試卷測驗 - 110 年 - [無官方正解]110 國立臺灣大學_碩士班招生考試_部分系所:輸送現象及單元操作#101948-阿摩線上測驗
Yi Zhen剛剛做了阿摩測驗,考了100分
3. Which of the followings is NOT an assumption of the McCabe-Thicle method?
(A) Components have similar values
(B) Molar flowrates of vapor and liquid are constant in the rectifying section.
(C) Distillation column is well-insulated.
(D) There is a significant pressure drop in the column.
4. Which of the followings is the volume-surface means diameter of a mixture of particles?
(A)
(B)
(C)
(D)
xi: mass fraction in a given increment; N: number of particles in a fraction; NT: total particle number;
: average particle diameter in an increment
7.Aconical tank with a bottom opening of cross-sectional area A is filled with water and is
mounted on supports as shown in the figure. What is the force F with which plate X must be pushed
up to prevent water from leaking? Assume that the density of air is negligible as compared to the
density of water pL.
Support
(A) PL• Vg
(B) PL• Vg/2
(C) PL• A·Hg
(D) pL• AHg/2
Problem5(15 points) A 0.3 m-inner-diameter U-glass tube containing a 3-m-long packed bed with 250,000 spherical quartz particles (density p = 7800 kg/m3; diameter Dp, = 1 cm). The particles are held between the two sieves. Brine (ρ = 1.193 g/cm3; μ= 1.2 cp) flows through the U-glass tube at 0.1 m/s.
(a) What is the void fraction (ε) of the packed bed? (3 pts)
(c) What is the water level of the brine inlet above the top of the brine outilet (H)? (6 pts)
Problem 6 (10 points) Blood is composed of plasma and blood cells. When blood flows
through blood vessels with small diameters, the red cells are not uniformly distibuted across the
vessel Iumen, but, instead, they are enriched in the central region of the blood vessel, and a thin cell-
free layer is formed along the tube wall. Assuming that in each region the fow is considered to be
Newtonian, the viscosities of the core region and the plasma layer are pe and Jo, respectively, the
radius of the vessel is R and the thickness of the plasma layer is δ,
(2) Write down the boundary conditions. (5 points)
Equation of continuity:
Equation of motion:
Problem7(15 points)
A transistor, which may be approximated as a hemispherical heat source of radius ro = 0.1 mm, is
embedded in a large silicon substrate (k = 125 W/m• K) and dissipates heat at a rate g. All
boundaries of silicon are maintained at an ambient temperature of T∞ = 27℃, except for the top
surface, which is well insulated.
Problem8 Fill-in-the-Blank (10 points)
A countercurrent extraction plant is used to extract acetone from its mixture with water by means of
methyl isobutyl ketone (MIK) at a temperature of 25℃. The feed consists of 40 percent acetone and
60 percent water. Pure solvent equal in mass to the feed is used as the extracting liquid. In such an
extraction process, you need (a) 5pt ideal stages to extract 99 percent of the acetone fed, and the
extract composition is (b) 5pt... after removal of the solvent. (Hint. The following phase diagran
can be used)
Problem 9 Fill-in-the-Blank (5 points)
Tests are made on the absorption of carbon dioxide from a carbon dioxide-air mixture in a solution
containing 100 kg/m3 of caustic soda, using a 250 mm diameter tower packed to a height of 3 m with
19 mm Raschig rings. The results obtained at atmospheric pressure were: Gas rate, G' - 0.34 kg/m2•s.
Liquid rate, L' = 3.94 kg/m2•s. The carbon dioxide in the inlet gas was 315 parts per million and the
carbon dioxide in the exit gas was 31 parts per million. Therefore the valve of the overall gas transfer
coefficient KGa is(a) 5pt
Problem 10 Fill-in-the-Blank (10 points)
0.126 kg/s of a solid product containing 4 per cent water is produced in a dryer from a wet feed
containing 42 per cent water on a wet basis. Ambient air at 294 K and of40 per cent relative humidity
is heated to 366 K in a preheater before entering the dryer from which it leaves at 60 per cent relative
humidity. Assuming that the dryer operates adiabatically, what must be the flowrate of air to the
preheater (a) 2pt ? and how much heat must be added to the preheater (b) 3pt ? Conditions
change if the air enters the dryer at 340 K and sufficient heat is supplied within the dryer so that the
air again leaves at 340 K with a relative humidity of 60 per cent, what must be the flowrate of air to
the preheater (c) 2pt ? and how much heat must be added to the preheater (d) 3pt ? (Hint. The
following humidity chart can be used)
Problem 11 Fill-in-the-Blank (10 points)
A continuous rectifying column handles a mixture consisting of 40 per cent of benzene by mass and
60 per cent of toluene at the rate of 4 kg/s, and separates it into a product containing 97 per cent of
benzene and a liquid containing 98 percent toluene. The feed is liquid at its boiling-point. In such an
operation the mass flow of distillate is (a) 2ptand the mass flow of waste liquor is(b) 2pt .
If a reflux ratio of 3.5 is employed, (c) 3pt plates are required in the rectifying part of the column.
Ifthe plate-efficiency is now requires 60 percent, then (d) 3pt actual number of plates are needed.