal microfluidic platform. The pump is integrated on a passive and microstructured polymer disk which is sealed by an elastomer lid featuring paramagnetic inlays. The rotational motion of this hybrid over a stationary magnet induces a designated sequence of Volume displacements of the elastic lid, leading to a net transport of Gas. The pumping pressure was determined as a function of the frequency of rotation, with a maximum observable pressure of 4.1 kPa without further optimization. The first application of this rotary device is the production of Gas–liquid flows by pumping ambient air into a continuous centrifugal flow of liquid. The Injected Gas Volume segments the liquid stream into a series of liquid compartments. Apart from such multi-phase flows, the new pumping technique supplements a generic air-to-liquid sampling method to centrifugal microfluidic platforms.

  • A Centrifugo-Magnetically Actuated Gas Micropump
    19th IEEE International Conference on Micro Electro Mechanical Systems, 2006
    Co-Authors: S. Haeberle, N. Schmitt, R. Zengerle, J. Ducree
    Abstract:

    This paper describes a novel Gas micropump on a centrifugal microfluidic platform. The pump is integrated on a passive and microstructured polymer disk which is sealed with an elastomer lid featuring paramagnetic inlays. The rotational motion of this hybrid disk over a stationary magnet induces a designated sequence of Volume displacements of the elastic lid, leading to a net transport of Gas. The pumping pressure scales linearly with the frequency, with a maximum observable pressure of 4.1 kPa. The first application of this rotary device is the production of Gas-liquid flows by pumping ambient air into a continuous centrifugal flow of liquid. The Injected Gas Volume segments the liquid stream into a series of liquid compartments. Apart from such multi-phase flows, the new pumping technique supplements a generic air-to-liquid sampling method to centrifugal microfluidic platforms.

Georges L. Chahine - One of the best experts on this subject based on the ideXlab platform.

  • Thrust Enhancement Through Bubble Injection Into an Expanding-Contracting Nozzle With a Throat
    Journal of Fluids Engineering, 2014
    Co-Authors: Sowmitra Singh, Tiffany Fourmeau, Jin-keun Choi, Georges L. Chahine
    Abstract:

    This paper addresses the concept of thrust augmentation through bubble injection into an expandingcontracting nozzle with a throat. The presence of a throat in an expanding-contracting nozzle can result in flow transition from the subsonic regime to the supersonic regime (choked conditions) for a bubbly mixture flow, which may result in a substantial increase in jet thrust. This increase would primarily arise from the fact that the Injected Gas bubbles expand drastically in the supersonic region of the flow. In the current work, an analytical 1-D model is developed to capture choked bubbly flow in an expanding-contracting nozzle with a throat. The study intends to provide analytical/numerical confirmation to observed phenomena and to serve as a design tool to guide practical experiments aimed at creating and studying choked bubbly flows through nozzles. Starting from the 1-D mixture continuity and momentum equations along with an equation of state for the bubbly mixture, expressions for mixture velocity and Gas Volume fraction were derived. Starting with a fixed geometry, an imposed upstream pressure and assuming choked flow in the nozzle, the derived expressions were iteratively solved to obtain the exit pressures and velocities for different Injected Gas Volume fractions. The variation of thrust enhancement with the Injected Gas Volume fraction was also studied. Additionally, the geometric parameters were varied (area of the exit, area of the throat) to understand the influence of the nozzle geometry on the thrust enhancement and on the flow conditions at the inlet. This parametric study provides a performance map that can be used to design a bubble augmented waterjet propulsor that can achieve and exploit supersonic flow. It was found that the optimum geometry for choked flows, unlike the optimum geometry under purely subsonic flows, had a dependence on the Injected Gas Volume fraction. Furthermore, for the same Injected Gas Volume fraction the optimum geometry for choked flows resulted in greater thrust enhancement compared to the optimum geometry for purely subsonic flows.

