Spray_Angle

[Chris]

Hi everybody,
What is the Standard-Sprinklers Spray Angle? Is 50, 55 (which means
40° to 35° south latitude) correct, or is it steeper? I'm really not
sure what to use. And do I have to change the OFFSET-Parameter in some
special case? This is the radius of the sphere where the droplets are
initially placed whithout been broken up. I just let it like it was.
Thanks for help.
Cheers
Chris

[daserra]

I only know the German types, but the data are specific for each type.
There is no generic standard sprinkler. For the German sprinklers
there are type sheets on the internet.

[Paul Hart]

The spray angle can be unique to each sprinkler. The sprinkler files
in the database for FDS4 contained two sprinklers K-5 and K-11 with
spray angles of 55,70 and 30,80, respectively.

The offset parameter is usually set through the measurement process
and generally represents the point at which the initial water stream
has broken up into droplets.

I do question if the description of spray angle is accurate in the
FDS5 users manual. I ran some verification cases and it appears to me
that the definition of spray angle is more inline with the FDS4
description "...The angles outline a conical pattern relative to the
south pole of the sphere centered at the sprinkler with radius
OFFSET_DISTANCE. For example, a minumum spray angle of 20 degrees and
a maximum spray angle of 80 degrees directs the water droplets to
leave the sprinkler through a conical region 20 degrees north of the
south poll and 10 degrees south of the equator>>>"

The FDS5 description is "...The angles outline a conical spray pattern
relative to the south pole of the sphere centered at the sprinkler
with a radius offset. For example, SPRAY_ANGLE=30.,80. direct the
water droplets to leave the sprinkler through a band between 60
degrees and 10 degrees south latitude...".

The verification case used is:

&HEAD CHID='Water1',TITLE='Example of Spray Angle'/

&MESH IJK=16,16,25,XB=-4,4,-4,4,0,16/

&TIME TWFIN=600/

&MISC TMPA=20 /

&VENT MB='XMIN',SURF_ID='OPEN' /
&VENT MB='XMAX' ,SURF_ID='OPEN' /
&VENT MB='YMIN',SURF_ID='OPEN' /
&VENT MB='YMAX' ,SURF_ID='OPEN' /
&VENT MB='ZMIN' ,SURF_ID='INERT' /

&PART ID='WATER_DROPLETS', WATER=.TRUE.,DROPLETS_PER_SECOND=5000,
DT_INSERT=.01 /

&PROP ID ='TEST SPRINKLER', QUANTITY='SPRINKLER LINK
TEMPERATURE',PART_ID='WATER_DROPLETS',
OPERATING_PRESSURE = 3, K_FACTOR = 155, RTI=124.,
C_FACTOR = 1, ACTIVATION_TEMPERATURE=0, OFFSET= 0.20,
DROPLET_VELOCITY=50,
SPRAY_ANGLE=70,75 /

&DEVC ID='TEST1', XYZ= 8.88178419700125E-16 ,
8.88178419700125E-16 , 13.72 ,
PROP_ID='TEST SPRINKLER' /

&SLCF PBY=0,QUANTITY='WATER_DROPLETS_FLUX_Z'

&TAIL /

[dr_jfloyd]

FDS4 example is 20,80 and says it goes from 20 degress north of the
pole to 10 degrees south of the equator. This is the same as saying
10 degrees to 70 degrees south lattitude (on a globe the equator is 0
deg S lat and pole is 90 deg S lat).

How is the FDS5 example incorrect? 30 to 80 is (90 deg S lat - 30
deg) to (90 deg S lat - 80 deg) or 60 deg S lat to 10 deg S lat.

To test if a spray pattern is coming out as I want it, I find it is
often helpful to run a test case where I have all boundaries open
(mininize the effect of entrainment), turn off gravity (drops move in
a straight line), use large drops (drag takes effect more slowly as
mass is r^3 and drag r^2), and only insert a small number at a low
flowrate (minimize the amount of air entrained). The effects of
gravity, air current from entrainment, and drag, espeicially with
large numbers of small drops and/or a high flowrate, very quickly
perturb the apparent distribution.

> > > Chris- Hide quoted text -
>
> - Show quoted text -

[DavidShep]

I haven't checked the water distribution with FDS5 yet, but as far as
I know the physics of the water trajectory model have not changed.

If you specify a water spray using the simple method using the
spray_angles variable on the PROP namelist your water spray will not
resemble a real sprinkler spray. For example, real pendant sprinklers
provide a well defined relatively uniform water distribution below the
head. When the PROP spray_angles variable is used with zero as the
first angle, the water distribution will be cone shaped with the
delivered water density decreasing almost exponentially as the
distance from the sprinkler increases. If a non-zero first angle is
chosen, the water distribution will be donut shaped with the maximum
water density at the inside edge and decreasing almost exponentially
as the distance from the sprinkler increases.

The only way to get even close to real water distribution is to use
the more complicated tabular functions described in 8.5.3.

[Paul Hart]

I was incorrect in my questioning regarding the spray angle as I was
misinterpreting the meaning of "south of latitude". The FDS5
description of spray angle is thus correct.