Lower Layer Temperature and Interface Height

[Peter Murton]

My current modelling runs gives me the Upper Layer Temperatures in each compartment but the lower layer temperature and interface heights are all 'zero'. Any suggestions as to what is amiss ??

Thanks,

Peter Murton

[Richard Peacock]

Can you post an input file to look at? Are you modeling the compartments as shafts? That would lead to only having an upper layer temperature.

[Peter Murton]

Thanks Richard.

 

At some stage I must have changed to 'shaft' for the modelling - I have changed back to Normal two-zone model and all OK now in relation to lower layer temperature and interface height.

 

I still have some problems which you can hopefully advise on. I have attached the input file for reference.

 

In order to solve the heat release problem, I have divided the warehouse into 12 compartments with walls removed ( as horizontal vents ) to simulate the large warehouse. I have only identified one permanently open wall vent.

 

There are six roof vents that are to be normally closed, and are to open when the temperature at the thermal link reaches 98 ⁰C. In order to get the temperature up above this setting I have placed large fires in compartments near vents. HOWEVER, when I run the simulation the Log states that the vents “ opening change triggered by temperature at 0.s “.   This I cannot seem to correct nor understand as the Open/Close Criterion is Temperature, and the vents are open from the start. 

Maybe this has been part of my difficulties from the start.

 

There are sprinklers in the warehouse that will also come into play but I need to get the base venting sorted out first before I complicate the situation more.

 

Your assistance would be greatly appreciated.

 

Peter Murton.

[Burkhard Forell]

Dear all,

I would like to study the temperature of the reinforcement bars in the concrete ceiling of an enduring compartment fire.

Two layers of bars are located one close to the bottom and one close to the top of the ceiling slab.

I modelled the bars by targets from concrete with ceiling thickness.

Unfortunately, the back side of the targets becomes hotter than the center of the targets. Obviously, the back side is not cooled by ambient conditions but sees some part/fraction of the fire.

Could you explain and recommend how to position and model the targets?

Best Regards

Burkhard

[Kevin McGrattan]

This sounds like a 3-D heat conduction problem. CFAST does not have this capability.

[Peter Murton]

Hi Richard – just checking to see if you have had a chance to look at my problems for me as per my reply with the Input file posted last week.

 

Many thanks,

 

Peter Murton.

On Friday, September 13, 2019 at 5:41:25 PM UTC+9:30, Peter Murton wrote:

[Richard Peacock]

On the ceiling vent opening issue, this is a bug in CFAST that prevents the vent opening from working correctly for temperature and flux triggers.  The code has been fixed and an updated version will be available once we've run it through the V&V process.  

As a workaround, you have to run the model and see when the associated targets reach the trigger temperature (CFAST uses the surface temperature of the target) and then add a time-based opening for that corresponding time. With multiple ceiling vents, you may need to run the model multiple times.

[Peter Murton]

Richard,

I am still having difficulties with roof vent opening. I have not as yet been able to get a vent to open even when the temperature at the target positioned at the roof vent location is way in excess of the opening temperature set.

I have tried the time based opening workaround, but even though I set the opening time to correspond supposedly at the target temperature to open the vent I find that when Smokeview is run the vent is seen to be open all the time.

Can you suggest what may be the problem ?  The latest CFAST release is stated to have vent opening by temperature rectified but I cannot get venting to work correctly for either time or temperature.

Thanks,

Peter Murton

On Friday, September 13, 2019 at 5:41:25 PM UTC+9:30, Peter Murton wrote:

[fde]

Speaking for temperature triggered VENT, did you check _w.csv file to confirm the surface temperature of the target reaches to the trigger value?

[Richard Peacock]

Smokeview doesn't seem to show closed ceiling/floor vents, but the flow is still visualized.  Here's a one compartment case that includes a ceiling vent that opens by temperature and one that opens later by time.  Both open at the correct time. Are you using the most recent version of CFAST?