  • Thrust Enhancement Through Bubble Injection Into an Expanding-Contracting-Nozzle With a Throat
    Volume 7: Fluids and Heat Transfer Parts A B C and D, 2012
    Co-Authors: Sowmitra Singh, Tiffany Fourmeau, Jin-keun Choi, Georges L. Chahine
    Abstract:

    This paper addresses the concept of thrust augmentation through bubble injection into an expanding-contracting nozzle with a throat. The presence of a throat in an expanding-contracting nozzle can result in flow transition from the subsonic regime to the supersonic regime (choked conditions) for a bubbly mixture flow, which may result in a substantial increase in jet thrust. This increase would primarily arise from the fact that the Injected Gas bubbles expand drastically in the supersonic region of the flow. In the current work, an analytical 1-D model is developed to capture choked bubbly flow in an expanding-contracting nozzle with a throat. The study intends to provide analytical/numerical confirmation to observed phenomena and to serve as a design tool to guide practical experiments aimed at creating and studying choked bubbly flows through nozzles.Starting from the 1-D mixture continuity and momentum equations along with an equation of state for the bubbly mixture, expressions for mixture velocity and Gas Volume fraction were derived. Starting with a fixed geometry, an imposed upstream pressure and assuming choked flow in the nozzle, the derived expressions were iteratively solved to obtain the exit pressures and velocities for different Injected Gas Volume fractions. The variation of thrust enhancement with the Injected Gas Volume fraction was also studied. Additionally, the geometric parameters were varied (area of the exit, area of the throat) to understand the influence of the nozzle geometry on the thrust enhancement and on the flow conditions at the inlet. This parametric study provides a performance map that can be used to design a bubble augmented waterjet propulsor that can achieve and exploit supersonic flow. It was found that the optimum geometry for choked flows, unlike the optimum geometry under purely subsonic flows, had a dependence on the Injected Gas Volume fraction. Furthermore, for the same Injected Gas Volume fraction the optimum geometry for choked flows resulted in greater thrust enhancement compared to the optimum geometry for purely subsonic flows.Copyright © 2012 by ASME

William R. Rossen - One of the best experts on this subject based on the ideXlab platform.

  • Steady-State Flow Behavior of CO2 Foam
    All Days, 2004
    Co-Authors: Jisung Kim, Yan Dong, William R. Rossen
    Abstract:

    Abstract Foams can improve oil recovery by reducing Gas mobility and the effects of reservoir heterogeneity. Numerous studies report that foam flow in porous media comprises two regimes. In the "high-quality regime," pressure gradient is nearly independent of Gas superficial velocity. In the "low-quality regime," pressure gradient is nearly independent of liquid superficial velocity. Previous published data from CO2 foam studies lie either in the high- or low-quality regime, but no single study shows both regimes. Delineating the two foam-flow regimes is essential to modeling and predicting the behavior of CO2 foam in petroleum applications. Experiments were performed with a sand-pack and a fired Berea and Boise sandstone cores at a back-pressure of 1500 or 2000 psig, above and below the critical temperature of CO2. The data from the sand-pack, Berea and Boise-sandstone experiments at room temperature do not show the two conventional foam-flow regimes. Instead, these experiments find a third regime evidently related to the low-quality regime. This same behavior was observed in the sand-pack above the critical temperature of CO2. In this new regime, pressure gradient decreases with increasing liquid superficial velocity at constant Gas superficial velocity. The Boise-sandstone experiment above the critical temperature of CO2 did find the two conventional foam-flow regimes, however. No single experimental factor appears to explain the difference in results. Earlier theoretical work of Hirasaki and Lawson and de Vries and Wit can partially explain the flow regime seen in our study. A model combining a bundle-of-tubes approach with the effective-viscosity function of Hirasaki and Lawson predicts the behavior in this new regime. Introduction In producing the oil from a reservoir, on average about two thirds of oil originally in place is left in the reservoir at the end of waterflooding (Lake, 1989). The goal of enhanced oil recovery (EOR) is to increase the fraction of oil recovered from a reservoir. Injecting steam, carbon dioxide (CO2) and field Gas have been the most productive EOR methods (Moritis, 2002). CO2 is Injected into oil reservoirs because CO2 dissolves into oil easily, reduces oil viscosity, and can extract the light components of crude oil at sufficiently high pressure, and CO2 can become miscible with oil at lower pressure than other Gases (Abdassah et al., 2000). The CO2 process can be highly effective within rock strata where it contacts oil (Lake, 1989). However, actual oil recovery with CO2 in the field is much lower, due to poor sweep efficiency: the Gas contacts and sweeps only a small portion of oil in the reservoir. Poor sweep efficiency is caused by the low viscosity and density of CO2 and by reservoir heterogeneity. These effects cause early Gas breakthrough and low sweep efficiency. Foam can improve the sweep efficiency of the Injected Gas by reducing Gas mobility and the effects of reservoir heterogeneity (Heller, 1994). Foams are also used in matrix acid well-stimulation treatments (Gdanski, 1993; Robert and Mack, 1995; Rossen and Wang, 1999) and environmental remediation (Hirasaki et al., 2000). Field trials of CO2 foam showed some success (Jonas et al., 1990; Stephenson et al., 1993; Chou et al., 1992; Heller and Watts, 1993; Hoefner et al., 1994; Martin et al., 1995). A number of foam EOR field trials with other miscible or near-miscible Gases have been carried out as well (Chad et al., 1988; Liu and Besserer, 1988; Kuehne et al., 1990; Krause et al., 1992; Skauge et al., 2002). Two Foam-Flow Regimes in Porous Media Osterloh and Jante (1992) found two distinct regimes for foam flow in porous media: a "high-quality regime" and a "low-quality regime" (Fig. 1). Foam "quality" is Injected Gas Volume fraction. In the high-quality regime (upper-left portion of Fig. 1), pressure gradients are nearly independent of Gas superficial velocity Ug. In this regime foam collapse at a "limiting capillary pressure" Pc* (Khatib et al., 1988; Ettinger and Radke, 1992; Rossen and Zhou, 1995) dominates behavior. In the low-quality regime (lower-right portion of Fig. 1), pressure gradients are nearly independent of liquid superficial velocity Uw. It is thought that in this regime Pc< Pc*, foam is controlled by Gas trapping and mobilization, bubble size is fixed, and water saturation changes with flow rates (Rossen and Wang, 1999; Alvarez et al., 2001).

  • A Model for Foam Generation in Homogeneous Media
    All Days, 2002
    Co-Authors: Seung Ihl Kam, William R. Rossen
    Abstract:

