Basic Equations for Transfer of Heat, Mass, and Momentum

1 Basic Equations for Transfer of Heat, Mass, and Momentum 

The equation for one-dimensional stationary heat conduction is the first of Fourier s laws Jean Fourier, see box)  

The analogous equations for mass transport of species A by diffusion (Pick s 

Adolf Eugen Pick (1829-1901) A German physiologist, who introduced in 1855 Pick s law of diffusion. Pick is also credited with the invention of contact lenses. 

Equation (3.1.54) represents the usual form of Pick s first law of mass transport, but this equation is not correct if a temperature gradient exists (Westerterp, van Swaaij, and Beenackers, 1980 Cengel, 2002, Topic 3.1.2). For example, a temperature difference of AT =Ti T2 in an ideal gas, that is, =PaJ RT) = Yfij / RTj, leads to a concentration difference AcA = yA,iP/(f T i) — Ya, / RT2)- Nevertheless, this will not lead to a mass flux of species A if the mole fractions are equal (yA.i = yA.2), although a concentration gradient exists for Ti / T2. Thus, the general and correct form of Eq. (3.1.54) is  

---