Temperature and Water Drop Size in the Pollak Counter

Abstract

An extensive series of measurements was made of the performance of the Pollak counter during adiabatic expansion. Temperature was measured by a resistance wire, 0.0005-in. (0.0127-mm) diameter, which was stretched the length of the counter. The temperature drop, pressure drop, and the fog formed during wet adiabatic expansion were observed on an oscilloscope and photographed with a Polaroid camera. The temperature drop was observed to be 8°C, whether room aerosol (about 50,000 particles · cm⁻³, causing dense fog) or filtered air (slight fog) was introduced. A temperature drop of 16°C was observed during dry adiabatic expansion. To obtain this condition, prolonged drying with dry air from a tank was necessary to rid the Pollak counter of the 200 cm³ of water in the ceramic lining. The same temperature was observed whether room aerosol or Altered air was introduced, but no fog was formed in either case. The water drop size was also measured by three methods: direct observation of sedimentation; calculations made from the water released in wet adiabatic expansion; and calculations from Pollak's calibration table. The three methods agree well among themselves and with the data in the literature, showing that the drop diameter varies from 45 μ at a concentration of 100 particles · cm⁻³ to 2 μm at 10⁶ · cm⁻³.

*This article is followed by a note by P. E. Wagner, Universitat Wien, Austria, and a response by the authors.

Notes

*This article is followed by a note by P. E. Wagner, Universitat Wien, Austria, and a response by the authors.