    Abstract Foam is a promising means to reduce Gas influx into oil wells, control Gas flow in improved oil recovery processes, direct acid flow in matrix acid well treatments, and improve the efficiency of environmental-remediation processes. Recent laboratory research in a wide range of porous media shows that creating foam in steady flow in homogeneous media requires exceeding a minimum pressure gradient. Data fit trends predicted by a theory in which foam generation depends on attaining sufficient ?p to mobilize liquid lenses present before foam generation. Data show three regimes: a coarse-foam regime at low ?p, strong foam at high ?p, and, in between, an transient regime alternating between weaker and stronger foam. Here for the first time a population-balance foam model incorporates bubble-creation function that depends on pressure gradient. The new model reproduces the three foam regimes seen in the laboratory, the abrupt occurrence of foam generation at a threshold velocity or pressure gradient, hysteresis in experimental results, the interplay between foam stability and foam generation, the effect of Injected liquid fractional flow on foam generation, and foam behavior in the high-quality and low-quality steady-state strong-foam regimes. The details of the lamella-creation function have little effect on rheology of strong foam, which is controlled by other mechanisms. The predicted fractional-flow curves are complex. This model is a necessary step toward quantitative prediction of foam performance in the field. Introduction Gas injection is one of the most popular methods to enhance oil recovery from petroleum reservoirs worldwide.1 But the low viscosity and density of the Gas phase causes instability and inefficiency in the displacement front because of gravity override, Gas channeling, and viscous fingering.2 Foams are capable of reducing Gas mobility within porous media and therefore greatly improving sweep efficiency.3,4 Moreover, foam can reduce Gas mobility more in higher-permeability strata and thereby help mitigate the effects of reservoir heterogeneity. Foam is used as well in matrix acid well stimulation5,6 and on a pilot basis for environmental remediation.7,8 Foam in porous media can be defined as a dispersion of Gas phase in liquid phase such that the liquid phase is connected and at least some Gas paths are blocked by thin liquid films, called lamellae. Foam Generation Application of foam in porous media requires foam generation. Foam generation, at least in some cases, requires high flow rates or high pressure gradients.9–12 In some applications, such as acid diversion in well stimulation, foam may already be created in flow down the injection string, and high pressure gradient near the well may provide favorable conditions for foam generation. But in some applications where pressure gradient is limited, or foam is to be created far from the injection well, foam generation may be problematic. In foam-enhanced aquifer remediation, pressure gradient may be very restricted throughout the region of application.7 "Foam generation" as observed in the laboratory is condition where the rate of lamellae creation greatly exceeds the rate of lamella destruction. As a result, one observes a large, often sudden, reduction in Gas mobility. Most experimental studies of foam generation have been conducted at fixed, increasing flow rates and fixed foam quality (Injected Gas Volume fraction) and find a drastic increase in pressure gradient at the onset of foam generation. Foam Generation Application of foam in porous media requires foam generation. Foam generation, at least in some cases, requires high flow rates or high pressure gradients.9–12 In some applications, such as acid diversion in well stimulation, foam may already be created in flow down the injection string, and high pressure gradient near the well may provide favorable conditions for foam generation. But in some applications where pressure gradient is limited, or foam is to be created far from the injection well, foam generation may be problematic. In foam-enhanced aquifer remediation, pressure gradient may be very restricted throughout the region of application.7 "Foam generation" as observed in the laboratory is condition where the rate of lamellae creation greatly exceeds the rate of lamella destruction. As a result, one observes a large, often sudden, reduction in Gas mobility. Most experimental studies of foam generation have been conducted at fixed, increasing flow rates and fixed foam quality (Injected Gas Volume fraction) and find a drastic increase in pressure gradient at the onset of foam generation.

  • Simulating Foam Processes at High and Low Foam Qualities
    All Days, 2000
    Co-Authors: L. Cheng, A.b. Reme, D. Shan, D.a. Coombe, William R. Rossen
    Abstract:

    Abstract Foams used for Gas or acid diversion exhibit two flow regimes, depending on foam quality. Two foam simulators, one the most widely used commercial foam simulator and the other developed at our university, fit steady-state foam behaviour in both regimes. A simple procedure is described for fitting simulator parameters to a set of steady-state core flood data and examples are shown. Fitting model parameters to a single core flood data can err by fitting this datum to the wrong flow regime. Shear-thinning reported in the "low-quality regime" can increase foam injectivity in radial flow. Foams in low-quality regime fit the same correlation for overcoming gravity override previously derived for foam in the high-quality regime. The flow regime does greatly affect the effect of capillary crossflow on foam diversion between layers differing in permeability, however. Capillary crossflow harms diversion between adjacent layers, as found earlier, but the magnitude of the effect is much less for foam in the low-quality regime, and no single correlation matches all the results. Capillary crossflow can actually increase (by a small amount) diversion from adjacent layers differing somewhat in permeability to distant layers with much-different permeability. Introduction Foams find application in diversion of acid in well-stimulation treatments,1,2 diversion of Gas in improved-oil-recovery processes,3,4 and diversion of treatment fluids in environmental remediation processes.5,6 These processes differ from foam drilling, fracturing, cementing and well cleanout processes in that foam flows through the porous medium itself. Foam exhibits at least two steady-state flow regimes as a function of foam quality ƒg (Injected Gas Volume fraction), as illustrated in Fig. 1.7–10 At high foam qualities (upper left portion of figure), pressure gradient ?p is nearly independent of Gas flow rate. This "high-quality" or "coalescence"11 regime is controlled by bubble coalescence at the "limiting capillary pressure" Pc*.12,13 In this regime, both capillary pressure Pc and water saturation Sw remain at Pc* and Sw* = Sw(Pc*), respectively, independent of Gas and liquid flow rates. As a function of overall flow rate (at fixed back-pressure), behaviour can be shear-thinning, as shown in Fig. 1 (cf. also Ref. (12)), Newtonian,11,14 or even shear-thickening.10 In the "low-quality regime" (lower right portion of Fig. 1), ?p is nearly independent of liquid flow rate. It is thought that in this regime bubble size is fixed,8,10 but water saturation does change with flow rates. The low-quality regime is shear-thinning as a function of overall flow rate. The transition between regimes occurs at a foam quality ƒg*. These two foam-flow regimes are reported with both N2 and CO2 Gas, with various surfactants, and in various porous media, including sand- and bead packs, relatively uniform Berea sandstone, strongly layered Antolini sandstone, and field cores.7–10 Fig. 2 shows an example from Alvarez et al.10 in Berea sandstone. Alvarez et al. made no attempt to smooth these data, to avoid possibly biasing the trend of the contours, but the vertical trend of the ?p contours in the high-qulaity regime and nearly horizontal trend in the low-quality regime and nearly horizontal trend in the low-quality regime are both evident in the figure. It is not yet clear whether the tow flow regimes apply to "weak" forms, with relatively small decreases in Gas mobility; examples uncovered to date have show large reductions in mobility. The transition form quality ƒg* that separates low- and high-quality regimes depends on surfactant formulation and concentration, probably other compositional factors (Gas type, ionic strength, etc.), and one permeability and possibly other properties of the porous medium.10 For instance, ƒg* increases as permeability increases. Fig. 3 shows how more-restricted studies of foam at fixed foam quality or fixed overall flow rate appear on a plot like Figs. 1 or 2.

  • Modeling Foams for Acid Diversion
    All Days, 1997
    Co-Authors: William R. Rossen, M.-w. Wang
    Abstract:

    SPE Members Abstract Successful foam diversion in matrix acid treatments depends on foam mobility during foam injection and liquid (acid) mobility after foam injection. We present new coreflood data for both flow regimes. At fixed quality and high flow rates, we find that foam behaves as a shear-thinning fluid with power-law exponent of about 0.6. For qualities below about 80%, when Gas and liquid flow rates are varied separately, pressure gradient is nearly independent of water flow rate, as reported by Osterloh and Jante (1992) for foam below a threshold foam quality. Upon liquid injection after foam, pressure gradient falls to a steady-state value that varies little with liquid flow rate. The transition to this steady-state pressure gradient is strongly affected by Gas expansion as pressure falls, which makes extrapolation from laboratory coreflood to field application tricky. However, although some Gas escapes during this transition period, the foam front does not advance; that is, this escaping Gas moves as free Gas, not foam. These findings are intermediate between the simple quasi-Newtonian model of Zhou and Rossen (1994) and the extremely shear-thinning behavior reported by Parlar et al. (1995) and Robert and Mack (1995). A simple new model accounts for many of the trends observed. This model assumes that foam mobility is controlled, not by foam coalescence and capillary pressure as for high-quality foams, but by trapping and mobilization of foam bubbles of fixed size. This model explains how foam mobility can be independent of liquid flow rate; why steady-state pressure gradient falls moderately during liquid injection following foam; and why this pressure gradient is relatively insensitive to liquid flow rate. Implications of the model for design of foam processes are discussed. Introduction Since at least the 1960's foams have been used to divert acid into damaged, less-permeable and oil-saturated strata in matrix acidization treatments (Smith et al., 1969; Kennedy et al., 1992; Bernardiner et al., 1992; Gdanski, 1993; Thompson and Gdanski, 1993; Zerhboub et al., 1994; Robert and Rossen, 1997). Foam-acid diversion acts by placing a large Volume of Gas into the near-well region during foam injection and then trapping this Gas in place during acid injection after foam (Zhou and Rossen, 1994; Robert and Rossen, 1997). A high Gas saturation reduces liquid relative permeability during acid injection and leads to acid diversion. Low Gas mobility during foam injection leads to the high Gas saturation in place. Thus the two keys to effective foam-acid diversion are low Gas mobility during foam injection and effective trapping of Gas during acid injection. (Strictly, this description applies to processes with alternating slugs of acid and foam. If a single, large slug of foamed acid is Injected instead, then low mobility during foam injection alone controls the process (Zhou and Rossen, 1994; Kibodeaux et al., 1994; Parlar et al., 1995.) In previous years we developed a model for foam/acid diversion in sandstones based on several simplifications (Zhou and Rossen, 1994; Kibodeaux et al., 1994; Zeilinger et al., 1995). This model assumes that foam mobility during foam injection is governed by capillary pressure, which causes foam collapse at a single water saturation (Khatib et al., 1988). The implications of this assumption, which is supported by research on foams for improved oil recovery (IOR) (Rossen and Zhou, 1995), are profound. For instance, during foam flow, local pressure gradient is proportional to liquid flow rate and independent of Gas flow rate. At fixed foam quality (Injected Gas Volume fraction), foam behaves as a Newtonian fluid. Initial experiments (Kibodeaux et al., 1994) suggested Newtonian rheology to be a acceptable approximation for foams for acidization. This model, combined with tractional-flow methods, gives several important insights: for instance, a possible mechanism of foam diversion between layers differing in permeability, the benefits of a surfactant preflush before foam injection, and importance of formulating acid for compatibility with foam. The model also assumes, as suggested by data of Persoff et al. (1990), that all Gas present in the foam is trapped by injection of a foam-compatible acid after foam. P. 525^

