Characterization Of Flow Regimes Research Articles

Horizontal two-phase flow characterization for small diameter tubes with a capacitance sensor

Two-phase flow modelling is strongly dependent on flow patterns. For the purpose of objective flow pattern identification, a capacitance sensor was developed for horizontal two-phase flow in small diameter tubes. Finite element simulations were made during design to study the effect of vapour distribution, wall thickness and electrode angle. A test rig was constructed and a series of experiments was done with horizontal air–water flow in a 9 mm tube. The sensor test results are presented in time, amplitude and frequency domain. Flow regime characterization with the capacitance measurements is clearly possible.

The characterization of flow regimes with power spectral density distributions of pressure fluctuations during condensation in smooth and micro-fin tubes

This paper presents an objective predictor of the prevailing flow regime during refrigerant condensation inside smooth-, micro-fin and herringbone tubes. The power spectral density (PSD) distribution of the fluctuating condensing pressure signal was used to predict the prevailing flow regime, as opposed to the traditional (and subjective) use of visual-only methods, and/or smooth-tube flow regime maps. The prevailing flow regime was observed by using digital cameras and was validated with the use of the conventional smooth-tube flow regime transition criteria, Froude rate criteria, as well as a new flow regime map that was developed for micro-fin tube condensation. Experimental work was conducted for condensing R-22, R-407C, and R-134a at an average saturation temperature of 40 °C with mass fluxes ranging from 300 to 800 kg/m 2 s, and with vapour qualities ranging from 0.85–0.95 at condenser inlet to 0.05–0.15 at condenser outlet. Tests were conducted with one smooth-tube condenser and three micro-fin tube condensers (with helix angles of 10°, 18°, and 37°, respectively). It is shown that the micro-fin tubes cause a delay in the transition from annular to intermittent flow by at least 19% (compared to the smooth tube), thus significantly contributing to the enhancement of heat transfer.

Characterization of Flow Regimes in Bubble Columns through CCF Analysis of Pressure Fluctuations

Pressure fluctuations in bubble columns are analyzed for regime identification. Cross-correlation function (CCF) analysis was used to retrieve hydrodynamic information contained in the pressure time series. The characteristic time of CCF gave approximate information about the liquid flow structure and allowed the evaluation of the velocity of liquid flow near the wall. This method was shown to be an efficient indicator in distinguishing between three flow regimes.

Characterization of the hydrodynamic flow regime in bubble columns via computed tomography

The current work evaluates the potential of Computed Tomography (CT) measurements for flow regime characterization. Experiments were carried out in a pilot scale (0.162 m diameter) bubble column using an air–Therminol LT system at ambient as well high operating pressures (0.4 and 1 MPa). The superficial gas velocities were varied from 1 to 20 cm/s at intervals of 1 cm/s. The steepness of the gas holdup radial profile was analyzed to demarcate the hydrodynamic flow regime. The regime transition velocities obtained from CT measurements are compared with the drift flux model. An increase in operating pressure was found to delay the regime transition and at higher pressures, a transition occurred over a range of superficial gas velocities. The current state of correlation prediction is evaluated against the experimental transition velocities.

Experimental characterization of flow regimes in various porous media — III: limit of Darcy's or creeping flow regime for Newtonian and purely viscous non-Newtonian fluids

Experimental characterization of flow regimes in various porous media — III: limit of Darcy's or creeping flow regime for Newtonian and purely viscous non-Newtonian fluids

Acoustic chemometrics for fluid flow quantifications—II: a small constriction will go a long way

