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CFD MODELLING OF PRESSURE DROP AND FLOW DISTRIBUTION IN PACKED BED FILTERS K Taylor & AG Smith - S&C Thermoflui

CFD MODELLING OF PRESSURE DROP AND FLOW DISTRIBUTION IN PACKED BED FILTERS K Taylor & AG Smith - S&C Thermofluids Ltd S Ross & MW Smith - DERA Porton Down. OVERVIEW. Packed bed filters remove toxic agents from contaminated airstreams

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CFD MODELLING OF PRESSURE DROP AND FLOW DISTRIBUTION IN PACKED BED FILTERS K Taylor & AG Smith - S&C Thermoflui

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  1. CFD MODELLING OF PRESSURE DROP AND FLOW DISTRIBUTION IN PACKED BED FILTERS K Taylor & AG Smith - S&C Thermofluids LtdS Ross & MW Smith - DERA Porton Down

  2. OVERVIEW • Packed bed filters remove toxic agents from contaminated airstreams • CFD potential design tool for predicting the flow and pressure drop • Mathematical model for predicting radial voidage distribution in bed • Non-uniform voidage distribution included in CFD model • Validated against measurements of pressure drop and velocity distribution • Potential for CFD modelling of adsorption process also investigated

  3. GEOMETRY OF FILTER BED

  4. VOIDAGE DISTRIBUTION IN CYLINDRICAL FILTER BEDS • Radial voidage distribution in ‘snowstorm’ packed filter beds is a function of the ratio: particle size/bed diameter • Affects the velocity distribution within the filter bed • Measurements made of voidage distribution for range of particle sizes • Fitted to modified ‘Mueller’ model

  5. e = eb + (1- eb)e-brJo(ar*)

  6. GEOMETRY OF FILTER BED

  7. CFD MODEL • 2-d axi-symmetric BFC model • Grid distribution determined from voidage distribution to ensure adequate grid resolution near walls • Local voidage distribution coupled to Ergun-Orning equation for pressure loss through bed: Dp/L = 5 So2(1-e)2mU/e3 + 0.29 So(1-e)rU2/e3 | | viscous loss turbulent loss • Substantial improvement in predictions compared to model using average voidage

  8. PRESSURE DROP - 3mm PARTICLES

  9. PRESSURE DROP VS GRID DENSITY

  10. VELOCITY DISTRIBUTIONS

  11. ADSORPTION MODEL • Transient model to predict ‘breakthrough’ • Steady state flowfield used as initial conditions • Adsorption rate source term: -¶C/¶t = 1/e So k (C - Ci) • Rate of uptake in adsorbent: ¶m/¶t = e/(1-e) (-¶C/¶t)/rz • Maximum uptake from isotherm equation: mmax = a.b.RH/(1 - RH)

  12. VAPOUR UPTAKE IN FILTER BED

  13. VAPOUR PENETRATION

  14. IMPLEMENTATION WITHIN PHOENICS • Pre-processor - interprets voidage distribution and basic input parameters - outputs Q1 file • Additional Q1 commands for adsorption model • GROUND coding for - porosity from voidage distribution inlet boundary conditions source terms for pressure loss and adsorption rate

  15. CONCLUDING REMARKS • Method for prediction of pressure and flow distribution validated for range of parameters • Implemented within PHOENICS user routines • Potential for adsorption model demonstrated • Areas for further work: improvement and validation of asdorption model improved user interface turbulence modelling within the filter bed

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