Articles with tag: "water drops"

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 …

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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 …

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3. NACA-TN-2510

   "a need has arisen for a more complete understanding of the physical properties of supercooled water because few of the physical properties of water have been investigated at temperatures much below 0° C"

   "Experimental Values of the Surface Tension of Supercooled Water" ¹

   

   Abstract

   The results of surface-tension measurements for supercooled water are presented. A total of 702 individual measurements of surface tension of triple-distilled water were made in the temperature range, 27° to -22.2° C, with 404 of these measurements at temperatures below 0° C. The increase in magnitude of surface tension with decreasing temperature, as indicated by measurements above 0° C, continues to -22.2° C. The inflection point in the surface-tension-temperature relation in the vicinity of 0° C, as indicated by the International Critical Table values for temperatures down to -8° C, is substantiated by the measurements in the temperature range, 0° to -22.2° C …

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4. 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 …

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5. 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 …

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6. 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 …

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7. Methods of Water Drop Impingement Quantification

   "One of the first essentials ... is a method for estimating or calculating the area over which water will strike the wing, and the distribution of water impingement over that area"

   From NACA-TN-1397.

   
   From NACA-TN-3839.

   Summary

   Several methods were used to quantify the water-drop impingement on a surface, such as a wing.

   Discussion

   We already saw in the Icing on Cylinders thread calculations made for impingement on a cylinder. The technique was expanded in NACA-TN-1397 to include Joukowski type airfoils. This allowed a transformation of the flow solution around a cylinder to be mapped into airfoil coordinates, and then used to solve for water drop trajectory calculations, similar to those used for cylinders.

   NACA-TN-1397 said one could calculate "the trajectory a single drop without the utilization of a differential analyzer". We saw the differential analyzer in the Icing on Cylinders thread, in particular detail in NACA-TN-2904. However, the example given (Table …

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8. Water Drop Imaging

   "it is necessary to measure the sizes of the droplets within the clouds." ¹

   NACA-RM-E50K01a, "Flight Camera for Photographing Cloud Droplets in Natural Suspension in the Atmosphere"

   NACA-RM-E51G05, "Adaptation of a Cascade Impactor to Flight Measurement of Droplet Size in Clouds"

   NACA-TN-3592, "An Oil-Stream Photomicrographic Aeroscope for Obtaining Cloud Liquid-Water Content and Droplet Size Distribution in Flight"

   Summary

   Three strategies were explored for water drop imaging.
   In NACA-RM-E50K01a, a telephoto arrangement allowed imaging water drops in situ.
   In NACA-RM-E51G05, water drops were put through a particle size sorting cascade, impacting on slides, and imaged.
   In NACA-TN-3592, water drops were captured in an oil stream exposed to the ambient flow, and then imaged.

   Key Points

   1. Three methods for obtaining images of water drops are discussed.
   2. Images of enough water drops allowed the calculation of the drop size distribution.
   3. These instruments had limited influence in the NACA-era.

   Abstract

   NACA-RM-E50K01a:

   A camera designed …

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9. Let's Build a 1D Water Drop Trajectory Simulation

   

   "The discrepancies are of the magnitude to be expected from ... the step by step integration". ¹

   Let's build a 1D water drop trajectory simulation

   Summary

   Water impingement values on a cylinder are calculated with step-by-step integration.

   Key points

   1. 1D equations of motion were implemented.
   2. Results agree well with the minimum drop size required for impingement.
   3. Water drops may contact the cylinder at very low K values.
   4. The methods appears accurate enough to use for other applications.

   Discussion

   We are going to start with a one dimensional simulation along a single line, the stagnation line of flow around a cylinder, y=0 in the figure above.

   We will implement the equations of motions for a drop around a cylinder from "Mathematical Investigation of Water Droplet Trajectories" ¹.

   Readers unfamiliar with "Mathematical Investigation of Water Droplet Trajectories" may wish to review it before proceeding further herein, especially to be familiar with the …

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10. NACA-TN-3024

    "evaporation losses are ... very small (less than 1 percent) in the case of smaller obstacles (of icing-rate-measurement-cylinder size)."

    "Maximum Evaporation Rates of Water Droplets Approaching Obstacles the Atmosphere under Icing Conditions" ¹

    

    Summary

    Less that 1% of drops evaporate approaching an obstacle for most cases.

    Key points

    1. Equations are detailed for the evaporation of water drops approaching an obstacle.
    2. Less that 1% of drops evaporate approaching an obstacle for most cases.

    Abstract

    When a closed body or a duct envelope moves through the atmosphere, air pressure and temperature rises occur ahead of the body or, under ram conditions, within the duct. If cloud water droplets are encountered, droplet evaporation will result because of the air-temperature rise and the relative velocity between the droplet and stagnating air. It is shown that the solution of the steady-state psychrometric equation provides evaporation rates which are the maximum possible when droplets are entrained in …

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11. "Mathematical Investigation of Water Droplet Trajectories"

    "IT IS DESIRED to calculate the trajectories of small water droplets (fog) in air moving at high velocities across a cylinder."

    

    Summary

    Langmuir drop size distributions are defined, and water drop impingement on a collection of cylinders for use as an icing instrument is described.

    Key points

    1. The Langmuir drop size distributions are defined
    2. The water drop impingement terms E, Beta, K, and Ko are defined
    3. The use of cylinders of different sizes and detailed calculations to determine water drop sizes

    Abstract

    Calculations are given of the trajectories of small water droplets moving in air at high velocities across a cylinder. The calculations were made by means of a differential analyzer (D.A.). A few calculations are also given for the case of a sphere and a ribbon.

    Each D. A. trajectory represents the motion of a single particle. The theoretical curves for the efficiency of deposition of very large …

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