Ventilation for control of the work environment

VENTILATION FOR CONTROL OF THE WORK ENVIRONMENT......Page 4
CONTENTS......Page 8
List of Units......Page 16
Preface......Page 18
1 Ventilation for Control......Page 20
1.1 Control Options......Page 21
1.2 Ventilation for Control of Air Contaminants......Page 22
1.3 Ventilation Applications......Page 24
1.4 Case Studies......Page 26
1.5 Summary......Page 28
References......Page 30
2 Principles of Airflow......Page 31
2.2 Density......Page 32
2.3 Continuity Relation......Page 33
2.4.1 Pressure Units......Page 35
2.4.2 Types of Pressure......Page 36
2.5 Head......Page 37
2.6 Elevation......Page 39
2.7 Pressure Relationships......Page 41
2.7.1 Reynolds Number......Page 43
2.8.1 Frictional Losses......Page 45
2.8.2 Shock Losses......Page 47
2.9.1 Expansions......Page 49
2.9.2 Contractions......Page 51
2.9.3 Elbows......Page 54
2.9.4 Branch Entries (Junctions)......Page 55
List of Symbols......Page 57
Problems......Page 58
3 Airflow Measurement Techniques......Page 62
3.1 Measurement of Velocity by Pitot–Static Tube......Page 64
3.1.1 Pressure Measurements......Page 66
3.1.2 Velocity Profile in a Duct......Page 69
3.1.3 Pitot–Static Traverse......Page 76
3.1.4 Application of the Pitot–Static Tube and Potential Errors......Page 79
3.2.1 Rotating Vane Anemometers......Page 80
3.2.2 Deflecting Vane Anemometers (Velometer)......Page 87
3.2.3 Bridled Vane Anemometers......Page 90
3.3 Heated-Element Anemometers......Page 91
3.4.1 Vortex Shedding Anemometers......Page 94
3.4.3 Venturi Meters......Page 95
3.5 Hood Static Pressure Method......Page 96
3.6 Calibration of Instruments......Page 98
3.7 Observation of Airflow Patterns with Visible Tracers......Page 99
3.7.1 Tracer Design......Page 100
3.7.2 Application of Visible Tracers......Page 103
List of Symbols......Page 104
References......Page 105
Problems......Page 106
4 General Exhaust Ventilation......Page 109
4.1 Limitations of Application......Page 110
4.2 Equations for General Exhaust Ventilation......Page 112
4.3 Variations in Generation Rate......Page 118
4.4 Mixing......Page 119
4.5 Inlet/Outlet Locations......Page 120
4.6 Other Factors......Page 121
4.7 Comparison of General and Local Exhaust......Page 124
References......Page 125
Problems......Page 126
5 Hood Design......Page 127
5.1.1 Enclosures......Page 128
5.1.2 Exterior Hoods......Page 129
5.1.3 Receiving Hoods......Page 134
5.2 Design of Enclosing Hoods......Page 135
5.3.1 Determination of Capture Velocity......Page 139
5.3.2 Determination of Hood Airflow......Page 144
5.4.1 Canopy Hoods for Heated Processes......Page 154
5.4.2 Hoods for Grinding Operations......Page 157
5.5 Evaluation of Hood Performance......Page 160
References......Page 161
Appendix: Exterior Hood Centerline Velocity Models......Page 163
Problems......Page 167
6 Hood Designs for Specific Applications......Page 170
6.1.1 Hood Design......Page 171
6.1.2 Airflow......Page 174
6.2.1 Hood Design......Page 178
6.2.2 Airflow......Page 182
6.3 Processing and Transfer of Granular Material......Page 184
6.4 Welding, Soldering, and Brazing......Page 188
6.5 Chemical Processing......Page 196
6.5.1 Chemical Processing Operations......Page 197
6.6 Semiconductor Gas Cabinets......Page 206
6.6.1 Entry Loss......Page 209
6.6.2 Optimum Exhaust Rate......Page 210
6.7 Low-Volume/High-Velocity Systems for Portable Tools......Page 211
Example 6.1 Calculation of Exhaust Rate for Open-Surface Tanks......Page 218
Example 6.2 Design of a Low-Volume/High-Velocity Exhaust System......Page 219
List of Symbols......Page 220
References......Page 221
7 Chemical Laboratory Ventilation......Page 223
7.1.1 Vertical Sliding Sash Hoods......Page 224
7.1.2 Horizontal Sliding Sash Hoods......Page 228
7.1.3 Auxiliary Air Supply Hoods......Page 231
7.2 Face Velocity for Laboratory Hoods......Page 233
7.3 Special Laboratory Hoods......Page 235
7.4.1 System Configuration......Page 236
7.4.2 Construction......Page 237
7.5.1 Layout of Laboratory......Page 239
7.5.2 Work Practices......Page 241
7.6.1 Reduce Operating Time......Page 243
7.6.2 Limit Airflow......Page 244
