A NEW APPARATUS FOR DETECTING THE CONCENTRATION OF FREEZING NUCLEI IN WATER

In order to measuring the relative concentration of freezing nuclei in hydrometeors, based on Vali’s even drops freezing experiment method，a new system of automatically detecting drop frozen signals and processing test data have been developed. The main body is a cold stage cooled by a set of thermocouples, 49 thermosensitive elements are adhered to the stage with proportional spacing. One of them is affixed with a small Pt100 temperature element to measure the temperature, another one acts as a signal reference, and each of the rest 47 thermosensitive elements supports one drop of tested water sample. When experiment running the stage and drops are linearity cooled at a cooling rate controlled by an 818P4 Eurotherm temperature controller. The freezing latent heat released by each freezing drop will be detected by the thermosensitive element，then transformed into a voltage signal by the arithmetic circuitries, a series of equal signal produced by all drops freezing will be real time monitored by computer. The freezing temperature and freezing time spectra of drops are then obtained, and the differential and accumulative concentrationtemperature spectra of freezing nuclei are derived by a suit of software. The apparatus works well with better precision and efficiency than our former device. The apparatus structure, functions of software, and experiment procedure are introduced, and the testing results for several water samples are given in this paper. The apparatus would be useful for testing the freezing nuclei in water and the research of cloud seeding agent. The artificial ice nuclei(such as AgI) is often used in precipitation enhancement operations, if taking the rain water samples before and after cloud seeding, the apparatus might help to find the differences in their freezing nuclei contents, thus beneficial to the assessment of the cloud seeding effect.