On the growth of homogeneously nucleated water droplets in nitrogen: an experimental study

Abstract

A pulse-expansion wave tube method to determine homogeneous nucleation rates of water droplets has been improved. In particular, by accounting for background scattering, the experimental light scattering can be fitted extremely well with the Mie scattering theory. This results in an accurate determination of the droplet growth curve, which is well defined owing to the sharp monodispersity of the droplet cloud generated by the nucleation pulse method. With this method, water condensation is effectively decoupled in birth (nucleation) and growth of droplets. Droplet growth curves yield information on the diffusion coefficient, which only depends on pressure and temperature and on the supersaturation of the individual experiments. Here, we propose to use this information in the interpretation of nucleation rate data. Experimental results are given for homogeneous nucleation rates of supercooled water droplets at nucleation temperature 240 K and pressure 1.0 MPa and for growth of supercooled water droplets at temperature 247 K and pressure 1.1 MPa. The supersaturation was varied between 10 and 14, resulting in nucleation rates varying between 10 $$^{14}$$ m $$^{-3}$$ s $$^{-1}$$ and 10 $$^{17}$$ m $$^{-3}$$ s $$^{-1}$$ . For the diffusion coefficient, a value of 1.51 $$\pm$$ 0.03 mm $$^2$$ s $$^{-1}$$ was found (247 K, 1.1 MPa) in agreement with previously reported results. It is discussed how the information from droplet growth data can be used to assess the quality of the individual water nucleation experiments.