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- Author or Editor: John C. Carstens x
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Abstract
The interaction of two growing droplets in a supersaturated atmosphere has been examined, and the temperature and vapor density profiles have been determined. It is found that the smaller droplet tends to “catch up” with the larger at a slower rate than predicted by conventional diffusion theory. Consideration of droplet fallspeeds leads to the conclusion that, under atmospheric conditions, growth interaction becomes significant only for droplet “pairs” having equal or nearly equal radii. The number of such pairs is generally small enough so that the effect on the size distribution is quite small. Of a much greater importance is the possibility of a resulting attractive diffusio-phoretic force between two growing drops which, in turn, gives rise to a net velocity of one drop toward the other. If this diffusion force of attraction becomes sufficiently strong to overcome the hydrodynamic and thermo-phoretic forces acting in the opposite direction, both collision efficiencies and coagulation of small droplets could be further enhanced, thus accounting for departures from monodispersity in actual atmospheric clouds.
Abstract
The interaction of two growing droplets in a supersaturated atmosphere has been examined, and the temperature and vapor density profiles have been determined. It is found that the smaller droplet tends to “catch up” with the larger at a slower rate than predicted by conventional diffusion theory. Consideration of droplet fallspeeds leads to the conclusion that, under atmospheric conditions, growth interaction becomes significant only for droplet “pairs” having equal or nearly equal radii. The number of such pairs is generally small enough so that the effect on the size distribution is quite small. Of a much greater importance is the possibility of a resulting attractive diffusio-phoretic force between two growing drops which, in turn, gives rise to a net velocity of one drop toward the other. If this diffusion force of attraction becomes sufficiently strong to overcome the hydrodynamic and thermo-phoretic forces acting in the opposite direction, both collision efficiencies and coagulation of small droplets could be further enhanced, thus accounting for departures from monodispersity in actual atmospheric clouds.
Abstract
The measurement of the temperature drop in a dry Pollak condensation nucleus counter by Israel and Nix has been interpreted as an indication that the expansion process does not yield as high a supersaturation as predicted by thermodynamics. An analysis of the heat and vapor diffusion from the walls of the chamber indicates that the counter does indeed develop the supersaturations predicted by thermodynamics in the absence of dropwise condensation and that the natural sensitive time is of the order of 0.3 sec. The measurements of Israel and Nix can be explained in terms of a thermal analysis of the thermocouple itself. The seemingly rapid response of the thermocouple is an indication of the attainment of the steady-state heat flow from the thermocouple and is not an indication that the thermocouple is reading the temperature of the ambient gas accurately. Moreover, the anomalous temperature drop observed about 1 sec after the expansion marks the point at which convection currents sweep away the heated gas which has accumulated immediately adjacent to the thermocouple.
Abstract
The measurement of the temperature drop in a dry Pollak condensation nucleus counter by Israel and Nix has been interpreted as an indication that the expansion process does not yield as high a supersaturation as predicted by thermodynamics. An analysis of the heat and vapor diffusion from the walls of the chamber indicates that the counter does indeed develop the supersaturations predicted by thermodynamics in the absence of dropwise condensation and that the natural sensitive time is of the order of 0.3 sec. The measurements of Israel and Nix can be explained in terms of a thermal analysis of the thermocouple itself. The seemingly rapid response of the thermocouple is an indication of the attainment of the steady-state heat flow from the thermocouple and is not an indication that the thermocouple is reading the temperature of the ambient gas accurately. Moreover, the anomalous temperature drop observed about 1 sec after the expansion marks the point at which convection currents sweep away the heated gas which has accumulated immediately adjacent to the thermocouple.
Abstract
A numerical model has been developed to describe the early stage of cloud formation in a relatively small simulation chamber. The results for adiabatic expansion show a tendency for the cloud droplet spectrum to narrow, similar to the results obtained by other authors. The influence of updraft fluctuations is not as important as the fluctuation of temperature which depends upon the amplitude and frequency of the fluctuations, and the expansion rate of volume. Simple models of the sedimentation of the drops show that sedimentation might be a factor limiting the rate of expansion. Nuclei suddenly introduced into the cloud parcel indicate that the seeding effect depends significantly on the concentration and size of predominantly larger nuclei.
Abstract
A numerical model has been developed to describe the early stage of cloud formation in a relatively small simulation chamber. The results for adiabatic expansion show a tendency for the cloud droplet spectrum to narrow, similar to the results obtained by other authors. The influence of updraft fluctuations is not as important as the fluctuation of temperature which depends upon the amplitude and frequency of the fluctuations, and the expansion rate of volume. Simple models of the sedimentation of the drops show that sedimentation might be a factor limiting the rate of expansion. Nuclei suddenly introduced into the cloud parcel indicate that the seeding effect depends significantly on the concentration and size of predominantly larger nuclei.
