Ventilation for control of the work environment

List of Units xiii Preface xv 1 Ventilation for Control 1 1.1 Control Options / 2 1.2 Ventilation for Control of Air Contaminants / 3 1.3 Ventilation Applications / 5 1.4 Case Studies / 7 1.5 Summary / 9 References / 11 2 Principles of Airflow 12 2.1 Airflow / 13 2.2 Density / 13 2.3 Continuity Relation / 14 2.4 Pressure / 16 2.4.1 Pressure Units / 16 2.4.2 Types of Pressure / 17 2.5 Head / 18 2.6 Elevation / 20 2.7 Pressure Relationships / 22 2.7.1 Reynolds Number / 24 2.8 Losses / 26 2.8.1 Frictional Losses / 26 2.8.2 Shock Losses / 28 2.9 Losses in Fittings / 30 2.9.1 Expansions / 30 2.9.2 Contractions / 32 2.9.3 Elbows / 35 2.9.4 Branch Entries (Junctions) / 36 2.10 Summary / 38 List of Symbols / 38 Problems / 39 3 Airflow Measurement Techniques 43 3.1 Measurement of Velocity by Pitot–Static Tube / 45 3.1.1 Pressure Measurements / 47 3.1.2 Velocity Profile in a Duct / 50 3.1.3 Pitot–Static Traverse / 57 3.1.4 Application of the Pitot–Static Tube and Potential Errors / 60 3.2 Mechanical Devices / 61 3.2.1 Rotating Vane Anemometers / 61 3.2.2 Deflecting Vane Anemometers (Velometer) / 68 3.2.3 Bridled Vane Anemometers / 71 3.3 Heated-Element Anemometers / 72 3.4 Other Devices / 75 3.4.1 Vortex Shedding Anemometers / 75 3.4.2 Orifice Meters / 76 3.4.3 Venturi Meters / 76 3.5 Hood Static Pressure Method / 77 3.6 Calibration of Instruments / 79 3.7 Observation of Airflow Patterns with Visible Tracers / 80 3.7.1 Tracer Design / 81 3.7.2 Application of Visible Tracers / 84 List of Symbols / 85 References / 86 Manufacturers of Airflow Measuring Instruments / 87 Manufacturers of Smoke Tubes / 87 Problems / 87 4 General Exhaust Ventilation 90 4.1 Limitations of Application / 91 4.2 Equations for General Exhaust Ventilation / 93 4.3 Variations in Generation Rate / 99 4.4 Mixing / 100 4.5 Inlet/Outlet Locations / 101 4.6 Other Factors / 102 4.7 Comparison of General and Local Exhaust / 105 List of Symbols / 106 References / 106 Problems / 107 vi CONTENTS 5 Hood Design 108 5.1 Classification of Hood Types / 109 5.1.1 Enclosures / 109 5.1.2 Exterior Hoods / 110 5.1.3 Receiving Hoods / 115 5.1.4 Summary / 116 5.2 Design of Enclosing Hoods / 116 5.3 Design of Exterior Hoods / 120 5.3.1 Determination of Capture Velocity / 120 5.3.2 Determination of Hood Airflow / 125 5.3.3 Exterior Hood Shape and Location / 135 5.4 Design of Receiving Hoods / 135 5.4.1 Canopy Hoods for Heated Processes / 135 5.4.2 Hoods for Grinding Operations / 138 5.5 Evaluation of Hood Performance / 141 List of Symbols / 142 References / 142 Appendix: Exterior Hood Centerline Velocity Models / 144 Problems / 148 6 Hood Designs for Specific Applications 151 6.1 Electroplating / 152 6.1.1 Hood Design / 152 6.1.2 Airflow / 155 6.2 Spray Painting / 159 6.2.1 Hood Design / 159 6.2.2 Airflow / 163 6.3 Processing and Transfer of Granular Material / 165 6.4 Welding, Soldering, and Brazing / 169 6.5 Chemical Processing / 177 6.5.1 Chemical Processing Operations / 178 6.6 Semiconductor Gas Cabinets / 187 6.6.1 Entry Loss / 190 6.6.2 Optimum Exhaust Rate / 191 6.7 Low-Volume/High-Velocity Systems for Portable Tools / 192 Example 6.1 Calculation of Exhaust Rate for Open-Surface Tanks / 199 Example 6.2 Design of a Low-Volume/High-Velocity Exhaust System / 200 List of Symbols / 201 References / 202 CONTENTS vii 7 Chemical Laboratory Ventilation 204 7.1 Design of Chemical Laboratory Hoods / 205 7.1.1 Vertical Sliding Sash Hoods / 205 7.1.2 Horizontal Sliding Sash Hoods / 209 7.1.3 Auxiliary Air Supply Hoods / 212 7.2 Face Velocity for Laboratory Hoods / 214 7.3 Special Laboratory Hoods / 216 7.4 Laboratory Exhaust System Features / 217 7.4.1 System Configuration / 217 7.4.2 Construction / 218 7.5 Factors Influencing Hood Performance / 220 7.5.1 Layout of Laboratory / 220 7.5.2 Work Practices / 222 7.6 Energy Conservation / 224 7.6.1 Reduce Operating Time / 224 7.6.2 Limit Airflow / 225 7.6.3 Design for Diversity / 227 7.6.4 Heat Recovery / 227 7.6.5 Ductless Laboratory Hoods / 227 7.7 Performance of Laboratory Hoods / 228 7.8 General Laboratory Ventilation / 229 References / 229 Problems / 230 8 