Session 4, Unit 7 Plume Rise

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Session 4, Unit 7 Plume Rise Powered By Docstoc
					Session 4, Unit 7

Plume Rise
Qualitative Descriptions
  Plume rise h
      H=hs + h
  Driving forces
     Buoyancy
     Momentum
  Different phases
     Initial phase
     Thermal phase
     Breakup phase
     Diffusion phase
Qualitative Descriptions
  Influencing factors
     When there is no downwash
        Exit velocity
        Stack diameter
        Stack gas temperature
        Ambient temperature
        Wind speed
        Atmospheric stability
        Wind shear
     Downwash
Holland Plume Rise Formula
  Simple
  More suitable for power plant
  For neutral conditions
        d s vs                3  Ts  Ta    
   h         1.5  2.68  10 P T         d s 
                                              
          u                           s      
     The wind speed ū is adjusted to the stack height.
  For non-neutral conditions
            St 
      CF     0.7
            10 
      hCF  (CF ) h
Briggs Plume Rise Formulas
  More complicated
  Buoyancy flux parameter
             d s2    Ts  Ta 
    Fb  gvs        
                     T      
              4          a   

  Momentum flux parameter
           v s2 d s2    Ta   
      Fm              
                       T     
                              
               4        s    
Briggs Plume Rise Formulas
  Determination of buoyancy dominated or
  momentum dominated plumes
     Calculate (T)c
        For unstable or neutral (A-D)
                                                      1
               For Fb <55                0.0297TsVs       3
                            T c 
           

                                               2
                                             ds 3
              For Fb55                            2
                                         0.00575TsVs 3
                            T c            1
        For stable (E,F)                    ds 3
                                                              1
                            (T ) c  0.01958TsVs s               2

     If T (=Ts-Ta)  (T)c , it’s buoyancy dominated
     If T (=Ts-Ta) < (T)c , it’s momentum dominated
Briggs Plume Rise Formulas
  For buoyancy dominated plume under
  unstable or neutral conditions (A-D)
     x* = distance at which atmospheric
      turbulence begins to dominate entrainment
        For Fb55 m4/sec3, x*=34 Fb2/5
        For Fb<55 m4/sec3, x*=14 Fb5/8
     xf=distance to the final rise, m
        xf=3.5x*
     Final plume rise:         1
                                            *
                                                2
                                    3               3
                           1.6 Fb (3.5 x )
                    h 
                                        u
Briggs Plume Rise Formulas
  For buoyancy dominated plume under stable
  conditions (E and F)
     Stability parameter, s
               g   
          s          
               Ta  T 
        Default values for   
                                
                             z 

              0.02 K/m for E stability
              0.035 K/m for F stability
Briggs Plume Rise Formulas
     Final plume rise
                                     1
                   Fb                  3
         h  2.6  
                   us 
     Distance to final rise
                         u
          x f  2.0715       1
                                 2
                         s
Briggs Plume Rise Formulas
  For momentum dominated plume under
  unstable or neutral conditions (A-D)
                 3d s v s
          h 
                    u
  For momentum dominated plume under
  stable conditions (E,F)
                            1
                 Fm  3
        h  1.5
                    
                     
                 u s
     Calculate both and use the lower one.
Briggs Plume Rise Formulas
  Gradual rise
  Distance < distance to final rise (i.e.,
  x<xf) and Buoyancy dominated plume
                 1        2
                     3        3
            1.6 Fb ( x)
     h 
                 u
Briggs Plume Rise Formulas
  Distance < distance to final rise (i.e.,
  x<xf) and momentum dominated plume
     Jet entrainment coefficient
             1   u
        j  
             3   vs

     Unstable conditions (A-D)
                        1
              3F x        3

        h   m 2 
              2 
             ju 
Briggs Plume Rise Formulas
        X=downwind distance with max value of:

                  4d s (v s  3u ) 2
         xmax                         For Fb  0
                        vs u
         Xmax=49Fb5/8 for 0<Fb<55 m4/sec3
         xmax=119Fb2/5 for Fb> 55 m4/sec3
     Stable conditions (E,F)
                                          1
                        sin( x s / u 
                                              3

            h  3Fm                 
                 
                          ju s 
                             2
                                      
        with
                             u
                x m ax  0.5
                               s
Briggs Plume Rise Summary
           Unstable and                           Stable
           neutral

Buoyancy                  1               2                          1
                                                             Fb 
                              3       *       3                          3
                  1.6 Fb (3.5 x )
           h                                     h  2.6  
                                  u                          us 

