2 Volumes Final Proceedings - Washington 1984.pdf - IARC Research

265into the open sea, melting of the ice's surface andsides intensified. By the end of July, due to thedecrease in the ice massif's thickness, it came tolayered ice production, taking into account coolingdown to -lO'C, increases substantially when the airthe water surface and broke up during a storm. temperature decreases to -2OOC. Lowering the airStudies of layered ice production from sea water temperature further does relatively little tounder laboratory conditions were Undertaken, in increase the ice production rate. The effect proadditionto in-situ ice production. To do this, a duced by the wind velocity is more obvious. Withwind tunnel was designed in the underground refrig- an increase of wind velocity 1 from to 5 m/sec,erating chamber of the Permafrost Institute of the the rate of ice production increased 1.3-1.4 timesSiberian Branch of the USSR Academy of Sciences. and twice as much at a wind velocity of 15 m/sec.Inside the wind tunnel there was a special 3 0 8x4 ~cm thermoinsulated pan, equipped with sensors for TABLE 1. Duration (hr) of production and coolingmeasuring water and ice temperature. The airof sea water ice to a temperature -1O'C of (thicktemperaturewas constant during all the tests in ness of water layer is 25 mm)the chamber, the temperature ranging from -12 to-30°C. The air speed in the tube above the panwas held at from 1 to 15 m/s.AirWind speed h/s)The pan was filled with sea water0°C and temperatureplaced in the working part of the wind tunnel,("C) 1 2 5 10 15then the ventilation system was switched on. Readingsof the temperature sensors indicated the time -12 14.5 13.8 11.1 8.3 6.5for water freezing and ice cooling to down the-14 12.7 11.8 9.8 7.4 5.7control temperature of -10'~.-16 11.8 11.2 9.1 6.8 5.3The thickness of the layer of frozen water in -18 11.2 10.3 8.3 6.2 4.9the pan was recorded from 5 to 40 mm. To deter--20 10.7 9.8 7.9 6.0 4.6mine the relationship between the rate of ice-25 9.8 9.0 7.3 5.5 4.2production and the air temperature and wind velocity,-30 9.1 8.4 6.8 5.1 4.0a series of tests related to freezing a 25 mm layerof water were undertaken (Table 1). In addition,experiments have been carried out on freezing waterlayers of different thicknesses at constant temperatureand wind speed. On the basis of thesetests, it was found that the time t6 required for agiven water layer to freeze and for the ice to cooldown to -1OOC is in approximate linear dependenceon this layer thickness 6 (within 5 and 30 nnn) andcan be expressed by the empirical formula6t6 = t25Figure 1. As indicated in the plot, the rare ofwhere 6 is the thickness of the freezing waterlayer in mm, t25 is the time required to freeze awater layer 25 mm thick and to cool it down to-10°C.The time it took to freeze a water 40 layer mmthick was t6 = 1,7 t25. This means that by freez-0 -to -20 -30'cing a water layer with a thickness greater than30 mm, the linear dependence changes towards theFIGURE 1. The water layer freezing rate (J) vsair temperature and wind speed (V).increase of freezing rime, when compared to theabove-mentioned formula. When the layer of freezingwater is thin, the rate of layered ice productiondemonstrates negligible dependence on thethickness of the freezing water layers if do theynot exceed 30 m. This can be explained by theThe strength of the layered ice depends to agreat extent on its salt content. To define thisdependence more accurately a series of ice stresstests were conducted. Ice samples 73 mm in diameterand 130 mm high were produced by freezing layers offact that the intensity of the heat emanating from water having a given salinity. For this purposethe surface of the freezing layer by means of tur- sea water was diluted with fresh water, The testsbulent heat exchange as the next water layer begins were carried out at four temperature points, Theto freeze is presumably determined by temperatureand wind velocity; only when the ice thickness exceeds30 nun does the reduction of the intensity ofrate of load application in all the trials wasequal to 2 MPa/min. The results of these experimentsare presented in Table 2.the heat being given off become pronounced as well A pronounced increase in the ultimate strengthas usual decrease in water freezing rate when ice of the ice is observed at an ice temperature ofthickness increases.-4.5'C, as its salinity decreases. This dependenceFrom the aforementioned considerations, theactual rate of layer-wise production process canbe estimated based on the test results of freezingbecomes more complicated at lower temperatures. Aslight increase in ice salinity resultsin increasedstrength as compared to ice produced from fresh25 mm thick layers of sea water (Table 1). The water, whereas further increaseice salinitydependence of the rate of production upon the air leads to decreased strength. In all cases thetemperature at different wind speeds is shown in strength of ice increased as the temperature was