Simulation of droplet heating and desolvation in an inductively coupled plasma — Part I (original) (raw)
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Spectrochimica Acta Part B-atomic Spectroscopy, 2003
A numerical model is developed to consider for the first time droplet coalescence along with transport, heating and desolvation in an argon inductively coupled plasma (Ar ICP). The direct simulation Monte Carlo (DSMC) method and the Ashgriz-Poo model are used, respectively, to compute droplet-droplet interactions and to determine the outcome of droplet collisions. Molecular dynamics (MD) simulations support the use of the Ashgriz-Poo coalescence model for small droplet coalescence. Simulations predict spatial maps of droplet number and mass densities within an Ar ICP for a conventional nebulizer-spray chamber arrangement, a direct injection high efficiency nebulizer (DIHEN), and a large bore DIHEN (LB-DIHEN). The primary findings are: (1) even at 1500 W, the collisions of the droplets in the plasma lead primarily to coalescence, particularly for direct aerosol injection; (2) the importance of coalescence in a spray simulation exhibits a complex relationship with the gas temperature and droplet size; (3) DIHEN droplets penetrate further into the Ar ICP when coalescence is considered; and (4) droplets from a spray chamber or the LB-DIHEN coalesce less frequently than those from a DIHEN. The implications of these predictions in spectrochemical analysis in ICP spectrometry are discussed. ᮊ
Computerized simulation of aerosol-droplet desolvation in an inductively coupled plasma
Spectrochimica Acta Part B: Atomic Spectroscopy, 2002
A mathematical model for the desolvation of solvent droplets has been used in conjunction with an existing code for simulation of ICP fundamental parameters. The combination has been used for the calculation of droplet histories and desolvation behavior along the central channel of an ICP. Calculations have been performed for droplets of various sizes and under a variety of ICP operating conditions. As central-channel gas flow rate increases, the point of complete desolvation of the droplet shifts upward in the plasma, away from the load coil. This relationship is fairly linear. As forward power increases, the point of complete desolvation moves down in the discharge, closer to the load coil. This is approximately an inverse relationship. Finally, simulation of behavior for a log-normal size distribution of a large number of droplets (10 ) shows that the number of surviving droplets falls sigmoidally with 8 height above the load coil. For most nebulizeryspray chamber systems, the desolvation process is complete at a welldefined height in the plasma. ᮊ
In Situ Visualization and Characterization of Aerosol Droplets in an Inductively Coupled Plasma
Analytical Chemistry, 2005
Laser-scattering techniques are utilized for the first time to visualize the aerosol droplets in an inductively coupled plasma (ICP) torch from the nebulizer tip to the site of analytical measurements. The resulting images provide key information about the spatial distribution of the aerosol introduced by direct injection and conventional sample introduction devices: (1) a direct injection highefficiency nebulizer (DIHEN); (2) a large-bore DIHEN; and (3) a MicroFlow PFA nebulizer with a PFA Scott-type spray chamber. Moreover, particle image velocimetry is used to study the in situ behavior of the aerosol before interaction with the plasma, while the individual surviving droplets are explored by particle tracking velocimetry. Directly introduced aerosols are highly scattered across the plasma torch as a result of their radial motion, indicating less than optimum sample consumption efficiency for the current direct injection devices. Further, the velocity distribution of the surviving droplets demonstrates the importance of the initial droplet velocities in complete desolvation of the aerosol for optimum analytical performance in ICP spectrometries. These new observations are critical in the design of the next-generation direct injection devices for lower sample consumption, higher sensitivity, lower noise levels, suppressed matrix effects, and developing smart spectrometers.
Spectrochimica Acta Part B: Atomic Spectroscopy, 1988
Drop size distributions have been determined for two inductively coupled plasma concentric nebulizers using laser diffraction measurements. The influence on drop size distributions of (1) gas and liquid flows (2) physical properties of several solvents and gases, and (3) principal dimensions of the nebulizers are reported. An empirical equation is developed which allows the prediction of two key parameters of primary aerosols (e.g. Sauter mean diameter and span). The equation has been checked by estimating Sauter mean diameters and spans for two additional concentric nebulizers, and good agreement has been obtained between experimental and estimated values. By comparison, estimates of Sauter mean diameters obtained from the Nukiyama and Tanasawa equation have been shown to differ markedly from experimental values. From the present study it may be concluded that gas velocity is the most critical variable in nebulizer operation, and that in order to obtain aerosols with small mean drop sizes and narrow distributions, a nebulizer with small gas cross-sectional area should be used, and operated with high gas flows. Organic solvents possessing low surface tensions are shown to lead to smaller mean drop sizes than aqueous solvents under all comparable operating conditions.
