10th PHOENICS User Conference Melbourne, Australia A CFD presentation by Dr. Paddy Phelps (...

10th PHOENICS User 10th PHOENICS User ConferenceConference

Melbourne, AustraliaMelbourne, Australia

A CFD presentation by A CFD presentation by

Dr. Paddy Phelps ( Flowsolve Dr. Paddy Phelps ( Flowsolve Ltd ]Ltd ]

&&

Mr. John Gibson [ Scott Wilson Mr. John Gibson [ Scott Wilson Ltd ] Ltd ] May 2004

Predicting the Dispersion Predicting the Dispersion Consequences of Gaseous Consequences of Gaseous Releases from a University Releases from a University

Research Facility Research Facility in an Urban Environmentin an Urban Environment

A CFD presentation A CFD presentation

on behalf of the authors byon behalf of the authors by

Dr. John LudwigDr. John Ludwig

( CHAM Ltd )( CHAM Ltd )

Outline of PresentationOutline of Presentation

Industrial ContextIndustrial Context Objectives of StudyObjectives of Study Benefits of using CFDBenefits of using CFD Description of CFD ModelDescription of CFD Model Outline of simulations performedOutline of simulations performed Sample Results ObtainedSample Results Obtained ConclusionsConclusions

Consequences of release dispersion Consequences of release dispersion from from

an urban university research facilityan urban university research facility


Industrial ContextIndustrial Context

The research facility is housed in a The research facility is housed in a pre-existing building on the pre-existing building on the campus of a city-based UK University. campus of a city-based UK University.

The site is a built-up area with private The site is a built-up area with private and college accommodation, shops, and college accommodation, shops, hospital and university buildings in hospital and university buildings in the immediate vicinity.the immediate vicinity.


The building contains research The building contains research laboratories, from which air and laboratories, from which air and fume-cupboard extracts need to be fume-cupboard extracts need to be vented thoughtfully and considerately vented thoughtfully and considerately to atmosphere .to atmosphere .

Whilst not necessarily toxic, the Whilst not necessarily toxic, the releases can occasionally be tainted releases can occasionally be tainted by unpleasant aromas ...by unpleasant aromas ...


The building, at present a two-The building, at present a two-storey building with roof-top plant storey building with roof-top plant room, is to be refurbished.room, is to be refurbished.

A third storey and a new plant A third storey and a new plant

room are to be added.room are to be added.

Gaseous discharges from the labs Gaseous discharges from the labs

will be vented from tall stackswill be vented from tall stacks


Opposite the research building, a Opposite the research building, a major campus re-development major campus re-development project is under construction .project is under construction .

New buildings will include a massive New buildings will include a massive

“Glass Pavilion” and linked “Plant “Glass Pavilion” and linked “Plant

Wall” Wall” Some adjacent street areas will Some adjacent street areas will

become pedestrian precinctsbecome pedestrian precincts


There is a history of local complaints about There is a history of local complaints about poor dispersion of “unpleasant smells”poor dispersion of “unpleasant smells”

The new buildings will create a local The new buildings will create a local

impediment to airflow, and may impediment to airflow, and may

significantly alter local air flow patternssignificantly alter local air flow patterns ““Pedestrianisation” of street areas will Pedestrianisation” of street areas will

remove vehicular air stirring and increase remove vehicular air stirring and increase awareness of ground-level concentrationsawareness of ground-level concentrations


Will releases from the roof-top stacks of the Will releases from the roof-top stacks of the research building have adequate dilution / research building have adequate dilution / dispersion consequences ?dispersion consequences ?

Could effluent plumes impinge upon Could effluent plumes impinge upon openable windows or HVAC intakes in openable windows or HVAC intakes in nearby buildings, or public access areas ?nearby buildings, or public access areas ?

If a hazard to the public exists, what is the If a hazard to the public exists, what is the

extent, and how may it be eradicated ?extent, and how may it be eradicated ?

Flow Geometry Close-upFlow Geometry Close-up

Overview of Site “as Overview of Site “as planned”planned”

Objectives of Study - 1Objectives of Study - 1

Use simulation tools to predict mixing Use simulation tools to predict mixing of rooftop extract releases from the of rooftop extract releases from the research building with the ambient research building with the ambient airflow over the adjacent buildings airflow over the adjacent buildings

Provide input to the design of Provide input to the design of discharge arrangements which will discharge arrangements which will lead to acceptable environmental lead to acceptable environmental impactimpact

Objectives of Study - 2Objectives of Study - 2

What constitutes “acceptable What constitutes “acceptable environmental impact” ?environmental impact” ?

