WMOD00462

• Contract/Permit #: 87-1999
• Title: Development of Empirical Equations of Ice Crystal Growth Microphysics for Modeling Analysis - Final Report
• Date: 9/1/1988
• Weather Modification - Doc Type: Report

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steam left the pressure cooker located outside the cold room, and reached the

fog preparation chamber through the connecting tube.

Turbulent mixing of cold air and steam took place, when they entered

into the fog chamber. This turbulent fog flowed around the shelves, and

gained the extra time necessary to ensure that the air mixture becomes

sufficiently homogeneous with respect to temperature and cloud droplet

concentration before reaching the honeycomb section. The honeycomb

consisted of drinking straws packed inside a square frame with a side length

of 20 em. These straws, each with a diameter of 6 mm and a length of 10 em,

suppressed the remaining turbulence to create a laminar flow as the air

approached the suspension chamber from below. The straws also tended to

accumulate frost on the upstream side, causing excessive obstruction to the

flow, which motivated the design of a honeycomb that could easily be

replaced.

After passing through the honeycomb section, the supercooled fog

flowed upward though the ice crystal suspension chamber. This chamber was

a vertical square tunnel shaped like a truncated pyramid that has a height of

89 em and a cross sectional width of 20 em at the base shrinking to 11 em at

the top. The converging design increased the updraft speed near the edges of

the chamber with little enhancement around the center. The resultant

vertical velocity profile kept the suspended ice crystal close to the center and

the combination of the velocity profile and laminar flow maintained

horizontal stability during crystal suspension. In other words, this unique

tunnel design allows the crystal to be suspended in air for indefinite periods

of time by simply matching the upward flow speed with the crystal's terminal

faIl speed.

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