enhancement of laminar flow heat transfer - hexaghtri xchanger suite, aspentech edr, cfx for cfd ......
TRANSCRIPT
Page 1© Copyright Cal Gavin 2010 www.calgavin.com
Enhancement of laminar flow heat
transfer
Peter Drögemüller / R & D Manager Cal Gavin ltd
Page 2© Copyright Cal Gavin 2010 www.calgavin.com
Cal Gavin LTD:
• Designing new enhanced exchangers
• De-bottlenecking – engineering solutions
to overcome plant and process limitations
• Simulating performance and upgrading existing exchangers
• Range of Software Tools available
(HTRI Xchanger Suite , Aspentech EDR, CFX for CFD
studies, INTHEAT for heat exchanger Network solutions)
Research, development and manufacture of enhancement
technology for heat exchangers
Page 3© Copyright Cal Gavin 2010 www.calgavin.com
Hydrodynamic
• Plain empty tube
Page 4© Copyright Cal Gavin 2010 www.calgavin.com
Laminar Flow, 20mm tube diameter
Page 5© Copyright Cal Gavin 2010 www.calgavin.com
U/U
mean
2
2
12r
s
U
U
mean
x
n
mean
x
r
s
U
U1
122.1
Laminar Turbulent:
0.2
0.6
1
1.4
-10 -5 0 5 10
0.5
1.5
2.5
-10 -5 0 5 10
Radial position (mm)
meassuredTheory
Radial position (mm)
Velocity profile –LDV measurements plain tube - without heat transfer
Re 500 Re 10000
Page 6© Copyright Cal Gavin 2010 www.calgavin.com
Isothermal Flow development in tubes
Entrance length considerable in laminar flow
Short entrance length in turbulent flow
Page 7© Copyright Cal Gavin 2010 www.calgavin.com
Heat Transfer
• Plain empty tube
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In house test facility:
Experimental Parameters:
flow rate 50kg/hr < V < 4000kg/hr (Gear pump)
Viscosity Range: 0.3cP < eta < 200cP
Dimensionless numbers:
Reynold Range 5 0< Re < 100000
Prandtl Range 2 < Pr < 4000
Heat Balance accuracy ~ +- 5%
Dimensions:
- 2500mm test section
- tubes: 10mm ID to 32mm ID
- max heat load: 18 kW
Page 9© Copyright Cal Gavin 2010 www.calgavin.com
Typical curve for plain empty tube heat transfer
Reminder: turbulent region 2x Reynolds ~
1.7 Heat transfer
Laminar region hardly any improvement
in heat transfer with Reynolds that means
flow velocity
In general:
Multi passing in laminar flow heat
exchangers does not yield the
same heat transfer improvement
compared to turbulent flow
Page 10© Copyright Cal Gavin 2010 www.calgavin.com
Computational flow dynamic CFD
Goal:
understanding of heat
transfer
In tube side laminar flow
• Employment of:
ANSYS CFX
Simulation package
Page 11© Copyright Cal Gavin 2010 www.calgavin.com
Verifying CFD Simulation results with experiments
Page 12© Copyright Cal Gavin 2010 www.calgavin.com
Mixed and forced laminar convection
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Flow map for laminar flow according to Eckards
Page 14© Copyright Cal Gavin 2010 www.calgavin.com
Forced convection, coolingCooling; 60C Inlet temperature; 50C Wall temperature ; Re ~ 1000
Page 15© Copyright Cal Gavin 2010 www.calgavin.com
Mixed convection, coolingcooling:
70C Inlet temperature; 7C Wall temperature; Re~ 250
Page 16© Copyright Cal Gavin 2010 www.calgavin.com
Mixed convection, heatingHeating;
60C Inlet temperature; 123C Wall temperature; Re~250
Page 17© Copyright Cal Gavin 2010 www.calgavin.com
Stratification Dependency on Reynolds Number:
Simulation with verified experimental data for different Reynolds numbers
