Example: ⊲ A boiler is a counter-flow heat exchanger. Specific heat capacity
of the combustion gas is approximately equal to cgas = 1075 J/kg-K. What is
the limit of the performance of the boiler?
HRSG: Pinch Point Analysis
Dr. Md. Zahurul Haq, Ph.D., CEA, FBSME, FIEB
Professor
Department of Mechanical Engineering
Bangladesh University of Engineering & Technology (BUET)
Dhaka-1000, Bangladesh
http://zahurul.buet.ac.bd/
ME 307: Heat Transfer Equipment Design
http://zahurul.buet.ac.bd/ME307/
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© Dr. Md. Zahurul Haq (BUET)
HRSG: Pinch Point Analysis
ME 307 (2024)
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© Dr. Md. Zahurul Haq (BUET)
12000
700
Duty of HX, Q̇ = ṁgas cgas (Tgas,in − Tgas,out )
h30bar ,30o C ≃ h30o C ,sat = 125.8 kJ/kg
320
3043.4
360
3138.7
400
3230.9
500
Super-heated steam-table
280
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600
hsat ,f ,30bar = 1008.4 kJ/kg, hsat ,v ,30bar = 2804.2 kJ/kg
T (o C)
h (kJ/kg)
ME 307 (2024)
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9 Tsat ,30bar = 233.9o C
HRSG: Pinch Point Analysis
440
3321.5
500
3456.5
600
3682.3
9
300
700
3911.7
Q̇ = ṁw (hw ,out − hw ,in )
0
0
Along the whole length of the HX, Th must be greater than Tc .
Pinch point, ∆Tpp ≡ min(Th − Tc ).
T1015
Ideally, ∆Tpp ⩾ 0, practically ∆Tpp ⩾ 5o C.
102000
302000
89 402000
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Q̇ = ṁgas cgas (Tgas,in − Tgas,out ) = 39.775 kW.
Q̇ = ṁw (hw ,out − hw ,in ) → Tw ,out >700o C, actually 913.5o C.
Tgas,out =30o C, violation of second-law of thermodynamics.
© Dr. Md. Zahurul Haq (BUET)
HRSG: Pinch Point Analysis
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© Dr. Md. Zahurul Haq (BUET)
HRSG: Pinch Point Analysis
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!"#$%&'()*+
700
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300
0
0
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T1016
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0
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!"#$%&'()310
12000 302000 312000 402000 412000
89 Q̇ = ṁgas cgas (Tgas,in − Tgas,out ) = 26.875 kW.
Q̇ = ṁw (hw ,out − hw ,ii ) → Th,out = 348.2o C.
Violation of second-law of thermodynamics. WHY?
700
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!"#$%&'()441
600
9
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0
0
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302000
89 © Dr. Md. Zahurul Haq (BUET)
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Q̇ = ṁgas cgas (Tgas,in − Tgas,out ) = 18.81 kW.
Q̇ = ṁw (hw ,out − hw ,ii ) → Xh,out =0.67.
Tgas,out
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9 9 32000
HRSG: Pinch Point Analysis
% &
© Dr. Md. Zahurul Haq (BUET)
=225o C, NO-violation of second-law of thermodynamics.
© Dr. Md. Zahurul Haq (BUET)
HRSG: Pinch Point Analysis
ME 307 (2024)
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© Dr. Md. Zahurul Haq (BUET)
HRSG: Pinch Point Analysis
ME 307 (2024)
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Pinch Analysis: Target-temperature Line Method
Temperature
Tc,out
√
∆Tpp
t lin
e
Targ
Th,out
×
Th,in
Pevap,j = Psat (Tr,j )
e
√
D
mwf,j = hj −hjc,in
Tc,in
T1804
j=0
j
Duty, D
j = 1000
Optimization of an Organic Rankine Cycle-Based Waste Heat Recovery
System Using a Novel Target-Temperature-Line Approach,
ASME J. Energy Resour. Technol. 143(9): 092101:1-12.
paper link
© Dr. Md. Zahurul Haq (BUET)
HRSG: Pinch Point Analysis
ME 307 (2024)
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