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# 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.

## Presentation on theme: "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."— Presentation transcript:

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 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

GEOMETRY OF FILTER BED

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

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

GEOMETRY OF FILTER BED

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/e So(1-e)rU2/e3 | | viscous loss turbulent loss Substantial improvement in predictions compared to model using average voidage

PRESSURE DROP - 3mm PARTICLES

PRESSURE DROP VS GRID DENSITY

VELOCITY DISTRIBUTIONS

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)

VAPOUR UPTAKE IN FILTER BED

VAPOUR PENETRATION

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

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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