Plume core is diluted and dispersed to Plume core is diluted and dispersed to a safe level at nearby a safe level at nearby HVAC intakesHVAC intakes Opening windowsOpening windows Public access areasPublic access areas

Criterion of AcceptabilityCriterion of Acceptability

A safe levelA safe level is taken as a dilution is taken as a dilution level of 1:10level of 1:1044 ( i.e. a concentration ( i.e. a concentration of 100 ppm ) from stack releaseof 100 ppm ) from stack release

The plume coreThe plume core is the spatial is the spatial envelope of this critical dilution / envelope of this critical dilution / concentrationconcentration

Overview of Release Overview of Release ConditionsConditions



Industrial ContextIndustrial Context Objectives of StudyObjectives of Study Benefits of using CFDBenefits of using CFD Description of CFD Model Description of CFD Model Outline of simulations performedOutline of simulations performed Sample Results ObtainedSample Results Obtained ConclusionsConclusions

Benefits of CFD Approach Benefits of CFD Approach (1)(1)

No scale-up problemNo scale-up problem Three-dimensional, steady or transientThree-dimensional, steady or transient Interrogatable predictionsInterrogatable predictions Handles effect of Handles effect of

blockages in domainblockages in domainrecirculating flowrecirculating flowmultiple inlets and outletsmultiple inlets and outletsmultiple interacting releasesmultiple interacting releases

Benefits of CFD Approach Benefits of CFD Approach (2)(2)

TechniqueTechnique allows for rapid allows for rapid and and cost-effective cost-effective assessment of alternative assessment of alternative remedial strategiesremedial strategies

Solution DomainSolution Domain

3-D PLUME DISPERSION MODEL3-D PLUME DISPERSION MODEL Solution domain encompasses the Solution domain encompasses the

principal neighbouring buildings for principal neighbouring buildings for

at least one block on each side of the at least one block on each side of the research facilityresearch facility

PHOENICS VR objects (plus some bespoke PHOENICS VR objects (plus some bespoke objects for roofs) used for blockages, in objects for roofs) used for blockages, in absence of CAD models to importabsence of CAD models to import

Domain 216m by 243m by 68m highDomain 216m by 243m by 68m high

CFD Model Description - CFD Model Description - 11

Representation of the effects ofRepresentation of the effects of blockage due to the presence of blockage due to the presence of

internal obstaclesinternal obstacles multiple inlets and outlets for multiple inlets and outlets for

air/effluent releases air/effluent releases Influence of buoyancy on plume Influence of buoyancy on plume

trajectorytrajectory ambient wind velocity, temperature ambient wind velocity, temperature

and turbulence profilesand turbulence profiles


Dependent variables solved for :Dependent variables solved for : pressure (total mass conservation)pressure (total mass conservation) axial, lateral and vertical velocity componentsaxial, lateral and vertical velocity components air / effluent mixture temperatureair / effluent mixture temperature effluent concentration in mixture effluent concentration in mixture turbulence kinetic energyturbulence kinetic energy turbulence energy dissipation rateturbulence energy dissipation rate

Independent Variables:Independent Variables: 3 spatial co-ordinates (x,y,z) and time3 spatial co-ordinates (x,y,z) and time


The set of partial differential equations The set of partial differential equations is solved within the defined solution is solved within the defined solution domain and on a prescribed numerical domain and on a prescribed numerical gridgrid

The equations represent conservation The equations represent conservation of mass, energy and momentum of mass, energy and momentum

The momentum equations are the The momentum equations are the familiar Navier-Stokes Equations which familiar Navier-Stokes Equations which govern fluid flowgovern fluid flow


The equations may each be written in The equations may each be written in the formthe form

D( ) /Dt + div ( U - grad ) = S{

Terms represent transience, convection, Terms represent transience, convection, diffusion and sources respectivelydiffusion and sources respectively

Equation is cast into finite volume form Equation is cast into finite volume form by integrating it over the volume of by integrating it over the volume of each celleach cell


““Guess and correct” solution procedure Guess and correct” solution procedure used iteratively to until “convergence” of used iteratively to until “convergence” of schemescheme

Around 1500 “sweeps” of domain required Around 1500 “sweeps” of domain required for convergencefor convergence

Typical nodalisation level - 500,000Typical nodalisation level - 500,000 Convergence therefore involves Convergence therefore involves

formulation and solution of around 6 billion formulation and solution of around 6 billion simultaneous linked differential equationssimultaneous linked differential equations

Boundary Conditions:Boundary Conditions:Ambient Wind Ambient Wind

Specification [ 1 ]Specification [ 1 ]

