Enhancement of laminar flow heat transfer - HexagHTRI Xchanger Suite, Aspentech EDR, CFX for CFD ... dimensionless heat transfer coefficient 1 10 100 10 100 1000 10000 Re[-] ... 94.5

Page 1© Copyright Cal Gavin 2010 www.calgavin.com

Enhancement of laminar flow heat

transfer

Peter Drögemüller / R & D Manager Cal Gavin ltd


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


Hydrodynamic

• Plain empty tube


Laminar Flow, 20mm tube diameter


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


Isothermal Flow development in tubes

Entrance length considerable in laminar flow

Short entrance length in turbulent flow


Heat Transfer

• Plain empty tube


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


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


Computational flow dynamic CFD

Goal:

understanding of heat

transfer

In tube side laminar flow

• Employment of:

ANSYS CFX

Simulation package


Verifying CFD Simulation results with experiments


Mixed and forced laminar convection


Flow map for laminar flow according to Eckards


Forced convection, coolingCooling; 60C Inlet temperature; 50C Wall temperature ; Re ~ 1000


Mixed convection, coolingcooling:

70C Inlet temperature; 7C Wall temperature; Re~ 250


Mixed convection, heatingHeating;

60C Inlet temperature; 123C Wall temperature; Re~250


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


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


Comparison with theoretical correlations


Location in flow map


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


hiTRAN Wire Matrix Elements

• changing fluid dynamics

• increasing heat transfer

• reducing fouling


Hydrodynamik

• Flow field with hiTRAN


Video – Click to start playing


-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


Heat Transfer / Pressure drop

• Measuring Heat Transfer Coefficients

• Measuring Pressure drop


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


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


hiTRAN range in comparison to plain empty tube data


Equal pressure drop design with hiTRANviscous oil 18cp

Re=1700


Computational flow dynamic CFD, with hiTRAN InsertsGoal:

• Goal: Understanding of heat transfer In tube side flow with hiTRAN Inserts


Hydrodynamic: Velocity profiles

LDV-Measurements

hiTRAN

CFD – Simulations

hiTRAN

CFD – simulations

Plain empty


Simulating isothermal velocity profile with hiTRAN

Isothermal flow, Reynolds 17

Heat transfer oil, Viscosity: 150cP Inlet temp.: 7C


Fluid movement hiTRANVelocity profile at outlet


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


Residence time distribution

2.5m tube; Re ~ 250; Inlet 70C; wall 7C; 18cP


• 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:


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


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


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


Many Thanks

Documents

Enhancement of laminar flow heat transfer - HexagHTRI Xchanger Suite, Aspentech EDR, CFX for CFD ... dimensionless heat transfer coefficient 1 10 100 10 100 1000 10000 Re[-] ... 94.5