Presentation on theme: "UNDERSTANDING THE BASICS... How They Work & Considerations for Their Use A Review of Current Information Snow Hardening Products for the Preparation of."— Presentation transcript:
UNDERSTANDING THE BASICS... How They Work & Considerations for Their Use A Review of Current Information Snow Hardening Products for the Preparation of Race Surfaces for Alpine Skiing Prepared for the North American FIS TD Updates Calgary AB & Lake Placid NY, October 2011 Doug Campbell #1019
Sources of Information: Print Resources Manufacturer’s Instructions Practical Experience Scientific Research What do we actually know about this?
Snow Surface Preparation Alpine Ski Racing requires a hard, durable snow surface and sub- surface to promote safety and fairness. Proper Mechanical Working Procedures are the primary method to prepare a suitable race surface.
Snow Surface Preparation Water Treatment of snow surfaces may be necessary to increase snow strength to suitable levels when this cannot be accomplished by mechanical methods alone. Snow density and physical connections between snow crystals may be increased with the addition of water
Snow Surface Preparation Snow Hardening Products are the only method to increase snow strength when the temperature is above the freezing point of water. However, the use of snow hardening products may be minimized, even during melting temperatures, when snow surfaces have otherwise been properly prepared by mechanical means or by the addition of water. Snow Hardening Products Most Commonly Used in North America Sodium Chloride - NaCl Urea - CO(NH 2 ) 2 Ammonium Nitrate - NH 4 NO 3
PRINT RESOURCES Snow Hardening Products Sources of Information
How Do They Work? Snow hardening by the application of chemicals is primarily the effect of melting point depression The dissolution of “salts” in water will depress the melting point. Snow grains or ice in contact with the solute may melt. This change of phase from solid to liquid requires heat, which is withdrawn from the surrounding snow causing a net cooling effect.
Snow Hardening Products How Do They Work? This simple diagram illustrates how: (a) Is at equilibrium with the number of water molecules freezing to the ice, equal to the number of frozen water molecules melting. (b) With the introduction of a solute, is now out of equilibrium with fewer water molecules available to freeze to the ice relative to the number of water molecules melting. Kurschner, P; Maki-Marttunen, T; Vestergaard, S; Wandl, S., Modelling & Simulation of Ice/Snow Melting, 2008
Snow Hardening Products How Do They Work? The animated model at this web-link better illustrates melting point depression.
Snow Hardening Products How Do They Work? This may be modeled mathematically...and is only slightly more complex than a race points calculation If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is. ~John Louis von Neumann Kurschner, P; Maki-Marttunen, T; Vestergaard, S; Wandl, S., Modelling & Simulation of Ice/Snow Melting, 2008
Snow Hardening Products How Do They Work? The dissolution of salts also consumes energy to break bonds between the ions of the salt molecule. The larger and more complex the salt molecule, the more energy is consumed to dissolve it. Research indicates; however, that the net cooling effect of this process is insignificant relative to that of melting point depression. However, this process plays a significant role in how different snow hardening products work.
Snow Hardening Products Scientific Research Researchers at the Swiss Federal Institute for Snow and Avalanche Research have published valuable information on this specialized area of interest, including this 2002 handbook. Fauve, M.; Rhyner, H.; Schneebeli, M., 2002: Preparation and maintenance of pistes. Handbook for practitioners. Davos, Swiss Federal Institute for Snow and Avalanche Research
Snow Hardening Products Scientific Research Researchers at the same Institute provided an overview for TD’s, ROCs and Coaches that was shared at the North American FIS TD Update in 2008
Snow Hardening Products Scientific Research The same group of researchers at the Swiss Federal Institute has completed additional valuable research that was circulated as a draft manuscript in 2010 with the possible title, Effects of Snow Hardeners on the Snow Cover of Ski Runs The following slides contain an overview of some interesting information contained in the draft document.
Comparison of Ammonium Nitrate to NaCl Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Both Products are NaCl The Difference is Grain Size Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Snow Strength....and so it’s not all about how cold how fast? Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Snow Hardening Products Scientific Research Model illustrating the dissolution of the salt (SH), the increasing and infiltrating solute concentration (SC), the withdrawal of heat represented by the black arrows, and the temperature at depth represented by (T) Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Snow Hardening Products Scientific Research A more detailed model of the same process. Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Snow Hardening Products Some Observations and Considerations Relative grain size of the product influences the rate of reaction. The smaller the grain size, the more immediate the reaction and vice versa. NaCl causes a faster and deeper heat withdrawal than Ammonium Nitrate as the dissolution of NaCl is more spontaneous. This; however, causes a relatively increased solute concentration and infiltration which damages snow structure and results in relatively lower snow strength On the other hand, the spontaneous dissolution of NaCl quickly produces its own water and therefore requires less snow humidity to react than Ammonium Nitrate.
Snow Hardening Products Some Observations and Considerations Continued... Ammonium Nitrate application can result in higher snow strength relative to NaCl Although Ammonium Nitrate requires more humidity than NaCl to produce a comparable accelerated cooling effect, it appears that the addition of water results in overall reduced snow strength. The lower solute concentration and slower infiltration rate of Ammonium Nitrate can result in greater snow strength.
Snow Hardening Products Some Observations and Considerations Continued... Increased temperature will increase the rate of dissolution and subsequently increase the rate of reaction and reduce the duration of the hardening effect. NaCl is corrosive and may kill vegetation while nitrogen based fertilizers such as urea and ammonium nitrate, if not over applied, may promote vegetation growth.
Snow Hardening Products General Considerations and Leading Practices Local experience is an asset Experiment with test patches, not the race. Respect the environment and area regulations These products are corrosive and hygroscopic and will burn skin. Wear appropriate personal protective equipment.