Experimental investigation of the evaporation rate of supercooled water droplets at constant temperature and varying relative humidity

Abstract. Contact freezing of single supercooled water droplets colliding with kaolinite dust particles has been investigated. The experiments were performed with droplets levitated in an electrodynamic balance at temperatures from 240 to 268 K. Under relatively dry conditions (when no water vapor was added) freezing was observed to occur below 249 K, while a freezing threshold of 267 K was observed when water vapor was added to the air in the chamber. The effect of relative humidity is attributed to an influence on the contact freezing process for the kaolinite-water droplet system, and it is not related to the lifetime of the droplets in the electrodynamic balance. Freezing probabilities per collision were derived assuming that collisions at the lowest temperature employed had a probability of unity. Mechanisms for contact freezing are briefly discussed.

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The Effect of Relative Humidity on the Nucleating Properties of Photolyzed Silver Iodide *

Bulletin of the American Meteorological Society ◽

10.1175/1520-0477-33.10.431 ◽

1952 ◽

Vol 33 (10) ◽

pp. 431-434 ◽

Cited By ~ 11

Author(s):

S. J. Birstein

Keyword(s):

Water Vapor ◽

Relative Humidity ◽

Ultraviolet Light ◽

Silver Iodide ◽

Supercooled Water ◽

Adsorbed Water ◽

Ice Formation ◽

Water Droplets ◽

Bright Sunlight ◽

A Cell

The effect of adsorbed water vapor on the photolysis of silver iodide has been studied. Inn has found that when silver iodide nuclei are exposed to ultraviolet light before injection into a cold chamber containing a cloud of supercooled water droplets, no ice formation is observed. Reynolds, Hume, Vonnegut and Schaefer have investigated the effect of bright sunlight on the action of silver iodide as a sublimation nucleus, and have found a decrease in the magnitude of nucleating effectiveness which is less than that observed by Inn. The studies in this laboratory have been concerned with the effect of relative humidity on the photolysis and subsequent nucleating properties of silver iodide particles. Known amounts of water vapor were introduced into a stream of nitrogen passing over a silver iodide generator. The silver iodide particles, covered with adsorbed water, were collected in a cell and exposed to ultraviolet light of known intensity for varying amounts of time. After irradiation, the silver iodide particles were injected into a cloud of supercooled water droplets and ice formation was watched for. The nucleating effectiveness of silver iodide exposed to ultraviolet light was found to be directly dependent on the relative humidity of the gas stream passing over the generator.

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Freezing of water droplets colliding with kaolinite particles

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-2417-2009 ◽

2009 ◽

Vol 9 (1) ◽

pp. 2417-2433

Author(s):

E. A. Svensson ◽

C. Delval ◽

P. von Hessberg ◽

M. S. Johnson ◽

J. B. C. Pettersson

Keyword(s):

Relative Humidity ◽

Aerosol Particles ◽

Supercooled Water ◽

Dust Particles ◽

Freezing Process ◽

Atmospheric Conditions ◽

Water Droplets ◽

Electrodynamic Balance ◽

Dry Conditions ◽

Modelling Studies

Abstract. Contact freezing of single supercooled water droplets colliding with kaolinite dust particles has been investigated. The experiments were performed with droplets levitated in an electrodynamic balance at temperatures from 240 to 268 K. Under dry conditions freezing was observed to occur below 249 K, while a freezing threshold of 267 K was observed at high relative humidity. The effect of relative humidity is attributed to an influence on the contact freezing process for the kaolinite-water droplet system, and it is not related to the lifetime of the droplets in the electrodynamic balance. Freezing probabilities per collision were derived assuming that collisions at the lowest temperature employed had a probability of unity. The data recorded at high humidity should be most relevant to atmospheric conditions, and the results indicate that parameterizations currently used in modelling studies to describe freezing rates are appropriate for kaolinite aerosol particles. Mechanisms for contact freezing are briefly discussed.

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On the Use of Monolayers to Reduce Evaporation From Stationary Water Pools

Journal of Heat Transfer ◽

10.1115/1.2910650 ◽

1993 ◽

Vol 115 (1) ◽

pp. 209-214 ◽

Cited By ~ 9

Author(s):

T. D. Tang ◽

M. T. Pauken ◽

S. M. Jeter ◽

S. I. Abdel-Khalik

Keyword(s):

Experimental Investigation ◽

Relative Humidity ◽

Water Surface ◽

Surface Film ◽

Free Water ◽

Vapor Concentration ◽

Controlled Environment ◽

Stearyl Alcohol ◽

Water Pool ◽

Evaporation Suppression

An experimental investigation has been conducted to quantify the extent by which monolayers of fatty alcohols can reduce evaporation from a deep stationary water pool within a controlled environment. Octadecanol (stearyl alcohol), C17H35–CH2–OH, was chosen as the surface film and ethanol was selected to be the spreading agent. Evaporation suppression of 60 percent was achieved at a water temperature of 25°C with an air temperature of 20°C and a relative humidity of 70 percent. The experimental techniques and data have been validated by comparing the measured evaporation rates for film-free water with earlier data published by other investigators. Data for the evaporation rates of water covered by octadecanol films were correlated as a function of vapor concentration differences between the water surface and air.

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Heterogeneous freezing of water droplets containing kaolinite particles

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-4191-2011 ◽

2011 ◽

Vol 11 (9) ◽

pp. 4191-4207 ◽

Cited By ~ 183

Author(s):

B. J. Murray ◽

S. L. Broadley ◽

T. W. Wilson ◽

J. D. Atkinson ◽

R. H. Wills

Keyword(s):

Cooling Rate ◽

Surface Area ◽

Clay Mineral ◽

Constant Temperature ◽

Hydrophobic Surface ◽

Supercooled Liquid ◽

Stochastic Approach ◽

Solid Particles ◽

Rate Coefficients ◽

Water Droplets

Abstract. Clouds composed of both ice particles and supercooled liquid water droplets exist at temperatures above ~236 K. These mixed phase clouds, which strongly impact climate, are very sensitive to the presence of solid particles that can catalyse freezing. In this paper we describe experiments to determine the conditions at which the clay mineral kaolinite nucleates ice when immersed within water droplets. These are the first immersion mode experiments in which the ice nucleating ability of kaolinite has been determined as a function of clay surface area, cooling rate and also at constant temperatures. Water droplets containing a known amount of clay mineral were supported on a hydrophobic surface and cooled at rates of between 0.8 and 10 K min−1 or held at constant sub-zero temperatures. The time and temperature at which individual 10–50 μm diameter droplets froze were determined by optical microscopy. For a cooling rate of 10 K min−1, the median nucleation temperature of 10–40 μm diameter droplets increased from close to the homogeneous nucleation limit (236 K) to 240.8 ± 0.6 K as the concentration of kaolinite in the droplets was increased from 0.005 wt% to 1 wt%. This data shows that the probability of freezing scales with surface area of the kaolinite inclusions. We also show that at a constant temperature the number of liquid droplets decreases exponentially as they freeze over time. The constant cooling rate experiments are consistent with the stochastic, singular and modified singular descriptions of heterogeneous nucleation; however, freezing during cooling and at constant temperature can be reconciled best with the stochastic approach. We report temperature dependent nucleation rate coefficients (nucleation events per unit time per unit area) for kaolinite and present a general parameterisation for immersion nucleation which may be suitable for cloud modelling once nucleation by other important ice nucleating species is quantified in the future.

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