Solid to particle heat transfer in FDS

[Lukas148]

Hi all,

I'm trying to simulate cooling of steel block by water stream from fire hose nozzle, but compared to real experiment, water stream has very insignificiant influence on steel temperature in the FDS model.

I was trying various DIAMETER, MINIMUM_DIAMETER and MAXIMUM_DIAMETER, but it doesn't have any influence on cooling rate of steel surface.

Does FDS support solid surface to particle heat transfer, or there is possible only heat transfer from solid to air, and afterward from air to particles? Is there some way to influence heat tranfer rate beetween water and solid surface?

Here is a part of code, where I define nozzle parameters:

&SPEC    ID='WATER VAPOR',
        DENSITY_LIQUID=1000.0, MELTING_TEMPERATURE=0.0, SPECIFIC_HEAT_LIQUID=4.18, HEAT_OF_VAPORIZATION=2257.0, VAPORIZATION_TEMPERATURE=100.0 /


&PART    ID='WATER', SPEC_ID='WATER VAPOR', AGE=10.0,
        DIAMETER=2000.0, MINIMUM_DIAMETER=500.0, MAXIMUM_DIAMETER=4000.0, DISTRIBUTION='ROSIN–RAMMLER–LOGNORMAL', GAMMA_D=2.4,
        INITIAL_TEMPERATURE=10.0,
        QUANTITIES='PARTICLE DIAMETER','PARTICLE TEMPERATURE','PARTICLE VELOCITY', SAMPLING_FACTOR=1 / puvodne initial_temperature=4.



&PROP    ID='NOZZLE', PART_ID='WATER', PARTICLES_PER_SECOND=5000,
        FLOW_RATE=200.0, DROPLET_VELOCITY=9.0, SPRAY_ANGLE=0.,2.5, SMOKEVIEW_ID='nozzle'



&DEVC    ID='PROUDNICE', PROP_ID='NOZZLE', ORIENTATION=0.99,0,0.06,
        QUANTITY='TIME', SETPOINT=0.0,
        XYZ=0.1,0.5,0.1 /

Meshes and block of steel is defined like this:

&MESH     ID='mesh_nozzle', IJK=8,6,4, XB=0.0,0.8,0.2,0.8,0.0,0.4/ síť pro zkušení místnost, 800 buněk
&MESH     ID='mesh1', IJK=20,20,20, XB=1.0,1.2,0.4,0.6,0.0,0.2/ síť pro zkušení místnost, 8000 buněk
&MESH     ID='mesh2', IJK=12,12,8, XB=0.8,1.4,0.2,0.8,0.0,0.4/ síť pro zkušení místnost, 4800 buněk

&MATL    ID='STEEL', SPECIFIC_HEAT=0.49, CONDUCTIVITY=50.0, DENSITY=7850.0 /
&SURF    ID='STEELBLOCK', COLOR='GRAY', MATL_ID='STEEL', THICKNESS=0.01, TMP_INNER=600.0 /
&OBST    SURF_ID='STEELBLOCK', BNDF_OBST=.TRUE., XB=1.1,1.12,0.4,0.6,0.0,0.2 /
&DEVC    QUANTITY='WALL TEMPERATURE' XYZ=1.1,0.5,0.1, IOR=-1, ID='SURF_TEMP' /

[dr_jfloyd]

FDS does not have the physics need for a hose stream. The droplet-surface heat transfer in FDS is based on single particle or thin film heat transfer and not a jet of water from a hose. 

[Lukas148]

That's what I suspected, but it's better to ask before give up. Thank you. :)

Dne sobota 30. listopadu 2019 16:04:44 UTC+1 dr_jfloyd napsal(a):

[Randy McDermott]

Ok, but you can specify a constant or custom heat transfer coefficient.

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[dr_jfloyd]

You may have one coefficient at the center of the stream, another at the edge of the stream, another above and to the sides from splatter, another below due to flow of the water, etc. Those coefficients and the areas to which they apply may vary depending on the flow rate and stream angle of the hose. For a static test with a fixed in place hose and a fixed nozzle setup you could probably tune it for that specific test. If the ultimate goal is a real hose held by a fire team, that hose will not have a constantly spray pattern, flow rate, stream angle and impact point. I think it is a stretch to try and get Lagragian particles with no particle-particle interactions and no bounce off surfaces to model a solid hose stream and the resulting water flow over a solid surface.

[Randy McDermott]

I don’t think it’s any more of a stretch than everything else we are asking particles to do, given the disperse phase formulation we use.

On Sun, Dec 1, 2019 at 11:23 AM dr_jfloyd <drjf...@gmail.com> wrote:

You may have one coefficient at the center of the stream, another at the edge of the stream, another above and to the sides from splatter, another below due to flow of the water, etc.  Those coefficients and the areas to which they apply may vary depending on the flow rate and stream angle of the hose. For a static test with a fixed in place hose and a fixed nozzle setup you could probably tune it for that specific test.  If the ultimate goal is a real hose held by a fire team, that hose will not have a constantly spray pattern, flow rate, stream angle and impact point. I think it is a stretch to try and get Lagragian particles with no particle-particle interactions and no bounce off surfaces to model a solid hose stream and the resulting water flow over a solid surface.

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