8.3-3 - Thermal Conductivity of a Gas Mixture at Low Density

Thermal conductivity of a gas mixture is estimated by:

where xi are mole fractions and ki are thermal conductivity for pure components. The F function is as follows:

The MATLAB program mixkt calculates the thermal conductivity given thermodynamic properties of each component.


function kt = mixkt(zs,T,j)

% mixkt(zs,T,j) finds the thermal conductivity of a 
% low density gas mixture
% zs gives the mol fraction of each compound
% T gives the temperature in the units of Tdeg
% j gives the indices of the compounds (if missing it includes
%   all compounds.)  zs must be consistent with j.
% Based on equations 8.3-17 & 18 in BS&L
% The thermal conductivity is given in W/m/K

global mw
if nargin<3
   j=1:length(mw);
end
phi=mixphi(T,j);
kts=ktpcalc(T,j);
den=phi*zs';
kt=zs*(kts./den);

% This file was created by m2html.

Example 8.3-3

Predict the thermal conductivity of the following gas mixture at 1 atm and 293 K based on data on the pure components at 1 atm and 293 K:

Species

i

xi

Mi

mix107 (g cm-1 sec-1)

kix107 (cal sec-1 cm-1 K-1)

CO2

1

0.133

44.010

1462

383

O2

2

0.039

32.000

2031

612

N2

3

0.828

28.016

1754

627

 

>> zs = [.133 .039 .828]

zs =

    0.1330    0.0390    0.8280

>> mixkt(zs,293,1:3)

ans =

    0.0231

From convu:

0.2310000E-01W/(m*K) = 0.5521130E-04cal/(cm*s*K)

Since this is an approximation, it is slightly off from BS&L, whose value is 0.584x10-4 cal cm-1 sec-1 K-1.