Ventilation for Control of the Work Environment 2e

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