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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 Down.

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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 Down."— Presentation transcript:

1 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

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 = b + (1- b )e -br J o (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: p/L = 5 S o 2 (1- ) 2 U/ S o (1- ) U 2 / 3 || 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/ S o k (C - C i ) Rate of uptake in adsorbent: m/ t = /(1- ) (- C/ t)/ z Maximum uptake from isotherm equation: m max = 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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