Please login or register to get all features
Wildgoose Chase Moto Guzzi
August 29, 2014, 08:08:33 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Free Classifieds, Auctions and Wanteds available now. Click HERE
 
   Home   Help Advertise Login Register Chat  
Pages: [1]   Go Down
  Print  
Author Topic: How do i calculate rate of evaporation of gas?  (Read 6392 times)
boatdetective
Trade Count: (0)
Guzzi Hero
*****
*
Offline Offline

Posts: 1953





Ignore
« on: February 22, 2011, 12:13:10 PM »
ReplyReply

Long story, but i need to calculate the rate at which gasoline evaporates in the open. I'm talking normal temperatures- 70-90F.  Any engimaneers out there who know a quick and dirty formula?
Logged

Jonathan K
Marblehead, MA

1981 V50III "Gina"
2007 Griso 1100 "Bluto" (departed but not forgotten)
2003 EV "Lola" gone to the "Ridin' Realtor" in Peoria
2007 1200 Sport "Ginger"

"Who's the cat who won't cop out, when there's danger all about?"  -Isaac Hayes

Gutsibits - The Moto Guzzi Spares Service
New, Used and Recon Spares & Accessories | Secure online ordering and rapid delivery worldwide
www.gutsibits.co.uk
Advertise Here
kitze2
Trade Count: (0)
Guzzi Hero
*****
*
*
Offline Offline

Age: 47
Location: San Lorenzo, ca
Posts: 2153





Ignore
« Reply #1 on: February 22, 2011, 01:23:10 PM »
ReplyReply

How about this...
Place a small amount in an open container (in a safe and temperature stable location)
Place the container on a reloading scale and weight the whole set up.
Then reweigh it and plot the change in weight.
Not super scientific but might get you what you need.
Logged

Doesn't matter what you ride....as long as you ride!
'05 SV650S  Track tool
'08 Norge, Black
'10 V7 Cafe, Green (Sold)
'89 XT600. We don't need no stink'n 'lectric start!
egschade
Trade Count: (0)
Guzzi Mentor
****
*
*
Offline Offline

Age: 57
Location: Basking Ridge, NJ
Posts: 349


Grandpa Frank 1929 - First MC cop in Caldwell, NJ




Ignore
« Reply #2 on: February 22, 2011, 02:37:26 PM »
ReplyReply

All I know is that lower octane = greater volitillity, hence regular causing detonatiion in higher compression engines.

Ethanol is lower volititlity so greater E percentage has an impact.
Logged

The oldest Eric in NJ
07 Breva 1100
09 Suzuki GSX650F
84 Honda Ascot VT500F
jreagan
Trade Count: (0)
Guzzi Hero
*****
*
*
Offline Offline

Age: 54
Location: Nicholasville KY
Posts: 851




Ignore
« Reply #3 on: February 22, 2011, 02:43:42 PM »
ReplyReply

It is going to depend on temperature of the gas, the temp of the air, altitude, vapor pressure, surface area of gas, even wind speed across the gas, etc. 
Logged

"Loud Valves Save Lives"

2004 Triumph Bonneville T100
2006 Breva 1100 (red)
Nicholasville KY USA
NOLAGuzzi
Trade Count: (0)
Guzzi Hero
*****
*
Offline Offline

Age: 39
Location: New Orleans LA
Posts: 851





Ignore
« Reply #4 on: February 22, 2011, 03:08:36 PM »
ReplyReply

You could do it empirically like this:

put a volume of gas in a graduated cylinder and record volume.

wait some period of time and record time

measure volume left in cylinder.

calculate rate of evap by (initial volume - final volume / time in min)
surface area would be an important factor too. so you could calculate the cross sectional surface area in cm2 of the cylinder (pi*r2) and then divide the rate by that to give units that show change in volume per time per surface area (ml evaporated/min)/cm2.

this would not be generalizable to all situations but it would give you an idea of what goes on at atmospheric conditions.


« Last Edit: February 22, 2011, 03:13:55 PM by NOLAGuzzi » Logged

04 Breva 750
NOLA = New Orleans LA
Sasquatch Jim
Trade Count: (0)
Guzzi Hero
*****
*
Offline Offline

Location: N.lat 20- 13' -58" * W.lon 155 - 48' - 31"
Posts: 5662


Sidecar - Best drive by shooting vehicle ever




Ignore
« Reply #5 on: February 22, 2011, 03:17:38 PM »
ReplyReply

You could do it empirically like this:

put a volume of gas in a graduated cylinder and record volume.

wait some period of time and record time

measure volume left in cylinder.

calculate rate of evap by (initial volume - final volume / time in min)
surface area would be an important factor too. so you could calculate the cross sectional surface area in cm2 of the cylinder (pi*r2) and then divide the rate by that to give units that show change in volume per time per surface area (ml evaporated/min)/cm2.

this would not be generalizable to all situations but it would give you an idea of what goes on at atmospheric conditions.



