Surface tension effects during low-Reynolds-number methanol droplet combustion

Raghavan, Vasudevan; Pope, Daniel N.; Howard, Damon; Gogos, George

doi:10.1016/j.combustflame.2006.02.001

Cited by 26 publications

(23 citation statements)

References 13 publications

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“…The particles might be somewhat aggregated during measurement dispersed by dry air because of their cohesive property. Anyway, the smaller surface tension of MeCN (19.1 dyn/cm) than that of water (72.7 dyn/cm) might result in finely splattered mists of MeCN solution as explained by Raghavan et al 24) As a result, the smaller particles were prepared from MeCN solution, which sizes are directly related to those of spray mists because the mists were freeze-dried while keeping their sizes and shapes. In addition, the difference in particle size would be also attributed to the volume change of MeCN and water when frozen as mentioned above.…”

Section: Results and Discussion Comparison Of Sfd Particles Prepared mentioning

confidence: 99%

Novel Spray Freeze-Drying Technique Using Four-Fluid Nozzle-Development of Organic Solvent System to Expand Its Application to Poorly Water Soluble Drugs

Niwa

Shimabara

Danjo

2010

CHEMICAL & PHARMACEUTICAL BULLETIN

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A significant number of active pharmaceutical ingredients (APIs) being discovered exhibit expected therapeutic behaviors, but unfortunately have undesirable drug-like properties such as low solubility and poor ADME performance, making formulation into an effective drug product challenging. In fact, more than 40% of the pharmaceutical candidates in the development pipelines are reported to be categorized as poorly soluble.1,2) These compounds are classified as biopharmaceutical classification system (BCS) class II for which their maximum bioavailability is limited by their rate of dissolution. 3,4) Improving the dissolution rate of these compounds is achieved through various approaches of formulation technology. These include particle size reduction/ milling, [5][6][7][8] solution-based precipitation, solid dispersion by hot melt extrusion 9) or spray-drying, 10,11) complexation with cyclodextrins 12,13) and so on, as also described extensively in reviews. 14,15) Cryogenic technologies such as freeze drying 16) and spray freezing into liquid (SFL), [17][18][19] in particular, have lately attracted considerable attention for BCS class II compounds. These processes use cryogen, particularly liquid nitrogen, to form a solid dispersion composed of nano-dispersed domains of API within the hydrophilic polymer matrix. In order to increase universality of unique lyophilization technique in SFL, authors have developed spray freeze-drying (SFD) technique before, which is combined the conventional spraydryer with freeze-dryer, both equipments are available in market. 20) In addition, SFD technique was further improved by adopting four-fluid nozzle (4N) to expand its application in pharmaceutical industry. 21) In the conventional process both API and a hydrophilic excipient, called drug and carrier in this report respectively, are necessary to be dissolved in common spray solution because two-fluid nozzle (2N) has only one liquid-supplying line. Using a common solvent would sometimes lead to restricted combination between API and the carrier. 4N having two liquid passages allows API and the carrier to be dissolved in separate solvents, overcoming this problem. In this research, the organic/aqueous co-solvent spray system was newly established in 4N-SFD process in which the poorly water-soluble drug was dissolved in organic solvent and the dissolution-modified carrier was dissolved in water, which is likely frequent combination for solubilization. Acetonitrile was selected as an organic spray solvent due to its good solvent property for many drugs, its relatively high melting point (Ϫ43.8°C) among organic solvents and its easily evaporated behavior with higher vapor pressure. Phenytoin and ciclosporin were used as a poorly water-soluble drug and two types of carrier were used as a dissolution modifier. In case using phenytoin, which is dissolved in aqueous alkaline solution as well as acetonitrile, 1) aqueous spray system (phenytoin dissolved in aqueous alkaline solution and the carrier dissolved in water; called 4N-SFD-aqua)...

