Frazil ice

Last updated
Frazil ice in Yosemite Creek Frazil ice in Yosemite Creek.png
Frazil ice in Yosemite Creek
Video of frazil ice in Yosemite National Park

Frazil ice is a collection of loose, randomly oriented ice crystals millimeter and sub-millimeter in size, with various shapes, e.g. elliptical disks, dendrites, needles and of an irregular nature. [1] [2] [3] [4] [5] Frazil ice forms during the winter in open-water reaches of rivers as well as in lakes and reservoirs, where and when the water is in a turbulent state, which is, in turn, induced by the action of waves and currents. Turbulence causes the water column to become supercooled, as the heat exchange between the air and the water is such that the water temperature drops below its freezing point (in order of a few tenths of  °C or less). [3] [5] [6] The vertical mixing associated with that turbulence provides enough energy to overcome the crystals' buoyancy, thus keeping them from floating at the surface. Frazil ice also forms in oceans, where windy conditions, wave regimes and cold air also favor the establishment of a supercooled layer. [7] [8] Frazil ice can be found on the downwind side of leads and in polynyas. In these environments, that ice can eventually accumulate at the water surface into what is referred to as grease ice.

Contents

Frazil ice is notorious for blocking water intakes [6] [9] [10] as crystals accumulate and build up on the intake trash rack. Such blockages negatively impact water supply facilities, hydropower plants, nuclear power facilities, and vessels navigating in cold waters, and can lead to unexpected shut downs of the facility or even collapse of the trash rack.

Formation

Frazil ice flowing in the mouth of the river Blanda in Iceland Mouth of Blanda river.jpg
Frazil ice flowing in the mouth of the river Blanda in Iceland

When the water surface begins to lose heat rapidly, the water becomes supercooled. Turbulence, caused by strong winds or flow from a river, will mix the supercooled water throughout its entire depth. The supercooled water will already be encouraging the formation of small ice crystals (frazil ice) and the crystals get taken to the bottom of the water body. Ice generally floats, but due to frazil ice's small size relative to current speeds, it has an ineffective buoyancy and can be carried to the bottom very easily.

Through a process called secondary nucleation, the crystals quickly increase in number, and because of its supercooled surrounding, the crystals will continue to grow. Sometimes, the concentration is estimated to reach one million ice crystals per cubic meter.

As the crystals grow in number and size, the frazil ice will begin to adhere to objects in the water, especially if the objects themselves are at a temperature below water's freezing point. The accumulation of frazil ice often causes flooding or damage to objects such as trash racks. Since frazil ice is found below the surface of water, it is difficult to detect its formation.

Usually, the frazil ice accumulates on the upstream side of objects and sticks to them. As more frazil is deposited, the growth will extend upstream and increase in width until the point where the frazil ice accumulations bridge together and block the water. As more and more water flows against this block, the pressure on the upstream side increases and causes a differential pressure (difference in pressure from the upstream side and the downstream side). This will cause the growth of the bridge to extend downstream. Once this happens, flooding and damage is likely unless otherwise prevented.

Frazil ice has also been demonstrated to form beneath temperate (or "warm-based") glaciers as water flows quickly downhill and supercools due to a rapid loss of pressure. This "glaciohydraulic supercooling" process forms an open network of platy ice crystals that can effectively trap silt from the sediment-laden water that flows beneath glaciers and ice sheets. Subsequent freezing and recrystallization can result in a layer of sediment-rich ice at the base of the glacier which, upon melting at the terminus, can result in significant accumulation of sediment in moraines. This phenomenon has been verified by elevated concentrations of tritium — produced by nuclear weapons testing and therefore almost entirely absent in ice frozen before 1945 — in the basal ice of several glaciers (signifying young ice) and the observation of rapid growth of ice crystals around water discharge vents at glacier termini.

Control

There are several ways to control frazil ice build up. They include suppression, mechanical control, thermal control, vibration, materials selection and damage mitigation.

