The density of natural ice accretions related to nondimensional icing parameters

Abstract

The meteorological conditions under which atmospheric icing occurs determine the density of the accreted ice. A density relationship developed by Macklin from artificially iced samples is often used to calculate rime ice density as a function of R (effective droplet radius multiplied by droplet impact speed divided by icing surface temperature). In this study icing data collected in natural conditions at the summit of Mt Washington in New Hampshire were used to test Macklin's relationship. the Mt Washington Observatory has been making icing measurements using rotating multicylinders since 1969. Meteorological and icing data from these observations were used along with accretion weight and volume data from each of the six cylinders in the multicylinder set to relate ice accretion density to Macklin's R parameter. the relationship obtained was compared with Macklin's and with those developed by other authors who also related their measured rime densities to R. However, R is difficult to calculate and has been defined differently by various researchers. Therefore, a multiple regression analysis was performed to relate the ice accretion density to easily calculated nondimensional numbers describing the icing process. the inertia coefficient, ϕ parameter, and a heat flux ratio were used to predict rime accretion density. For a given cylinder diameter the cloud median volume droplet diameter and the wind speed were found to be the most important factors in controlling the ice accretion density.