UNIVERSITY OF TECHNOLOGY, JAMAICA
COLLEGE/ FACULTY: Faculty of Engineering and Computing
SCHOOL/ DEPARTMENT: SOE/Chemical Engineering
Mid-semester Examination 2, Semester 1
Module Name:
Chemical Engineering Thermodynamics 1
Module Code:
CHE3003
Date:
November 19, 2013
Theory/ Practical: Theory
Groups:
B.ENG.3C
Duration:
1 hour & 45 minutes
Instructions
1. ANSWER ALL QUESTIONS
2. EACH QUESTION MUST BEGIN ON A NEW PAGE
3. LEAVE TWO LINES BETWEEN PARTS OF A QUESTION
4. READ EACH QUESTION CAREFULLY BEFORE ANSWERING
5. SHOW CLEARLY ALL EQUATIONS USED FOR CALCULATIONS
6. THE INTENDED MARK IS INDICATED AT THE BEGINNING OF EACH
QUESTION
7. ANSWER MUST BE NUMBERED IDENTICAL TO THE QUESTION BEING
ANSWERED
8. A FORMULA SHEET AND UNIT CONVERSION CHART ARE ATTACHED.
*** DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO ***
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Question #1 [25 marks] = 33.3%
a.) An inventor claims to have devised a cyclic engine which exchanges heat with reservoirs at
50 oC and 320 oC and which produces 0.45 kJ of work for each kJ of heat extracted from the
hot reservoir. Is the claim believable?
b.) A nuclear power plant generates 750 MW. The reactor temperature is 415oC and a river with
water temperature of 20oC is available.
i.) What is the maximum possible thermal efficiency of the plant and what is the minimum
rate at which heat must be discarded to the river?
ii.) If the actual thermal efficiency of the plant is 60% of the maximum, at what rate must
heat be discarded to the river, and what is the temperature rise of the river if it has a
flowrate of 165 m3/s. Take Cp = 4183 J/kg.K & ρ = 998.2 m3/kg.
Question #2 [25 marks] = 33.3%
An equimolar mixture of n-butane(1) and n-hexane(2) at pressure, P, is brought to a temperature
of 368.15K where it exists as a vapour/liquid mixture in equilibrium. If the mole fraction of nhexane in the liquid phase is 0.75 and assuming Raoult's law applies, what is:
a.) the total pressure?
b.) the composition of the vapour phase?
c.) the mole fraction of the system that is liquid?
Constants for the Antoine Equation are as follows:
n-butane:- A = 13.6608 B = 2154.70
C = -34.361
n-hexane:- A = 13.8193 B = 2696.04
C = -48.833
Question #3 [25 marks] = 33.4%
One hundred kmol per hour of sub-cooled liquid benzene at 300 K and 3 bar is heated at constant
pressure to saturated vapour in a steady-flow heat exchanger. If Tsat for benzene at 3 bar is
392.3K, estimate the exchanger duty (in kW).
Total Marks = 75
***** END OF PAPER *****
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Formula Sheet
𝑛
𝑄𝐻 = 𝑄𝐶 + 𝑊
𝜂=
𝜂𝑐 =
∑
𝑊 𝑄𝐻 − 𝑄𝐶
=
𝑄𝐻
𝑄𝐻
𝑖=1
𝐿+𝑉 =1
𝑇𝐻 − 𝑇𝐶
𝑇𝐶
=1−
𝑇𝐻
𝑇𝐻
𝑧𝑖 = 𝑥𝑖 L + yi V
𝐵
𝑇+𝐶
ln 𝑃 𝑠𝑎𝑡 /𝑘𝑃𝑎 = 𝐴 −
Riedel’s equation
∆𝐻 1.092(𝑙𝑛𝑃𝑐 − 1.013)
=
𝑅𝑇𝑛
0.930 − 𝑇𝑟𝑛
𝑦𝑖 𝑃 = 𝑥𝑖 𝑃𝑖 𝑠𝑎𝑡
𝑃 = ∑ 𝑥𝑖 𝑃𝑖 𝑠𝑎𝑡
Where, Pc is the critical pressure in bars and
Trn is the reduced temperature at Tn.
𝑖
𝑃𝑖 𝑠𝑎𝑡
𝐾𝑖 =
𝑃
𝑦𝑖 =
𝑧𝑖 𝐾𝑖
=1
1 + 𝑉(𝐾𝑖 − 1)
Watson’s equation
1 − 𝑇𝑟2 0.38
∆𝐻2
=(
)
∆𝐻1
1 − 𝑇𝑟1
𝑧𝑖 𝐾𝑖
1 + 𝑉(𝐾𝑖 − 1)
𝑇 𝐶𝑜
̂
∆𝐻
𝐵
𝐶
𝐷 𝜏−1
𝑝
=∫
𝑑𝑇 = 𝐴𝑇0 (𝜏 − 1) + 𝑇20 (𝜏2 − 1) + 𝑇30 (𝜏3 − 1) +
(
)
𝑅
2
3
𝑇0
𝜏
𝑇0 𝑅
where,
⟨𝐶𝑜𝑝 ⟩𝐻
𝑅
=𝐴+
𝜏=
𝑇
𝑇0
𝐵
𝐶
𝐷
𝑇0 (𝜏 + 1) + 𝑇20 (𝜏2 + 𝜏 + 1) + 2
2
3
𝜏𝑇0
̂ = ⟨𝐶𝑝𝑜 ⟩𝐻 (𝑇 − 𝑇0 )
∆𝐻
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