Suppression

Frazil ice forms in supercooled water which occurs because the surface water loses heat to cooler air above. Suppression is the idea of insulating the surface water with an intact, stable ice cover. The ice cover will prevent heat loss and warm the supercooled water that might have already formed. [11] Sufficient area needs to be covered in order for this method to work, but it is still unknown what is meant by "sufficient". The St. Lawrence River is explicitly managed to create "flow conditions that help form a stable ice cover" to prevent frazil ice and subsequent ice jams. [12]

Mechanical control

These methods include stabilizing freeze without restricting water flow, such as implementing weirs and ice booms, installing water jets to break up any accumulation that might occur, and using manual labour to rake away the accumulation. This final method is often not preferred because of high labour costs, cold, wet and late night working conditions. Back flushing is another technology that uses the idea of cancelling out the differential pressure caused by the frazil ice accumulation. This technology creates a high pressure on the downstream side of objects to reverse the differential pressure.[ citation needed ]

Thermal control

These methods either heat the structures in the water to prevent frazil ice adhesion or heat the water to prevent frazil ice from forming in the first place. When heating the structure, it must be heated to a temperature above freezing. Electrical resistance heaters have been found to work well, but these have potential safety problems. Installing hollow tubes in the structures through which steam or warm water is pumped also works, but this method has been judged as uneconomical to operate. [13] Other active methods are also available. Certain industrial processes, for example power production, draw water supplies for plant-cooling purposes. The warmed water byproducts thus produced, otherwise discharged as waste, can be released at locations of potential frazil accumulation, raising the water temperature by 0.1–0.2 °C (0.18–0.36 °F), often enough to prevent supercooled water from developing. Alternatively, the waste water may instead be recirculated to directly warm surfaces prone to frazil ice accumulation. Both these methods of warm water re-use require precise calculation of volumes, flow and placement, and relative water temperatures, in order to be reliable. [13]

Vibration

Although still in the experimental stages, blasting with dynamite is one form of vibrational control that will break loose any frazil ice accumulation. The charge must be precise such that the ice breaks, but surrounding structures and environment are not harmed. Safety of the blasting also is important and nearby residents might complain about sound pollution. For all these reasons, this method is not often used, except as an emergency last resort.[ citation needed ]

Materials selection

Man-made structures are often the objects to which frazil ice adheres. As such, the choice of materials for these structures should include consideration of ice adhesion. Steel structures, for example will rust, and rust-to-ice adhesion is very strong. Choosing a material with lower adhesion such as plastic, fiberglass, graphite or even an epoxy paint coating on the steel will reduce the adhesion probability. Although adhesion will still occur, using such materials makes other methods, such as raking, easier.[ citation needed ]

Damage mitigation

Damage could be reduced by protecting designated flood regions with mechanical structures.

See also

Related Research Articles

<span class="mw-page-title-main">Frost</span> Coating or deposit of ice

Frost is a thin layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is similar to the formation of dew, except it occurs below the freezing point of water typically without crossing through a liquid state.

<span class="mw-page-title-main">Ice</span> Frozen water: the solid state of water

Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 °C, 32 °F, or 273.15 K. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

<span class="mw-page-title-main">Snow</span> Precipitation in the form of ice crystal flakes

Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.

<span class="mw-page-title-main">Fog</span> Atmospheric phenomenon

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog affects many human activities, such as shipping, travel, and warfare.

<span class="mw-page-title-main">Freezing</span> Phase transition of liquid to solid

Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid or the liquid content of a substance, usually due to cooling.

<span class="mw-page-title-main">Ice crystal</span> Water ice in symmetrical shapes

Ice crystals are solid ice in symmetrical shapes including hexagonal columns, hexagonal plates, and dendritic crystals. Ice crystals are responsible for various atmospheric optic displays and cloud formations.

<span class="mw-page-title-main">Supercooling</span> Lowering the temperature of a liquid below its freezing point without it becoming a solid

Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. It is achieved in the absence of a seed crystal or nucleus around which a crystal structure can form. The supercooling of water can be achieved without any special techniques other than chemical demineralization, down to −48.3 °C (−54.9 °F). Supercooled water can occur naturally, for example in the atmosphere, animals or plants.

<span class="mw-page-title-main">Sea ice</span> Outcome of seawater as it freezes

Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface. Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world's sea ice is enclosed within the polar ice packs in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Polar packs undergo a significant yearly cycling in surface extent, a natural process upon which depends the Arctic ecology, including the ocean's ecosystems. Due to the action of winds, currents and temperature fluctuations, sea ice is very dynamic, leading to a wide variety of ice types and features. Sea ice may be contrasted with icebergs, which are chunks of ice shelves or glaciers that calve into the ocean. Depending on location, sea ice expanses may also incorporate icebergs.

