Plume rise from free burning fires Bo Yao April, 2007

Outline Introduction (previous work on plume rise of industrial emissions) Approaches: two models Experiments Results Conclusion Proposed work

Introduction Plume rise of industrial emissions Briggs plume rise equations: in neutral and unstable conditions ΔH=1.6Fb1/3(u)-1xf2/3 where Fb=8/π*V(Ts-Ta)/Ts is the buoyancy flux

Introduction Briggs plume rise equations: in convective conditions ΔH=3.0(Fb/u)3/5H*-2/5 where H*=(g/T0)(w’θ’)0 is the buoyancy flux at the surface due to the combined effects of heating and evaporation

Introduction Briggs plume rise equations: in a stable environment

Introduction Semi-empirical equations Apply to plume rise of industrial sources (stacks) only because they assume the heat is completely released into the plume as the plume is generated by the flare stacks

Approach Mills’ model Carter’s model

Approach Fb=0.037QH assuming Ta=293K L: diameter of the fire Mill’s model Briggs plume rise equation: altered into: ΔH=[(ΔhB)3+(L/2γ)3]1/3-L/2γ Fb=0.037QH assuming Ta=293K L: diameter of the fire ΔhB=1.6Fb1/3(u)-1xf2/3

Approach The Briggs equation becomes: (1) heat produced is reduced by 30% (2) L/2γ is inserted in the Briggs equation to take into account the initial diameter of the plume which is considered equal to the extent of the fire. γ = 0.6, entrainment coefficient for buoyant plume rise Δh=0.47QH1/3(u)-1xf2/3

Approach Carter’s model Moore’s formula modified into Δh=0.512f/u* ΔT0.125[gQX*2(X*+27L)/(CpTa)]0.25 where X*=XXt(X2+Xt2)-0.5 Xt=XsXn(Xs2+Xn2)-0.5 Xs=120uε-0.5 Xn=1920+19.2Z or 4224 if Z>120m f=0.16+0.007Z if Z<120m f=1 if Z>120m or u-2ε>2.5e-3

Approach Carter’s model suggested the use of Moore formula on the basis of general considerations without the peculiar characteristics of free burning fires. so the equation is valid for plume rising from any kind of sources. to compensate for area source, Carter estimates the virtual location of an equivalent point source.

Experiments

Experiments

Comparisons

Comparisons

Conclusions The rise of plumes from free burning should not be assessed by means for common industrial emissions. Good agreement between Mill’s model and experiments has been achieved. Carter equation has also shown good agreement with maximum differences of about 10%

Proposed work More complex models numerical simulation For larger area fires