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To lower the ice adhesion strength is the most efficient technique for passive ice removal for several applications. In this paper, the effect of different types of ice on the ice adhesion strength was investigated. The ice types precipitation ice, in-cloud ice and bulk water ice on the same aluminum substrate and under similar environmental conditions were investigated. The ice adhesion strength was measured with a centrifugal adhesion test and varied from 0.78 ± 0.10 MPa for precipitation ice, 0.53 ± 0.12 MPa for in-cloud ice to 0.28 ± 0.08 MPa for bulk water ice. The results indicate that the ice adhesion strength inversely correlates with the density of ice. The results inspire a new strategy in icephobic surface development, specifically tailored to the relevant ice type. © 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Measurements of the ultrasonic absorption of water have been made up to pressures of 2000 kg/cm2. The data show that both the shear and compressional losses decrease as the pressure is raised. Comparison of these results with the values predicted by Hall's theory of sound absorption in water shows that the theory must be modified to be in agreement with the experimental data. The modification consists of assuming that the open or ice type of packing is associated with the higher free‐energy state. If this modification is made, the observed data is in excellent agreement with theory. This result leads to the conclusion that even at 0°C less than 30 percent of the molecules in water are arranged in the ice type of packing. The results also indicate that the free‐energy difference between the two states of packing in water is temperature dependent.