<span class="mw-page-title-main">Mpemba effect</span> Natural phenomenon that hot water freezes faster than cold

The Mpemba effect is the name given to the observation that a liquid which is initially hot can freeze faster than the same liquid which begins cold, under otherwise similar conditions. There is disagreement about its theoretical basis and the parameters required to produce the effect.

In physics and chemistry, flash freezing is the process whereby objects are rapidly frozen. This is done by subjecting them to cryogenic temperatures, or it can be done through direct contact with liquid nitrogen at −196 °C (−320.8 °F). It is commonly used in the food industry.

<span class="mw-page-title-main">Trash rack</span>

A trash rack (US) or debris screen is a wooden or metal structure, frequently supported by masonry, that prevents water-borne debris from entering the intake of a water mill, pumping station or water conveyance. This protects water wheels, penstocks, and sluice gates from destruction during floods. They are sometimes fitted to storm drain inflows and outflows to prevent debris from entering a natural watercourse. Other names used as trash screen (US) or debris grille.

<span class="mw-page-title-main">Anchor ice</span> Submerged ice anchored to a river bottom or seafloor

Anchor ice is defined by the World Meteorological Organization as "submerged ice attached or anchored to the bottom, irrespective of the nature of its formation". It may also be called bottom-fast ice. Anchor ice is most commonly observed in fast-flowing rivers during periods of extreme cold, at the mouths of rivers flowing into very cold seawater, in the shallow sub or intertidal during or after storms when the air temperature is below the freezing point of the water, and the subtidal in the Antarctic along ice shelves or near floating glacier tongues, and in shallow lakes.

<span class="mw-page-title-main">Ice cave</span> Natural cave that contains significant amounts of year-round ice

An ice cave is any type of natural cave that contains significant amounts of perennial (year-round) ice. At least a portion of the cave must have a temperature below 0 °C (32 °F) all year round, and water must have traveled into the cave’s cold zone.

Freezing drizzle is drizzle that freezes on contact with the ground or an object at or near the surface. Its METAR code is FZDZ.

<span class="mw-page-title-main">Slurry ice</span> Refrigerant

Slurry ice is a phase changing refrigerant made up of millions of ice "micro-crystals" formed and suspended within a solution of water and a freezing point depressant. Some compounds used in the field are salt, ethylene glycol, propylene glycol, alcohols like isobutyl and ethanol, and sugars like sucrose and glucose. Slurry ice has greater heat absorption compared to single phase refrigerants like brine, because the melting enthalpy of the ice is also used.

<span class="mw-page-title-main">Ice jam</span> Accumulation of ice in a river

Ice jams occur when a topographic feature of the river causes floating river ice to accumulate and impede further progress downstream with the river current. Ice jams can significantly reduce the flow of a river and cause upstream flooding—sometimes called ice dams. Ice jam flooding can also occur downstream when the jam releases in an outburst flood. In either case, flooding can cause damage to structures on shore.

<span class="mw-page-title-main">Grease ice</span> Stage in the formation of sea ice

Grease ice is a very thin, soupy layer of frazil crystals clumped together, which makes the ocean surface resemble an oil slick. Grease ice is the second stage in the formation of solid sea ice after ice floes and then frazil ice.

<span class="mw-page-title-main">Pumpable ice technology</span> Type of technology to produce and use fluids or secondary refrigerants

Pumpable icetechnology (PIT) uses thin liquids, with the cooling capacity of ice. Pumpable ice is typically a slurry of ice crystals or particles ranging from 5 micrometers to 1 cm in diameter and transported in brine, seawater, food liquid, or gas bubbles of air, ozone, or carbon dioxide.

<span class="mw-page-title-main">Ice segregation</span> Geological phenomenon

Ice segregation is the geological phenomenon produced by the formation of ice lenses, which induce erosion when moisture, diffused within soil or rock, accumulates in a localized zone. The ice initially accumulates within small collocated pores or pre-existing cracks, and, as long as the conditions remain favorable, continues to collect in the ice layer or ice lens, wedging the soil or rock apart. Ice lenses grow parallel to the surface and several centimeters to several decimeters deep in the soil or rock. Studies between 1990 and present have demonstrated that rock fracture by ice segregation is a more effective weathering process than the freeze-thaw process which older texts proposed.