S. Haeberle - One of the best experts on this subject based on the ideXlab platform.

  • centrifugo magnetic pump for Gas to liquid sampling
    Sensors and Actuators A-physical, 2007
    Co-Authors: S. Haeberle, N. Schmitt, R. Zengerle, J. Ducree
    Abstract:

    Abstract This paper describes a novel Gas micropump realized on a centrifugal microfluidic platform. The pump is integrated on a passive and microstructured polymer disk which is sealed by an elastomer lid featuring paramagnetic inlays. The rotational motion of this hybrid over a stationary magnet induces a designated sequence of Volume displacements of the elastic lid, leading to a net transport of Gas. The pumping pressure was determined as a function of the frequency of rotation, with a maximum observable pressure of 4.1 kPa without further optimization. The first application of this rotary device is the production of Gas–liquid flows by pumping ambient air into a continuous centrifugal flow of liquid. The Injected Gas Volume segments the liquid stream into a series of liquid compartments. Apart from such multi-phase flows, the new pumping technique supplements a generic air-to-liquid sampling method to centrifugal microfluidic platforms.

  • A Centrifugo-Magnetically Actuated Gas Micropump
    19th IEEE International Conference on Micro Electro Mechanical Systems, 2006
    Co-Authors: S. Haeberle, N. Schmitt, R. Zengerle, J. Ducree
    Abstract:

    This paper describes a novel Gas micropump on a centrifugal microfluidic platform. The pump is integrated on a passive and microstructured polymer disk which is sealed with an elastomer lid featuring paramagnetic inlays. The rotational motion of this hybrid disk over a stationary magnet induces a designated sequence of Volume displacements of the elastic lid, leading to a net transport of Gas. The pumping pressure scales linearly with the frequency, with a maximum observable pressure of 4.1 kPa. The first application of this rotary device is the production of Gas-liquid flows by pumping ambient air into a continuous centrifugal flow of liquid. The Injected Gas Volume segments the liquid stream into a series of liquid compartments. Apart from such multi-phase flows, the new pumping technique supplements a generic air-to-liquid sampling method to centrifugal microfluidic platforms.

Sowmitra Singh - One of the best experts on this subject based on the ideXlab platform.