SummerSummer• Ambient temperature - 18 deg.CAmbient temperature - 18 deg.C• Wind from SW Wind from SW

Winter Winter • Ambient temperature - 5 deg.CAmbient temperature - 5 deg.C• Wind from NNEWind from NNE

Boundary Conditions:Boundary Conditions:Ambient Wind Ambient Wind

Specification [ 2 ]Specification [ 2 ]

Wind SpeedsWind Speeds• Still - 0.5 m/s Still - 0.5 m/s • Low - 2.5 m/sLow - 2.5 m/s• Medium - 8.0 m/sMedium - 8.0 m/s

Wind Profiles Wind Profiles • Pasquill D stability profilesPasquill D stability profiles

Internal Sources:Internal Sources:Rooftop Release Rooftop Release

SpecificationSpecification

Laboratory Extract Stacks (2 off)Laboratory Extract Stacks (2 off)

• Vertical stacksVertical stacks• Stack diameter 0.95 m.Stack diameter 0.95 m.• Height 3 m. above plant room roofHeight 3 m. above plant room roof• Release temperature - 24 deg.CRelease temperature - 24 deg.C• Release velocity - 15 m/sRelease velocity - 15 m/s• Flowrate 2.84 mFlowrate 2.84 m33/s each stack/s each stack

Boundary Condition Boundary Condition Independent RegionIndependent Region



Industrial ContextIndustrial Context Objectives of StudyObjectives of Study Benefits of using CFDBenefits of using CFD Description of CFD ModelDescription of CFD Model Outline of simulations performedOutline of simulations performed Sample results ObtainedSample results Obtained ConclusionsConclusions

Overview of WorkscopeOverview of Workscope

Model build andModel build and

25 Simulations 25 Simulations performed in performed in

4 “stages”4 “stages”

Workscope for Stage 1Workscope for Stage 1

““As Planned” Building GeometryAs Planned” Building Geometry Model Construction & Testing Model Construction & Testing

Initial Scoping StudiesInitial Scoping Studies

Objective :Objective :• Determine whether proposed arrangement Determine whether proposed arrangement

leads to adequate dilution / dispersion of leads to adequate dilution / dispersion of

effluent releases under various wind effluent releases under various wind

conditionsconditions


Original “As Was” Building Geometry :Original “As Was” Building Geometry :

““Worst Case” Wind Vector Worst Case” Wind Vector combinationscombinations

Objective :Objective :• to predict consequences of new neighbour to predict consequences of new neighbour

buildings on plume dispersion if no buildings on plume dispersion if no refurbishment is carried outrefurbishment is carried out

• to provide base case data for comparison to provide base case data for comparison with “as planned” post-refurbishment with “as planned” post-refurbishment geometrygeometry


2-D “Venturi” Stack Design Model2-D “Venturi” Stack Design Model• Model construction & testingModel construction & testing• Parametric study of various design Parametric study of various design

parametersparameters

Objective :Objective :• to investigate effectiveness of various to investigate effectiveness of various

designs of venturi stack, subject to designs of venturi stack, subject to given constraintsgiven constraints


““As Planned” Geometry + Venturi StackAs Planned” Geometry + Venturi Stack

““Worst Case” Wind Vector Worst Case” Wind Vector combinationscombinations

Objective :Objective :• to investigate dispersion effectiveness of to investigate dispersion effectiveness of

“as planned” post-refurbishment “as planned” post-refurbishment geometry with venturi stackgeometry with venturi stack



Industrial ContextIndustrial Context Objectives of StudyObjectives of Study Benefits of using CFDBenefits of using CFD Description of CFD ModelDescription of CFD Model Outline of simulations performed Outline of simulations performed Sample Results ObtainedSample Results Obtained ConclusionsConclusions

Stage 1 Simulations:Stage 1 Simulations:

Initial Scoping StudiesInitial Scoping Studies

• ““As Planned” Building GeometryAs Planned” Building Geometry• Twin Vertical Stack releases Twin Vertical Stack releases • Summer (18Summer (1800C ambient, 24C ambient, 2400C release); C release); • Winter (5Winter (500C ambient, 20C ambient, 2000C release)C release)• Wind velocities 0.5, 2.5, 5 and 8 m/sWind velocities 0.5, 2.5, 5 and 8 m/s• Various wind directionsVarious wind directions

