fundamentals ofair cleaningtechnology
TRANSCRIPT
Zhonglin Xu
Fundamentals of Air
Cleaning Technologyand Its Applicationin Cleanrooms
Authored by Zhonglin Xu (in Chinese),Translated by Bin Zhou
TECHNiSCHE
IN FORMATIONSB! BLIOTHEK
UNIVERSITATSBI8LIOTHEK
HANNOVERV
—J
Springer
Contents
1 Particle and Size Distribution 1
1.1 Particle Classification 1
1.1.1 Classification with Particle Formation Methods 1
1.1.2 Classification with Particle Origin 2
1.1.3 Classification with Particle Size 2
1.1.4 Common Classification Method 2
1.2 Evaluation of Particle Scale 4
1.2.1 Particle Size 4
1.2.2 Average Particle Size 5
1.3 Statistical Distribution of Particle Size 12
1.3.1 Particle Size Distribution Curve 12
1.3.2 Normal Distribution and Lognormal Distribution 21
1.3.3 Particle Size Distribution on Log-Log Graph Paper. . . 28
1.3.4 Distribution Based on Density 29
1.4 Concentration Degree of Particle Size Distribution 32
1.5 Application of Lognormal Distribution 38
1.5.1 Determination of Concentration Degree 38
1.5.2 Calculation of Average Diameter 40
1.5.3 Relationship Between Particle Size Distributions 42
1.6 Statistic Parameter of Particle Number 43
References 45
2 Airborne Particles in Outdoor Air: Atmospheric Dust 47
2.1 Concept of Atmospheric Dust 47
2.2 Source of Atmospheric Dust 49
2.2.1 Natural Source and Artificial Source 49
2.2.2 Generation Amount of Atmospheric Dust 52
vii
viii Contents
2.3 Composition of Atmospheric Dust 57
2.3.1 Inorganic Nonmetallic Particles 57
2.3.2 Metal Particle 60
2.3.3 Organic Particle 65
2.3.4 Vital Particle 67
2.3.5 Composition of Atmospheric Dust 68
2.4 Concentration of Atmospheric Dust 68
2.4.1 Methods to Express Concentrations 68
2.4.2 Background Value of Atmospheric
Dust Concentration 69
2.4.3 Gravimetric Concentration 69
2.4.4 Particle Counting Concentration 91
2.4.5 Comparison Between Particle Counting Concentration
and Gravimetric Concentration 93
2.5 Particle Size Distribution of Atmospheric Dust 97
2.5.1 Full Particle Size Distribution 97
2.5.2 Distribution on Log-Log Probability Paper 99
2.5.3 Distribution Along Vertical Height Ill
2.6 Influencing Factors for Concentration and Distribution
of Atmospheric Dust 113
2.6.1 Influence of Wind 113
2.6.2 Influence of Humidity 116
2.6.3 Influence of Afforestation 123
2.7 Distribution of Atmospheric Microorganism 125
2.7.1 Concentration Distribution 125
2.7.2 Particle Size Distribution 128
References 130
3 Filtration Mechanism of Fine Particle 133
3.1 Filtration and Separation 133
3.2 Fundamental Filtration Process of Air Filters 137
3.3 Filtration Mechanism of Fibrous Air Filters 137
3.3.1 Interception (or Contact/Hook.) Effect 137
3.3.2 Inertial Effect 138
3.3.3 Diffusion Effect 139
3.3.4 Gravitational Effect 140
3.3.5 Electrostatic Effect 141
3.4 Procedures to Calculate Efficiency of Fibrous Air Filters....
141
3.5 Particle Capture Efficiency of Isolated Single Fiber:
Isolated Cylinder Method 142
3.5.1 Interception Efficiency 142
3.5.2 Inertial Efficiency 145
3.5.3 Diffusion Efficiency 146
3.5.4 Gravitational Efficiency 147
3.5.5 Electrostatic Efficiency 148
3.5.6 Total Efficiency of Isolated Single Fiber 148
Contents ix
3.6 Particle Capture Efficiency of Single Fiber Inside Filter:
Influence of Fiber Interference and Correction Method 150
3.6.1 Effective Radius Method 150
3.6.2 Nonuniform Coefficient Method of Structure 151
3.6.3 Experimental Coefficient Method 152
3.6.4 Semiempirical Equation Method 153
3.7 Logarithmic Penetration Expression for Calculation of Total
Efficiency of Fibrous Filter 154
3.7.1 Logarithmic Penetration Expression 154
3.7.2 Applicability of Logarithmic Penetration Expression 157
3.8 Influencing Factors for Efficiency of Fibrous Filters 160
3.8.1 Influence of Particle Size 160
