April 18, 2009

Viscosities of Pure Gases at low Pressure-2

In the previous post, I discussed about a method called Chapman & Enskog, while also mentioned about another method called Yoon & Thodos. So in this part I will discuss the second method which is also apllicable for polar & non-polar gases both but still at low pressure say till 5 atm.

First method of Chapman Enskog is available Here or at the end of this post.

Viscosity by Yoon & Thodos correlation
There are two things to remember - 1 Polar Gas, 2 Non Polar Gas.

So for Non Polar Gas the equation is -

Vis * zeta = 4.610 * Tr^0.618 - 2.04* exp(-0.449 * Tr)+ 1.94 * exp(-4.058 Tr) + 0.1

Here
Tr = Reduced temperature with its usual definition i.e Tr = T / Tc
zeta is given by the following equation.

zeta = [Tc ^ (1/6)]/ [ M ^ 0.5 * Pc ^ (2/3) ]

So its more simpler than first method of Chapman & Enskog.

Now for Polar Gases there are two parts. One is for Tr Hydrogen bonding & second is non hydrogen bonding. The equations are -

For Hydrogen bonding gases, the applicability is Tr < 2.0

Vis x zeta = (0.755 Tr - 0.055 ) * [Zc ^ (-1.25)]

For Non Hydrogen bonding gases, the applicability is Tr < 2.5

Vis x zeta = [(1.90 Tr - 0.29 )^0.8 ] * [Zc ^ (-2/3)]

Zc = Compressibility factor at critical point, usually available.
zeta = is already given above.

Yes again the unit of viscosity here is micropoise.

List of other property estimation methods on this Blog.


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