Page 330 - Modelling in Transport Phenomena A Conceptual Approach
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310 CHAPTER 8. STEADY MICROSCOPIC BALANCES WITHOUT GEN.
Analysis
System: Benzene droplet
The inventory rate equation for mass of A gives
- Rate of moles of A out = Rate of accumulation of moles of A (1)
where p: is the density of species A in the liquid phase.
The rate of evaporation from the droplet surface, +LA, can be determined from
Eq. (8.5-28). However, remember that Eq. (8.5-28) was developed for a steady-
state case. For the unsteady problem at hand, the pseudo-steady-state assumption
implies that Eq. (8.5-28) holds at any given instant, i.e.,
Substitution of Eq. (3) into Eq. (2) and rearrangement gives
where R, is the initial radius of the liquid droplet. Carrying out the integrations
in Eq. (4) yields
Since
P PPt
c=- and c* - -
UT A- RT
Eq. (5) tamss the Jvrm
The plot of R2 versus t is shown below.
