Experimental Research On Freezing Theory Of Heterogeneous Nucleation Of Water Drop

Heterogeneous nucleation freezing is an important process in cloud physics. Depth studying the effect of different cooling rate and drops size on freezing is very significant, but previous research usually use clean water sample like distilled and tap water, lack of the research on water sample with a lot of impurities. In this paper, we choose three kinds of water, rainwater, pure water and bottled water, use the device of uniform drops freezing experiment designed by CAMS, assisting water drop freezing experimental facility with video camera, to finish the constant cooling rate experiments for three kinds of water and the constant temperature experiment for rainwater. Freezing experiment of different water drops size in nano AgI water sample was also conducted. These experiments in order to verify previous experiment results and find a quantitative relationship between the freezing of water drops and temperature and time, examine the interaction of two hypotheses. At the same time, uniform drop freezing experiments of natural water sample and uniform drop freezing experiments of artificial water sample were conducted in this article. In addition, two cases of freezing experiment are finished, The main results are as follows:In general, with the decreasing temperature, the accumulative freezing fraction in slow cooling rate set is larger than which in fast cooling rate set, and this phenomenon is more obvious for pure water and bottled water; The average freezing temperature and median freezing temperature in water sample are colder for the higher rate of cooling, the distinction for different water are logarithm relationship between freezing temperature and cooling rate in rainwater and linear relationship in bottled water; The probability of freezing exponential increase with decreasing temperature in each water sample, and the exponential coefficient decreasing exponentially increasing cooling rate in bottled water; At constant temperature period, the probability of freezing decays exponentially with time in rainwater, decaying faster in first two minutes, and becomes slower later, there is no freezing event occurs after 15 minutes. This phenomenon can be explained by stochastic hypothesis and singular hypothesis, when the temperature of drops reach or colder than characteristic temperature, water molecules need a period of time to aggregation on freezing nucleus, this is the reason why drop freezing occur in constant temperature period. The results in this paper not only verify the previous results of distilled water, but also provide a better experimental basis for application of numerical model.The more smaller of the drops size, the more harder to freezing under the same conditions, the average freezing temperature lowering logarithmically with decreasing drop diameter, the probability of freezing exponential increase with decreasing temperature, the coefficient of exponential function has a linear relationship with drop volume; the drop freezing temperature and the content of freezing nucleus of hail melting water are higher than of snow melting water, the thunderstorm water has lowest value; the average freezing temperature of nano AgI water sample are higher than normal AgI’s, the pure water has lowest value, the exponential coefficient in the probability of freezing function decreases with two orders of magnitude in three kinds of water sample, indicating that artificial nucleus has a significant effect to enhance the probability of freezing of water drops. Ice nucleating efficiency of the S-8 type AgI pyrotechnic agents immersion freezing experiment has been finished. Nucleating efficiency increases exponentially with increasing supercooled temperature. Results were influenced by the ratio of sample volume to water volume. Collecting artificial precipitation modified by 37 anti-aircraft artillery and using the drop freezing experiment method to detect the content of freezing nucleus in artificial precipitation, It indicates that the content of freezing nucleus and drop freezing temperature of artificial rainfall are higher than natural precipitation one.