&HEAD VERSION = 7400, TITLE = 'CFAST Simulation' /
 
!! Scenario Configuration
&TIME SIMULATION = 1000 PRINT = 60 SMOKEVIEW = 15 SPREADSHEET = 0 /
&INIT PRESSURE = 101325 RELATIVE_HUMIDITY = 50 INTERIOR_TEMPERATURE = 20 EXTERIOR_TEMPERATURE = 20 /
&MISC  LOWER_OXYGEN_LIMIT = 0.15 /
 
!! Material Properties
&MATL ID = 'GYPSUM' MATERIAL = 'Gypsum Board (1/2 in)',
      CONDUCTIVITY = 0.28 DENSITY = 810 SPECIFIC_HEAT = 1, THICKNESS = 0.0127 EMISSIVITY = 0.9 /
 
!! Compartments
&COMP ID = 'Comp 1'
      DEPTH = 4 HEIGHT = 4 WIDTH = 4 CEILING_MATL_ID = 'OFF' WALL_MATL_ID = 'OFF' FLOOR_MATL_ID = 'OFF'
      ORIGIN = 0, 0, 0 GRID = 50, 50, 50 /
 
!! Wall Vents
&VENT TYPE = 'WALL' ID = 'WallVent_1' COMP_IDS = 'Comp 1' 'OUTSIDE'  TOP = 3, BOTTOM = 1, WIDTH = 0.5
  CRITERION = 'TIME' T = 0, 5, 6 F = 0, 0, 1 FACE = 'FRONT' OFFSET = 1.75 /
 
!! Ceiling and Floor Vents
&VENT TYPE = 'CEILING' ID = 'CeilFloorVent_1' COMP_IDS = 'OUTSIDE', 'Comp 1' AREA = 0.25, SHAPE = 'ROUND'
      CRITERION = 'TEMPERATURE', SETPOINT = 60, DEVC_ID = 'Targ 1' PRE_FRACTION = 0, POST_FRACTION = 1 OFFSETS = 1, 1 /
&VENT TYPE = 'CEILING' ID = 'CeilFloorVent_2' COMP_IDS = 'OUTSIDE', 'Comp 1' AREA = 0.25, SHAPE = 'ROUND'
      CRITERION = 'TIME' T = 0, 400, 401 F = 0, 0, 1 OFFSETS = 3, 3 /
 
!! Fires
&FIRE ID = 'New Fire 1'  COMP_ID = 'Comp 1', FIRE_ID = 'New Fire 1'  LOCATION = 1, 1 /
&CHEM ID = 'New Fire 1' CARBON = 1 CHLORINE = 0 HYDROGEN = 4 NITROGEN = 0 OXYGEN = 0 HEAT_OF_COMBUSTION = 50000 RADIATIVE_FRACTION = 0.35 /
&TABL ID = 'New Fire 1' LABELS = 'TIME', 'HRR' , 'HEIGHT' , 'AREA' , 'CO_YIELD' , 'SOOT_YIELD' , 'HCN_YIELD' , 'HCL_YIELD' , 'TRACE_YIELD'  /
&TABL ID = 'New Fire 1', DATA = 0, 0, 0, 0.001, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 30, 10.54, 0, 0.01881082, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 60, 42.16, 0, 0.05702374, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 90, 94.86, 0, 0.1090942, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 120, 168.64, 0, 0.1728637, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 150, 263.5, 0, 0.2470357, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 180, 379.44, 0, 0.3307118, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 210, 516.46, 0, 0.4232185, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 240, 674.56, 0, 0.5240247, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 270, 853.74, 0, 0.6326969, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 300, 1054, 0, 0.7488722, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 600, 1054, 0, 0.7488722, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 630, 853.74, 0, 0.6326969, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 660, 674.56, 0, 0.5240247, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 690, 516.46, 0, 0.4232185, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 720, 379.44, 0, 0.3307118, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 750, 263.5, 0, 0.2470357, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 780, 168.64, 0, 0.1728637, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 810, 94.86, 0, 0.1090942, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 840, 42.16, 0, 0.05702374, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 870, 10.54, 0, 0.01881082, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 900, 0, 0, 0, 0.01, 0.01, 0, 0, 0 /
&TABL ID = 'New Fire 1', DATA = 910, 0, 0, 0.09, 0.01, 0.01, 0, 0, 0 /
 
!! Devices
&DEVC ID = 'Targ 1' COMP_ID = 'Comp 1' LOCATION = 2, 2, 0 TYPE = 'PLATE' MATL_ID = 'GYPSUM'  NORMAL = 0, 0, -1 TEMPERATURE_DEPTH = 0.5 /

You should see an entry in the log file on the vent opening such as

CFAST


Release Version  : CFAST 7.4.3
Revision         : CFAST7.4.3-4-ga293992d
Revision Date    : Wed Nov 6 14:36:15 2019 -0500
Compilation Date : Fri 11/08/2019  09:19 AM


Ceiling/Floor vent #1 from compartment 2 (Outside) to compartment 1 (Comp 1), opening change triggered by temperature at 244. s
Total execution time =  0.484     seconds
Total time steps =       2050
Normal exit from CFAST routine: CFAST