SLCF quantity (mass frac)
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Kate Mccombe
Jul 21, 2016, 11:06:09 AM7/21/16
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Hi,
I have a basic code for a gas being released from a vent. The velocity slice file is showing properly in Smokeview but the Mass Fraction slice file is showing zero values for the whole time period. Can anyone tell me what I'm missing in my code?
&SPEC ID='HYDROCHLORIC ACID', LUMPED_COMPONENT_ONLY=.TRUE./
&SPEC ID='HYDROFLUORIC ACID', LUMPED_COMPONENT_ONLY=.TRUE./
&SPEC ID='FUMES',
SPEC_ID(1)='HYDROCHLORIC ACID', MASS_FRACTION(1)=0.5,
SPEC_ID(2)='HYDROFLUORIC ACID', MASS_FRACTION(2)=0.5,
MASS_EXTINCTION_COEFFICIENT=10 /
&SURF ID='SUPPLY', SPEC_ID='FUMES', MASS_FLUX_TOTAL=5, RAMP_V='SUPPLY RAMP', TAU_V=5 /
&RAMP ID='SUPPLY RAMP', T=0., F=0.0/
&RAMP ID='SUPPLY RAMP', T=1., F=1.0/
&RAMP ID='SUPPLY RAMP', T=3., F=1.0/
&RAMP ID='SUPPLY RAMP', T=4., F=0.0/
&RAMP ID='SUPPLY RAMP', T=60., F=0.0/
&VENT XB=-1.046, -1.046, 0.0, 0.2, 1.0, 1.2, SURF_ID='SUPPLY', COLOR='RED' /
&PLOT3D_SPEC_ID = 'FUMES'
&SLCF XB=-2.0, -1.046, 0.0, 0.2, 1.0, 1.2, QUANTITY='VELOCITY', VECTOR=.TRUE./
&SLCF XB=-2.0, -1.046, 0.0, 0.2, 1.0, 1.2, QUANTITY='MASS FRACTION', SPEC_ID = 'FUMES'/
&DUMP PLOT3D_QUANTITY(1:5)='VOLUME FRACTION','U-VELOCITY','V-VELOCITY','W-VELOCITY','HRRPUV', PLOT3D_SPEC_ID = 'FUMES', DT_PL3D = 1, DT_SL3D = 1/
&TAIL/
dr_jfloyd
Jul 21, 2016, 12:04:27 PM7/21/16
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Read the User's Guide section on species. FDS has predefined species for HF and HCl with correct molecular weights and thermophysical properties.
You haven't defined any MASS_FRACTION for your SURF. Per the User's Guide the default MASS_FRACTION is 0. So you are just injecting the background species which is AIR. Look at the examples in 9.1.6 of the User's Guide.
Kate M
Jul 22, 2016, 8:53:15 AM7/22/16
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Hi Dr jfloyd,
I'm not sure I understand why I have to set up the mass fraction on the surf lines. I have done this by saying that the Spec_ID for that surface is 'Fumes' which has a defined composition above. If I try to put a mass fraction specification on the surf line I get an error saying that I can't specify velocity and mass fraction on the surf line. ?
Kate M
Jul 22, 2016, 9:17:52 AM7/22/16
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It seems to have fixed my problem to use Mass_flux instead of Mass_flux_total.
Randy McDermott
Jul 22, 2016, 9:17:56 AM7/22/16
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Are you sure? You can't specify VEL and MASS_FLUX on SURF, but you certainly can specify VEL and MASS_FRACTION. Please post your input file or a snippet. Thanks.
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Randy McDermott
Jul 22, 2016, 9:26:27 AM7/22/16
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MASS_FLUX_TOTAL effectively applies a velocity bc by setting UW = MASS_FLUX_TOTAL/RHO_F where RHO_F is the density on the surface (FACE). RHO_F depends on temperature and composition on the face. So, if you expect a certain species flux to be exact you will be disappointed. If you want to get an exact mass flux of fuel you need to specify MASS_FLUX(1)=..., SPEC_ID(1)='my fuel' on the SURF. This is effectively what HRRPUA does.
