source: http://webserver.dmt.upm.es/~isidoro/tc3/Radiation%20View%20factors.pdf
function viewFactorRectRectPar extends Modelica.Icons.Function; input Real A "Area of surface"; input Real d "Distance between surfaces"; input Real l "Length of surface"; output Real vieFac "View factor between surfaces"; end viewFactorRectRectPar;