Laboratory formation of border ice and frazil slush

Abstract

Ice formation under controlled conditions was studied in a cold room using a cylindrical steel tank 120 cm in diameter and 76 cm deep. Paddles turned by a variable speed motor moved the water about the axis of the tank. Twenty-one thermistors were used to record temperatures above and below the surface of the water. Ice was allowed to form with the cold room temperature held at −2 °C, −5 °C, −10 °C, and −20 °C and with water speeds (measured 4 cm from the tank wall) from 0 to 73 cm/s.At zero water speed ice formed first as needles randomly oriented over the surface. With flowing water, border ice width increased linearly with time, but independently of water speed. The rate of increase of the border width w fits the equation dw/dt = (4/9)|Ta|0.68 where Ta is the Celsius air temperature.Frazil was never observed at water speeds less than 24 cm/s, but was always formed at this or greater speeds, regardless of cold room temperature. The volume of slush accumulated was greater at greater water speeds and at colder air temperatures. Observed slush volumes are compared with semiempirical values of the ice mass obtained from theoretical equations. The data suggest that growth of ice crystals began when the water was supercooled by approximately 0.02 °C.