A new approach for non-invasive quantitative measurement of volume flow rate, multicomponent mixture concentrations as well as density and other physico-chemical intensive parameters of liquid mixtures flowing in pipelines is presented, based on novel application extensions of the well-known orifice plate principle (extensively used for flow measurement in pipes). By deliberately transgressing the conventional usage limits, the orifice plate configuration may now also be used for a range of new measurement types, all based on acoustic sensor technology. R&D has been carried out since 1987 by Sensorteknikk A/S and since 1994 in collaboration with ACRG. The acoustic chemometrics concept is characterized by easy ‘clamp-on’ deployment of acoustic sensors (primarily accelerometers), followed by an essential, integrated signal analysis/multivariate calibration data modelling, well known from chemometrics. The signal analysis step in this endeavour is often critical although rarely outside conventional electrical engineering scopes. We present three fluid/fluid or fluid/solid mixture application type cases: (1) trace oil-in-water determination (representing one-analyte systems); (2) jet-fuel/glycol mixture determination (representing two-analyte systems); (3) paper-pulp constituent(s) determination (representing analyte–interferents systems). We also describe extension studies of these first quantitative acoustic chemometrics forays, e.g. for alternative measurement of (conventional) flow velocities of both fluid/fluid and fluid/solid (slurries) systems (average volume flow rate of heterogeneous multiphase systems), for flow regime characterization and for measurement of the effective in-line density of (fluid/fluid and fluid/solid) mixtures. There would appear to be a vast potential for technological and industrial applications of this new type of acoustic chemometric process and product characterization/monitoring. Copyright © 1999 John Wiley & Sons, Ltd.

Acoustic chemometrics for fluid flow quantifications - II: a small constriction will go a long way

A new approach for non-invasive quantitative measurement of volume flow rate, multicomponent mixture concentrations as well as density and other physico-chemical intensive parameters of liquid mixtures flowing in pipelines is presented, based on novel application extensions of the well-known orifice plate principle (extensively used for flow measurement in pipes). By deliberately transgressing the conventional usage limits, the orifice plate configuration may now also be used for a range of new measurement types, all based on acoustic sensor technology. R&D has been carried out since 1987 by Sensorteknikk A/S and since 1994 in collaboration with ACRG. The acoustic chemometrics concept is characterized by easy ‘clamp-on’ deployment of acoustic sensors (primarily accelerometers), followed by an essential, integrated signal analysis/multivariate calibration data modelling, well known from chemometrics. The signal analysis step in this endeavour is often critical although rarely outside conventional electrical engineering scopes. We present three fluid/fluid or fluid/solid mixture application type cases: (1) trace oil-in-water determination (representing one-analyte systems); (2) jet-fuel/glycol mixture determination (representing two-analyte systems); (3) paper-pulp constituent(s) determination (representing analyte–interferents systems). We also describe extension studies of these first quantitative acoustic chemometrics forays, e.g. for alternative measurement of (conventional) flow velocities of both fluid/fluid and fluid/solid (slurries) systems (average volume flow rate of heterogeneous multiphase systems), for flow regime characterization and for measurement of the effective in-line density of (fluid/fluid and fluid/solid) mixtures. There would appear to be a vast potential for technological and industrial applications of this new type of acoustic chemometric process and product characterization/monitoring. Copyright © 1999 John Wiley & Sons, Ltd.

Experimental characterization of flow regimes in various porous media—II: Transition to turbulent regime

This work deals with hydrodynamics in porous media beyond the end of the stable laminar regime, at higher Reynolds numbers. Local measurements of current fluctuations were carried out with electrochemical probes located at different positions in the porous media. Owing to the use of the electrochemical transfer function, the spectrum of velocity gradient fluctuations at the micro-electrodes and the velocity gradient fluctuating rate were determined. In packed beds of particles, a stabilization of this fluctuation rate was observed at most electrodes in the Reynolds number range covered. It is shown that this stabilization corresponds to a locally turbulent flow. In reticulated media, no such stabilization was observed. The characteristic length scales of the flow, i.e. the order of magnitude of the flow eddies dimensions, were evaluated from the autocorrelation function of the velocity gradient fluctuations calculated from the spectrum. They were compared to the pore diameter calculated from the capillary model proposed by Comiti and Renaud [(1989), Chem Engng Sci. 44, 1539–1545]. The stable values of the length scales obtained for high Reynolds numbers confirm the turbulent nature of the flow regime. The flow regime transition is gradual from laminar to turbulent in the entire bed, it is characterized with the pore Reynolds number, Re p , based on the employed capillary model: in packed beds presenting an isotropy in the plane perpendicular to the main direction of the fluid flow, the laminar regime ends at Re p =180 whereas a value of Re p =900 corresponds to the stabilization of the velocity gradient fluctuating rate at 90% of the electrodes. Calculations, based on a pressure drop model related to the capillary representation, show that the percentage of inertial effect on the pressure drop is then about 90% at this Reynolds number in these packed beds.

