Analysis of the Heat and Vapor Propagation from the Walls of the Nolan, Pollak and Gardner Type Condensation Nucleus Counters

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.