Size, velocity and evaporation rate of droplets in an Ar inductively coupled plasma (ICP) are simultaneously measured for the first time using a novel laser based imaging technique. In interferometric droplet imaging (IDI), an interference pattern created by the reflected and refracted rays from a droplet are collected in an out-of-focus image. The droplet diameter is determined by counting the number of fringes in the collected interference pattern. Combination of IDI and particle tracking velocimetry (PTV) provides the capability of monitoring droplet properties during the journey inside ICP. Using a demountable-direct injection high efficiency nebulizer, droplets in the range of 3-30 mm in diameter traveling at 15-70 m s À1 are observed in the analytical zone of the ICP. The upper velocity threshold for surviving droplets is determined by the nebulizer gas flow rate, whereas the lower threshold is mainly influenced by thermal expansion of the plasma gas. Droplet evaporation rates (0.26-0.36 mm 2 s À1 ) are in good agreement with other reports and theoretical simulations for droplets in a 3000 K Ar environment.
Analytical Sciences, 2013
We developed an injection gas heating system for introducing large droplets, because we want to effectively to measure elements in a single cell. This system was applied to ICP-atomic emission spectrometry (ICP-AES), to evaluate it performance. To evaluate the effect of the emission intensity, the emission intensity of Ca(II) increased to a maximum of tenfold at 147 C and the peak was shifted upstream of the plasma. To investigate in detail the effect of an injection gas heating system, we studied different conditions of the injection gas temperature and droplet volume. When the injection gas temperature was 89 C, smaller droplets were easily ionized. At 147 C, the emission intensity ratio and the absolute amount of the sample including the droplet exhibited close agreement. These results show the advantages of the injection gas heating system for large droplet introduction, and the sufficient reduction in the solvent load. The solvent load could be reduced by heating to 147 C using the system.
Plasma and Aerosols: Challenges, Opportunities and Perspectives
Applied Sciences
The interaction of plasmas and liquid aerosols offers special advantages and opens new perspectives for plasma–liquid applications. The paper focuses on the key research challenges and potential of plasma-aerosol interaction at atmospheric pressure in several fields, outlining opportunities and benefits in terms of process tuning and throughputs. After a short overview of the recent achievements in plasma–liquid field, the possible application benefits from aerosol injection in combination with plasma discharge are listed and discussed. Since the nature of the chemicophysical plasma-droplet interactions is still unclear, a multidisciplinary approach is recommended to overcome the current lack of knowledge and to open the plasma communities to scientists from other fields, already active in biphasic systems diagnostic. In this perspective, a better understanding of the high chemical reactivity of gas–liquid reactions will bring new opportunities for plasma assisted in-situ and on-dem...
Modeling droplet impact in plasma spray processes
Pure and Applied Chemistry, 1998
A model is described to predict the splat shape in plasma spray process. The results show that the impact process is comprised of spreading and recoil. The degree of spreading increases with Re 25; while spreading time is proportional to the ratio of the initial diameter to the impact speed. Under most conditions, simultaneous solidification plays a secondary role in arresting the spreading. Extension of the model to 3-dimensional situations and some preliminary results are also discussed.
Applied Spectroscopy, 1993
Aerosol droplet sizes and velocities from a direct injection nebulizer (DIN) are measured with radial and axial spatial resolution by phase Doppler particle analysis (PDPA). The droplets on the central axis of the spray become finer and their size becomes more uniform when ~ 20% methanol is added to the usual aqueous solvent. This could explain why the analyte signal is a maximum at this solvent composition when the DIN is used for inductively coupled plasma-mass spectrometry (ICP-MS). Mean droplet velocities are 12 to 22 m s 'with standard deviations of _+4 to +_7 m s-'. The outer fringes of the aerosol plume tend to be enriched in large droplets. The Sauter mean diameter (D3,~) and velocity of the droplets also vary substantially with axial position in the aerosol plume.