Experimental characterisation of flow regimes in various porous media—I: Limit of laminar flow regime

This work is part of a global study of flow regimes in porous media beyond Darcy regime. In view of determining the end of stable laminar regime in various porous media such as beds packed with spheres, stratified media and reticulated media, electrochemical micro-probes are inserted inside the medium and at the wall of test sections. Local instantaneous measurements of the limiting current intensity are implemented. Spectral analysis of the signal fluctuations enables an accurate determination of the end of stable laminar regime in the studied media. The comparison between internal measurements and those implemented at the wall of the cell shows that the latter are representative of the flow in the case of reticulated media but not in the case of packed beds of particles for which the use of internal probes is necessary. Results are expressed thanks to a pore Reynolds number Re p , based on a capillary representation of the porous media. Re p ≈180 characterises the end of the stable laminar regime in packed beds of particles presenting an isotropy in the plane perpendicular to the main direction of the fluid flow. A ‘laminarising effect’ is observed for synthetic foams. For each porous media tested, the percentage of viscous and inertial contributions in the pressure drop are given at the onset of fluctuations.

Rapid characterization of flow regimes in multiphase reactors through box-counting dimensions with an embedding dimension of two

The performance of multiphase reactors is greatly affected by their flow regime. The box-counting dimension of a probe signal characterizes its intrinsic, dimensionless structure and is not significantly affected by moderate changes in probe calibration constants. Using the box-counting dimension to characterize the flow regime can, thus, eliminate problems associated with changes in probe, liquid or solid characteristics. This study uses an approximate box-counting dimension which is so rapidly calculated that it could be used for on-line control. The box-counting dimension of the raw signal from a bubble probe allows the accurate detection of gas maldistribution in bubble columns and gas-liquid-solid fluidized beds. The box-counting dimension of the raw signal from a local conductivity probe allows the accurate detection of liquid maldistribution in bubble columns and gas-liquid-solid fluidized beds. The fluidization regime of liquid-solid and gas-liquid-solid beds can be accurately identified from the box-counting dimension of the signal recorded with either local probes or cross-sectional probes. The complete fluidization of a liquid-solid bed of splinter-like particles can be determined from the box-counting dimension of the signals from either a local probe or trace rinjection experiments.

Characterization of flow regime in concentric annuli and pipes for yield-pseudoplastic fluids

This paper presents an analysis of the laminar-turbulent transition for flow of yield-pseudoplastic fluids in pipes and concentric annuli. The yield-pseudoplastic rheology is represented by the three-parameter Robertson-Stiff model. A modified Reynolds number is developed based on an equivalent diameter including characteristic parameters of the flow situations under consideration. Using the literature data, Hanks' theory of laminar flow stability is reanalyzed in comparison with other correlations. On account of the generality of Hanks' stability criterion and its experimentally proven success to some extent, it is used herein to calculate critical values of the modified Reynolds number. Numerical results are presented in terms of the dimensionless rheological parameters and the annulus aspect ratio. Further, it is shown that constant critical value of Hanks' stability parameter (Kmc = 404) does not necessarily apply to non-Newtonian fluids. This fact is demonstrated for pipe flow of Bingham plastic fluids.