70° C Inlet temperature; 7°C Wall temperature 2.5m tube length; Viscosity 12cP
70° C Inlet
Outlet bulk
CFD 62° C; measured 61.8°C
Velocity profile
Reynolds 253
• Stratified flow
• Long residence
time
at bottom of tube
• Low heat transfer
70° C Inlet
Reynolds 935
Outlet bulk
CFD 66.2° C; measured 66.2°C
Page 18© Copyright Cal Gavin 2010 www.calgavin.com
Temperature Pinch in stratified flow
Temperature pinch not accounted for in
Heat Exchanger design Software
can lead to lower heat transfer than calculated
70C inlet
Reynolds 56
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Comparison with theoretical correlations
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Location in flow map
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Summary: Plain empty tube heat transfer
• Heat transfer in laminar flow much more complex than in
turbulent flow
• Laminar forced and mixed convection regimes possible
• Stratification likely in mixed laminar convection
• Only small improvement in heat transfer with increased flow
velocity
• Long residence time at the wall for some of the fluid
• Heat exchanger Software does not predict very well if
Temperature pinch present
• Much reduced heat transfer in vertical flow conditions
Page 22© Copyright Cal Gavin 2010 www.calgavin.com
hiTRAN Wire Matrix Elements
• changing fluid dynamics
• increasing heat transfer
• reducing fouling
Page 23© Copyright Cal Gavin 2010 www.calgavin.com
Hydrodynamik
• Flow field with hiTRAN
Page 24© Copyright Cal Gavin 2010 www.calgavin.com
Video – Click to start playing
Page 25© Copyright Cal Gavin 2010 www.calgavin.com
-0.2
0
0.2
0.4
0.6
0.8
1
-10 -5 0 5 10
Radial position [mm]0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
distance from wall [mm]
u / u
max [
-]
92.9% voidage
97.3%
voidage
Turbulent theory
LDV measurement: Velocity profile hiTRAN Re = 500
Laminar theory
Observations:
• Velocity profile near to the wall similar to turbulent
flow with: small boundary layer, high shear rates
Page 26© Copyright Cal Gavin 2010 www.calgavin.com
Heat Transfer / Pressure drop
• Measuring Heat Transfer Coefficients
• Measuring Pressure drop
Page 27© Copyright Cal Gavin 2010 www.calgavin.com
Heat Transfer and pressure drop
measurements at in-house test facility
Overview:
2500mm test section
tubes: 10mm ID to 32mm ID
more than 600 different Insert
Geometries were tested
Reynolds Range:
5 < Re < 200000
Prandtl Range:
2 < Pr < 4000
Page 28© Copyright Cal Gavin 2010 www.calgavin.com
Heat Transfer: correlationSingle Phase: Heat transfer
dimensionless heat transfer coefficient
1
10
100
10 100 1000 10000
Re[-]
Nu
* P
r^
-(1
/n)
Vis = 9cP; Pr=160
Vis = 15cp; Pr=210
Vis = 20cp; Pr=290
Vis = 30cp; Pr=430
Vis = 50cp; Pr=670
Page 29© Copyright Cal Gavin 2010 www.calgavin.com
hiTRAN range in comparison to plain empty tube data
Page 30© Copyright Cal Gavin 2010 www.calgavin.com
Equal pressure drop design with hiTRANviscous oil 18cp
Re=1700
Page 31© Copyright Cal Gavin 2010 www.calgavin.com
Computational flow dynamic CFD, with hiTRAN InsertsGoal:
• Goal: Understanding of heat transfer In tube side flow with hiTRAN Inserts
Page 32© Copyright Cal Gavin 2010 www.calgavin.com
Hydrodynamic: Velocity profiles
LDV-Measurements
hiTRAN
CFD – Simulations