Momentum           3d s v s                                 Fm 
                                                                         1
                                                                             3
           h                                     h  1.5    
                      u                                        
                                                            u s
Buoyancy Induced Dispersion
  Air entrainment due to “boiling-like action”
  enlarges the plume
  Small impact on ground level concentration in
  most cases
  The impact can be reflected in 
     Initial plume size
                         h
          y0   z0 
                         3.5
     Effective dispersion coefficients
          ye  ( y   y 0 ) 0.5
                   2     2


         ze  ( z2   z20 ) 0.5
Session 4, Unit 8


Averaging Time, Multiple
Sources, and Receptors
Chimney, Building, and
Terrain Effects
Averaging Time
  The concentration calculated from the
  Gaussian equations should represent
  the averaging time that is consistent
  with the averaging time of 
  Short-term:  1 month
  Long-term: > 1 month
Averaging Time
  If longer averaging time is desired, use
  the following power law
                              p
                    tk   
           Cs  Ck 
                   t     
                          
                    s    

     P=0.17-0.75, suggested value is 0.17
Crosswind Averaging
  Integrate y from - to 
                2 Q
                    1
                         1 H
                        2                    
                                                 2
                                                     
        Ccw    1    exp                 
                                                    
                zu
                  2      2  z
                                                   
                                                     

  Average over a sector
             2
                    1
                        2
                                Q          1 H         
                                                             2
                                                                 
    C ( )                          exp           
                                                                
                          z u      2  z
                                                               
                                                                 
Crosswind Averaging
  Average over a sector considering
  distribution of wind speeds and stability
  classes

                                      2
                                             1
                                                 2
                                                         Q          1 H     
                                                                                  2
                                                                                      
       C ( , u, S )  f n ( , u, S )                        exp       
                                                                                     
                                                   z u      2  z
                                                                                    
                                                                                      

     ISCLT3 and STAR
Crosswind Averaging
  Smoothing transition from sector to
  sector
     Weighted smoothing function, WS
            (  |  ad   |)
       WS                      for |  ad   | 
                   
       WS  0 for |  ad   | 
     Smoothed average concentration
                                     2
                                            1
                                                2
                                                     Q(WS )        1 H     
                                                                                 2
                                                                                     
      C ( , u, S )  f n ( , u, S )                        exp       
                                                                                    
                                                  z u      2  z
                                                                                   
                                                                                     
Multiple Sources
  The max from each source do not
  exactly overlap
  Use of multiple stack factor
  More accurate method – modeling with
  a consistent coordinate system
Receptors
  Receptor grid
     Cartesian coordinate system
     Polar coordinate system
  Single stack, but the origin of the coordinate
  system is not at the stack base
  Multiple stacks
  Presentation of results
     Concentration isopleths
Example Calculation
  Chapter 10
Chimney Effects
 Stack tip downwash
     Low pressure behind stack
               vs
        When         1.5
               u
                       vs   
        h  hs  2d s   1.5
         '
         s
                      u     
       ū is at the stack top level
     No plume rise (“plume sink”)
 Avoid stack tip downwash
               vs
       When          1.5
               u
       hs'  hs
Building Effects
  General description
  Expanded meaning of “building”
  Reduce building effects – rule of thumb
  hs>2.5hb
  Too conservative for tall thin buildings
Briggs Procedure to Minimize
Downwash
   Five steps:
  1.   Correction for stack induced downwash
  2.   Correction for building effects
  3.   Determine if plume is entrained in the
       cavity. If entrained, treat it as a ground
       level source
  4.   Buoyancy effect
  5.   Calculate downwind concentration
Cavity
  Description
  Cavity length
     Short buildings (L/H2)
        L affects cavity length xr
             xr   L   A(W H )
                   
             H H 1.0  B (W H )
     Long buildings (L/H>2)
        L does not affect cavity length xr
              xr   1.75 (W H )
                 
              H 1.0  0.25 (W H )
Cavity
  Max cavity width
      2 yr                        W
            1.1  1.7 exp   0.55 
      W                           H
     It’s location long x direction
         xmy                      W
             0.3  2.0 exp  0.55 
          W                       H

  Max height
         zr                       L
             1.0  1.6 exp   1.3 
         H                        H
Cavity
  Concentrations within cavity
        Q
    C
       cu A p
    OR
         QK
    C
         u b
Wake Downwind of Cavity
  Treated as a ground level source
  Turner method (virtual source)
  Gifford method
  Gifford-Slade method (total dispersion
  parameters)
  Huber-Snyder method
Sources Downwind of
Buildings
  Briggs method
     Beyond 3b  no building effect
     Within 3b  treat them as ground level
      sources
Complex Terrain
  Definition
     Simple terrain
     Complex terrain
     Intermediate terrain
  Plume behavior in complex terrain
Complex Terrain
  Modeling approaches
     Briggs
                        he
                    h 
                     '
                     e      z st
                        2
     Egan
                                 z st
                    he'  he 
                                  2
     Bowne
        Modified dispersion coefficients
     ISC3 (COMPLEX 1) – to be discussed later
GEP Stack Height
  Definition
     Greater of
        65 m
        HG=H+1.5L (for stacks in existance on Jan 12,
        1979, HG=2.5H)
     Structures to be considered: within 5L
  In modeling analyses, no credit is given
  for stack height above the GEP

				
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