Stage 1 Simulation MatrixStage 1 Simulation Matrix

RUN SEASON WIND VECTOR

DIRN SPEED

1 Summer SOUTH WEST 8.0




5 Winter NORTH NORTH EAST 8.0




9 Winter EAST 0.5

10 Winter NORTH 0.5

11 Winter WEST 0.5



14 Winter NORTH 2.5


16 Winter NORTH 8.0

17 Winter WEST 2.5

18 Winter WEST 8.0

““AS PROPOSED” SCHEME; LOW WIND IN AS PROPOSED” SCHEME; LOW WIND IN WINTERWINTER

Wind vector Wind vector 0.50.5 m/s m/s from from NNENNE Ambient temperature Ambient temperature 5 500CC Release temperature Release temperature 212100CC Vertical release through twin stacksVertical release through twin stacks Release velocity Release velocity ~15 m/s~15 m/s Chiller air curtain Chiller air curtain OFFOFF

Stage 1 Simulations:Stage 1 Simulations:Predictions for Case 7Predictions for Case 7

Stage 1 “ As Proposed ” Stage 1 “ As Proposed ” Results :Results :

Winter wind vector 0.5 m/s Winter wind vector 0.5 m/s from NNEfrom NNE

““PROPOSED” SCHEME; HIGH WIND IN PROPOSED” SCHEME; HIGH WIND IN SUMMERSUMMER

Wind vector Wind vector 8.08.0 m/s m/s from from SWSW Ambient temperature Ambient temperature 181800CC Release temperature Release temperature 242400CC Vertical release through twin stacks Vertical release through twin stacks Release velocity Release velocity ~ 15 m/s~ 15 m/s Chiller air curtain Chiller air curtain OFFOFF


Stage 1 “ As Proposed ” Stage 1 “ As Proposed ” Results :Results :

Summer wind vector 8 m/s Summer wind vector 8 m/s from SWfrom SW

The imminent construction of the massive The imminent construction of the massive new buildings on the opposite side of the new buildings on the opposite side of the street will irrevocably change the ambient street will irrevocably change the ambient air flow patterns in the vicinity of the release air flow patterns in the vicinity of the release site. site.

With new pedestrian precincts, moving With new pedestrian precincts, moving vehicular traffic can no longer be relied upon vehicular traffic can no longer be relied upon to generate dilution mixing at low elevationsto generate dilution mixing at low elevations

Pedestrians will be more sensitive to the Pedestrians will be more sensitive to the impact of odour-tinged discharge plumesimpact of odour-tinged discharge plumes

Stage 1 Simulations:Stage 1 Simulations:Outcome of Predictions Outcome of Predictions

- 1 - 1

The plume trajectories at higher wind The plume trajectories at higher wind speeds were flatter than their low-wind speeds were flatter than their low-wind counterparts, and dispersed more rapidly.counterparts, and dispersed more rapidly.

At lower wind speeds the core envelope At lower wind speeds the core envelope was more erect at the point of release; in was more erect at the point of release; in the winter case, this was assisted by a the winter case, this was assisted by a contribution from buoyancy-driven uplift.contribution from buoyancy-driven uplift.


- 2- 2

For the “as proposed” geometry & release For the “as proposed” geometry & release configuration, predictions indicated that configuration, predictions indicated that releases from stacks could be entrained releases from stacks could be entrained into the recirculation regions in the lee of into the recirculation regions in the lee of the downwind buildings .the downwind buildings .

Effluent concentrations in excess of Effluent concentrations in excess of recommended limit could thus occur at recommended limit could thus occur at ground level and over building surfaces ground level and over building surfaces with openable windows.with openable windows.


- 3- 3

Under low wind conditions in winter, Under low wind conditions in winter, the street level concentrations were the street level concentrations were above the 1:10above the 1:1044 acceptable dilution acceptable dilution criterioncriterion

Under high wind conditions in summer, Under high wind conditions in summer, the plume core just failed to clear roof the plume core just failed to clear roof and upper storey regions in adjacent and upper storey regions in adjacent downwind buildingsdownwind buildings


- 4- 4

Stage 1 ConclusionsStage 1 Conclusions

Need to change release conditions and Need to change release conditions and / or location to get acceptable / or location to get acceptable dispersion at higher wind speeds in dispersion at higher wind speeds in summer; low wind speeds in winter.summer; low wind speeds in winter.

How would dispersion patterns compare How would dispersion patterns compare

if no refurbishment was done ?if no refurbishment was done ?

How can dispersion patterns be How can dispersion patterns be

improved during refurbishment ?improved during refurbishment ?

Stage 2 Simulations : Stage 2 Simulations : ObjectiveObjective

The “Masterly Inactivity” Option:

How would the original How would the original discharge concept have coped, discharge concept have coped, given the large-scale buildings given the large-scale buildings being constructed across the being constructed across the Street ?Street ?

