Articles with tag: "freezing"

1. NACA-RM-E51L17

   "complete knowledge of the physical conditions under which supercooled clouds may exist, and the factors that cause a supercooled cloud to transform to an ice-crystal cloud is necessary"

   "A Photographic Study of Freezing of Water Droplets Falling Freely in Air" ¹

   

   Abstract

   SUMMARY

   A photographic technique for investigating water droplets of diameter less than 200 microns falling freely in air at temperatures between 0° C and -50° C has been devised and used to determine:
   (1) The shape of frozen droplets
   (2) The occurrence of collisions of partly frozen or of frozen and liquid droplets
   (3) The statistics on the freezing temperatures of individual free-falling droplets

   A considerable number of droplets were found to have a non-spherical shape after freezing because of various protuberances and frost growth, and droplet aggregates formed by collision. The observed frequency of collision of partly frozen droplets showed good order of magnitude agreement with the …

   read more

2. NACA-TN-2532

   "supercooled water was concluded to become progressively more ice-like as the temperature is lowered"

   "X-Ray Diffraction Study of the Internal Structure of Supercooled Water" ¹

   

   SUMMARY

   A Bragg X-ray spectrometer equipped with a volume-sensitive Geiger counter and Soller slits and employing filtered molybdenum Kα, radiation was used to obtain a set of diffracted intensity curves as a function of angle for supercooled water. Diffracted intensity curves in the temperature region of 21° to -16° C were obtained. The minimum between the two main diffraction peaks deepened continuously with lowering temperature, indicating a gradual change in the internal structure of the water. No discontinuity in this trend was noted at the melting point. The internal structure of supercooled water was concluded to become progressively more ice-like as the temperature is lowered.

   Discussion

   The extensive equations included in this publication area not detailed herein.

   APPARATUS AND PROCEDURE

   A Bragg X-ray spectrometer equipped …

   read more

3. NACA-TN-2234

   "very few supercooled droplets exist at temperatures lower than -35° C and the existence of an icing cloud at such low temperatures is probably an unusual occurrence."

   "Statistical Explanation of Spontaneous Freezing of Water Droplets" ¹

   

   Abstract

   A statistical theory based on the presence of small crystallization nuclei suspended in water is developed, to explain experimental results showing that on the average small droplets can be supercooled. to lower temperatures than large ones. Small nuclei of crystallization are assumed responsible for causing supercooled water to freeze spontaneously.

   The average behavior of supercooled droplets is reproduced on the basis of probability theory with an assumed distribution of crystallization nuclei with respect to the temperatures at which the nuclei cause freezing. The most probable distribution curves of spontaneous freezing temperatures for water droplets of various sizes within the size range found in clouds are obtained.

   Discussion

   In this study, data from the …

   read more

4. NACA-TN-2142

   "Although supercooled water has been observed and reported for over two centuries, considerable disagreement exists as to the degree of supercooling possible and the factors that influence supercooling."

   "Photomicrographic Investigation of Spontaneous Freezing Temperatures of Supercooled Water Droplets" ¹

   

   Abstract

   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 …

   read more

5. Properties of Water

   "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."

   
   From NACA-RM-E51L17.

   Introduction

   There was limited data for properties of liquid water below the temperature of 0° C (supercooled water) at the start of the NACA-era. The five studies reviewed here sought to improve the data available.

   The authors were well-informed of other studies available at the time. New instruments were conceived and built for these studies.

   These five studies largely considered water drops, although much of the data are also applicable to more general aircraft icing analysis.

   Four of the studies concern the temperature at which supercooled water drops will spontaneously freeze (freeze without outside influence other than temperature).

   Several of the studies note similarities of the properties …

   read more