3.8.2 Influence of Particle Type 165
3.8.3 Influence of Particle Shape 166
3.8.4 Influence of Fiber Size and Cross-Sectional Shape . .167
3.8.5 Influence of Filtration Velocity 167
3.8.6 Influence of Solid Fraction 173
3.8.7 Influence of Air Temperature 173
3.8.8 Influence of Air Humidity 173
3.8.9 Influence of Airflow Pressure 174
3.8.10 Influence of Dust Holding Capacity 174
3.9 Capillary Model Theory 176
3.10 Efficiency of Granule Air Filter 180
References 182
4 Characteristics of Air Filters 185
4.1 Function and Classification of Air Filtration System 185
4.2 Performance Index of Air Filtration 191
4.3 Face Velocity and Filtration Velocity 191
4.4 Efficiency 192
4.4.1 Efficiency 192
4.4.2 Penetration 193
4.4.3 Decontamination Factor 194
4.5 Pressure Drop 194
4.5.1 Pressure Drop of Filter Media 194
4.5.2 Total Pressure Drop of Air Filter 197
4.6 Dust Holding Capacity 203
4.7 Design Efficiency of Air Filter 205
4.8 Efficiency of Air Filters in Series 209
4.8.1 Efficiency of HEPA Filters in Series 209
4.8.2 Efficiency of Medium-Efficiency Air Filters
in Series 212
4.9 Service Life 212
4.9.1 Lifetime of Air Filter 212
4.9.2 Relationship Between Lifetime and Flow Rate 214
x Contents
4.10 Estimate of Arrestance 219
4.11 Filter-Paper Filter 221
4.11.1 Folded Filter-Paper Filter 221
4.11.2 Cylindrical Filter-Paper Filter 224
4.11.3 Filter Paper Used in Filter-Paper Filter 227
4.11.4 General Features of Filter Paper 235
4.11.5 Development of Filter-Paper Air Filter 238
4.12 Fibrous Layer Filter 242
4.13 Foam Air Filter 248
4.14 Electrostatic Cleaner 249
4.14.1 Application of Electrostatic Cleaner 249
4.14.2 Working Principle of Electrostatic Cleaner 249
4.14.3 Structure of Electrostatic Cleaner 252
4.14.4 Efficiency of Electrostatic Cleaner 254
4.14.5 Electrostatic Cleaner with Two-Stage Ionization.. .
257
4.15 Special Air Filters 260
4.15.1 Activated Carbon Filter 260
4.15.2 Antibacterial Filter 263
References 264
5 Structural Design of HEPA Filter 267
5.1 Flow State in the Passage of HEPA Filter 267
5.2 Total Pressure Drop of HEPA Filter 269
5.2.1 Pressure Drop of Filter Media AP, 270
5.2.2 Frictional Resistance of Air Passage AP2 271
5.2.3 Local Resistance of Both Inlet and Outlet C 273
5.2.4 Total Pressure Drop AP 273
5.3 Optimal Height of Corrugation 274
5.4 Optimal Depth 277
5.5 Corrugation Crest Angle 278
5.6 Structural Parameters for Filters Without Separator 280
5.7 Calculation of Tubular Filter 283
References 288
6 Movement of Indoor Fine Particle 289
6.1 Force Acting on Particles 289
6.2 Gravitational Sedimentation of Particles 290
6.3 Movement of Particles Under the Action of Inertia Force. . .
295
6.4 Diffusional Movement of Particles 296
6.5 Deposition of Particles on Surface 298
6.5.1 Diffusional Deposition of Particles on Vertical
Surface of Room Without Air Supply 298
6.5.2 Deposition of Particles on Undersurface of Room
Without Air Supply 300
6.5.3 Deposition of Particles on Interior Surface of Room
with Air Supply 301
Contents xi
6.6 Influence of Airflow on Particle Movement 309
6.6.1 Influence Factors of Indoor Particle Distribution 309
6.6.2 Migration of Particles 311
6.6.3 Influence of Heat Convection Airflow 314
6.6.4 Influence of Secondary Airflow by Movement
of Occupant 322
6.7 Coagulation of Particles in Airflow 324
6.8 Enclosure Line of Point Pollution in Parallel Flow 326
6.8.1 Enclosure Line of Point Pollution 327
6.8.2 Actual Particle Distribution of Pollution Source 329
6.8.3 Calculation of Enclosure Line of Pollution 330
References 337
7 Classification of Air Cleanliness 339
7.1 Development of Air Cleanliness Standards (Classification). . .339
7.2 Mathematical Expression of Air Cleanliness Levels 344