Design of Single-Hood Systems 232 8.1 Design Approach / 233 8.2 Design of a Simple One-Hood System (Banbury Mixer Hood) / 234 8.3 Design of a Slot Hood System for a Degreasing Tank / 241 8.3.1 Loss Elements in a Complex Hood / 241 8.3.2 Degreaser Hood Design Using Velocity Pressure Calculation Sheet (Example 8.2) / 245 8.4 Pressure Plot for Single-Hood System / 247 List of Symbols / 247 Example 8.1 Banbury Mixer System Designed by the Velocity Pressure Method / 248 Example 8.2 Degreaser System Designed by the Velocity Pressure Method / 250 References / 251 Appendix: Metric Version of Example 8.1 / 252 Problems / 252 viii CONTENTS 9 Design of Multiple-Hood Systems 254 9.1 Applications of Multiple-Hood Systems / 254 9.2 Balanced Design Approach / 256 9.3 Static Pressure Balance Method / 260 9.3.1 Foundry Cleaning Room System (Example 9.1) / 260 9.3.2 Electroplating Shop (Example 9.2) / 262 9.4 Blast Gate Balance Method / 265 9.5 Other Computational Methods / 265 List of Symbols / 266 Example 9.1 Foundry Cleaning Room Designed by Static Pressure Balance Method / 267 Example 9.2 Electroplating Shop System Designed by Static Pressure Balance Method / 272 References / 278 Additional Reading / 279 Appendix: Metric Version of Example 9.1 / 280 10 Fans and Blowers 282 10.1 Types of Air Movers / 283 10.1.1 Axial Flow Fans / 283 10.1.2 Centrifugal Fans / 285 10.1.3 Air Ejectors / 287 10.2 Fan Curves / 288 10.2.1 Static Pressure Curve / 289 10.2.2 Power Curve / 291 10.2.3 Mechanical Efficiency Curve / 293 10.2.4 Fan Laws / 295 10.2.5 Relationship between Fan Curves and Fan Tables / 297 10.3 Using Fans in Ventilation Systems / 298 10.3.1 General Exhaust Ventilation Systems / 298 10.3.2 Local Exhaust Ventilation Systems / 300 10.4 Fan Selection Procedure / 305 List of Symbols / 308 References / 309 Problems / 309 11 Air-Cleaning Devices 311 11.1 Categories of Air-Cleaning Devices / 312 11.1.1 Particle Removers / 312 11.1.2 Gas and Vapor Removers / 322 11.2 Matching the Air-Cleaning Device to the Contaminant / 325 11.2.1 Introduction / 325 11.2.2 Device Selection / 326 CONTENTS ix 11.3 Integrating the Air Cleaner and the Ventilation System / 326 11.3.1 Gravity Settling Devices / 330 11.3.2 Centrifugal Collectors / 330 11.3.3 Filters / 331 11.3.4 Electrostatic Precipitators / 334 11.3.5 Scrubbers / 334 11.3.6 Gas and Vapor Removers / 335 List of Symbols / 336 References / 337 Problems / 337 12 Replacement-Air Systems 338 12.1 Types of Replacement-Air Units / 340 12.2 Need for Replacement Air / 341 12.3 Quantity of Replacement Air / 342 12.4 Delivery of Replacement Air / 344 12.4.1 Replacement-Air System 1 (RAS-1), Melting Furnaces / 349 12.4.2 Replacement-Air System 2 (RAS-2), Floor Casting / 349 12.4.3 Replacement-Air System 3 (RAS-3), Sand Handling / 350 12.4.4 Replacement-Air System 4 (RAS-4), Shakeout / 351 12.5 Replacement Air for Heating / 352 12.6 Energy Conservation and Replacement Air / 353 12.7 Summary / 356 References / 356 13 Quantification of Hood Performance 358 13.1 Hood Airflow Measurements / 359 13.2 Hood Capture Efficiency / 360 13.2.1 Influence of Cross-Drafts on Hood Performance / 361 13.2.2 Relationship between Airflow Patterns and Capture Efficiency / 363 13.2.3 Shortcomings of the Centerline Velocity Approach / 370 13.3 Use of Capture Efficiency in Hood Design / 372 List of Symbols / 372 References / 373 14 Application of Computational Fluid Dynamics to Ventilation System Design 374 14.1 Introduction / 374 14.2 Methods / 376 14.2.1 Grid-Based Methods / 377 14.2.2 Grid-Free Methods / 378 x CONTENTS 14.3 Applications / 379 14.3.1 Historical Perspectives / 379 14.3.2 Current Progress / 380 14.4 Issues on the Use of Computational Fluid Dynamics / 386 14.5 Commercial Codes: Public-Domain Information / 387 References / 387 Appendix / 389 15 Reentry 391 15.1 Airflow around Buildings / 393 15.2 Measurement of Reentry / 396 15.3 Calculation of Exhaust Dilution / 401 15.4 Scale Model Measurement / 404 15.5 Design to Prevent Reentry / 406 15.5.1 Stack Height Determination / 407 15.5.2 Good Engineering Practices for Stack Design / 408 List of Symbols / 412 References / 413 Problems / 415 Index 417