lectrure 04_14 jul
TRANSCRIPT
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LECTURE 4 External Forced Convection
Flow Across Tube Banks/Bundles
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Lesson Outcomes
Understand the basic principle of flow across tube banks/tube
bundles
Understand the characteristics of aligned and staggered
arrangement in tube banks
Solve a problem in flow across tube banks/tube bundles
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At the end of this lecture, students should be able to :
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Flow Across Tube Banks/Bundles
Heat transfer in flow across a bank of tubes is of
particular importance in the design of heat exchangers.
Heat exchangers are found in numerous industrial
applications, such as steam generation in a boiler or air
cooling in the coil of an air conditioner.
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Flow Across Tube Banks/Bundles
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Flow Across Tube Banks/Bundles
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Flow Across Tube Banks/Bundles
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Flow Across Tube Banks/Bundles
V
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All properties, are evaluated at the mean temperature :
Ti Te Ts
2
)( eim
TTT
Flow Across Tube Banks/Bundles
Ts
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The tubes in a tube bank are usually arranged either
in-line/aligned or staggered in the direction of fluid flow.
The characteristic length of tube bundle is the outer tube
diameter, D
The number of row and column in a tube bank are
defined as longitudinal direction, NL (row) and transverse
direction, NT (column), respectively
The total number of tubes in bank = N
Flow Across Tube Banks/Bundles
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Flow Across Tube Banks/Bundles
In-line/Aligned Staggered
V V
Transverse, NT = 6 Transverse, NT = 5
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Flow Across Tube Banks/Bundles
NT = ? NL = ? N = ?
NT = ? NL = ? N = ?
NT = ? NL = ? N = ?
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Flow Across Tube Banks/Bundles
NT = 6 NL = 4 N = 24
NT = 3 NL = 5 N = 15
NT = 5 NL = - N = 22
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Total surface area in tube bundles :
Ti Te
Ts
Flow Across Tube Banks/Bundles
Ts
)( NDLAs
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Flow Across Tube Banks/Bundles
In aligned tubes :
- transverse pitch (ST)
- longitudinal pitch (SL)
- transverse plane (A1)
In staggered tubes :
- transverse pitch (ST)
- longitudinal pitch (SL)
- diagonal pitch (SD)
- transverse plane (A1)
- diagonal plane (A2)
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In-line/Aligned Tubes
D = tube diameter ST = transverse pitch SL = longitudinal pitch A1 = transverse plane
A1 = ST - D
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D = tube diameter ST = transverse pitch SL = longitudinal pitch SD = diagonal pitch A1 = transverse plane A2 = diagonal plane
Staggered Tubes
A1 = ST - D
A2 = SD - D
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Flow Across Tube Banks/Bundles
Heating Process – boiler
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Ti = 100°C
Ts = 20°C
Te = 80°C
Heating Process
Flow Across Tube Banks/Bundles
Tm = 90°C
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Flow Across Tube Banks/Bundles
Heating Process – boiler
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Ti = 20°C Ts = 100°C Te = 40°C
Cooling Process
Flow Across Tube Banks/Bundles
Tm = 30°C
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Flow Across Tube Banks/Bundles
Cooling Process – heat exchanger
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Flow Across Tube Banks/Bundles
Ti
Ti
Te
Te
Ts
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Flow Across Tube Banks/Bundles
isiese TTTTTT and
)/ln(ln
ie
ie
TT
TTT
Logarithmic mean
temperature difference
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Flow Across Tube Banks/Bundles
)/ln(ln
ie
ie
TT
TTT
Logarithmic mean
temperature difference
Heat transfer rate in tube banks :
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Flow Across Tube Banks/Bundles
Mass flow rate of fluid:
V V
LSNm TTVρ air
* Properties of fluid is evaluated at an inlet temperature
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Flow Across Tube Banks/Bundles
Reynolds Number :
V V
Re = VmaxD /υ