Stage 2 Simulations : Stage 2 Simulations : Geometry Representation Geometry Representation

ModificationsModifications

Removal of third floor and new plant roomRemoval of third floor and new plant room

Substitution of original plant room on Substitution of original plant room on

second-floor roofsecond-floor roof

Removal of vertical discharge stacksRemoval of vertical discharge stacks

Discharge from basement extract Discharge from basement extract

arranged through louvred sides of plant arranged through louvred sides of plant

room.room.

Masterly inactivity: Masterly inactivity: “as was” facility geometry“as was” facility geometry

““AS WAS” GEOMETRY; LOW WIND IN AS WAS” GEOMETRY; LOW WIND IN WINTERWINTER

Wind vector Wind vector 0.50.5 m/s m/s from from NNENNE Ambient temperature Ambient temperature 5 500CC Release temperature Release temperature 212100CC Horizontal release through plant room Horizontal release through plant room

louvred sideslouvred sides Release velocity Release velocity ~0.4 m/s~0.4 m/s Chiller air curtain Chiller air curtain OFFOFF


Stage 2 “ As Was ” Results Stage 2 “ As Was ” Results ::


Stage 2 “ As Was ” Results Stage 2 “ As Was ” Results : :


““AS WAS” GEOMETRY; HIGH WIND IN AS WAS” GEOMETRY; HIGH WIND IN SUMMERSUMMER

Wind vector Wind vector 8.08.0 m/s m/s from from SWSW Ambient temperature Ambient temperature 181800CC Release temperature Release temperature 242400CC Horizontal release through plant room Horizontal release through plant room

louvred sides louvred sides Release velocity Release velocity ~ 0.4 m/s~ 0.4 m/s Chiller air curtain Chiller air curtain OFFOFF


Stage 2 “ As Was ” Results Stage 2 “ As Was ” Results : :

Summer wind vector 8 m/s Summer wind vector 8 m/s from SWfrom SW

Stage 2 Conclusions Stage 2 Conclusions - 1- 1

These stage 2 predictions confirm These stage 2 predictions confirm that the dispersion plume that the dispersion plume consequences consequences

would have been unacceptable if would have been unacceptable if the discharge arrangements at the the discharge arrangements at the research building had remained research building had remained unaltered once the major building unaltered once the major building works are completed opposite . . .works are completed opposite . . .

End of Stage 2 Status End of Stage 2 Status [ 1 ] [ 1 ]

The modified discharge arrangements, The modified discharge arrangements, proposed for the refurbishment of the proposed for the refurbishment of the building, result in considerable building, result in considerable improvements in dilution dispersion. improvements in dilution dispersion.

Under still Winter conditions, street-Under still Winter conditions, street-level concentrations would be reduced level concentrations would be reduced by two orders of magnitude.by two orders of magnitude.

End of Stage 2 Status End of Stage 2 Status [ 2 ] [ 2 ]

Despite the improvements, Despite the improvements, concentration levels at ground concentration levels at ground elevation would still not be acceptable elevation would still not be acceptable under worst case wind conditions under worst case wind conditions

Dilution of effluent at point of release Dilution of effluent at point of release would ameliorate this situation would ameliorate this situation

A venturi stack arrangement might A venturi stack arrangement might provide a low cost solution . . . . provide a low cost solution . . . .

Stage 3 Simulations : Stage 3 Simulations : BackgroundBackground

A venturi-type stack discharge concept has no moving parts

It uses the momentum of the discharge jet to induce dilution mixing with the surrounding (free) ambient air flow

Stage 3 Simulations : Stage 3 Simulations : ObjectiveObjective

What dilution level might be

achieved using a venturi-type stack discharge concept in the present instance?

Stage 3 Simulations : Stage 3 Simulations : Venturi Stack design parametersVenturi Stack design parameters

Discharge pipe diameterDischarge pipe diameter

Discharge nozzle diameterDischarge nozzle diameter

Venturi sheath bottom diameterVenturi sheath bottom diameter

Venturi sheath top diameterVenturi sheath top diameter

Venturi sheath lengthVenturi sheath length

Internal baffles ?Internal baffles ?

Stage 3 Simulations:Stage 3 Simulations:Venturi Stack Design ParametersVenturi Stack Design Parameters

Stage 3 Simulations : Stage 3 Simulations : Venturi Stack design constraintsVenturi Stack design constraints

Total height not to exceed 3 m.Total height not to exceed 3 m.

