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题号(Part No.)	I	II	III	IV	V	VI	VII	VIII	总分(Sum)
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安 徽 工 业 大 学 试 题 纸

2020~2021学年第一学期期末考试《化工原理B》试卷（A）

Final Exam of Unit Operations of Chemical Egnineering B for Bachelors 2020 Fall（A）
Part I True or False (10 points)

1. 
   ( )When the gas temperature increases, its viscosity will decrease.
   
2. 
   ( ) Water need not to be added during the start of centrifugal pump because it has priming function.
   
3. 
   ( ) If the volume flow rate Q increases, the developed head H of centrifugal pumps will decrease.
   

(4) ( ) The relationship among dry-bulb temperature t, wet-bulb temperature t_w, dew-point t_d of saturated moist air is t> t_w > t_d.

(5) ( ) Flash distillation is used most for separating components that boil at very large different temperatures.

Part II Choose the correct the answers (20 points)

(1) The removal of uncondensable gas in the condensing vapor will ( )

A increase condensing film coefficient h; B decrease condensing film coefficient h;

C do not change condensing film coefficient h; D be uncertain.

(2) The stream relationships for the various thermal conditions of feed

• 
  Cold feed ( )
  
• 
  Feed at bubble point ( )
  
• 
  Feed partly vapor ( )
  
• 
  Feed at dew point ( )
  
• 
  Feed is a superheated vapor ( )
  

A) L=L′ B)V=V′ C) L′=L+ q F D) V=V′+(1-q)F

E) L′=L+F F)V=V′+F G) q>1 H)q<0 I) 0

(3) The revolution n of centrifugal pump increase, its volumetric flow rate Q will ( ), its developed head H will ( ).

A increase; B decrease; C be the same; D be uncertain

(4) In the constant-rate drying period, the rate of evaporation is ( ) of the solid, and is ( ) of the properties and flow type of air.

A) independent B) dependent C) uncertain

(5) In general, the liquid rate for the absorber should be ( ) times the minimum rate, too high a value requires ( ) and the ( ) of recovering, a small value results in ( )

A) a large-diameter tower B) 1 C) 2.5 D) 1.1-2.0 E) cost F) a high tower

( 6) Based on the temperature distribution as shown in figure, which has largest temperature drop（ ）, and which has the largest thermal conductivity（ ） if the thickness of each layer is the same?

A) layer A; B) layer B; C) layer C

(7) “Gas phase is controlling” means that the major resistance through both the gas and liquid phases is in the ( ), and the solute A in a gas phase is ( )

A) very insoluble in the liquid B) very soluble in the liquid

C) can’t make sure D) gas phase E) liquid phase F) the gas and liquid phases

(8) Rising the pressure in an absorption process of gas, the Henry’s constant m will

( ), and the rate of absorption will ( )

1. 
   decrease; B) increase; C) be the same
   

Part III Fill the blank (10 points)

(1) Rising the pressure in an absorption process of gas, the Henry’s constant m will

( ), and the rate of absorption will ( )

(2) The pressure of 10 m H₂O is equal to （ ）mmHg. If atmospheric pressure is 1 atm and the reading of centrifugal pump outlet gauge is 5000Pa(N/m²)= （ ）(absolute pressure).

(3) When the rates of feed and of both the overhead and bottom products are ( ), called total reflux and the slopes of both operating lines are ( ).

(4) The separations of binary mixtures by a distillation operation are based on differences in vapor- and liquid-phase compositions arising from the ( ) of a liquid mixture or the ( ) of a vapor mixture.

(5) Optimum reflux ratio is the point of ( ), and ( ) much larger than the minimum reflux ratio.

Part IV Calculations (60 points)

1. 
   (15 points) A continuous fractionating column is used to separate 4000kg/h of a mixture of 30 percent
   

CS and 70 percent CCl . Bottom product contain 5 percent CS at least, and the rate of recovery of CS in the overhead product is 88% by weight,required. Calculate (a) the moles flow of overhead product per hour .(b) the mole fractions of CS and CCl in the overhead product, respectively.

2. 
   (15 points) A dryer is used to dry material from 5 percent moisture to 0.5 percent moisture (wet basis).
   

The production capacity of dryer is 1.5 kg dry material/s. Hot air enters at 127℃ and 0.007kg water/kg dry air and leaves at 82℃.The temperature of the material in the inlet and outlet are 21℃ and 66℃, respectively. The specific heat of wet material is 1.8KJ/（kg℃）。If the heat loss of the dyer can be ignored, then calculate a) the consumption of the wet air. b) the temperature of the air leaving the dryer.

(3) (15 points) Water (=1000kg/m³) flows from the top tank to the low one with a velocity 2m/s, as shown in Fig. There are one orifice and a gate valve in the pipeline with 573mm. The total pipe length including all local frictional equivalent length is 60 m. If the frictional coefficient =4f is 0.036 and K_v (local loss coefficient of valve) is 7.5 (wide open), Find

(1) mass flow rate in pipeline, in kg/s.

(2) liquid surface height difference Z between top and low tanks.

(3)pressure drop through the valve and reading R₂ of U-shape pressure gauge.

(4) if the valve is closed a little bit, there is 20% decreases of reading R₁ for U-shape pressure meter. Assume orifice coefficient C_o keeps unchanged, what is the mass flow rate in the pipeline, in kg/s?

Hint: velocity equation in orifice u_o=C_o[(2R₁g(_o-)/)^1/2 , and _o is 13600kg/m³.

4. 
   (15 points) A liquid containing 40 mole percent methanol and 60 mole percent water is to be separated in a continuous fractional column at 1 atm pressure .Calculate the value of q under the three following conditions (a) the feeding is liquid at 40 C (b) the feeding is saturated liquid. The equilibrium data for methanol-water liquid at 1 atm pressure are given in the attached table. If the column is fed with 100koml/h.The molar fractions of methanol in overhead product and bottom product are 0.95 and 0.04,respectively. A reflux ratio at the top of column is 2.5. Calculate (a) the mole flow of overhead product per hour (b) the mole flow of liquid in rectifying column (c) the mole flow of vapor in stripping column .Assume that the constant molar flow applies to this system .
   

A

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