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Investigating Phase Transition of Water-alcohol Systems in a Supersonic Nozzle

Sun, Tong
http://rave.ohiolink.edu/etdc/view?acc_num=osu165772089092095

Abstract Details

2022, Doctor of Philosophy, Ohio State University, Chemical Engineering.
This work studies the effect of low concentration short-chain alcohols on the freezing of nano-sized aqueous droplets. Alcohols with varying chain lengths are of interest because of their potentially different surface partitioning propensities. The distribution of alcohol molecules between surface and bulk phase of the nanodroplets is calculated using a monolayer model to show the large discrepancies of the partitioning preferences between 1-propanol and 1-pentanol at a supercooled temperature. Aerosols with the radius ~ 6 nm are generated in a supersonic nozzle via vapor-liquid nucleation and are subsequently frozen by the continuous cooling. The properties and phase transition behavior of the aerosols are characterized by pressure trace measurement and Fourier Transform Infrared spectroscopy. The results show that when small amounts of short-chain alcohol are added to water, the nucleation is significantly promoted to higher temperatures since the interfacial free energy of particle formation and the equilibrium vapor pressure of the mixture decrease. The O-H stretch region of the IR spectra are analyzed using self-modeling curve resolution method, where a spectrum is decomposed to a combination of three linearly independent components. By quantifying these underlying basic components of the IR spectra for the water-alcohol mixtures at varying concentrations, the change of the freezing temperature, kinetics and the ice structure are discussed. It is found that 1-propanol starts to perturb freezing kinetics and the ice component structure at a lower concentration than 1-pentanol. This phenomenon is consistent with the lower surface partitioning propensity of 1-propanol. The freezing point decreases as alcohol concentration increases, and the ice nucleation rate decreases within an order of magnitude for all studied cases. Next, we extend our study by increasing the alcohol chain length to C6 and changing -OH group position from the terminal to the middle carbon. Spectroscopic evidence of alcohol surface partitioning, such as the disappearance of the dangling H peak upon the addition of alcohols and the alignment of the C-H peaks with vapor or liquid phase alcohols, are shown. It is found that the 3-isomers partition less on the droplet surface than their 1-isomers due to their larger molecular area and higher solubilities in water. As a result, they disrupt the tetrahedral ice structure at lower overall concentrations. Lastly, we investigate the clustering of methanol in the gaseous phase during nucleation. Equilibrium constants of cluster formation are calculated based on the thermodynamic formulations and the Helmholtz free energies derived from the Monte Carlo simulation. The cluster model is validated by our previous methanol nucleation data where the temperature is directly measured, and liquid droplet formation is detected by small angle x-ray scattering. The results show that including dimer, tetramer, pentamer and hexamer could adequately account for the clustering heat. Upon addition of small amounts of water, clustering is not significantly perturbed but the temperature of liquid formation increases. Binary nucleation of methanol-water over the whole concentration range is systematically studied and mutual enhancement in nucleation onset condition at 220 K is observed. The correct prediction by classical nucleation theory is challenged by the need to extrapolate data to the subcooled region and by the inapplicability of explicit cluster models that require a minimum of 12 molecules in the critical cluster.
Barbara Wyslouzil, Dr. (Advisor)
250 p.
Chemical Engineering

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Citations

  • Sun, T. (2022). Investigating Phase Transition of Water-alcohol Systems in a Supersonic Nozzle [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu165772089092095

    APA Style (7th edition)

  • Sun, Tong. Investigating Phase Transition of Water-alcohol Systems in a Supersonic Nozzle. 2022. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu165772089092095.

    MLA Style (8th edition)

  • Sun, Tong. "Investigating Phase Transition of Water-alcohol Systems in a Supersonic Nozzle." Doctoral dissertation, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu165772089092095

    Chicago Manual of Style (17th edition)

osu165772089092095
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