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Section: Results and Discussion Comparison Of Sfd Particles Prepared mentioning

confidence: 99%

Novel Spray Freeze-Drying Technique Using Four-Fluid Nozzle-Development of Organic Solvent System to Expand Its Application to Poorly Water Soluble Drugs

Niwa

Shimabara

Danjo

2010

CHEMICAL & PHARMACEUTICAL BULLETIN

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“…Results of several theoretical and numerical studies of methanol droplet combustion, which include water absorption, have been presented in the past [9][10][11][12][13][14]. One-dimensional numerical simulations [9] with detailed chemical kinetics for methanol showed that liquid-phase molecular diffusion of condensed water in the droplet interior is too slow to be consistent with the observed large amount of water present in the droplets during the experiments.…”

Section: Introductionmentioning

confidence: 87%

“…The results showed that the perfect liquid-phase mixing model predicts extinction diameters close to the experimentally observed values, and it was speculated that diffusocapillary (or solutal-Marangoni) instability, caused by the difference between the surface tension of water and that of methanol, could lead to strong internal circulation. Axisymmetric numerical simulations with surface-tension effects included have shown that this type of Marangoni effect in fact has a strong influence during methanol droplet evaporation and combustion [11][12][13]. Water absorption with a well-mixed liquid-phase thus is a reasonable approximation for describing methanol droplet combustion.…”

Section: Introductionmentioning

confidence: 96%

Methanol droplet extinction in carbon-dioxide-enriched environments in microgravity

Hicks

Nayagam

Williams

2010

Combustion and Flame

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“…Thus, to achieve more reliable modeling of spray ignition and combustion, the influence of convective gas flow and relative acceleration of droplet and gas phase on the ignition and combustion of fuel droplets has to be investigated. A smaller number of studies deal with the influence of a convective air flow on the ignition or combustion behavior of fuel droplets [16][17][18][19][20][21][22][23][24][25][26][27], although in practical spray combustion devices, droplets are sub-jected to a convective environment. Tsai and Sterling [16] have studied the combustion of linear droplet arrays numerically by a quasi-steady approach with a one-step, finite-rate kinetic model.…”

Section: Introductionmentioning

confidence: 99%

“…engines at high pressure. Transient numerical studies of surface tension effects and water absorption are performed by Raghavan et al in the case of methanol droplet combustion under forced convection at different Reynolds numbers [25,26]. A significant dependence of the amount of absorbed water on the surface tension as well as on the Reynolds number was found.…”

Section: Introductionmentioning

confidence: 99%

The ignition of methanol droplets in a laminar convective environment

Stauch

Maas

2008

Combustion and Flame

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Numerical simulations of the ignition of methanol droplets in a laminar convective environment are performed using detailed reaction mechanisms and detailed transport models. The flow velocities of the forced convection ranges from 0.01 up to 5 m/s, whereas the ambient gas temperature is varied between 1300 and 1500 K. The ignition delay time of a single droplet is found to decrease with increasing velocity of the convective gas flow. This decrease is attributed to the steepening of the spatial gradients of the profiles of physical variables, such as species mass fractions or temperature. This steepening is originated by a stronger gas flow and leads to a speed-up of the physical transport processes. For the studied flow conditions, an acceleration of the gas flow on the order of the gravitational acceleration does not show a significant influence on the ignition delay time. A downstream movement of the local ignition point with increasing flow velocity is observed. For higher flow velocities, an ignition in the wake of the droplet followed by an upstream flame propagation is found. After ignition, the formation of an envelope flame is detected. The structure of this envelope flame is studied.

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Surface tension effects during low-Reynolds-number methanol droplet combustion

Cited by 26 publications

References 13 publications

Novel Spray Freeze-Drying Technique Using Four-Fluid Nozzle-Development of Organic Solvent System to Expand Its Application to Poorly Water Soluble Drugs

Novel Spray Freeze-Drying Technique Using Four-Fluid Nozzle-Development of Organic Solvent System to Expand Its Application to Poorly Water Soluble Drugs

Methanol droplet extinction in carbon-dioxide-enriched environments in microgravity

The ignition of methanol droplets in a laminar convective environment

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