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Temperature dependence of liquid viscosityThe temperature dependence of liquid viscosity is the phenomenon by which liquid viscosity tends to fall (or, alternatively, its fluidity tends to increase) as its temperature increases. This can be observed, for example, by watching how cooking oil appears to move more fluidly upon a frying pan after being heated by a stove. It is usually expressed by one of the following models: Additional recommended knowledge
Exponential model
where T is temperature and μ_{0} and b are coefficients. See firstorder fluid and secondorder fluid. This is an empirical model that usually works for a limited range of temperatures. Arrhenius modelThe model is based on the assumption that the fluid flow obeys the Arrhenius equation for molecular kinetics: where T is temperature, μ_{0} is a coefficient, E is the activation energy and R is the universal gas constant. A firstorder fluid is another name for a powerlaw fluid with exponential dependence of viscosity on temperature. WilliamsLandelFerry modelThe WilliamsLandelFerry model or WLF for short is usually used for polymer melt's or other fluids that have a glass transition temperature. The model is: where Ttemperature, C_{1}, C_{2}, T_{r} and μ_{0} are empiric parameters (only three of them are independent from each other). If one selects the parameter T_{r} based on the glass transition temperature, then the parameters C_{1}, C_{2} become very similar for the wide class of polymers. Typically, if T_{r} is set to match the glass transition temperature T_{g}, we get
and
Van Krevelen recommends to choose
and
Using such universal parameters allows one to guess the temperature dependence of a polymer by knowing the viscosity at a single temperature. In reality the universal parameters are not that universal, and it is much better to fit the WLF parameters from the experimental data. Seeton FitThe Seeton Fit is based on curve fitting the viscosity dependence of many liquids (refrigerants, hydrocarbons and lubricants) versus temperature and applies over a large temperature and viscosity range:
Viscosity of water equation accurate to within 2.5% from 0 °C to 370 °C: μ (Temp)= 2.414*10^5 (N·s/m²) * 10^(247.8 K/(Temp  140 K))


This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Temperature_dependence_of_liquid_viscosity". A list of authors is available in Wikipedia. 