标题： 液滴成核在快速膨胀气溶胶腔中 显示英文标题

标题： Droplet Nucleation In a Rapid Expansion Aerosol Chamber

摘要： 我们介绍了一种新的实验设施，用于在受控条件下研究液滴和冰粒子的成核和生长，并表征与云微物理过程相关的现象：快速膨胀气溶胶腔（REACh）。 REACh是一个中等尺寸的腔体（约0.14 m$^3$），结合了膨胀腔的原理，并能够探测湍流的影响。 通过突然的压力下降伴随温度下降实现成核，这在适当的热力学条件下可以使潮湿空气凝结成雾滴云。 REACh具备对初始水蒸气饱和比、种子气溶胶粒子的种类和浓度、温度、压力和空气流动混合的严格控制和监测，以及对气溶胶和雾滴大小和数量的高速实时测量。 在这里，我们证明，在每次膨胀过程中达到的最低温度可以通过干或湿绝热过程的热力学合理描述，适用于广泛的初始相对湿度。 形成的雾滴大小和数量以及云的总体寿命被表征为气溶胶浓度和初始水蒸气饱和比的函数。 总雾滴浓度与注入的气溶胶浓度呈线性关系，表明所有注入的气溶胶粒子都作为凝结核。 虽然形成的总雾滴数量随着气溶胶浓度的增加而增加，但由于可用水蒸气的竞争，平均雾滴大小随着种子气溶胶的浓度增加而减小。 理论考虑提供了在广泛条件下平均雾滴大小的定量预测。 显示英文摘要

摘要： We present a new experimental facility to investigate the nucleation and growth of liquid droplets and ice particles under controlled conditions and characterize processes relevant to cloud microphysics: the rapid expansion aerosol chamber (REACh). REACh is an intermediate size chamber (~0.14 m$^3$) combining the principle of an expansion chamber with the ability to probe the influence of turbulent flows. Nucleation is achieved via a sudden pressure drop accompanied by a temperature drop, which can cause humid air to condense into a cloud of droplets under the appropriate thermodynamic conditions. REACh features tight control and monitoring of the initial saturation ratio of water vapor, identity and concentration of seeding aerosol particles, temperature, pressure, and air flow mixing, together with high speed real time measurements of aerosol and droplet size and number. Here, we demonstrate that the minimum temperature reached during each expansion can be reasonably described by the thermodynamics of dry or moist adiabats, for a wide range of initial relative humidity. The size and number of droplets formed, and the overall lifetime of the cloud, are characterized as a function of the aerosol concentration and initial water vapor saturation ratio. The total droplet concentration scales linearly with the seeding aerosol concentration, suggesting that all injected aerosol particles serve as condensation nuclei. While the total number of droplets formed increases with aerosol concentration, the mean droplet size decreases with the concentration of seeding aerosols as a result of competition for the available water vapor. Theoretical considerations provide a quantitative prediction for the mean droplet size for a wide range of conditions.