Abstract
A theoretical analysis of non-steady-state supersaturation distributions in thermal-diffusion-type cloud nuclei counters is presented for the particular case when the incoming air sample is saturated. The transport of heat and water vapor is assumed to proceed by molecular diffusion alone. We consider a chamber 1 cm high having top and bottom plate temperatures of 20 and 16C, respectively. Transient supersaturations exceeding steady-state values arise if the sample is colder than the top plate. Specifically, when the temperature of the sample equals that of the bottom plate, the chamber experiences peak transient supersaturations which exceed the maximum steady-state value at the center by a factor of about 3. The time constant to attain steady state is found to be directly proportional to the square of the height of the chamber.
