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Generation of frazil ice in large-scale laboratory experiments
Martin Richard
1,2
, Louis Poirier
1
, John Marquardt
1
1. National Research Council Canada, Ocean, Coastal and River Engineering Research Centre
2. Memorial University of Newfoundland, Civil Engineering Department, St. John’s, NL, Canada
Generation of Frazil Ice in Large-Scale Laboratory Experiments
OBJECTIVES
• Modify M32’s ice tank to allow turbulent conditions to form so that frazil could potentially form
• Generate frazil ice in M32’s ice tank under controlled conditions
• Develop procedures to reliably repeat experiments • Measure frazil ice crystals generated in the tank
• Quantify frazil ice over the course of several active frazil formation events and under different conditions
INTRODUCTION
Frazil Ice
• Frazil ice is a type of ice that forms in fast-flowing supercooled water
• Small ice crystals in suspension within the water column
• Notorious for adhering to submerged objects they come in contact with
• Frazil ice regularly blocks water intakes in rivers and on vessels, as crystals stick and build up on the
intakes’ trash racks.
• Blockages negatively impact water supply facilities, hydropower plants, nuclear power facilities, and
vessels navigating in cold waters
• Blockages can lead to dramatic impacts, such as a town being left with insufficient water reserves for fire protection, a nuclear facility not getting the cold water required for cooling, or a vessel being forced to shut down its engines and drift.
Current Gaps
• Field and laboratory data on frazil ice is difficult to obtain and hence still relatively scarce
• New experimental research is needed to:
- Gain an improved understanding of frazil growth and its interaction with structures
- Develop and validate effective strategies for mitigating negative impacts caused by frazil
• Experimental research on frazil should be carried out at a sufficiently large scale and under controlled
conditions
NRC’s Ice Tanks
• NRC owns two ice tanks:
- M32 (Ott.): 21/18 m (L, total/useable) x 7 m (W) x 1
m (H); 126 m3
- St. John’s: 90/76 m (L, total/useable) x 12 m (W) x
3 m (H); 2,736 m3
• Unique opportunity to generate frazil at large scales under controlled conditions
LABORATORY SETUP
Setup of Ice Tank at
NRC’s M-32 Building
Instrumentation & Sampling
RESULTS
Water Temperatures & Duration of Events
• Average durations of supercooling events < ~30minutes
• Maximum supercooling generally occurred ~15 minutes after the onset of supercooling
• Maximum supercooling ~ 0.15-0.20 ºC
Frazil Detection and Quantification
• Over 150 frazil ice samples were collected
• All crystals appear to be roughly similar in size
(suggesting a fairly uniform distribution), discoid in shape, and the vast majority had a diameter of
approximately 1 mm
• Maximum values of volumetric concentration estimates are in the range of 0.03 to 0.08% (with a relative
uncertainty of ±20%)
• Estimated 3 to 6 million crystals/m3
RESULTS (cont’d)
FUTURE WORK
• Relationships between acoustic measurements & in
situ sampling
• Quantify influence of wind, currents, air temperatures & frazil concentrations
• Better characterize crystals (numbers, sizes, shapes) • Comprehensive heat budget & numerical modelling
• Larger scale (St. John’s – from 126 m3 to 2,736 m3)
• Water intakes blockages
Sketch of the current generation system in the 21 m by 7 m ice tank
SIMILAR PREVIOUS WORK
• University of Iowa (Ettema et al., 2003; Chen et al., 2004)
- Ice tank 21 m (L) x 7 m (W) x 0.55 m (H); 58 m3
- Small water intake (inflow speed ~0.15 m/s) - No thrusters, minimal currents and turbulence
- Fans used to produce wind; air temperature -10 ºC
- Max. supercooling levels at 0.02 ºC
- Four frazil samples, corresponding to volumetric concentrations ~0.12% over a 30-minute period • HSVA, by University of Bergen (Smedsrud, 2001)
- Ice tank 20 m (L) x 6 m (W) x 1 m (H); 120 m3
- frazil ice entrainment of sediment in salt water
(36-38‰)
- Used thrusters to generate currents ~0.3 m/s
- Fans used to produce wind; Air temperature -14 to
-18 ºC - Volumetric concentrations ~0.02-0.13% Current generation system equipment: • partition walls • Flow straighteners • curved guide walls • underwater thrusters Fans used to generate wind Velocity sensors: a) 1.5 MHz upward-looking sonar, b) 3 MHz side-looking sonar; c) 10 MHz 3-axis ADV.
Apparatus for sampling frazil:
• sampling frame
• Sampling frame submerged • rectangular wire mesh (1 mm
x 1 mm) with deposited ice crystals
PROCEDURE
• Procedure developed to reliably generate frazil ice in an optimized manner
• Tests could be conducted at a rate of up to two frazil events per 8-hour day
• Required very tight control over water temperature, heating and cooling.
• Air temperature typically set at -20 ºC
• Currents set at 1 m/s (center channel) • Max. wind speeds ~50 km/h
• Took between 2-4 hours for the water to cool from
~0.5ºC to its freezing point.
• No other external seeding was required to initiate the generation of frazil ice
• When supercooling started, frazil production increased rapidly and large amounts of crystals were produced over a short period of time
Water temperature
measured during a typical frazil event showing
supercooling to -0.02°C
a) Minimum water temperature as a function of flow speed; b) Duration of supercooling events as a function of flow speed.
Volumetric frazil concentration estimates calculated using samples of frazil crystals, as a function of the time since the onset of supercooling (the duration of the active
period corresponds to the mean of all events) Maximum frazil ice concentration as a function of flow speed during the supercooling period only
Preliminary
experiments for
testing blockages of water intakes by frazil ice
REFERENCES
Chen, Z., Ettema, R., and Y. Lai, 2004. Ice-Tank and Numerical Study of Frazil Ingestion by Submerged Intakes. Journal of Hydraulic Engineering, 130(2): 101–111
Ettema, R., Chen, Z. and J. Doering, 2003. Making frazil ice in a large ice tank. Proceedings of the 12th CRIPE conference, Edmonton, AB
Smedsrud, L.H., 2001. Frazil-ice entrainment of sediment: large-tank laboratory experiments. Journal of Glaciology, 47(158): 461-471
CONTACT
Martin Richard, Ph.D., P.Eng.
National Research Council Canada Memorial University of Newfoundland St. John's, NL, Canada
P: (709) 772-8750
E: martin.richard@nrc-cnrc.gc.ca
ACKNOWLEDGEMENTS
The authors would like to acknowledge the contributions & help from, and
discussions they had with: Dave Hnatiw, Yvan Brunet, Michel Brassard, Nathalie Brunette, Dr. Andy Cornett, Prof. Brian Morse and Dr. Steve Daly