7.3 Conversion Relationship of Particle Number
for Different Sizes 347
7.4 Parallel Lines for Air Cleanliness Levels 347
7.5 Controlled Object for Corresponding Air Cleanliness 350
7.5.1 Minimum Controlled Size 351
7.5.2 Number of Controlled Particles 354
7.6 Specific Conditions for Controlled Particle Concentration....
354
7.7 Theoretical Method to Determine the Yield by Air
Cleanliness 356
7.7.1 Influence of Air Cleanliness on Yield 356
7.7.2 Theoretical Expression for Yield 359
7.8 Level of AMC in Clean Environment 372
References 375
8 Principle of Cleanroom 377
8.1 Approach to Control Contaminants 377
8.2 Flow State 378
8.2.1 Several Fundamental Fluid States 378
8.2.2 Physical State of Turbulent Flow 380
8.3 Principle of Cleanroom with Mixed Flow 382
8.3.1 Principle of Cleanroom with Mixed Flow 382
8.3.2 Air Inlet in Mixed Flow Cleanroom 384
8.3.3 Effect of Mixed Flow Cleanroom 387
8.4 Principle of Cleanroom with Unidirectional Flow 388
8.4.1 Classification of Unidirectional Flow Cleanrooms. . . .
388
8.4.2 Principle of Unidirectional Flow Cleanrooms 395
8.5 Three Characteristic Indexes for Unidirectional
Flow Cleanroom 401
8.5.1 Parallel Degree of Flow Lines 401
8.5.2 Turbulence Intensity 404
8.5.3 Lower-Limit Velocity 409
xii Contents
8.6 Principle of Radial Flow Cleanroom 418
8.6.1 Type of Radial Flow Cleanroom 418
8.6.2 Principle of Radial Flow Cleanroom 419
8.7 Pressure of Cleanroom 423
8.7.1 Physical Meaning of Differential Pressure 423
8.7.2 Function of Differential Pressure 425
8.7.3 Determination of Differential Pressure to Prevent
Leakage from Gap Between Cleanroom
and Adjacent Room 427
8.7.4 Determination of Differential Pressure to Prevent
Leakage from Gap Between Cleanroom and Outdoor
(or the Room Open to the Atmosphere) 427
8.7.5 Determination of Differential Pressure to Prevent Air
Pollution During the Open of Door in Turbulent Flow
Cleanroom 428
8.7.6 Determination of Differential Pressure to Prevent Air
Pollution During the Open of Door in Unidirectional
Flow Cleanroom 432
8.7.7 Recommended Differential Pressure 433
8.8 Buffer and Isolation 434
8.8.1 Airlock Chamber 434
8.8.2 Buffer Chamber with Positive Pressure 435
8.8.3 Buffer Chamber with Negative Pressure 438
8.8.4 Airshower Chamber 439
8.9 Feature of Cleanroom with Full-Ceiling Air Supply
and Two-Bottom-Side Air Return 446
8.9.1 Line Sink Model 447
8.9.2 Feature of Flow 454
8.9.3 Allowable Room Width 462
References 464
9 Theory of Biological Cleanroom 467
9.1 Application of Biological Cleanrooms 467
9.2 Main Characteristics of Microbe 474
9.2.1 Preparation Period or Delayed Period 474
9.2.2 Logarithmic Growth Period 479
9.2.3 Stable Period or Quiescent Period 479
9.2.4 Decay Period 479
9.3 Microbial Pollution Routes 479
9.4 Equivalent Diameter of Biological Particles 480
9.4.1 Size of Microorganism 480
9.4.2 Equivalent Diameter of Biological Particles 481
9.5 Biological Particle Standard 485
9.5.1 Microbial Concentration 485
9.5.2 Airborne Bacteria Number and Standard 487
9.5.3 Number of Sedimentation Bacteria and Related
Standard 489
Contents xiii
9.6 Relationship Between Settlement Bacteria and Airborne
Bacteria 492
9.6.1 Proof of OMenflHCKHH Equation 493
9.6.2 Correction of Settlement Formula 494
9.6.3 Application of Settlement Bacteria and Airborne
Bacteria Methods in Cleanroom 497
9.7 Bacterial Remove with Filter 498
9.7.1 Filtration Efficiency of HEPA Filter
for Microorganism 499
9.7.2 Penetration of Filter Medium for Bacteria 501
9.7.3 Reproduction of Microorganisms on Filter Material. 502
9.8 Disinfection and Sterilization 503
9.8.1 Concept 503
9.8.2 Main Disinfection Methods 503
9.8.3 Disinfection and Sterilization with Ultraviolet 504
9.9 General Biological Cleanroom 515
9.9.1 Type 515
9.9.2 Air Velocity 518
