The Melting of Natural Snowflakes Suspended in a Vertical Wind Tunnel.

摘要

In order to study the atmospheric snowflake melting process, it is desirable to suspend a natural snowflake freely in an airstream. Previously, researchers have suspended the snowflake either by using nets, wires, etc. or by catching and then inserting it into a suspension chamber. Applying a number of new concepts, an apparatus capable of suspending the natural snowflake in an upward stream of air has been developed. Using the apparatus, the snowflake melting process has been studied under natural conditions. The new apparatus employs a diverging design with a concave upward velocity profile. This velocity profile cradles the snowflake in the bottom, thus centering it in the observation section. An insertion tube with a spring-loaded opening allows the snowflake to fall into the apparatus and be caught by the upward airflow. While being suspended freely in this column of air, it melts under conditions of controlled relative humidity and temperature. This permits measurements of its velocity, size and shape changes. The behavior of the snowflake during the melting process is also recorded by cameras.