Transfer Process Chemical Engineering

CE2004

1 of 6 Paper CE2004

June 2020 This assessment is subject to the University Assessment Regulations for Candidates

 

SECTION A 1. The results in Table Q1 were obtained from a test on a single stage centrifugal

pump running at constant speed with water as the working fluid.

TABLE Q1

Delivery: Q (m³ h-1) 26.5 20.6 13.9 9.1 3.4 0

Total head H (m) 9.3 12.6 15.4 16.9 17.8 18.4

Overall efficiency: η (%) 58.9 63.3 58.9 47.5 22.4 0

Two identical pumps are connected in parallel with common suction and

delivery pipes of 75 mm diameter. The system static lift is 6 m and the pipework length is 85 m. Take the coefficient of friction, f, to be 0.006.

(a) Calculate and tabulate the flow rates, pump heads and efficiencies

for the two pumps in parallel using the single pump data shown in Table Q1.

(3 marks) (b) Calculate and tabulate the system head for the actual system.

(8 marks) (c) Use the graph provided in APPENDIX Q1 to plot the ‘2 pumps’ and

the system head characteristics and estimate the ‘2 pumps’ delivery, head and pump efficiency.

(4 marks) (d) Calculate the total shaft power required to drive the pumps.

(3 marks) (e) If one pump is removed from the installation, what will be the delivery

obtained from the one remaining pump and what will be its power consumption?

(3 marks) (f) Briefly comment on the advantages of using two pumps in parallel

instead of a single pump. (4 marks)

 

SUBMIT COMPLETED APPENDIX Q1 EXCEL

AS PART OF YOUR ANSWER BOOK THROUGH TURNITIN

 

 

 

 

CE2004

2 of 6 Paper CE2004

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2. (a) State and explain the four rules governing view factor relations in radiation.

(8 marks)

(b) In a shell-and-tube heat exchanger, what factors should be taken into consideration when deciding whether a fluid should be allocated to the shell side or tube side?

(5 marks) (c) A shell-and-tube heat exchanger with 2 shell passes and 4 tube passes

is used to heat glycerine from 20 °C to 50 °C using hot water, which enters the thin-walled 20 mm diameter tubes at 80 °C and leaves at 40 °C. The total length of tubing in the heat exchanger is 460 m. The convective heat transfer coefficient on the shell side is 45 W m-2 K-1 and that on the tube side 250 W m-2 K-1. The outer surface of the tubes has accumulated deposits causing a fouling resistance of 0.0008 m2 K W-1.

Using the appropriate equations from Table Q2 and the chart in

APPENDIX Q2, determine the rate of heat transfer from the water to the glycerine, stating any assumptions.

(12 marks)

TABLE Q2

Dittus-Boelter equation, turbulent pipe flow n

PrRe023.0Nu 8.0

=

(n = 0.3 cooling, 0.4 heating)

Colburn’s equation, turbulent pipe flow

14.0

w

0.338.0 PrRe023.0Nu 

 

   

 =

Sieder-Tate expression, laminar pipe flow

14.0

w

33.0

PrRe86.1Nu   

   

  

  

  

  

 =

l

d

 

 

 

 

CE2004

3 of 6 Paper CE2004

June 2020 This assessment is subject to the University Assessment Regulations for Candidates

 

SECTION B 3. Chlorine water for pulp bleaching is being prepared by absorption of chlorine

in water in a packed tower operating at 20 °C and atmospheric pressure. At one point in the tower the chlorine partial pressure is 0.5 atm and the concentration in the liquid is 1 kg m-3. The molecular weight of chlorine is 71 and it may be assumed that the density of the liquid is the same as that of the water (1000 kg m-3). Data on the solubility of chlorine in water expressed in mole fractions are presented in Table Q3 below:

TABLE Q3

 

y 0.12 0.2 0.3 0.49 0.75 0.9

x 0.00029 0.0004 0.0006 0.001 0.0015 0.0018

(a) Draw the equilibrium line and determine the slope of the equilibrium

line. (4 marks)

(b) If 85% of the resistance to mass transfer lies in the liquid phase,

calculate the interfacial compositions. (21 marks)

 

SUBMIT GRAPH AS PART OF YOUR ANSWER BOOK THROUGH TURNITIN

 

 

 

CE2004

4 of 6 Paper CE2004

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4. A gas stream containing 3% of component A is passed through a packed bed column in which 99% of A is removed using pure water. The absorber operates at 25 °C and 1 atm, and the gas and liquid fluxes are 20 mol ft-2 h-1 and 100 mol ft-2 h-1 respectively. Assume isothermal operation and neglect changes in gas and liquid flow rates.

 

(a) Calculate T

h using Oy

N and Oy

H .

(11 marks)

(b) Calculate T

h using OxN and OxH .

(11 marks)

(c) Determine the percentage of the total resistance that comes from the gas phase.

(3 marks)

Given: Equilibrium equation: 𝑦∗ = 3.1𝑥 at 25°C

60=ak x

mol ft-3 h-1 mol fraction

15=ak y

mol ft-3 h-1 mol fraction

 

TABLE Q4 – LIST OF EQUATIONS

Overall height of transfer unit based on gas phase

𝐻𝑂𝑦 = 𝐺𝑀 𝐾𝑦𝑎

 

Overall height of transfer unit based on liquid phase

𝐻𝑂𝑥 = 𝐿𝑀 𝐾𝑥𝑎

 

Overall number of transfer units based on gas phase

𝑁𝑂𝑦 = 𝑦𝑖𝑛 − 𝑦𝑜𝑢𝑡 (𝑦 − 𝑦∗)𝑀

 

Overall number of transfer units based on liquid phase

𝑁𝑂𝑥 = 𝑥𝑜𝑢𝑡 − 𝑥𝑖𝑛 (𝑥∗ − 𝑥)𝑀

 

Mean logarithmic average of the gas mole fractions

(𝑦 − 𝑦∗)𝑀 = (𝑦𝑖𝑛 − 𝑦𝑖𝑛

∗ ) − (𝑦𝑜𝑢𝑡 − 𝑦𝑜𝑢𝑡 ∗ )

𝑙𝑛[(𝑦𝑖𝑛 − 𝑦𝑖𝑛 ∗ ) (𝑦𝑜𝑢𝑡 − 𝑦𝑜𝑢𝑡

∗ )⁄ ]

Mean logarithmic average of the liquid mole fractions

(𝑥∗ − 𝑥)𝑀 = (𝑥𝑜𝑢𝑡

∗ − 𝑥𝑜𝑢𝑡) − (𝑥𝑖𝑛 ∗ − 𝑥𝑖𝑛)

𝑙𝑛[(𝑥𝑜𝑢𝑡 ∗ − 𝑥𝑜𝑢𝑡) (𝑥𝑖𝑛

∗ − 𝑥𝑖𝑛)⁄ ]

 

END OF QUESTIONS

 

 

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APPENDIX Q2

 

 

 

CE2004

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END OF PAPER