Discharge velocity not to exceed 15 m/sDischarge velocity not to exceed 15 m/s

Venturi sheath diameter maximum 1.2 Venturi sheath diameter maximum 1.2

m.m.

Fixed (high) effluent flowrateFixed (high) effluent flowrate

Single Venturi sheath for each pipeSingle Venturi sheath for each pipe

( max. two on roof ) ( max. two on roof )

Stage 3 Simulations:Stage 3 Simulations:Outline of SimulationsOutline of Simulations

2-D stand-alone venturi stack model2-D stand-alone venturi stack model

• 2-D (small sector) model from symmetry 2-D (small sector) model from symmetry considerationsconsiderations

• BFC grid configurationBFC grid configuration• Influence of various design parameters Influence of various design parameters

investigated, subject to stated constraints investigated, subject to stated constraints • 36 different arrangements compared 36 different arrangements compared

Stage 3 Simulations:Stage 3 Simulations:Stack parameters & entrainment Stack parameters & entrainment

rates rates

RUN DPIPIN DNOZZ DTUBE DTOP LPIPE MASSIN MASSOUT COUT OUT/IN ENT/IN VELOUTm. m. m. m. m. kg/s kg/s % - - m/s

1 0.25 0.2 0.75 0.75 3.00 0.00446 0.01777 25.08 3.99 2.99 -

3 0.8 0.49 1.00 1.00 2.50 0.02674 0.04522 59.13 1.69 0.69 -5 0.8 0.49 1.00 1.00 3.00 0.02674 0.04761 56.16 1.78 0.78 -6 0.8 0.49 1.00 1.00 3.50 0.02674 0.04952 54.00 1.85 0.85 -6B 0.8 0.49 1.00 1.00 3.50 0.02674 0.04974 53.76 1.86 0.86 -7 0.8 0.49 1.00 1.00 2.00 0.02674 0.04217 63.41 1.58 0.58 -8 0.8 0.49 1.20 1.20 3.00 0.02674 0.04255 62.84 1.59 0.59 -9 0.8 0.49 0.90 0.90 3.00 0.02674 0.04118 64.93 1.54 0.54 -10 0.8 0.49 1.00 1.00 7.50 0.02674 0.05861 45.62 2.19 1.19 -11 0.8 0.49 1.00 1.00 15.00 0.02674 0.05943 44.99 2.22 1.22 -12 0.6 0.35 0.80 0.80 2.50 0.01364 0.02689 50.73 1.97 0.97 -13 0.6 0.35 0.70 0.70 2.50 0.01364 0.02604 52.38 1.91 0.91 -14 0.6 0.35 0.90 0.90 2.50 0.01364 0.02822 48.33 2.07 1.07 -15 0.6 0.35 1.00 1.00 2.50 0.01364 0.02923 46.66 2.14 1.14 -16 0.6 0.35 1.20 1.20 2.50 0.01364 0.03005 45.40 2.20 1.20 -16A 0.6 0.35 1.20 1.20 2.50 0.01364 0.02927 46.60 2.15 1.15 -16B 0.6 0.35 1.20 1.20 2.50 0.01364 0.02917 46.76 2.14 1.14 -17 0.4 0.25 1.00 1.00 2.50 0.00696 0.01989 34.99 2.86 1.86 -18 0.4 0.25 1.20 1.20 2.50 0.00696 0.02040 34.12 2.93 1.93 -19 0.4 0.25 1.20 1.20 3.00 0.00696 0.02365 29.43 3.40 2.40 -19A 0.4 0.25 1.20 1.20 3.00 0.00696 0.02333 29.83 3.35 2.35 -20 0.4 0.25 0.70 0.70 3.00 0.00696 0.01827 38.09 2.63 1.63 -

Stage 3 Simulations:Stage 3 Simulations:Stack parameters & entrainment Stack parameters & entrainment

ratesrates

RUN DPIPIN DNOZZ DTUBE DTOP LPIPE MASSIN MASSOUT COUT OUT/IN ENT/IN VELOUTm. m. m. m. m. kg/s kg/s % - - m/s

21 0.6 0.4 1.20 1.20 3.00 0.02684 0.05920 45.35 2.21 1.21 11.6122 0.6 0.5 1.20 1.20 3.00 0.02684 0.04973 53.98 1.85 0.85 8.4623 0.5 0.3 1.20 1.20 3.00 0.02684 0.07525 35.67 2.80 1.80 16.5024 0.6 0.45 1.20 1.20 3.00 0.02684 0.05377 49.92 2.00 1.00 9.8825 0.6 0.35 1.20 1.20 3.00 0.02684 0.06569 40.87 2.45 1.45 13.97