9.9.3 Local Airflow 520
9.10 Isolated Biological Cleanroom 523
9.10.1 Biological Risk Standard 523
9.10.2 Isolation Methods 523
9.10.3 Biosafety Cabinet 531
9.10.4 Classification of Biosafety Laboratory 534
9.10.5 Negatively Pressurized Isolation Ward 534
9.10.6 Safety of Exhaust Air from Isolated BiologicalCleanroom 537
References 543
10 Calculation Theory of Uniform Distribution in Cleanroom 549
10.1 Three-Stage Filtration System in Cleanroom 549
10.2 Instantaneous Particle Concentration in Turbulent Flow
Cleanroom 551
10.3 Steady-State Particle Concentration in Turbulent Flow
Cleanroom 554
10.3.1 Steady-State Expression for Single Room 554
10.3.2 Steady-State Expression for Multiroom 555
10.4 Steady-State Particle Concentration with Local Air Cleaning
Equipment 557
10.5 Physical Meaning of Instantaneous and Steady-State
Expressions 558
10.6 Other Calculation Methods for Turbulent Flow Cleanroom. .
560
10.7 Calculation of Dust Concentration in Unidirectional Flow
Cleanroom 561
xivContents
10.8 Calculation of Self-Purification Time and Pollution Time
in Turbulent Flow Cleanroom562
10.8.1 Concept562
10.8.2 Calculation of Self-Purification Time 563
10.8.3 Calculation of Pollution Time 568
10.9 Calculation of Self-Purification Time in Unidirectional
Flow Cleanroom569
References570
11 Calculation Theory of Nonuniform Distribution in Cleanroom . .
573
11.1 Influence of Nonuniform Distribution 573
11.1.1 Impact of Air Distribution (Including Air Supply
Outlet and Its Position) 573
11.1.2 Impact of the Number of Air Supply Outlet 574
11.1.3 Impact of the Air Change Rate 575
11.1.4 Impact of the Type of Air Supply Outlet 575
11.2 Three-Zone Nonuniform Distribution Model 577
11.3 Mathematical Model for Three-Zone Nonuniform
Distribution579
11.4 Physical Meaning of N-n General Formula 582
11.5 Comparison Between Uniform Distribution and Nonuniform
Distribution585
References585
12 Characteristics of Cleanroom587
12.1 Characteristic of At-Rest State 587
12.2 Dynamic Characteristic 595
12.2.1 To Increase the Particle Generation Rate After
Steady State Is Reached by Self-Cleaning Process . .595
12.2.2 Increase the Particle Generation Rate Before the
Steady State of Self-Cleaning Process 597
12.3 Characteristic Curve of Nonuniform Distribution 601
12.4 Inhomogeneity of Concentration Field 605
12.4.1 Concentration Ratio Between the Mainstream Area
and the Return Air Area: 605
12.4.2 Concentration Ratio Between the Mainstream Area
and the Vortex Area: 607
12.4.3 Concentration Ratio Between the Vortex Area
and the Mainstream Area: 608
12.4.4 Concentration Ratio Between Uniform Distribution
and Nonuniform Distribution 608
12.5 Particle Load Characteristic of Fresh Air 610
12.5.1 Effect of Three-Stage Air Filtration for Fresh Air.. .
610
12.5.2 Particle Load Ratio of Fresh Air 611
12.5.3 Relationship Between Particle Load Ratio of Fresh
Air and Lifetime of Component 615
References617
Contents xv
13 Design Calculation of Cleanroom 619
13.1 Determination of Indoor and Outdoor Parameters
for Calculation 619
13.1.1 Atmospheric Dust Concentration 619
13.1.2 Particle Generation Rate per Unit Volume
of Indoor Air 620
13.1.3 Fresh Air Ratio 627
13.2 Calculation of HEPA Cleaning System 631
13.2.1 Calculation of the Value N 632
13.2.2 Calculation of the Value n 633
13.2.3 Calculation of the Value T 634
13.2.4 Three Principles of Design Calculation 639
13.2.5 Examples 639
13.3 Calculation for Applications with Local Filtration Device. . . 644
13.3.1 Computer Room with Both Central Air-ConditioningSystem and Special Air Conditioner 645
13.3.2 Computer Room with Special Air Conditioner
and Air Handling Unit for Fresh Air 646
References 647
14 Local Clean Area 649
14.1 Application of Mainstream Area Concept 649