7.6.5 Ductless Laboratory Hoods......Page 246
7.7 Performance of Laboratory Hoods......Page 247
References......Page 248
Problems......Page 249
8 Design of Single-Hood Systems......Page 251
8.1 Design Approach......Page 252
8.2 Design of a Simple One-Hood System (Banbury Mixer Hood)......Page 253
8.3.1 Loss Elements in a Complex Hood......Page 260
8.3.2 Degreaser Hood Design Using Velocity Pressure Calculation Sheet (Example 8.2)......Page 264
List of Symbols......Page 266
Example 8.1 Banbury Mixer System Designed by the Velocity Pressure Method......Page 267
Example 8.2 Degreaser System Designed by the Velocity Pressure Method......Page 269
References......Page 270
Problems......Page 271
9.1 Applications of Multiple-Hood Systems......Page 273
9.2 Balanced Design Approach......Page 275
9.3.1 Foundry Cleaning Room System (Example 9.1)......Page 279
9.3.2 Electroplating Shop (Example 9.2)......Page 281
9.5 Other Computational Methods......Page 284
List of Symbols......Page 285
Example 9.1 Foundry Cleaning Room Designed by Static Pressure Balance Method......Page 286
Example 9.2 Electroplating Shop System Designed by Static Pressure Balance Method......Page 291
References......Page 297
Additional Reading......Page 298
Appendix: Metric Version of Example 9.1......Page 299
10 Fans and Blowers......Page 301
10.1.1 Axial Flow Fans......Page 302
10.1.2 Centrifugal Fans......Page 304
10.1.3 Air Ejectors......Page 306
10.2 Fan Curves......Page 307
10.2.1 Static Pressure Curve......Page 308
10.2.2 Power Curve......Page 310
10.2.3 Mechanical Efficiency Curve......Page 312
10.2.4 Fan Laws......Page 314
10.2.5 Relationship between Fan Curves and Fan Tables......Page 316
10.3.1 General Exhaust Ventilation Systems......Page 317
10.3.2 Local Exhaust Ventilation Systems......Page 319
10.4 Fan Selection Procedure......Page 324
List of Symbols......Page 327
Problems......Page 328
11 Air-Cleaning Devices......Page 330
11.1.1 Particle Removers......Page 331
11.1.2 Gas and Vapor Removers......Page 341
11.2.1 Introduction......Page 344
11.3 Integrating the Air Cleaner and the Ventilation System......Page 345
11.3.2 Centrifugal Collectors......Page 349
11.3.3 Filters......Page 350
11.3.5 Scrubbers......Page 353
11.3.6 Gas and Vapor Removers......Page 354
List of Symbols......Page 355
Problems......Page 356
12 Replacement-Air Systems......Page 357
12.1 Types of Replacement-Air Units......Page 359
12.2 Need for Replacement Air......Page 360
12.3 Quantity of Replacement Air......Page 361
12.4 Delivery of Replacement Air......Page 363
12.4.2 Replacement-Air System 2 (RAS-2), Floor Casting......Page 368
12.4.3 Replacement-Air System 3 (RAS-3), Sand Handling......Page 369
12.4.4 Replacement-Air System 4 (RAS-4), Shakeout......Page 370
12.5 Replacement Air for Heating......Page 371
12.6 Energy Conservation and Replacement Air......Page 372
References......Page 375
13 Quantification of Hood Performance......Page 377
13.1 Hood Airflow Measurements......Page 378
13.2 Hood Capture Efficiency......Page 379
13.2.1 Influence of Cross-Drafts on Hood Performance......Page 380
13.2.2 Relationship between Airflow Patterns and Capture Efficiency......Page 382
13.2.3 Shortcomings of the Centerline Velocity Approach......Page 389
List of Symbols......Page 391
References......Page 392
14.1 Introduction......Page 393
14.2 Methods......Page 395
14.2.1 Grid-Based Methods......Page 396
14.2.2 Grid-Free Methods......Page 397
14.3.1 Historical Perspectives......Page 398
14.3.2 Current Progress......Page 399
14.4 Issues on the Use of Computational Fluid Dynamics......Page 405
References......Page 406
Appendix......Page 408
15 Reentry......Page 410
15.1 Airflow around Buildings......Page 412
15.2 Measurement of Reentry......Page 415
15.3 Calculation of Exhaust Dilution......Page 420
15.4 Scale Model Measurement......Page 423
15.5 Design to Prevent Reentry......Page 425
15.5.1 Stack Height Determination......Page 426
15.5.2 Good Engineering Practices for Stack Design......Page 427
List of Symbols......Page 431
References......Page 432
Problems......Page 434
Index......Page 436