Page 350 - Modelling in Transport Phenomena A Conceptual Approach

330 CHAPTER 9. STEADY MICROSCOPIC BALANCES WITH GEN.

Elimination of (Po - PL) between Eqs. (9.1-27) and (9.1-33) leads to

(9.1-34)

For flow in non-circular ducts, the Reynolds number based on the hydraulic equiv-
alent diameter was defined in Chapter 4 by Eq. (4.537). Since Dh = 2B, the
Reynolds number is
2B(VZ)P
Reh = - (9.1-35)
c1
Therefore, Eq. (9.1-34) takes the final form as

(9.1-36)

9.1.2 Falling Film on a Vertical Plate

Consider a film of liquid falling down a vertical plate under the action of gravity
as shown in Figure 9.2. Since the liquid is in contact with air, it is necessary to
consider both phases. Let superscripts L and A represent the liquid and the air,
respectively.

Figure 9.2 Falling film on a vertical plate.