hiTRAN
CFD – simulations
Plain empty
Page 33© Copyright Cal Gavin 2010 www.calgavin.com
Simulating isothermal velocity profile with hiTRAN
Isothermal flow, Reynolds 17
Heat transfer oil, Viscosity: 150cP Inlet temp.: 7C
Page 34© Copyright Cal Gavin 2010 www.calgavin.com
Fluid movement hiTRANVelocity profile at outlet
Page 35© Copyright Cal Gavin 2010 www.calgavin.com
CFD Simulation Plain empty tube compared to enhance hiTRAN flow
Example Simulation verified with experimental data:
70° C Inlet temperature; 7°C Wall temperature
2.5m tube length; Reynolds number 253; mass flow 195kg/hr; Viscosity 12cP
70° C Inlet 70° C Inlet
Outlet bulkCFD 62° C; measured 61.8°C
Outlet bulkCFD 50.7°C; measured 49.9°C
hiTRAN tube
Velocity profile plain
plain tube
Velocity profile hiTRAN
• Stratified flow
• Long residence
time
at bottom of tube
• Low heat transfer
• Good fluid
distribution
• High heat transfer
with low outlet
temperature
Page 36© Copyright Cal Gavin 2010 www.calgavin.com
Residence time distribution
2.5m tube; Re ~ 250; Inlet 70C; wall 7C; 18cP
Page 37© Copyright Cal Gavin 2010 www.calgavin.com
• Up to 16 times tube side heat transfer
• Can be used to improve duty in revamp
• Can be used to design more compact units
• Shorter residence time at tube wall
• No flow stratification
• More even residence time
• No sudden change in heat transfer (laminar -
turbulent)
• All available pressure drop is utilised, hiTRAN
design meets pressure drop requirements
Summary hiTRAN in laminar flow:
Page 38© Copyright Cal Gavin 2010 www.calgavin.com
hiTRAN.SP
Standalone Software and plug-in
• Fully Integrated hiTRAN® Insert calculation HTRI &
Aspen EDR Software
• Standalone tube side calculation
• Free available for download from CalGavin.com
Page 39© Copyright Cal Gavin 2010 www.calgavin.com
Double enhanced helical baffle / hiTRANDalia FPSO – Total Oil, Angola
• design capacity of 240,000 barrels per day of crude, two million barrels of
storage capacity
• shell side 1073500kg/hr wet crude oil is heated from 50.5 C to 60.7 C
• tube side 802170kg/hr dry crude oil is cooled from 87.5 C to 70.1C
TEMA Type BES
Temp. shell in / out [°C] 50.5 / 60.7
Temp. tube in / out [°C] 87.5 / 70.1
Massflow shell / tube [kg/s] 298.2 /
222.8
Duty [MW] 7.94
Tube OD diameter [mm] 25.4
FPSO Dalia with installed Crude / Oil
Interchangers on the Top deck
Case Study 2
Page 40© Copyright Cal Gavin 2010 www.calgavin.com
Size comparison -Conventional / HELITRAN
plain /
single.Se
gmental.
hiTRAN® /
helical
baffle
gain
OHTC [W/m2K] 59.9 245 4x
Tube side:
HTC [W/m2K] 95 789 8x
dp [bar] 140 100
Flow velocity [m/sec] 0.92 0.45 ½
Reynolds [-] 1680 800 ½
Residence time [sec] 102 27 ¼
Shell side
HTC [W/m2K] 455 789 ~2
dp [bar] 1.50 1.25
Flow velocity [m/sec] 0.41 1.3 3
Reynolds 250 635
Wall temperatures [°C] 59.2 65.6
Geometry
Shell in series [-] 3 1
Shell in parallel [-] 3 2
Total no. of Shells [-] 9 2 ~4
Tube Flow path [m] 94.5 12.2 1/8
Tube length [m] 5.25 6.096
Total tube count [-] 16002 3640 ~¼
Tube passes [-] 6 2
Total HT area [m2] 6420 1704 ~¼
Plot space [m2] 104.5 26.2 ¼
Weight wet [kg] 401148 130716 1/3
Exchanger costs [%] 100 35 ~1/3
Conventional HELITRAN
Helical baffle
on outside
hiTRAN
tubeside
Page 41© Copyright Cal Gavin 2010 www.calgavin.com
Many Thanks