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A Comparison of Air Supply Diffusers and A Comparison of Air Supply Diffusers and the Effects on Fume Hood Performance the Effects on Fume Hood Performance
byby
Thomas C. SmithThomas C. Smith
Exposure Control Technologies, Inc. Exposure Control Technologies, Inc.
Fume Hood Performance
Containment is affected by:Containment is affected by:
•• Fume Hood DesignFume Hood Design
•• Flow (Face Velocity)Flow (Face Velocity)
•• Work PracticesWork Practices
•• Room Air SupplyRoom Air Supply
Effects of Supply DiffusersEffects of Supply Diffusers
Hood Opening
Air Supply Diffusers
ObjectivesObjectives
Evaluate Affect of Different Diffusers on Hood PerformanceEvaluate Affect of Different Diffusers on Hood Performance
–– Range of Flow RatesRange of Flow Rates
–– Range of Supply Discharge Temperatures Range of Supply Discharge Temperatures
–– Different Lab Configurations Different Lab Configurations
Assess Ability of Diffuser to Complement or Degrade Hood Assess Ability of Diffuser to Complement or Degrade Hood
PerformancePerformance
Test MethodsTest Methods
HP Fume HoodHP Fume Hood–– Vertical Sash Full Open Vertical Sash Full Open
–– 6060--fpm Average Face Velocityfpm Average Face Velocity
3 Lab Configurations3 Lab Configurations–– 1010--ft Ceiling and 5ft Ceiling and 5--ft from Hood ft from Hood
OpeningOpening
5 Supply Diffusers5 Supply Diffusers
3 Air Supply Flows ( 250 cfm 3 Air Supply Flows ( 250 cfm –– 650 650 cfm)cfm)
2 Supply Temperature Challenges 2 Supply Temperature Challenges
3 Test Cycles 3 Test Cycles –– 5 minute duration 5 minute duration eacheach
Lab Configuration 1Lab Configuration 1
Diffuser
Hood
Lab Configuration 2Lab Configuration 2
Diffuser
Hood
Lab Configuration 3Lab Configuration 3
Diffuser
Hood
Supply Diffuser Supply Diffuser Flow MeasurementFlow Measurement
Fume Hood Test ApparatusFume Hood Test Apparatus
Velocity ProbesVelocity Probes
Cross Draft Cross Draft Velocity ProbesVelocity Probes
Flow MonitorFlow Monitor
Computer,Computer,HoodPRO HoodPRO SoftwareSoftware&&DAQDAQ
EjectorEjector
Temp ProbeTemp Probe
MannequinMannequin
DetectorDetector
Tracer GasTracer Gas
Supply Supply Temp ProbeTemp Probe
Duct Sox Diffuser Duct Sox Diffuser
Lab Configuration 2Lab Configuration 2
Radial Face Diffuser Radial Face Diffuser
Lab Configuration 2Lab Configuration 2
Flat Face Radial Flat Face Radial Diffuser Diffuser
Lab Configuration 2Lab Configuration 2
4 Way Diffuser4 Way Diffuser
Lab Configuration 3Lab Configuration 3
Lab Configuration 2 and 3Lab Configuration 2 and 3Tracer Gas Test Results Tracer Gas Test Results
AVG <0.01 0.01 <0.01 <0.01 0.01
Max 0.02 1.00 0.10 0.02 0.30
AVG <0.01 <0.01 <0.01 <0.01 <0.01
Max 0.40 0.02 0.13 0.10 0.20
AVG <0.01 <0.01 <0.01 <0.01 0.10
Max 0.40 0.10 0.02 0.20 0.90
AVG <0.01 <0.01 <0.01 <0.01 0.04
Max 0.07 0.02 0.02 0.03 0.10
Normal Challenge
Temp Challenge
Lab Configuration
3
DuctSox C Flat Face Radial
4 Way Diffuser
Lab Configuration
2
Normal Challenge
Temp Challenge
DuctSox A Radial Face
Test Configuration 2 - Normal Challenge DuctSOX A Diffuser
Face Velocity and Tracer Gas Data
0
20
40
60
80
100
120
15 Minute Test
fpm
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
ppm
Face Velocity Tracer Gas Escape
Face Velocity - Temporal Variation = 10%Containment - Control Level = <0.01 ppm
Test Configuration 3 - Normal Challenge Four Way Diffuser
Face Velocity and Tracer Gas Data
0
20
40
60
80
100
120
15 Minute Test
fpm
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
ppm
Face Velocity Tracer Gas Escape
Face Velocity - Temporal Variation = 10%Containment - Control Level = 0.10 ppm
Test Configuration 2 - Normal Challenge DuctSOX A Diffuser
Cross Draft and Tracer Gas Data
0
20
40
60
80
100
120
15 Minute Test
fpm
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
ppm
Cross Draft (P) Tracer Gas Escape
Test Configuration 3 - Normal Challenge Four Way Diffuser
Cross Draft and Tracer Gas Data
0
20
40
60
80
100
120
15 Minute Test
fpm
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
ppm
Cross Draft (P) Tracer Gas Escape
ResultsResults
Preferred Diffuser Location = Configuration 2Preferred Diffuser Location = Configuration 2
Minimize Drafts < 50% of AVG Face VelocityMinimize Drafts < 50% of AVG Face Velocity
Increase Distance and Decrease VolumeIncrease Distance and Decrease Volume
Lab Lab ConfigConfig. 2. 2 Lab Lab ConfigConfig. 3. 3
Findings and ConclusionsFindings and Conclusions
Fabric 2x4 diffusers and Radial Perforated Diffusers Provide Fabric 2x4 diffusers and Radial Perforated Diffusers Provide Equivalent PerformanceEquivalent Performance
Diffusers should be located at least 5 feet from HoodDiffusers should be located at least 5 feet from Hood
Diffusers should be located to the side of the hood rather Diffusers should be located to the side of the hood rather than in front of the hood than in front of the hood
Containment affected by high face velocity turbulence Containment affected by high face velocity turbulence associated with high cross draft velocitiesassociated with high cross draft velocities
High Velocity Directional Diffusers or Linear Slot Diffusers High Velocity Directional Diffusers or Linear Slot Diffusers are Not Appropriate for Labsare Not Appropriate for Labs
Diffuser Location and Discharge Temperature Can Affect Diffuser Location and Discharge Temperature Can Affect Hood Performance and Should Be Investigated FurtherHood Performance and Should Be Investigated Further
RecommendationsRecommendations
Additional investigation of more lab configurationsAdditional investigation of more lab configurations
Include less than ideal lab conditions with high air change Include less than ideal lab conditions with high air change rates and different dimensionsrates and different dimensions
Evaluate performance of different hoods under similar Evaluate performance of different hoods under similar challenge conditionschallenge conditions
Diffusers specifications include discharge flow patterns at Diffusers specifications include discharge flow patterns at different flow rates and discharge temperaturesdifferent flow rates and discharge temperatures
Program and run CFD models to compare with empirical dataProgram and run CFD models to compare with empirical data
Final ThoughtsFinal Thoughts
Essential to characterize the phenomena associated with escape Essential to characterize the phenomena associated with escape –– Velocity Velocity
–– Pressure Pressure
–– TemperatureTemperature
–– Aerodynamic Design Aerodynamic Design
Information Necessary to Update Standards and GuidelinesInformation Necessary to Update Standards and Guidelines–– Lab Designs Lab Designs
–– Operating SpecificationsOperating Specifications
–– Test MethodsTest Methods
EndEnd
Questions?Questions?