| MadSci Network: Engineering |
Anika: Most fluids, but not all, flow faster at higher temperatures, and this is because the viscosity decreases with increasing temperature, just as you thought. (Viscosity also changes if chemicals are dissolved in the fluid.) The viscosity of a fluid is caused by electrical attraction among molecules. This makes it harder for the molecules to move apart. When the temperature increases, molecules jiggle and move about more vigorously, which tends to break the temporary bonds that form among molecules. Water molecules form very strong hydrogen bonds and this is why water has a relatively high viscosity. Many kinds of oil have even higher viscosities. This may result in part from an even stronger tendency for the molecules to bond together. Also, fluids made of larger molecules tend to be more viscous, and oil molecules are pretty large. Some fluids, including some motor oils, get MORE viscous at higher temperature. This is obviously because of some kind of electrochemical interaction among the molecules in the fluid, but I don't know exactly what happens. I suggest you contact an oil company and ask that question. I hope this helps. David C. Kopaska-Merkel Geological Survey of Alabama PO Box 869999 Tuscaloosa AL 35486-6999 (205) 349-2852 FAX (205) 349-2861 www.gsa.state.al.us
Try the links in the MadSci Library for more information on Engineering.