On Predicting Secondary Smoke Humidity Boundaries at Temperatures Below 0 deg. C.

This work reexamines work originally done in 1969 which estimated the humidity-temperature boundary conditions under which solid rocket exhaust gases containing hydrogen chloride HCl or hydrogen fluoride HF would be expected to interact with ambient moist air to form a secondary smoke or contrail. The original work has seen wide acceptance. However. the original work relied on extrapolations of water-HCl and water-HF vapor-pressure data taken at higher temperatures to regions below 0 deg C. which under some conditions were in substantial error. Low-temperature vapor-pressure data for the HCl-water system have since become available, permitting improved treatment of this regime, which is the major point of this work the HF work remains to be updated. In reworking the HCl problem, a decision was also made to use an alternative later set of literature data Fritz and Fuget, 1956 at temperatures above 0 deg C rather than the handbook data used in the 1969 paper. The various data sources involve significant disagreements, affecting results. Some minor adjustments to the Fritz and Fuget data were necessary to achieve internal consistency tor modeling purposes these adjustments appeared to be reasonable but cannot be justified in any scientific sense. The revised data are used here to recompute boundary conditions for a number of cases of interest. Results show minor changes which might be significant in some applications. The revised charts included here, until superseded or replaced by further work, are recommended for use in further work of this nature.