Finding or calculating almost good estimate of any physical property is very important for young engineers & therefore I emphasise a lot on these methods which are time tested and proven and gives sufficient approximations in calculated numbers. So I am writing few such post in the next coming weeks on properties or other quick methods.

I have already posted following useful posts on different properties estimation on this blog.

The two co-relatons are those of Chapman & Enskog and of Yoon & Thodos. Both of them require temperature, molecular weight, critical temperature, critical pressure of the pure gas.

First method of Chapman Enskog also require accentric factor w. Both the methods can handle polar gases also but then they need more physical constants. These correlations are valid only for low pressures may be upto 5 atm or less.

There are two things to remember - 1 Polar Gas, 2 Non Polar Gas.

So for

Vis = (5/16) x (pi x M R T)^0.5 / (pi x Sigma^2) / CI

Which can be simplified as below.

Vis = 26.69 x (M T)^0.5 / (Sigma^2) / CI

Here

M = Mol Wt of gas

T = Temperature of gas

Sigma is given by the following equation

Sigma = (2.3551 - 0.087 w) x Tc/Pc

Where

w = accentric factor of gas(This is a std property & available in any good reference)

Tc = Critical Temperature of Gas

Pc = Critical Pressure of Gas

CI in the above equation is given as below by Lennard Jones method

CI = ( A / TT^ B) + ( C / exp(D * TT) + E / exp(F * TT)

Where TT = (k /epsilon) * T

For TT calculation k / epsilon is available from below equation.

(epsilon/k) = (0.7915 + 0.1693 * w) * Tc

Now for

Yes the basic equation is same, the first one you read in the beginning however CI constant evaluation changes. Now the balance method remains same except calculate CI from the following Stockmayer equation.

CI (Stockmayer) = CI (Lennard Jones) + 0.2 * delta^2 / TT

TT is already given above, & delta is polarity of the gas.

Oops! I forgot to mention that viscosity is in micropoise here.

Yoon Thodos method shall be covered in next part of this post.

I have already posted following useful posts on different properties estimation on this blog.

- Calculate Diffusion Coefficient in Gases
- Calculate Diffusion Coefficient in Liquids
- Heat Capacities of dissolved solids & organic solutions - Quickest methods
- Heat capacities with dissolved solids
- Kinematic viscosity of air Vs Temperature
- Thermal Conductivity of air Vs Temperature
- How to calculate viscosity of liquid mixtures
- Surface Tension

The two co-relatons are those of Chapman & Enskog and of Yoon & Thodos. Both of them require temperature, molecular weight, critical temperature, critical pressure of the pure gas.

First method of Chapman Enskog also require accentric factor w. Both the methods can handle polar gases also but then they need more physical constants. These correlations are valid only for low pressures may be upto 5 atm or less.

**Viscosity by Chapman & Enskog correlation**There are two things to remember - 1 Polar Gas, 2 Non Polar Gas.

So for

**Polar Gas**the equation is -Vis = (5/16) x (pi x M R T)^0.5 / (pi x Sigma^2) / CI

Which can be simplified as below.

Vis = 26.69 x (M T)^0.5 / (Sigma^2) / CI

Here

M = Mol Wt of gas

T = Temperature of gas

Sigma is given by the following equation

Sigma = (2.3551 - 0.087 w) x Tc/Pc

Where

w = accentric factor of gas(This is a std property & available in any good reference)

Tc = Critical Temperature of Gas

Pc = Critical Pressure of Gas

CI in the above equation is given as below by Lennard Jones method

CI = ( A / TT^ B) + ( C / exp(D * TT) + E / exp(F * TT)

Where TT = (k /epsilon) * T

For TT calculation k / epsilon is available from below equation.

(epsilon/k) = (0.7915 + 0.1693 * w) * Tc

Now for

**Non Polar Gases**the equation is -Yes the basic equation is same, the first one you read in the beginning however CI constant evaluation changes. Now the balance method remains same except calculate CI from the following Stockmayer equation.

CI (Stockmayer) = CI (Lennard Jones) + 0.2 * delta^2 / TT

TT is already given above, & delta is polarity of the gas.

Oops! I forgot to mention that viscosity is in micropoise here.

Yoon Thodos method shall be covered in next part of this post.

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