The graduated cylinder would not be applicable to all situations as the tube shape of the cylinder would inhibit evaporation. I would go with the open dish and the accurate scale weight.

Sasquatch Jim
Logged

Sasquatch Jim        Humanoid, sort of.
NOLAGuzzi
Trade Count: (0)
Guzzi Hero
*****
*
Offline Offline

Age: 39
Location: New Orleans LA
Posts: 851





Ignore
« Reply #6 on: February 22, 2011, 04:31:54 PM »
ReplyReply

That is true Jim.  The cylinder is not applicable to all conditions.  Fill the cylinder all the way up, or most of the way, and measure for a short time.  Then it should not matter. 

About weighing gas, how can one back calculate to a volume by weighing a volatile liquid of unknown density with any kind of accuracy?  I am not nit picking, I'm just trying to understand how that would work.

I don't think of gasoline in terms of weight but in volume so that confuses me. 
Logged

04 Breva 750
NOLA = New Orleans LA
charlie b
Trade Count: (0)
Guzzi Hero
*****
Offline Offline

Age: 61
Location: Tijeras, NM
Posts: 4589




Ignore
« Reply #7 on: February 22, 2011, 04:39:41 PM »
ReplyReply

(mass loss rate)/(unit area) = (vapor pressure - ambient partial pressure)*sqrt( (molecular weight)/(2*pi*R*T) )

vapor pressure chart

           WINTER   WINTER    SUMMER  SUMMER  AVIATION  JET FUEL
         GASOLINE  GASOLIN GASOLIN GASOLIN GASOLINE  & KEROSENE
TEMP    REID       REID        REIDVP    REID
F        14-VP      12-VP      10-VP       8-VP  

40   4.8   4   3.4   2.8   2.2     0.9
50   5.9   4.9   4.1   3.4   2.8     1
60   7.4   6   5   4.1   3.5     1
70   8.9   7.4   6   5   4.2     1.2
80   10.7   9   7.1   5.9   5.1     1.4
90   12.8   10.6   8.6   7   6.2     1.7
100   14   12   10   8   7.4       2

And,for stagnant conditions you have to take into account the change in local ambient partial pressures as it vaporizes, ie, near the surface you'll get a layer of high partial pressures which will slow the evaporization.

If you have any wind blowing then I'd estimate it with a zero ambient or maybe 50% (ie, half the gas vapor pressure).

charlie
Logged

1984 850 T5
2010 Honda VT700VA (sold)
2009 Dodge Cummins 2500
2011 Honda Element
charlie b
Trade Count: (0)
Guzzi Hero
*****
Offline Offline

Age: 61
Location: Tijeras, NM
Posts: 4589




Ignore
« Reply #8 on: February 22, 2011, 04:40:52 PM »
ReplyReply

That is true Jim.  The cylinder is not applicable to all conditions.  Fill the cylinder all the way up, or most of the way, and measure for a short time.  Then it should not matter. 

About weighing gas, how can one back calculate to a volume by weighing a volatile liquid of unknown density with any kind of accuracy?  I am not nit picking, I'm just trying to understand how that would work.

I don't think of gasoline in terms of weight but in volume so that confuses me. 

Measure it first in a closed container.
Logged

1984 850 T5
2010 Honda VT700VA (sold)
2009 Dodge Cummins 2500
2011 Honda Element
radan2
Trade Count: (0)
Guzzi Hero
*****
*
*
*
Offline Offline

Location: Jacksonville, NC, USA
Posts: 2104





Ignore
« Reply #9 on: February 22, 2011, 04:44:55 PM »
ReplyReply

At this site is the procedures and formulas used by the industry:

www.epa.gov/ttn/chief/ap42/ch07/final/c07s01.pdf
AP-42, CH 7.1: Organic Liquid Storage Tanks

It is NOT quick and dirty.
Logged

Jim Wayne
Jacksonville, NC, USA
Red 07 Breva V750 "Scarlett the Red Menace"
Black 11 Norge 8V "Nerina the Black Terror"
Do what you can, with what you have, where you are (Theodore Roosevelt)
NOLAGuzzi
Trade Count: (0)
Guzzi Hero
*****
*
Offline Offline

Age: 39
Location: New Orleans LA
Posts: 851





Ignore
« Reply #10 on: February 22, 2011, 04:49:12 PM »
ReplyReply

That is true Jim.  The cylinder is not applicable to all conditions.  Fill the cylinder all the way up, or most of the way, and measure for a short time.  Then it should not matter. 

