• Version
• 129 Downloads
• 1.94 MB File Size
• 1 File Count
• December 9, 2016 Create Date
• December 9, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Photomicrographic Investigation of Spontaneous Freezing Temperatures of Supercooled Water Droplets

A photomicrographic technique for investigating supercooled
water droplets has been devised and used to determine the
spontaneous freezing temperatures of supercooled water droplets
of the size ordinarily found in the atmosphere. The freezing
temperatures of 4527 droplets ranging from 8.75 to 1000 microns
in diameter supported on a platinum surface and 571 droplets
supported on copper were obtained.

The average spontaneous freezing temperature decreased with
decrease in the size of the droplets. The effect of size on the
spontaneous freezing temperature was particularly marked below
60 microns. Frequency—distribution curves of the spontaneous
freezing temperatures observed for droplets of'a given size were
obtained. Although no droplet froze at a temperature above 20° F,
all droplets melted at 32° F. Results obtained with a copper
support did not differ essentially from those obtained with a
platinum surface. '

Although many important advances have been made in the control
of ice formation on aircraft in flight, little progress has been
made toward an understanding of the fundamental processes involved
in the formation of ice or the prediction of such formation.

Because the presence of supercooled water in the atmosphere
is primarily responsible for aircraft icing, it is necessary to
know the properties of supercooled water for a complete under-
standing of the icing process. Although supercooled water has been
observed and reported for over two centuries, considerable dis-
agreement exists as to the degree of supercooling possible and the
factors that influence supercooling.

During the last 20 years, a few systematic laboratory‘
investigations of supercooled water have been conducted. The
studies of Meyer and Pfaff (reference 1), Tammann and Bflckner
(reference 2), and Ben (presented in reference 3) in Germany,
Doucet (reference'é) in France Cwilong (reference 5) in England,
and.Dorsey (references 6 and 73 and Beverly (reference 8) in the
United States are of particular interest.'