课程名称︰分离程序
课程性质︰化工大三必修
课程教师︰刘怀胜
开课学院：工学院
开课系所︰化工系
考试日期（年月日）︰109.5.21
考试时限（分钟）：100 min
试题 :
Closed book:
1. (15%)
(a) Explain the similarity and difference between azeotropic and extractive
distillation, entrainer and solvent.
(b) What is absorption factor?
(c) What are total reflux and minimum reflux ratio?
2. (10%)
Please draw the concentration profiles near the gas-liquid interface during the
mass transfer of an "extremely" insoluble component from air into water, for
example the mass transfer of oxygen from air into water.(The solubility of
oxygen in water is roughly 8mg/L only.) Please also explain it briefly!
3. (15%)
A continuous disk type centrifuge is used to separate the roughly uniform solid
particles (5micro) from a suspension (viscosity=2cp). The centrifuge has 80
discs with an angle of 40 degrees, an outer diameter 15.7cm and inner diameter
of 6cm. The speed of this disk centrifuge is 16000rpm and the flowrate is
150L/hr. Under these conditions, the centrifuge works well. Due to the process
change, the diameter of particles becomes 2.5 micro, and viscosity of the
suspension becomes 6 cp. Under these new conditions, estimate the volumetric
rate that this centrifuge can be operated (conservatively).
4. (15%)
Please prove the following sigma definition for a disk centrifuge.
2Π ω^2 n cotΘ (r2^3-r1^3)
Σ= ────────────
3g
where n = number of disc channels
r1= inner diameter
r2= outer diameter
(有附上课讲义的图)
5. (15%)
If a linear equilibrium curve yc=mx+C applies in a dilute mixture case, please
show that the number of overall transfer unit(NoG) for gas absorption in packed
tower can be obtained as
╭y2 1 y1-y2
Nog = │ ──────── = ─────────
╯y1 (ye-y) (y-ye)lm
(y-ye)1-(y-ye)2
(y-ye)lm = ───────────
(y-ye)1
ln[─────]
(y-ye)2
Where subscript 2 indicates the top (where liquid enters) and subscript 1
indicates the bottom of the tower.
6. (10%)
Please derive Fenske's equation for distillation as below and specify all the
notations and assumptions.
╭ xA xB ╮
log│(──)d (──)s │
╰ xB xA ╯
n+1 = ─────────────
logαav
Open Book:
1.(20%)
The figure shows a simplified schematic diagram of a rotating packed bed that
consists of a rotor and a stationary housing. Liquid flows outward from the
inner edge of the rotor due to the centrifuge force. Gas flows inward
co-currently from the outer edge of the packed bed by the pressure-driving
force. Please derive a design equation for this rotating packed bed carried out
removing (stripping) enthanol from a liquid phase (water) to use a gas phase
(air). The design equation can be derived using mass balance and the transfer
unit concept.
Where Gm is the molar flow rate of gas; Pt is the total pressure in the system;
z is the axial height of the packing; KGa is the product of mass transfer
coefficient and interfacial area; Hc is the Henry's law constant expressed as
the ratio of the mole fraction in the gas phase to that in the liquid phase.
And Y1 and Y2 are the mole fraction of ethanol in the outlet and inlet air
streams, respectively. X2 is the mole fraction of ethanol in the outlet water
stream; r1 and r2 are the inner radius and outer radius of packing respectively
S is so-called "stripping factor" that you need to define when you derive the
design equation. Be sure to identify all other notations if needed.
Y1-HcX2
ln[(1-S)───── + S]
Gm Y2-HcX2
──── ───────────── = Π(r2^2-r1^2)
z KGa Pt S-1
2. (20%)
We illustrate a distillation with a "total condensor" in class as shown in
Fig(A) below. Now id we have a so-called "partial equlibrium condensor" shown
in Fig(B), please show your analysis and identify the corresponding
concentrations of in the
corresponding x-y chart in Fig(B). A partial equlibrium condensor suggest that
the time contact between vapor product and liquid reflux is sufficient, the two
will be in equlibrium with each other this arrangement will be convenient when
a vapor distillate is desired.