TY - JOUR TI - Thermal and mechanical properties of silicon tetrachloride (SiCl4) and germanium tetrachloride (GeCl4) in their vapor and liquid phases AU - PRAT, OP AU - CLOITRE, T AU - AULOMBARD, RL T2 - CHEMICAL VAPOR DEPOSITION AB - The most‐common physical properties of the precursor species SiCl 4 and GeCl 4 in their vapor and liquid phases are compiled from several sources in the literature. General expressions over a large range of temperature are proposed either by the use of referenced expressions or by the use of suitable empirical models. DA - 2007/// PY - 2007/// DO - 10.1002/cvde.200604242 VL - 13 IS - 5 SP - 199-+ ER - TY - JOUR TI - Simulation of flocculation in stirred vessels - Lagrangian versus Eulerian AU - PRAT, OP AU - DUCOSTE, JJ T2 - CHEMICAL ENGINEERING RESEARCH & DESIGN AB - A study has been performed to evaluate Lagrangian and Eulerian approaches for simulating flocculation in stirred vessels. The prediction of the transient floc size evolution was performed using the quadrature method of moments (QMOM) while flow field characteristics within the turbulent stirred vessel were obtained using computational fluid dynamics (CFD). The Eulerian and Lagrangian CFD/QMOM models were applied to a 28 l square tank using either a Rushton turbine or a fluid foil impeller. Simulations were performed with an initial concentration of 100 mg L−1 of 1 μm nominal clay particles for several average characteristic velocity gradients (40-, 70-, 90-, 150-s−1). For the Lagrangian approach, the results showed that the average floc size transient evolution curve does not predict a peak followed by a lower steady-state size as observed for higher shear rates with the Eulerian approach. However, the overall good agreement between the Eulerian and Lagrangian CFD/QMOM models, indicates that a Lagrangian approach combined with a QMOM model would be an efficient method to quantify the impact of non-fluid flow experimental conditions on the flocculation process. In addition, the Lagrangian CFD/QMOM approach may be a useful tool to study the dynamics of flocculation and determine appropriate coalescence/breakup kernels when performing an inverse problem technique. DA - 2007/// PY - 2007/// DO - 10.1205/cherd05001 VL - 85 IS - A2 SP - 207-219 KW - Eulerian KW - Lagrangian KW - quadrature method of moment KW - computational fluid dynamics KW - turbulence KW - flocculation ER - TY - JOUR TI - Exploring the use of a column model for the characterization of microphysical processes in warm rain: results from a homogeneous rainshaft model AU - Prat, O. P. AU - Barros, A. P. T2 - Adv. Geosci. AB - Abstract. A study of the evolution of raindrop spectra (raindrop size distribution, DSD) between cloud base and the ground surface was conducted using a column model of stochastic coalescense-breakup dynamics. Numerical results show that, under steady-state boundary conditions (i.e. constant rainfall rate and DSD at the top of the rainshaft), the equilibrium DSD is achieved only for high rain rates produced by midlevel or higher clouds and after long simulation times (~30 min or greater). Because these conditions are not typical of most rainfall, the results suggest that the theoretical equilibrium DSD might not be attainable for the duration of individual rain events, and thus DSD observations from field experiments should be analyzed conditional on the specific storm environment under which they were obtained. DA - 2007/// PY - 2007/// DO - 10.5194/adgeo-10-145-2007 VL - 10 SP - 145-152 ER - TY - JOUR TI - A robust numerical solution of the Stochastic collection-breakup equation for warm rain AU - PRAT, OP AU - BARROS, AP T2 - JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY AB - Abstract The focus of this paper is on the numerical solution of the stochastic collection equation–stochastic breakup equation (SCE–SBE) describing the evolution of raindrop spectra in warm rain. The drop size distribution (DSD) is discretized using the fixed-pivot scheme proposed by Kumar and Ramkrishna, and new discrete equations for solving collision breakup are presented. The model is evaluated using established coalescence and breakup parameterizations (kernels) available in the literature, and in that regard this paper provides a substantial review of the relevant science. The challenges posed by the need to achieve stable and accurate numerical solutions of the SCE–SBE are examined in detail. In particular, this paper focuses on the impact of varying the shape of the initial DSD on the equilibrium solution of the SCE–SBE for a wide range of rain rates and breakup kernels. The results show that, although there is no dependence of the equilibrium DSD on initial conditions for the same rain rate and breakup kernel, there is large variation in the time that it takes to reach steady state. This result suggests that, in coupled simulations of in-cloud motions and microphysics and for short time scales (<30 min) for which transient conditions prevail, the equilibrium DSD may not be attainable except for very heavy rainfall. Furthermore, simulations for the same initial conditions show a strong dependence of the dynamic evolution of the DSD on the breakup parameterization. The implication of this result is that, before the debate on the uniqueness of the shape of the equilibrium DSD can be settled, there is critical need for fundamental research including laboratory experiments to improve understanding of collisional mechanisms in DSD evolution. DA - 2007/// PY - 2007/// DO - 10.1175/JAM2544.1 VL - 46 SP - 1480-1497 ER -