che2162 - semester1 - 2011.pdf
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ENGINEERINGTRANSCRIPT
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Office Use Only
Monash University
Semester One Examination Period 2011
Faculty Of Engineering
EXAM CODES: CHE 2162
TITLE OF PAPER: Material and Energy Balances
EXAM DURATION: 3 hours writing time
READING TIME: 10 minutes
THIS PAPER IS FOR STUDENTS STUDYING AT:( tick where applicable)
Berwick Clayton Malaysia Off Campus Learning Open Learning
Caulfield Gippsland Peninsula Enhancement Studies Sth Africa
Pharmacy Other (specify)
During an exam, you must not have in your possession, a book, notes, paper, electronic device/s, calculator, pencil
case, mobile phone or other material/item which has not been authorised for the exam or specifically permitted as
noted below. Any material or item on your desk, chair or person will be deemed to be in your possession. You are
reminded that possession of unauthorised materials in an exam is a discipline offence under Monash Statute 4.1.
No examination papers are to be removed from the room.
AUTHORISED MATERIALS
CALCULATORS YES NO
(Only calculators with an 'approved for use' Faculty of
Engineering' or 'Faculty of Science' stickers are permitted)
OPEN BOOK YES NO
SPECIFICALLY PERMITTED ITEMS YES NO
if yes, items permitted are:
Candidates must complete this section if required to write answers within this paper
STUDENT ID __ __ __ __ __ __ __ __ DESK NUMBER __ __ __ __
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Instructions
Answer all questions clearly showing all steps and assumptions.
Table of data provided from page 6 to 11.
Dry air contains 79 mol% N2 and 21 mol% O2 (unless otherwise specified in the question) and the average molecular weight of air is 29 g/mol.
Relative atomic masses: H = 1, C = 12, N = 14, O = 16, S = 32
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Question 1 [15 Marks]
PART A
A sugar solution in water contains 0.145 kg sucrose/kg water (sucrose = C12H22O11) and the specific gravity of the solution is 1.045. Calculate –
(a) Mole fraction of sucrose in the solution. [3 marks]
(b) Density of the solution in lbm/ft3. [2 marks]
Part B
The sugar solution in Part A is stored in a tank such that the liquid level is 12 m above ground level. This solution is to be siphoned from the tank to a fermentation reactor which maintains a liquid level of 8.5m above ground level. The pressure in the storage tank and the reactor is maintained constant at 100 mmHg (gauge) pressure. The friction loss in the siphoning tube is 2.54 m2/s2. Estimate how long (min) it will take to siphon 2000 lbm. Clearly state any assumptions you make. [10 marks]
Given:
∆𝑃
𝜌+
∆𝑢2
2+ g∆z + 𝐹 = −
𝑊𝑠
𝑚
Question 2 [20 Marks]
A gas stream containing Methanol (CH3OH) vapour and a non-condensable mixture of CO and H2 in a ratio of 2 mol H2/mol CO at 100°C and 1000 mm Hg (absolute) enters a condenser operating at 0°C and 1 atm. The metered flow rate of the stream at the inlet condition is 750 m3/h and the relative saturation of methanol is 5.00%. The vapour and liquid streams exiting the condenser are at equilibrium (methanol should be considered as the only condensable species). Calculate the following and clearly state any assumptions you make –
(a) Draw a flow chart of the process and label all the streams with independent process variables
[5 marks]
Ground Level
12 m
8.5 m
0.75 inch tube O.D. 0.05 inch tube thickness Storage Tank
Fermentation Reactor
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(b) Determine the mole fractions of all the components in the inlet stream [5 marks]
(c) Using Raoult’s law for single condensable species, determine the percentage recovery of methanol in the
liquid stream [mol CH3OH condensed/mol CH3OH fed]. [10 marks]
Given:
Relative Saturation:
𝑠𝑟 =
𝑝𝑖
𝑝𝑖∗(𝑇)
× 100%
Raoult’s Law, Single Condensable Species (at vapour liquid equilibrium):
𝑝𝑖 = 𝑦𝑖𝑃 = 𝑝𝑖∗(𝑇)
Question 3 [15 marks]
A liquid mixture containing 40 mol% benzene and the balance toluene is fed to a single equilibrium adiabatic flash
evaporator. The feed stream is at 148.9°C and Pfeed (mmHg). Liquid stream (bottom) and vapour stream (top) leave
the evaporator at equilibrium at 2 atm and temperature Te (°C).
