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Brine is a solution of salt (usually sodium chloride) in water. In different contexts, brine may refer to salt solutions ranging from about 3.5% (a typical concentration of seawater, or the lower end of solutions used for brining foods) up to about 26% (a typical saturated solution, depending on temperature).
Brine is used to preserve vegetables, fruit, fish and meat in a process known as brining. Brine is also commonly used to age halloumi and feta cheeses, or for pickling foodstuffs, as a means of preserving them (or increasing taste). Brine is a common fluid used in large refrigeration installations for the transport of heat from place to place. It is used because the addition of salt to water lowers the freezing temperature of the solution and the heat transport efficiency can be greatly enhanced for the comparatively low cost of the material. The lowest freezing point obtainable for NaCl brine is −21.1 °C (−6.0 °F) at 23.3wt% NaCl. This is called the eutectic point. In colder temperatures, brine can be used to de-ice or reduce freezing temperatures on roads.
Brine also refers to naturally occurring salt water. The brine outcropping at the surface as saltwater springs are known as "licks" or "salines". The contents of dissolved solids in groundwater vary highly from one location to another on earth, both in terms of specific constituents (e.g. halite, anhydrite, carbonates, gypsum, fluoride-salts, and sulfate-salts) and regarding the concentration level. Using one of several classification of groundwater based on Total Dissolved Solids, brine is water containing more than 100,000 mg/L TDS. Brine is commonly produced during well completion operations, particularly after the hydraulic fracturing of a well.
|Water salinity based on dissolved salts in parts per thousand (g/L)|
|Fresh water||Brackish water||Saline water||Brine|
|< 0.5||0.5 – 30||30 – 50||> 50|
The thermal conductivity of seawater (3.5% dissolved salt by weight) is 0.6 W/mK at 25 °C. The thermal conductivity decreases with increasing salinity and increases with increasing temperature; these graphs and online calculations plot thermal conductivity for varying salinity and temperature: