DThurSep04

DThurSep04 - Thermodynamics Coldest Place on Earth 1...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Thermodynamics Coldest Place on Earth
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Viscosity u+ λ du/d x u u λ
Background image of page 2
3 Almost the last bit about Viscosity If each plane is of unit area and the molecules move u meters in unit time then the volume of the dotted figure is u m 3 . If there are N molecules in a volume V, then there are Nu/V molecules in the box. Half the molecules are moving up and half down, so the number that cross unit area in unit time is Nu/2V. The momentum transported in unit time is then: dx u d V m u N 2 λ
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 The Coefficient of Viscosity Force is the rate of change of momentum. We said earlier that the frictional force resisting the relative motion of the two adjacent plates was: dx u d A F η = Therefore, per unit area, equating these two equations we get: dx u d dx u d V m u N λ = 2 2 2 ρ u V u Nm = =
Background image of page 4
5 Implications Examination of this equation reveals: The viscosity of a gas is independent of pressure. This is because although at higher pressures more molecules jump between layers λ is smaller and therefore less momentum is transferred. Because the velocity increases with the absolute temperature then the viscosity increases with the absolute temperature. This last statement may seem counter intuitive but it is a consequence of the fact that because the velocity increases with temperature, so too, therefore does the transfer of momentum.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
6 Example The viscosity of carbon dioxide at 298 K and 1 atm. is 13.8 x 10 -6 kg m -1 s -1 . What is the molecular diameter? Use the mean free path to determine the molecular diameter … A A N d V 2 2 π λ= V u Nm u 2 2 λ ρ η = =
Background image of page 6
7 1 - 2 ms 411 044 . 0 298
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 20

DThurSep04 - Thermodynamics Coldest Place on Earth 1...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online