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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). Other levels of concentration are called in different names:
|Water salinity based on dissolved salts|
|Fresh water||Brackish water||Saline water||Brine|
|< 0.05%||0.05–3%||3–5%||> 5%|
It is held that 0 °F (−17.78 °C) was initially set as the zero point in the Fahrenheit temperature scale, as it was the coldest temperature that Daniel Gabriel Fahrenheit could reliably reproduce by freezing brine.
|NaCl, wt%||Freezing point (°C)||Density[a] (g/cm3)||Refractive index[b] at 589 nm||Viscosity[c] (mPa·s )|
At 100 °C (373.15 K, 212 °F), saturated sodium chloride brine is about 28% salt by weight i.e. 39.12 g salt dissolves in 100 mL of water at 100 °C. At 0 °C (273.15 K, 32 °F), brine can only hold about 26% salt.
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:
Brine is a common fluid used in large refrigeration installations for the transport of thermal energy 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.