text: There are notable similarities in the commonly used approximate differential equations for momentum, heat, and mass transfer. The molecular transfer equations of Newtons law for fluid momentum at low Reynolds number (Stokes flow), Fouriers law for heat, and Fick's law for mass are very similar, since they are all linear approximations to transport of conserved quantities in a flow field. 
  At higher Reynolds number, the analogy between mass and heat transfer and momentum transfer becomes less useful due to the nonlinearity of the Navier-Stokes equation (or more fundamentally, the general momentum conservation equation), but the analogy between heat and mass transfer remains good. A great deal of effort has been devoted to developing analogies among these three transport processes so as to allow prediction of one from any of the others.