(a) What is the minimum value of Pfeed (mmHg) required to keep the feed in the liquid state before entering the
evaporator (in other words what is the bubble-point pressure of the feed solution).
[5 marks]
(b) Without doing any calculation, use the information given in the data sheets to specify the minimum and
maximum value of Te (°C) if both liquid and vapour are present in the evaporator?
[3 marks]
(c) Briefly explain why Te cannot exceed the feed temperature if any vaporisation takes place? (consider the
fact that the evaporator is adiabatic)
[5 marks]
(d) What will be the effect on Te if the evaporator pressure is lowered and why? (chose one option from below)
[2 marks]
i. Lower Te
ii. Higher Te
iii. No Change
iv. Need more information to specify
Data:
𝑇 (°𝐶) =5
9 𝑇 °𝐹 − 32
𝑃 = 𝑥𝐴𝑝𝐴∗ 𝑇𝑏𝑝 + 𝑥𝐵𝑝𝐵
∗ 𝑇𝑏𝑝 + ⋯
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Question 4 [25 Marks]
An adult takes roughly 12 breaths each minute, inhaling approximately 500mL with each breath. However, during exercise the breathing rate increases by 50%. The molar compositions of the inhaled and exhaled air on a dry basis are as follows:
Species Inhaled air (mol %) Exhaled air (mol %)
O2 21 16.95
N2 79 79.1
CO2 0 3.95
The inhaled air is at 22.1°C and the exhaled air is at the body temperature (37°C). The relative humidity of
both inhaled and exhaled air is found to be 60%. If a person is exercising, calculate the following –
a. Calculate the amount of water (kmol H2O/100 kmol dry air) in the inhaled and exhaled air.
[5 marks]
b. Calculate the mole fractions of all the components in inhaled and exhaled air on a wet basis.
[5 marks]
c. Draw a flowchart of the respiration process and label all the streams with process variables.
[5 marks]
d. Calculate the rate (g/h) of O2, CO2 and H2O transferred from the lungs to the blood or vice versa
(specify which). [10 marks]
Question 5 [25 marks]
3. Sulfur dioxide (SO2) is converted to sulfur trioxide (SO3) using a catalyst in the following reaction:
2𝑆𝑂2 + 𝑂2 𝐶𝑎𝑡𝑎𝑙𝑦𝑡 2𝑆𝑂3
In a pilot plant run SO2 and 100% excess air are fed at 450°C and the product stream leaves at 500°C. The
fractional conversion of SO2 was calculated to be 55% and molar flow of SO3 required in the plant is 100
kmol/min. The reactor is surrounded by a cooling water jacket to remove heat at the rate of 𝑄 (𝑘𝑊) .
a. Draw a flowchart to illustrate the conversion process and label all the material and energy streams.
[5 marks]
b. Calculate the molar flow rates of all the species in the feed and the product streams.
[5 marks]
c. Calculate the extent of reaction and tabulate the molar streams including the enthalpy of each
stream. [5 marks]
d. Calculate the heat 𝑄 (𝑘𝑊) removed by the cooling water. [10 marks]
Data:
Specific enthalpy 𝐻 (𝑘𝐽/𝑚𝑜𝑙)
(Reference state: Gas, Tref = 25°C and Pref = 1 atm)
T (°C) SO2 SO3
450 19.62 27.63
500 22.19 31.44
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Selected Physical Property Data