Tracer In Liquid Phase Research Articles

Investigation of hydrodynamic behaviour of membranes using radiotracer techniques

The aim of the work was to study membrane devices using short-lived radioisotopes like Ba-137m and Ga-68 as tracers. These radioisotopes were obtained from radionuclide generators: Cs-137/Ba-137m and Ge-68/Ga-68. The first radionuclide, namely Ba-137m with a half-life of 2.55 minutes was applied as a liquid phase tracer for studying hydrodynamic conditions inside the membrane apparatus. The membrane module with ceramic membranes was tested by using Ba-137m. The experiments showed that this radionuclide with a short half-life is a perfect tracer for liquid phase, whereas Ga-68 with longer half-life equal to 68 minutes was considered as a solid phase (bentonite) tracer. Ga-68 was used to gain more knowledge about the phenomena occurring in the membrane boundary layer. After kinetic studies of isotope adsorption into the carrier material, the growth rate of the deposit layer as well as deposit's thickness on the flat-sheet membrane were studied. The influence of such process parameters like pressure, linear velocity of liquid and feed concentration on formation of the bentonite layer on the membrane surface was studied.

Characterization of two-phase flow regimes in horizontal tubes using 81mKr tracer experiments

The diagnosis of heat exchangers on duty with respect to flow mal-distributions needs the development of non-intrusive inlet–outlet experimental techniques in order to perform an online fault diagnosis. Tracer experiments are an example of such techniques. They can be applied to mono-phase heat exchangers but also to multi-phase ones. In this case, the tracer experiments are more difficult to perform. In order to check for the capabilities of tracer experiments to be used for the flow mal-distribution diagnosis in the case of multi-phase heat exchangers, we present here a preliminary study on the simplest possible system: two-phase flows in a horizontal tube. 81mKr is used as gas tracer and properly collimated NaI (TI) crystal scintillators as detectors. The specific shape of the tracer response allows two-phase flow regimes to be characterized. Signal analysis allows the estimation of the gas phase real average velocity and consequently of the liquid phase real average velocity as well as of the volumetric void fraction. These results are compared successfully to those obtained with liquid phase tracer experiments previously presented by Oriol et al. 2007. Characterization of the two-phase flow regimes and liquid dispersion in horizontal and vertical tubes using coloured tracer and no intrusive optical detector. Chem. Eng. Sci. 63(1), 24–34, as well as to those given by correlations from literature.

Characterization of the two-phase flow regimes and liquid dispersion in horizontal and vertical tubes by using coloured tracer and non-intrusive optical detector

The monitoring of heat exchangers on duty with respect to flow mal-distributions needs the development of inlet–outlet experimental techniques in order to perform a fault diagnosis. Within this framework and as a first attempt to solve this problem in the case of multi-phase heat exchangers, we propose to use a non-intrusive optical sensor associated to a liquid phase tracer experiment. In order to check the capabilities of this technique, we present here the results that we have obtained for the characterization of two phase flows in horizontal and vertical tubes. The difference between refractive index of the two phases allows estimating the void fraction on the section illuminated by the optical sensor and permits to characterize two-phase flow regime from the signal characteristics. Signal analysis and treatment of the absorbance variation due to the coloured tracer injected in the liquid phase permit to estimate the real liquid phase averaged velocity and consequently the real gas phase average velocity. We also calculated volumetric void fraction and compared it to usual correlations with a good agreement. Finally, the evolution of the experimental liquid phase Peclet number with the two-phase flow regime has been observed and qualitatively explained.

Liquid-phase tracer responses in a cold-flow counter-current trayed bubble column from conductivity probe measurements

Liquid-phase mixing in a cold-flow counter-current-flow bubble column reactor with trays has been evaluated. A developed filtering technique [P. Gupta, M.H. Al-Dahhan, M.P. Dudukovic’, P.L. Mills, A novel signal filtering methodology for obtaining liquid-phase tracer responses from conductivity probes, Flow Meas. Instrum. 11 (2) (2000) 123–131.] was used to extract the liquid-phase concentration responses from the conductivity probe data in two phase gas–liquid flow with systematic corruption. Conductivity probe responses to a pulse input of KCl liquid tracer were measured at various point-wise locations in an 8 in. diameter clear acrylic column using air and water as the gas–liquid system. The superficial gas and liquid velocities were selected to span those encountered in a commercial unit using a pipe-type gas sparger with a number of laterals. Results from tracer experiments are presented along with a cross-correlation of signals to estimate the characteristic residence time of the liquid on a tray. The utility of the filtering algorithm for a broader range of gas–liquid flows is also discussed.

Liquid phase mixing in trayed bubble column reactors

The compartmentalization of conventional bubble columns by perforated trays constitutes a very effective method to reduce the liquid backmixing. The effect of tray design and operating conditions on the overall liquid mixing was studied in a bench-scale trayed bubble column. The extent of liquid backmixing in the column was investigated in light of liquid-phase tracer response experiments. In average, a three fold reduction in the liquid backmixing was achieved in the trayed column as compared to the column without the trays. Moreover, the tray open area and the superficial liquid velocity were found to have the strongest effects on the liquid backmixing. The N-CSTR with Backmixing Model was found to match the experimental tracer response curves better than the Axial Dispersion Model.

