-
Beta Was this translation helpful? Give feedback.
Replies: 11 comments 9 replies
-
! This sample file is HEAT_OF_VAPORIZATION=100. &HEAD CHID='simple_testVA100', TITLE='Simple demonstration case.' / &MESH IJK=36,24,24, XB=0.0,3.6,0.0,2.4,0.0,2.4 / &TIME T_END=320.0 / &REAC FUEL='POLYETHYLENE', SOOT_YIELD=0.01,FORMULA='C2H4',HEAT_OF_COMBUSTION=40000 / &MATL ID = 'stuff' &SURF ID = 'BURNER' &RAMP ID='fire_ramp', T= 0.0, F=0.0 / !&SURF ID='BURNER', HRRPUA=1000., COLOR='RED' / &SURF ID='HOT', TMP_FRONT=2500., COLOR='BLACK' / &OBST XB=0.0,0.4,1.0,1.4,0.0,0.2, SURF_ID='HOT'/ &VENT XB=3.6,3.6,0.8,1.6,0.0,2.0, SURF_ID='OPEN' / &BNDF QUANTITY='GAUGE HEAT FLUX' / &DEVC ID='FIRE_SURFACE_TEMP' XB=0.0,0.4,1.0,1.4,0.0,0.2,QUANTITY='TEMPERATURE'/ &SLCF PBY=1.2, QUANTITY='TEMPERATURE', VECTOR=.TRUE. / &TAIL / |
Beta Was this translation helpful? Give feedback.
-
You are specifying the heat release rate with HRRPUA. That value is fixed and HEAT_OF_VAPORIZATION has no impact on it. HEAT_OF_VAPORIZATION is used in the solid phase 1D temperature calculation. Energy is removed from the solid at a rate of HRRPUA * HEAT_OF_VAPORIZATION, this helps keep the surface temperature from rising to unreasonably high values. |
Beta Was this translation helpful? Give feedback.
-
(1) Yes |
Beta Was this translation helpful? Give feedback.
-
If you are going to be working with the source code you should try to get familiar with tracing variables through the code to see how they are used. It will take a little time at first, but once you get some experience it will get faster. In many cases we do try to give a name that hints at what the variable does or in some cases point to a specific equation in the Tech Ref. M_DOT_G_PP_ADJUST is defined in the previous block of code where the comment is: Compute the mass flux of reaction gases at the surface. M for mass, DOT for rate of change (the dot used above symbols in equations in the Tech Ref), G for gas, PP for double prime ('' or per area). DX_S(1). DX, DY, DZ, DT, etc. these all indicate a discretized variable. For DX_S we have X for distances, S for solid; and (1) indicates it is the first item in an array. Earlier in the routine, DX_S is tied to either a surface defintion when there is no pyrolysis or to the wall arrays for a specific wall cell or particle when there is pyrolysis. DX_S is the thickness of the first wall node. |
Beta Was this translation helpful? Give feedback.
-
What is the relationship between q'''_s (source code value) and q'''_s (Tech Ref. Eq. 7.2, second term on the right side)? I was previously told that HEAT_OF_VAPORIZATION is used in the definition of q'''_s (the energy that it takes to convert the solid to the gas that can then burn in the gaseous phase). However, q'''_s (Tech Ref. Eq. 7.2) derives q'''_s in a different way than the source code equation. (Tech Ref. Eq. 7.3) Could you please explain the difference between these two variables (q'''_s (=HRRPUA*HEAT OF VAPORIZATION/HEAT OF COMBUSTION/node thickness) and q'''_s (Tech Ref. Eq. 7.3))? |
Beta Was this translation helpful? Give feedback.
-
7.2 is the conservation of energy for a solid element in derivative form. From left to right the terms are heat storage in the solid due to its temperature, conduction of heat through the solid, and heat generation in the solid. 7.3 is simply noting that there are multiple ways to generate heat in the solid. There are chemical processes (chemical reactions [e.g. pyrolysis], evaporation, condenstation, etc.) and there is the possibility for radiation to be absorbed in-depth. In your input file you do not have radiation absorption in-depth so the q dot s,r ''' term is 0 leaving just the chemical term which you do have in the form of the HEAT_OF_VAPORIZATION input. |
Beta Was this translation helpful? Give feedback.
-
|
Beta Was this translation helpful? Give feedback.
-
I see I think you mean Eq. 7.45. This equation says that the volumetric heat source (kW/m3) in the solid is the sum over all solid phase reactions of the reaction rate in kg/m3/s times a heat of reaction in kJ/kg. Which of these does the HEAT_OF_VAPORIZATION correspond to? |
Beta Was this translation helpful? Give feedback.
-
The HEAT_OF_VAPORIZATION is used as the heat of reaction. Your fuel is still a solid. The liquid evaporation model isn't invoked unless you have a boiling temperature. |
Beta Was this translation helpful? Give feedback.
-
Beta Was this translation helpful? Give feedback.
-
Until the material reaches its ignition temperature, the HRRPUA is zero and hence the heat of reaction source term is zero. Does your plot show this? Pleaes carefuly review the FDS technical reference guide and/or an introductory text on heat transfer on how to model 1D heat transfer. |
Beta Was this translation helpful? Give feedback.
Q_CONV in the hrr.csv file is not a solid phase quantity. See Section 22.10.1 of the User's Guide for how this term is defined.
CONVECTIVE HEAT FLUX is the heat flux into (or out of) the surface due to convection. It is not a measure of enthalpy inside the surface.
There isn't an output for q_dot_s'':
-Since you have a fixed HRRPUA with a HEAT_OF_VAPORIZATION, you can compute the value of this term which exists on in the first wall node in your case as you know the burning rate, H_O_V, and the first wall node thickness (look at the .out file).
-If you want to verify this you can add outputs to compute the energy balance in the first wall node. The net heat flux at the surface minus conduc…