110年 - 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

選擇題 (20)

1. The pressure drop increases proportionally to the mass flowrate for a turbulent flow in a pipe.(A)O(B)X

2) The power number Np is analogous to a friction factor or a drag coeficient.(A)O(B)X

3) With shear-thinning liquids, a turbine gives a much lower shear rate near the wall, and thus the velocity near the wall is much higher than that with a Newtonian fluid.(A)O(B)X

4) The settling of nanoparticles does not occur due to brownian movement.(A)O(B)X

5) The radial velocity decreases with the distance from the tip of a turbine blade, but the volumetric flow rate increases with the distance until the maxinum flow rate occurs.(A)O(B)X

6) The Froude number is a measure of the ratio of the inertial stress to the shear force per unit area acting on the fluid.(A)O(B)X

7) In a pseudoplastic liquid, blending times at Re ＜ 1,000 are much longer than in newtonian liquids under the same impeller conditions.(A)O(B)X

8) In the free mot otion of nonspherical particles through a fluid, the orientation is constantly changing. Thus, the effective drag on the particle is less than for the motion of the fluid past a fixed particle.(A)O(B)X

9) For an adiabatic process of airflow, the stagnation temperature is constant from the entrance to the exit of the conduit.(A)O(B)X

10) The drag coeficient of a spherical particle drops suddenly when the corresponding Reynolds number reaches 200,000.(A)O(B)X

1. In chemical dehumidification process (A)wet bulb temperature increases. (B) dry bulb temperature remains constant. (C) dew point temperature increases. (D)dry bulb temperature increases.

2) With increase in compression ratio, the volumetric efficiency of air compressor (A) increases. (B) decreases. (C) remains same. (D) may increase or decrease (depends on the suction pressure).

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; N_T: total particle number; : average particle diameter in an increment

5) You are asked to suspend solids in a low viscosity fluid. Which of the following impellers do you choose? (A) six-blade disk turbine (B) 3-blade propeller (C) helical ribbon (D) anchor

6) Two fluids are flowing through two similar pipes of the same diameter. The Reynold's numnber is same. For the same flow rate if the viscosity of a fluid is reduced to half the value of the first fluid, the pressure drop will (A) Increase (B) Decrease (C) Remain unchanged (D) Data insufficient to predict relative pressure drop x,D,

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

8. In isotropic turbulence, the____________ are equal to each other. (A) Temporal velocity components (B) Mean square of velocity fluctuations in the three co-ordinate directions (C) Root mean square of velocity fluctuations in the three co-ordinate directions (D) None of these

9.Pressure drop in a fluidized bed reactor is____________ that in a similar packed bed reactor. (A) Less than (B) Greater than (C) Same as (D) None of these

10. Which ofthe following facilitates close control of flow of fluids? (A) Gate valve (B) Check valve (C) Butterfly valve (D) Globe valve

申論題 (15)

Probiem 3 (3 points) What is cavitation? Why cavitation will occur in centrifugal pumps and not in displacement pumps?

Problem4(2 points) The x component of velocity is a steady, incompressible flow field in the xy plane is u = Ax, where A = 2 m²/s, and x is measured in meters. Find the simplest y component of velocity for this flow field.

(a) What is the void fraction (ε) of the packed bed? (3 pts)

(b) What is the pressure drop across the packed bed? (6 pts)

(1) Simplify the equations of change in cylindrical coordinates by deleting the zero or neglectable items. (5 points)

(2) Write down the boundary conditions. (5 points) Equation of continuity:
Equation of motion:

(a) Take the hemisphere transistor as your control volume, and determine the reduced heat equation.(5 pt)

(b) Determine the boundary conditions. (5 pt)

(c) Solve the equation from (a) and use the boundary conditions to obtain a general expression for the substrate temperature distribution. (3 pt)

(d) Obtain the general expression of heat rate. (2 pt)

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.

110年 - 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

試卷資訊

選擇題 (20)

申論題 (15)