Developments in tracer flow testing for geothermal production engineering

The chemical tracer flow test (TFT) technique for two-phase mass flow rate measurement has been in use since 1992 and is now employed routinely in the major geothermal fields of 6 countries. There have been continuous refinements in the TFT process over time, including introduction of new vapor and liquid tracers, and upgraded tracer metering equipment. Since TFT is now used by many operators around the world, it is important to ensure that the technique is consistent and robust, and not site-specific or sensitive to small deviations in methodology. Comparative data are presented for some of the various tracers, including recent tests on alcohol tracers. These tests show sulfur hexafluoride (SF 6) is the most versatile and accurate tracer for TFT steam measurements, while alcohol can be used in limited applications. Sodium benzoate remains the primary liquid-phase tracer, but recent tests using naphthalene sulfonic acids (NSA) look very promising. The SF 6 and NSA tracers allow miniaturization of the tracer metering equipment, resulting in greater portability and lower cost.

A novel signal filtering methodology for obtaining liquid phase tracer responses from conductivity probes

Local conductance measurements using a conductivity cell, consisting of electrode plates encased in plastic tubing, have been employed for point conductance measurements in two-phase gas–liquid flows. It is shown that such measurements can provide local liquid mixing information in gas–liquid flows such as those encountered in bubble and staged bubble columns either with an upward flow of gas in a batch liquid, or with co-current or counter-current flow of gas and liquid. This requires the characterization of the liquid phase conductance from the electrical signals acquired by such a conductivity probe (cell) in the presence of bubbles, which is non-trivial due to the systematic lowering of the conductance of the probe measurement volume when a bubble contacts or pierces the probe tip. Thus, application of standard digital filtering techniques to signals masked by frequent bubble passage results in an inaccurate representation of liquid conductance by filtered signals. A special purpose software filtering technique has been developed in this work to address this issue and to cleanly extract the actual liquid phase conductance from response signals representing the instantaneous point conductance of a bubbling two-phase gas–liquid mixture. The implementation of the new filtering algorithm has been achieved through coupling with standard Butterworth filters in MATLAB™, version 5.

Measurements of gas–liquid mixing in a stirred vessel using electrical resistance tomography (ERT)

The non-invasive measurement of mixing inside a stirred vessel in 3-D, using an 8×16 array of resistance tomography sensors, provides powerful opportunities for characterising and quantifying the process complexities [R. Mann, F.J. Dickin, M. Wang, T. Dyakowski, R.A. Forrest, P.J. Holden, Chem. Eng. Sci. 52 (1997) 2087–2097; P.J. Holden, M. Wang, R. Mann, F.J. Dickin, R.B. Edwards, A.I.Ch.E. JI. 44 (1998) 780–790]. Using the UMIST pilot plant 1.5m stirred vessel, new results are presented for gas–liquid mixing which can distinguish differences in liquid mixing behavior between water (low viscosity) and relatively viscous 0.05% carbopol solution. The slower liquid phase tracer mixing rates for the viscous case compared with water, as well as differences in the pattern of mixing, can be readily observed and portrayed in 3-D using linear back projection for the reconstruction. In addition, the variation of local gas hold-up (voidage) can also be simultaneously measured by identifying regions within the vessel which have high or low local conductivity/resistivity. Electrical resistance tomography (ERT) can thus provide simultaneous detailed information on two aspects of gas–liquid mixing, involving the isolation of liquid phase mixing when gas–liquid mixing is taking place. The ERT results can be processed to provide the local mixing curve, hence mixing times, for any nominated pixel.

CFD modeling of flow, macro‐mixing and axial dispersion in a bubble column

AbstractThe flow pattern in a bubble column depends upon the column diameter, height, sparger design, superficial gas velocity and the nature of gas–liquid system. In this paper, the effect of some of these parameters have been simulated using Computational Fluid Dynamics (CFD). The relationship of these parameters with the interphase force terms has been discussed. A complete energy balance has been established. Using this methodology, the flow patterns reported by Hills (1974), Menzel et al. (1990), Yao et al. (1991) and Yu and Kim (1991) have been simulated. Excellent agreement has been shown between the CFD predictions and the experimental observations. The above model has been extended to homogenization of an inert tracer. In order to confirm this model, mixing experiments were carried out in a 200 mm i.d. bubble column. A radioactive tracer technique was used for the measurement of mixing time. Tc‐99m (99m Tc), in the form of sodium pertechnate salt, was used as the liquid phase tracer. Good agreement has been shown between the predicted and the experimental values of mixing time. The model was further extended for the estimation of axial dispersion coefficient (DL). Excellent agreement between the simulated and the experimental values of the axial dispersion coefficient confirms the predictive capability of the CFD simulations for the mixing process.

Hydrogeological evaluation of a prototype in-situ leach cell in unsaturated lead-zinc mine and mill wastes

An abandoned waste impoundment located within a portion of the Bunker Hill Superfund Site constitutes a field research area for studying the feasibility of recovering heavy metals in-situ from unsaturated mine and mill wastes. A prototype in-situ leaching cell has been evaluated using liquid-phase tracer tests and other hydrogeologic tests prior to introducing a lixiviant. The results of the tests suggest that: 1) the cell can be operated excursion-free with a low-density lixiviant at an injection/withdrawal rate of approximately 0.32 Vs; and (2) each hydrogeologic unit is highly heterogeneous at the different scales studied.