Monday, 7 July 2014
The design and operation of a non-ideal static diffusion chamber is discussed. A static diffusion chamber is an apparatus that enables precise growth of ice crystals by controlling temperature, pressure and ice supersaturation conditions at the chamber enter. In order to maximize control over these conditions, non-ideal effects due to sidewall heating must be eliminated. The standard way to do this is to increase the ratio of chamber width to height up to about 10:1. In a recent study of electrical coronas on ice crystals, two high-voltage electrodes were required within the chamber in order to subject the ice crystals to strong electric fields. This was problematic due to space restrictions, so it was decided to increase the chamber aspect ratio to 2.4:1. This resulted in a significant increase in non-ideal sidewall effects, which were carefully observed. It was found that during the cool-down period, a toroidal circulation was set up inside the chamber. This circulation was reduced significantly as the chamber approached equilibrium, allowing the required ice growth and subsequent discharge observations. The details of this chamber and its characteristics will be discussed, where it is shown that the non-ideal behaviors are predictable, well-behaved and not necessarily problematic.
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