26 0.6 0.35 1.00 1.20 3.00 0.02684 0.06063 44.28 2.26 1.26 14.8927 0.6 0.35 1.20 1.40 3.00 0.02684 0.06115 43.90 2.28 1.28 14.5828 0.6 0.35 1.20 1.60 3.00 0.02684 0.05555 48.32 2.07 1.07 15.7129 0.6 0.35 1.20 1.00 3.00 0.02684 0.06618 40.56 2.47 1.47 14.03

30 0.6 0.35 1.20 1.20 3.00 0.02684 0.06635 40.46 2.47 1.47 13.0931 0.6 0.35 1.20 1.20 3.00 0.02684 0.06579 40.80 2.45 1.45 11.4332 0.6 0.35 1.20 1.20 3.00 0.02684 0.06704 40.04 2.50 1.50 11.6533 0.6 0.35 1.20 1.20 3.00 0.02684 0.07049 38.08 2.63 1.63 8.5134 0.6 0.35 1.20 1.20 3.00 0.02684 0.05177 51.85 1.93 0.93 6.3535 0.6 0.35 1.20 1.20 3.00 0.02684 0.06651 40.36 2.48 1.48 11.7636 0.6 0.35 1.20 1.20 3.00 0.02684 0.06134 43.76 2.29 1.29 11.80

TYPICAL STRAIGHT SHEATH DESIGNTYPICAL STRAIGHT SHEATH DESIGN Supply pipe diameter Supply pipe diameter 0.8 0 m.0.8 0 m. Supply nozzle diameter Supply nozzle diameter 0.49 m.0.49 m. Sheath entry diameter Sheath entry diameter 1.20 m.1.20 m. Sheath exit diameter Sheath exit diameter 1.20 m.1.20 m. Venturi Sheath length Venturi Sheath length 3.00 m.3.00 m. Sheath internal baffles ? Sheath internal baffles ? NONO

Stage 3 Predictions:Stage 3 Predictions:Results for Stack Results for Stack

Design # 8Design # 8

Stage 3 Simulations:Stage 3 Simulations:Venturi Stack Design #8Venturi Stack Design #8

TYPICAL DIFFUSER SHEATH DESIGNTYPICAL DIFFUSER SHEATH DESIGN Supply pipe diameter Supply pipe diameter 0.60 m.0.60 m. Supply nozzle diameter Supply nozzle diameter 0.36 m.0.36 m. Sheath entry diameter Sheath entry diameter 1.20 m.1.20 m. Sheath exit diameter Sheath exit diameter 1.60 m.1.60 m. Venturi Sheath length Venturi Sheath length 3.00 m.3.00 m. Sheath internal baffles ? Sheath internal baffles ? NONO



TWIN-BAFFLE STRAIGHT SHEATH TWIN-BAFFLE STRAIGHT SHEATH DESIGNDESIGN

Supply pipe diameter Supply pipe diameter 0.60 m.0.60 m. Supply nozzle diameter Supply nozzle diameter 0.35 m.0.35 m. Sheath entry diameter Sheath entry diameter 1.20 m.1.20 m. Sheath exit diameter Sheath exit diameter 1.20 m.1.20 m. Venturi Sheath length Venturi Sheath length 3.00 m.3.00 m. Sheath internal baffles ? Sheath internal baffles ? YESYES




The results obtained from using a The results obtained from using a venturi stack device represent a venturi stack device represent a balance between the discharge balance between the discharge velocity, the entrainment rate and the velocity, the entrainment rate and the degree of mixing possible in the sheath degree of mixing possible in the sheath

The constraints on the installation The constraints on the installation mean that effluent concentration levels mean that effluent concentration levels at the point of discharge can only be at the point of discharge can only be reduced to around 40% .reduced to around 40% .


Predictions indicate that an Predictions indicate that an

entrainment rate of 1.5 ( i.e. stack entrainment rate of 1.5 ( i.e. stack outflow rate of 2.5 times discharge outflow rate of 2.5 times discharge rate, making mean outlet rate, making mean outlet concentration 40% ) combined with a concentration 40% ) combined with a mean outlet velocity of around 12 m/s mean outlet velocity of around 12 m/s is a realistically attainable design is a realistically attainable design target. target.