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Kate M
Jul 22, 2016, 9:41:20 AM7/22/16
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I have just set MASS_FLUX = 5 (not mass flux for each component). My individual species mass fracs were identified in the SPEC_ID line. So have I just specified a total release rate of 5kg/s of a mix of HCl and HF at a mass ratio of 1:1?
Randy McDermott
Jul 22, 2016, 9:43:53 AM7/22/16
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Please send a snippet of your input file. I can't tell if is correct or not. Thanks.
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Kate M
Jul 22, 2016, 10:03:42 AM7/22/16
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&TIME T_END=60. /
&MISC TMPA=25. /
&MISC HUMIDITY=40. /
&SPEC ID='HYDROCHLORIC ACID', LUMPED_COMPONENT_ONLY=.TRUE./
&SPEC ID='HYDROFLUORIC ACID', LUMPED_COMPONENT_ONLY=.TRUE./
&SPEC ID='FUMES',
SPEC_ID(1)='HYDROCHLORIC ACID', MASS_FRACTION(1)=0.5,
SPEC_ID(2)='HYDROFLUORIC ACID', MASS_FRACTION(2)=0.5,
MASS_EXTINCTION_COEFFICIENT=10 /
&SURF ID='SUPPLY', SPEC_ID='FUMES', MASS_FLUX=5, RAMP_V='SUPPLY RAMP', TAU_V=5 /
&RAMP ID='SUPPLY RAMP', T=0., F=0.0/
&RAMP ID='SUPPLY RAMP', T=1., F=1.0/
&RAMP ID='SUPPLY RAMP', T=3., F=1.0/
&RAMP ID='SUPPLY RAMP', T=4., F=0.0/
&RAMP ID='SUPPLY RAMP', T=60., F=0.0/
&VENT XB=-1.046, -1.046, 0.0, 0.2, 1.0, 1.2, SURF_ID='SUPPLY', COLOR='RED' /
&PLOT3D_SPEC_ID = 'FUMES'
&SLCF XB=-2.0, -1.046, 0.0, 0.2, 1.0, 1.2, QUANTITY='VELOCITY', VECTOR=.TRUE./
&SLCF XB=-2.0, -1.046, 0.0, 0.2, 1.0, 1.2, QUANTITY='MASS FRACTION', SPEC_ID = 'FUMES'/
&DUMP PLOT3D_QUANTITY(1:5)='VOLUME FRACTION','U-VELOCITY','V-VELOCITY','W-VELOCITY','HRRPUV', PLOT3D_SPEC_ID = 'FUMES', DT_PL3D = 1, DT_SL3D = 1/
Randy McDermott
Jul 22, 2016, 10:09:43 AM7/22/16
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The area of your VENT is 0.2*1.2 = 0.24 m^2. Your mass flux is 5 kg/m^2/s, so your total is 1.2 kg FUMES / s. If you want 5 kg/s you need to specify a mass flux of 5/0.24 = 20.8333 kg/m^2/s. The RAMP_V does not apply here, you want RAMP_MF='SUPPLY RAMP'. Also TAU_V should not be used.
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Randy McDermott
Jul 22, 2016, 10:12:16 AM7/22/16
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Oops, you area is 0.2 * 0.2 = 0.04 m^2. So mass flux needs to be 5/.04 = 125. That is pretty high.
Kate M
Jul 22, 2016, 10:32:32 AM7/22/16
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Sorry, I meant 5 kg/m2/s. These numbers are all meaningless at the moment. I'm just trying to build a functional code. So I can use Mass_Flux(N) to specify the mass flux of the total fume flow (not components)? If so, what is the difference between this and Mass_Flux_total?
Randy McDermott
Jul 22, 2016, 10:36:37 AM7/22/16
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As I describe above, MFT is a velocity bc. The velocity determined the advective flux. But the total flux includes the diffusive flux. This has caused confusion in the past. There is some discussion of this in the user guide, see sec. 9.1.6.
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Kate M
Jul 22, 2016, 10:44:34 AM7/22/16
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Oh I see! Thank-you for clearing that up.
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