<span class="mw-page-title-main">Glossary of meteorology</span> List of definitions of terms and concepts commonly used in meteorology

This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.

References

  1. ↑ Bukina, L.A. (1967). "Size distribution of frazil ice crystals in turbulent flows". Izvestiya, Atmospheric and Oceanic Physics. 3 (1). Translated by Keehn, P.A.: 58–68.
  2. ↑ Gosink, J. P.; Osterkamp, T. E. (1983). "Measurements and Analyses of Velocity Profiles and Frazil Ice-Crystal Rise Velocities During Periods of Frazil-Ice Formation in Rivers". Annals of Glaciology. 4: 79–84. Bibcode:1983AnGla...4...79G. doi: 10.3189/S0260305500005279 . ISSN   0260-3055. S2CID   246047589.
  3. 1 2 Clark, Shawn; Doering, John (2008). "Experimental investigation of the effects of turbulence intensity on frazil ice characteristics". Canadian Journal of Civil Engineering. 35: 67–79. doi:10.1139/L07-086.
  4. ↑ McFarlane, Vincent; Loewen, Mark; Hicks, Faye (2017). "Measurements of the size distribution of frazil ice particles in three Alberta rivers". Cold Regions Science and Technology. 142: 100–117. Bibcode:2017CRST..142..100M. doi:10.1016/j.coldregions.2017.08.001. ISSN   0165-232X.
  5. 1 2 Schneck, Christopher C.; Ghobrial, Tadros R.; Loewen, Mark R. (2019). "Laboratory study of the properties of frazil ice particles and flocs in water of different salinities". The Cryosphere. 13 (10): 2751–2769. Bibcode:2019TCry...13.2751S. doi: 10.5194/tc-13-2751-2019 . ISSN   1994-0416. S2CID   210569242.
  6. 1 2 Daly, Steven F. (March 1991). "Frazil Ice Blockage of Intake Trash Racks" (PDF). Cold Region Technical Digest (91–1). CRREL: Cold Regions Research and Engineering Laboratory, US ARMY Corp of Engineers: 1−14. OCLC   465638709. Archived from the original on 17 April 2012.
  7. ↑ Wadhams, Peter (2000). Ice in the Ocean. CRC Press. ISBN   978-1-4822-8308-2.
  8. ↑ Weeks, Willy (2010). On Sea Ice. University of Alaska Press. ISBN   978-1-60223-101-6.
  9. ↑ Richard, Martin; Morse, Brian (2008-07-01). "Multiple frazil ice blockages at a water intake in the St. Lawrence River". Cold Regions Science and Technology. 53 (2): 131–149. Bibcode:2008CRST...53..131R. doi:10.1016/j.coldregions.2007.10.003. ISSN   0165-232X.
  10. ↑ Daly, Steven F.; Ettema, Robert (August 2006). "Frazil Ice Blockage of Water Intakes in the Great Lakes". Journal of Hydraulic Engineering. 132 (8): 814–824. doi:10.1061/(asce)0733-9429(2006)132:8(814). ISSN   0733-9429.
  11. ↑ Alley, Richard B.; Lawson, Daniel E.; Evenson, Edward B.; Strasser, Jeffrey C.; Larson, Grahame J. (1998). "Glaciohydraulic supercooling: a freeze-on mechanism to create stratified, debris-rich basal ice: II. Theory". Journal of Glaciology. 44 (148): 563–569. doi: 10.3189/S0022143000002070 .
  12. ↑ International Lake Ontario - St. Lawrence River Board (25 May 2018). Observed Conditions & Regulated Outflows in 2017 (PDF). International Joint Commission. p. 21. Retrieved 3 May 2019.
  13. 1 2 Halilovič, Miroslav; Urevc, Janez; Koc, Pino (May 2019). "Prediction of recirculation flow rate for icing prevention in water intake supply systems of nuclear power plants". Cold Regions Science and Technology. 161: 63–70. Bibcode:2019CRST..161...63H. doi:10.1016/j.coldregions.2019.02.013. S2CID   133902202.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.