  • Thrust Enhancement Through Bubble Injection Into an Expanding-Contracting Nozzle With a Throat
    Journal of Fluids Engineering, 2014
    Co-Authors: Sowmitra Singh, Tiffany Fourmeau, Jin-keun Choi, Georges L. Chahine
    Abstract:

    This paper addresses the concept of thrust augmentation through bubble injection into an expandingcontracting nozzle with a throat. The presence of a throat in an expanding-contracting nozzle can result in flow transition from the subsonic regime to the supersonic regime (choked conditions) for a bubbly mixture flow, which may result in a substantial increase in jet thrust. This increase would primarily arise from the fact that the Injected Gas bubbles expand drastically in the supersonic region of the flow. In the current work, an analytical 1-D model is developed to capture choked bubbly flow in an expanding-contracting nozzle with a throat. The study intends to provide analytical/numerical confirmation to observed phenomena and to serve as a design tool to guide practical experiments aimed at creating and studying choked bubbly flows through nozzles. Starting from the 1-D mixture continuity and momentum equations along with an equation of state for the bubbly mixture, expressions for mixture velocity and Gas Volume fraction were derived. Starting with a fixed geometry, an imposed upstream pressure and assuming choked flow in the nozzle, the derived expressions were iteratively solved to obtain the exit pressures and velocities for different Injected Gas Volume fractions. The variation of thrust enhancement with the Injected Gas Volume fraction was also studied. Additionally, the geometric parameters were varied (area of the exit, area of the throat) to understand the influence of the nozzle geometry on the thrust enhancement and on the flow conditions at the inlet. This parametric study provides a performance map that can be used to design a bubble augmented waterjet propulsor that can achieve and exploit supersonic flow. It was found that the optimum geometry for choked flows, unlike the optimum geometry under purely subsonic flows, had a dependence on the Injected Gas Volume fraction. Furthermore, for the same Injected Gas Volume fraction the optimum geometry for choked flows resulted in greater thrust enhancement compared to the optimum geometry for purely subsonic flows.

  • Thrust Enhancement Through Bubble Injection Into an Expanding-Contracting-Nozzle With a Throat
    Volume 7: Fluids and Heat Transfer Parts A B C and D, 2012
    Co-Authors: Sowmitra Singh, Tiffany Fourmeau, Jin-keun Choi, Georges L. Chahine
    Abstract:

    This paper addresses the concept of thrust augmentation through bubble injection into an expanding-contracting nozzle with a throat. The presence of a throat in an expanding-contracting nozzle can result in flow transition from the subsonic regime to the supersonic regime (choked conditions) for a bubbly mixture flow, which may result in a substantial increase in jet thrust. This increase would primarily arise from the fact that the Injected Gas bubbles expand drastically in the supersonic region of the flow. In the current work, an analytical 1-D model is developed to capture choked bubbly flow in an expanding-contracting nozzle with a throat. The study intends to provide analytical/numerical confirmation to observed phenomena and to serve as a design tool to guide practical experiments aimed at creating and studying choked bubbly flows through nozzles.Starting from the 1-D mixture continuity and momentum equations along with an equation of state for the bubbly mixture, expressions for mixture velocity and Gas Volume fraction were derived. Starting with a fixed geometry, an imposed upstream pressure and assuming choked flow in the nozzle, the derived expressions were iteratively solved to obtain the exit pressures and velocities for different Injected Gas Volume fractions. The variation of thrust enhancement with the Injected Gas Volume fraction was also studied. Additionally, the geometric parameters were varied (area of the exit, area of the throat) to understand the influence of the nozzle geometry on the thrust enhancement and on the flow conditions at the inlet. This parametric study provides a performance map that can be used to design a bubble augmented waterjet propulsor that can achieve and exploit supersonic flow. It was found that the optimum geometry for choked flows, unlike the optimum geometry under purely subsonic flows, had a dependence on the Injected Gas Volume fraction. Furthermore, for the same Injected Gas Volume fraction the optimum geometry for choked flows resulted in greater thrust enhancement compared to the optimum geometry for purely subsonic flows.Copyright © 2012 by ASME