Stage 4 SimulationsStage 4 SimulationsObjectiveObjective

To determine the extent of To determine the extent of improvement in ground-level improvement in ground-level footprint which would be obtained footprint which would be obtained by fitting a typical venturi extract by fitting a typical venturi extract device to the discharge stack from device to the discharge stack from the BSUthe BSU

CASE 25CASE 25 Wind vector Wind vector 0.5 m/s0.5 m/s from from NNENNE Ambient temperature Ambient temperature 5 500CC Release temperature Release temperature 212100CC Chiller air curtain Chiller air curtain ONON

Effect of Venturi Extract Effect of Venturi Extract Stack :Stack :

Consequence Consequence Comparisons - 1Comparisons - 1

Stage 4 “As Planned” + Venturi Stage 4 “As Planned” + Venturi Discharge Stack :Discharge Stack :

Winter wind vector 0.5 m/s from Winter wind vector 0.5 m/s from NNENNE

CASE 24CASE 24 Wind vector Wind vector 8.0 m/s8.0 m/s from from SWSW Ambient temperature Ambient temperature 181800CC Release temperature Release temperature 242400CC Chiller air curtain Chiller air curtain OFFOFF

Effect of Venturi Extract Effect of Venturi Extract Stack :Stack :

Consequence Consequence Comparisons - 2Comparisons - 2

Stage 4 “As Planned” + Venturi Stage 4 “As Planned” + Venturi Discharge Stack :Discharge Stack :

Summer wind vector 8.0 m/s Summer wind vector 8.0 m/s from SWfrom SW


Influence of Venturi StackInfluence of Venturi Stack

Using a venturi stack device with the Using a venturi stack device with the “as planned” geometry, the plume “as planned” geometry, the plume core clears adjacent buildings and has core clears adjacent buildings and has a safe ground level footprint, for worst a safe ground level footprint, for worst case winter wind vector. case winter wind vector.

For the summer high wind vector For the summer high wind vector condition, the plume core just brushes condition, the plume core just brushes downstream rooftops but has safe downstream rooftops but has safe ground level footprint ground level footprint


Influence of Chiller Air Influence of Chiller Air CurtainCurtain

Horizontal discharge provided by Horizontal discharge provided by

chiller air outlet will have a small a chiller air outlet will have a small a

positive influence on keeping plume positive influence on keeping plume

clear.clear. Bonus effects : Bonus effects :

—entrainment dilution of release into entrainment dilution of release into upward-moving air curtain upward-moving air curtain

—buoyant uplift, due to mixing of release buoyant uplift, due to mixing of release with warm chiller exhaust flowwith warm chiller exhaust flow



Industrial ContextIndustrial Context Objectives of StudyObjectives of Study Benefits of using CFDBenefits of using CFD Description of CFD ModelDescription of CFD Model Outline of simulations performed Outline of simulations performed Sample results ObtainedSample results Obtained Conclusions of StudyConclusions of Study

Study Conclusions - 1Study Conclusions - 1

Construction of large new structures Construction of large new structures adjacent to research facility will adversely adjacent to research facility will adversely affect airborne plume dispersion patterns.affect airborne plume dispersion patterns.

The worst case ambient conditions were The worst case ambient conditions were found to be:found to be:—Still wind conditions (0.5 m/s NNE) in winterStill wind conditions (0.5 m/s NNE) in winter—High wind conditions (8.0 m/s SW) in summerHigh wind conditions (8.0 m/s SW) in summer


If a venturi-type dilution If a venturi-type dilution discharge stack were to be fitted, discharge stack were to be fitted, the plume core would clear the plume core would clear regions with opening windows, regions with opening windows, and give acceptable ground level and give acceptable ground level concentration footprintsconcentration footprints


The environmental impact of the The environmental impact of the laboratory stack releases is a laboratory stack releases is a substantial improvement over the substantial improvement over the existing arrangements, and existing arrangements, and effluent levels meet exposure effluent levels meet exposure criteria which have been accepted criteria which have been accepted at similar research establishments.at similar research establishments.

Points of ContactPoints of Contactfor further informationfor further information

Flowsolve LtdFlowsolve Ltd

Dr. Paddy PhelpsDr. Paddy Phelps

130 Arthur Rd.130 Arthur Rd.

Wimbledon ParkWimbledon Park

SW19 8AASW19 8AA

0208 944 09400208 944 0940

[email protected]@flowsolve.com

Scott WilsonScott Wilson

Mr. John GibsonMr. John Gibson

127 Friars House127 Friars House

157-168 Blackfriars 157-168 Blackfriars RdRd

SE1 8EZSE1 8EZ

0207 401 39330207 401 [email protected]@scottwilson.com

10th PHOENICS User Conference Melbourne, Australia A CFD presentation by Dr. Paddy Phelps (...

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