14.2 Characteristics of Mainstream Area 654
14.2.1 Air Distribution Characteristic 654
14.2.2 Velocity Decay Characteristic 656
14.2.3 Particle Concentration Characteristic 658
14.2.4 Contamination Degree in Mainstream Area 663
14.2.5 Concept of Expanded Mainstream Area 667
14.3 Clean Area with Partial Wall 669
14.4 Air Curtain Cleaning Booth 671
14.4.1 Application 671
14.4.2 Isolation Effect of Air Curtain 674
14.4.3 Theoretical Analysis of the Isolation Effect
by Air Curtain Cleaning Booth 676
14.4.4 Performance of Air Curtain Cleaning Booth 679
14.5 Partition Curtain Cleaning Booth 683
14.5.1 Application 683
14.5.2 Theoretical Analysis of Cleaning Effect 685
14.5.3 Experimental Effect 691
14.6 Laminar Flow Hood for Cleaning Tunnel 691
14.6.1 Requirement of Anti-disturbance 691
14.6.2 Effect of Auxiliary Air Supply at the WorkingSurface 692
References 695
xvi Contents
15 Theory of Leakage Preventing Layer 697
15.1 Overview 697
15.2 Leakage Equation 698
15.3 Equation for Leakage Prevention 704
15.4 Leakage Prevention Effect 707
15.5 Mechanism of Leakage Prevention Layer 709
15.5.1 Leakage Prevention with Dilution Effect 709
15.5.2 Leakage Prevention with Filter 710
15.5.3 Leakage Prevention with Reduced Differential
Pressure 711
15.5.4 Barrier Leakage Prevention 712
15.6 Air Supply Terminal with Leakage Prevention Layer 713
15.6.1 Overview 713
15.6.2 Structure of Air Supply Terminal with LeakagePrevention Layer 713
15.6.3 Property of Air Supply Terminal of LeakagePrevention Layer 715
15.6.4 Application of Air Supply Terminal of LeakagePrevention Layer 720
15.6.5 Comparison of Several Air Supply Terminals 723
References 727
16 Sampling Theory 729
16.1 Sampling System 729
16.1.1 Orientation of the Sampling Probe 729
16.1.2 Position of Flowmeter 730
16.2 Isokinetic Sampling 736
16.2.1 Sampling in Flowing Air 736
16.2.2 Sampling in Quiescent Air 744
16.2.3 Calculation of the Diameter of the Sampling Probe.
746
16.3 Particle Loss in Sampling Line 746
16.3.1 Diffusionai Deposition Loss in Sampling Tube. . . .
746
16.3.2 Settlement Deposition Loss in Sampling Line 754
16.3.3 Collisional Loss in Sampling Line 755
16.3.4 Coagulation Loss in Sampling Line 757
16.3.5 Comparison with Experiment 759
16.3.6 Comprehensive Conclusion 762
16.4 The Minimum Sampling Volume 764
16.4.1 Background of the Problem 764
16.4.2 Nonzero Sampling Principle 765
16.4.3 The Principle of Minimum Total Particle
Number 770
16.4.4 The Minimum Sampling Volume of Airborne
Bacteria 773
16.5 The Minimum Deposition Area 774
References 775
Contents xvii
17 Measurement and Evaluation 777
17.1 Particle Concentration Measurement 777
17.1.1 Particle Mass Concentration Method 777
17.1.2 Particle Counting Method with Membrane
Microscope 780
17.1.3 Particle Counting Method with Light ScatteringParticle Counter 783
17.1.4 Other Particle Counting Method 799
17.1.5 Relative Concentration Method 800
17.1.6 Biological Particle Measurement Method 801
17.2 Air Filter Measurement 804
17.2.1 Measurement Range 804
17.2.2 Measurement of Filter Efficiency 806
17.2.3 Measurement of Dust Holding Capacity of Filter.. .
824
17.3 Leakage Detection 827
17.3.1 Leakage Detection of HEPA Filter 827
17.3.2 Leakage Detection of Isolation Bioclean Cabinet. . .841
17.4 Cleanroom Measurement 847
17.4.1 Measurement Types of Cleanroom 847
17.4.2 Test Status of Cleanroom 851
17.4.3 Necessary Sampling Points 853
17.4.4 Continuous Sampling Method 858
17.4.5 Factors Influencing Measurement Result 860
17.5 Evaluation of Air Cleanliness in Cleanroom 861
17.5.1 Evaluation Standard of Air Cleanliness
in Cleanroom 861
17.5.2 Dynamic-to-Static Ratio 867
17.5.3 Correction to Atmospheric Dust Concentration....
869
References 870