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Quantitative Evaluation of Experimental Results an the Heterogeneous Freezing Nucleation of Supercooled Liquids
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1971
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EngineeringNuclear PhysicsNuclear DataChemistryFreeze-thaw CyclingNucleationCumulative SpectrumThermodynamicsCumulative Nucleus SpectrumBiophysicsIce-water SystemPhysicsAtmospheric IcingDifferential SpectrumNuclear TheoryPhysical ChemistryCryosphereNuclear AstrophysicsExperimental ResultsHeterogeneous Freezing NucleationNatural SciencesChemical KineticsQuantitative Evaluation
Freezing experiments with many small drops are used to study homogeneous and heterogeneous nucleation, but the spread in freezing temperatures arises from nuclei of varying activity, and until now no quantitative assessment of nucleus content independent of drop size has been possible. This study demonstrates that the observed freezing temperatures of drops can be used to derive both differential and cumulative nucleus spectra. The differential spectrum quantifies the concentration of nuclei active at specific temperatures, while the cumulative spectrum gives the concentration of nuclei active at all temperatures warmer than a chosen threshold. Monte Carlo simulations show the derived spectra are accurate within factors of 2–4, and the average freezing temperature’s dependence on drop volume is governed by the nucleus spectrum shape, being approximately exponential for many spectra.
Freezing experiments using large numbers of small drops are frequently used for the study of both homogeneous and heterogeneous nucleation of water and of other substances. For heterogeneous nucleation, the spread in the observed freezing temperatures of drops has been shown to arise from the presence of nuclei of different activities in the sample. In the past no quantitative assessment of the nucleus content could be given independent of the drop sizes used. It is shown in this paper that from the observed freezing temperatures of the drops one can derive both a differential and a cumulative nucleus spectrum. The differential spectrum represents the concentrations of nuclei which are active at specific temperatures and the cumulative spectrum represents the concentrations of nuclei active at all temperatures warmer than the selected temperature. The accuracies of the derived spectra were examined by Monte Carlo simulation and are shown to be such that the concentrations are reliable to within factors of 2–4. The dependence of the average freezing temperature on drop volume is shown in general to be determined by the shape of the nucleus spectrum but is approximately exponential for many spectra.