arXiv subjects

Q. Tan

Publications and source records attributed to Q. Tan.

5 recordsLinked to original sources

arXiv2023

Thermal effects connected to crystallization dynamics: a lattice Boltzmann study

The possible impact of temperature differences during crystal growth is investigated in this study. The organic molecule considered is mandelic acid, an important component for the pharmaceutical industry. The productivity of generating pure mandelic acid crystals are largely determined by the growth process. Reaction conditions, purity of the components, supersaturation, temperature, but possibly also temperature gradients play a central role during crystal growth. In this study a numerical model based on a hybrid solver combining the lattice Boltzmann method with finite differences is developed to model the crystallization dynamics of (S)-mandelic acid (S-ma) taking quantitatively into account temperature effects. At first, the fourth-order finite-difference method used to model energy and species conservation is validated. Then, comparisons are carried out regarding temperature changes within the single-crystal growth cell. In practice, the molar heat generation at the crystal interface shows only a small effect on the temperature field in the surrounding domain, with temperature differences below $1.5$ degree. Finally, the study is extended to investigate the impact of forced convection on the crystal habits while taking into account temperature differences.

math-ph↗

arXiv2022

Mandelic acid single-crystal growth: Experiments vs numerical simulations

Mandelic acid is an enantiomer of interest in many areas, in particular for the pharmaceutical industry. One of the approaches to produce enantiopure mandelic acid is through crystallization from an aqueous solution. We propose in this study a numerical tool based on lattice Boltzmann simulations to model crystallization dynamics of (S)-mandelic acid. The solver is first validated against experimental data. It is then used to perform parametric studies concerning the effects of important parameters such as supersaturation and seed size on the growth rate. It is finally extended to investigate the impact of forced convection on the crystal habits. Based on there parametric studies, a modification of the reactor geometry is proposed that should reduce the observed deviations from symmetrical growth with a five-fold habit.

physics.flu-dyn↗

arXiv2022

The bending of the star-forming main sequence traces the cold- to hot-accretion transition mass over 0<z<4

We analyse measurements of the evolving stellar mass (M0) at which the bending of the star-forming main sequence (MS) occurs over 0 1.4 (for which we propose a revision in agreement with latest simulations). We hence argue that the MS bending is primarily due to the lessening of cold-accretion causing a reduction in available cold gas in galaxies and supports predictions of gas feeding theory. In particular, the rapidly rising M0 with redshift at z>1 is confirming evidence for the cold-streams scenario. In this picture, a progressive fueling reduction rather than its sudden suppression in halos more massive than Mshock/Mstream produces a nearly constant star-formation rate in galaxies with stellar masses larger than M0, and not their quenching, for which other physical processes are thus required. Compared to the knee M* in the stellar mass function of galaxies, M0 is significantly lower at z<1.5, and higher at z>2, suggesting that the imprint of gas deprivation on the distribution of galaxy masses happened at early times (z>1.5-2). The typical mass at which galaxies inside the MS become bulge-dominated evolves differently from M0, consistent with the idea that bulge-formation is a distinct process from the phasing-out of cold-accretion.

astro-ph.CO↗

arXiv2021

Modeling ice crystal growth using the lattice Boltzmann method

Given the multitude of growth habits, pronounced sensitivity to ambient conditions and wide range of scales involved, snowflake crystals are one of the most challenging systems to model. The present work focuses on the development and validation of a coupled flow/species/phase solver based on the lattice Boltzmann method. It is first shown that the model is able to correctly capture species and phase growth coupling. Furthermore, through a study of crystal growth subject to ventilation effects, it is shown that the model correctly captures hydrodynamics-induced asymmetrical growth. The validated solver is then used to model snowflake growth under different ambient conditions with respect to humidity and temperature in the plate-growth regime section of the Nakaya diagram. The resulting crystal habits are compared to both numerical and experimental reference data available in the literature. The overall agreement with experimental data shows that the proposed algorithm correctly captures both the crystal shape and the onset of primary and secondary branching instabilities. As a final part of the study the effects of forced convection on snowflake growth are studied. It is shown, in agreement with observations in the literature, that under such condition the crystal exhibits non-symmetrical growth. The non-uniform humidity around the crystal due to forced convection can even result in the coexistence of different growth modes on different sides of the same crystal.

physics.flu-dyn↗

arXiv2012

The Molecular Gas Content of z = 3 Lyman Break Galaxies; Evidence of a non Evolving Gas Fraction in Main Sequence Galaxies at z > 2

We present observations of the CO[3-2] emission towards two massive and infrared luminous Lyman Break Galaxies at z = 3.21 and z = 2.92, using the IRAM Plateau de Bure Interferometer, placing first constraints on the molecular gas masses (Mgas) of non-lensed LBGs. Their overall properties are consistent with those of typical (Main-Sequence) galaxies at their redshifts, with specific star formation rates ~1.6 and ~2.2 Gyr^(-1), despite their large infrared luminosities L_IR ~2-3 x 10^12 Lsun derived from Herschel. With one plausible CO detection (spurious detection probability of 10^(-3)) and one upper limit, we investigate the evolution of the molecular gas-to-stellar mass ratio (Mgas/M*) with redshift. Our data suggest that the steep evolution of Mgas/M* of normal galaxies up to z~2 is followed by a flattening at higher redshifts, providing supporting evidence for the existence of a plateau in the evolution of the specific star formation rate at z > 2.5.

astro-ph.CO↗