Thermal Shock as an Ice Multiplication Mechanism. Part II. Experimental

Abstract

Thermal shock tests were conducted on large numbers of ice spheres and plates, all of macroscopic size. The thermal shock was applied by cooling the specimens to the desired temperature, and then rapidly warming part of one surface by bringing water in contact with it. The spheres had a median cracking temperature of −16°C, and comparison with thermoelastic theory yielded tensile strength values for ice in the range 20–30 bars. Initiation of cracking in thick plates was a function of the temperature and of the ratio a/b (ratio of radius of warmed area to that of the cylindrical plate). For a/b=0.6, −20°C was the critical temperature, but for a/b≤0.2, which is a more appropriate scaling factor in terms of riming of cloud particles, the samples had to be colder than −35°C before any cracks appeared. None of the samples fragmented or separated. Because the experimentally applied temperature changes were more severe than would be experienced by rimed ice crystals in clouds, it is concluded that thermal shock is unlikely to be an important ice multiplication mechanism at −5°C.