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An improved approach for measuring immersion freezing in large droplets over a wide temperature range.

ABSTRACT: Immersion freezing (ice nucleation by particles immersed in supercooled water) is a key process for forming ice in mixed-phase clouds. Immersion freezing experiments with particles in microliter-sized (millimeter-sized) water droplets are often applied to detecting very small numbers of ice nucleating particles (INPs). However, the application of such large droplets remains confined to the detection of INPs active at temperatures much higher than the homogeneous freezing limit, because of artifacts related to freezing of water droplets without added INPs at temperatures of -25?°C or higher on a supporting substrate. Here I report a method for measuring immersion freezing in super-microliter-sized droplets over a wide temperature range. To reduce possible artifacts, droplets are pipetted onto a thin layer of Vaseline and cooled in a clean booth. In the Cryogenic Refrigerator Applied to Freezing Test (CRAFT) system, freezing of pure (Milli-Q) water droplets are limited at temperatures above -30?°C. An intercomparison of various techniques for immersion freezing experiments with reference particles (Snomax and illite NX) demonstrates that despite the use of relatively large droplets, the CRAFT setup allows for evaluating the immersion freezing activity of the particles over almost the entire temperature range (about -30?°C to 0?°C) relevant for mixed-phase cloud formation.

SUBMITTER: Tobo Y

PROVIDER: S-EPMC5011777 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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An improved approach for measuring immersion freezing in large droplets over a wide temperature range.

Tobo Yutaka Y

Scientific reports 20160906

Immersion freezing (ice nucleation by particles immersed in supercooled water) is a key process for forming ice in mixed-phase clouds. Immersion freezing experiments with particles in microliter-sized (millimeter-sized) water droplets are often applied to detecting very small numbers of ice nucleating particles (INPs). However, the application of such large droplets remains confined to the detection of INPs active at temperatures much higher than the homogeneous freezing limit, because of artifa ...[more]

PMID: 27596247

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Project description:Cyclohexene is an important intermediate during the combustion process of hydrocarbon and oxygenated fuels. In view of the lack of study on the combustion of cyclohexene in air, an experimental and modeling study is performed to investigate the chemistry of cyclohexene-air mixtures under a wide temperature range. The shock tube experiments are conducted at pressures of 2 and 10 atm with equivalence ratios of 0.5, 1.0 and 2.0 to determine the ignition delay times. The ignition data under 10 atm cover a wide temperature range varying from a low temperature of 770 K to a high temperature of 1222 K. No typical negative-temperature-coefficient is observed, but the ignition at low temperatures is shorter than the extrapolation at high temperatures. A detailed kinetic model of cyclohexene oxidation is proposed based on the low temperature mechanism of 1,3-cyclohexadiene and the existing high temperature mechanism of cyclohexene. The developed model reproduces the ignition delay times in air well, but it over predicts the ignition delays in argon conditions at higher temperatures. Sensitivity analyses under different temperatures and equivalence ratios are carried out to identify the key reactions affecting ignition. The reactions of H + O2 = O + OH and hydrogen abstraction reaction of cyclohexene with oxygen (CYHEXEN + O2 = CYHEXEN-3J + HO2) explain the change of ignition delay time of cyclohexene with equivalence ratios. Flux analysis gives the change of main reaction pathways under wide temperatures and different pressures. The retro-Diels-Alder reaction as the most important consumption channel of cyclohexene at the pressure of 2 atm and temperature of 1350 K is greatly suppressed when the pressure is increased to 10 atm, while the hydrogen abstraction reaction becomes the main consumption channel of cyclohexene at the high pressure. The proposed kinetic model for cyclohexene oxidation can be used to develop models of hydrocarbon and oxygenated fuels.

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An improved approach for measuring immersion freezing in large droplets over a wide temperature range.

Publications

An improved approach for measuring immersion freezing in large droplets over a wide temperature range.

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