About weighing gas, how can one back calculate to a volume by weighing a volatile liquid of unknown density with any kind of accuracy?  I am not nit picking, I'm just trying to understand how that would work.

I don't think of gasoline in terms of weight but in volume so that confuses me. 

Measure it first in a closed container.

Ahh that makes sense.
Logged

04 Breva 750
NOLA = New Orleans LA
RayB
Trade Count: (0)
Guzzi Hero
*****
Offline Offline

Location: NW Indiana
Posts: 898




Ignore
« Reply #11 on: February 22, 2011, 07:36:44 PM »
ReplyReply

I guess the precision you need depends on the problem you are trying to solve. If you are just curious, I would use the weight method rather than volume because of expansion, etc. I would, however take the temp of the liquid at the start time and end time.

If you have a real engineering problem that has a large $ impact based on the decision you make with the info, precision is justified.

If you tell us why you want to know this we could probably give you a better method.
Logged

01 EV
82 BMW R100
Sasquatch Jim
Trade Count: (0)
Guzzi Hero
*****
*
Offline Offline

Location: N.lat 20- 13' -58" * W.lon 155 - 48' - 31"
Posts: 5662


Sidecar - Best drive by shooting vehicle ever




Ignore
« Reply #12 on: February 22, 2011, 08:41:18 PM »
ReplyReply

And this knowledge of gas evaporation rates affects our riding by?

Sasquatch Jim
Logged

Sasquatch Jim        Humanoid, sort of.
boatdetective
Trade Count: (0)
Guzzi Hero
*****
*
Offline Offline

Posts: 1953





Ignore
« Reply #13 on: February 22, 2011, 09:13:05 PM »
ReplyReply

Sorry Jim, definitely NGC.  I have a boat fire investigation. One theory is that the supply hose (low pressure) from the tank was pulled off-line which wad the source of gas to start the fire. The hose was 24" x 3/8" ID. Volume of hose was only 1.5 oz.  There's a check valve on the tank- so that would have to limit leakage to the hose volume. So, we have 1.5 oz of fuel- but even that needs to vaporize.  Approx. Volume of the engine compartment is 50 cu. Ft.  Lower explosive limit of gasoline is 1.4%.  Ifwe grant that every drop of the gas varied (no way), the vapor would only amount to just under .5%.  Even if we could bump it up to the lel, there would be no additional fuel left to support the fire (these cases result in a big Ka-woof-but snuff out).  The final bit was that the engine compartment was open.  I think I'm pretty safe in finding this theory ca-rap.
Logged

Jonathan K
Marblehead, MA

1981 V50III "Gina"
2007 Griso 1100 "Bluto" (departed but not forgotten)
2003 EV "Lola" gone to the "Ridin' Realtor" in Peoria
2007 1200 Sport "Ginger"

"Who's the cat who won't cop out, when there's danger all about?"  -Isaac Hayes
cloudbase
Trade Count: (0)
Guzzi Hero
*****
Offline Offline

Location: Houston
Posts: 1642





Ignore
« Reply #14 on: February 23, 2011, 11:59:16 AM »
ReplyReply

Assuming the check valve didn't leak. 

Logged

ACTA NON VERBA
www.sagaw.org
As a general rule, the better it felt when you said it, the more trouble it's going to get you into.
Two Checks
Trade Count: (0)
Guzzi Hero
*****
Offline Offline

Location: STL Metro
Posts: 4469




Ignore
« Reply #15 on: February 23, 2011, 01:42:49 PM »
ReplyReply

I have found gas evaporates from my tank faster when I twist the grip further. :-)
BD good luck with your investigation. Reading the latest issue of Good Old Boat.
Logged

1990 Cal III f/f  "Il Duce' III"
1987 1000 SPII "Il Duce' II"
boatdetective
Trade Count: (0)
Guzzi Hero
*****
*
Offline Offline

Posts: 1953





Ignore
« Reply #16 on: February 23, 2011, 03:51:44 PM »
ReplyReply

TwoC, I'd rather be reading about good old boats, too. I'm living it now- chasing down 230 linear feet of @#$%! gloat stress cracks on my 1970 Betram in prep for dipping the whole thing in Awlgrip. Oy vay!
Logged

Jonathan K
Marblehead, MA

1981 V50III "Gina"
2007 Griso 1100 "Bluto" (departed but not forgotten)
2003 EV "Lola" gone to the "Ridin' Realtor" in Peoria
2007 1200 Sport "Ginger"

"Who's the cat who won't cop out, when there's danger all about?"  -Isaac Hayes
Offcamber1
Trade Count: (0)
Guzzi Hero
*****
Offline Offline

Posts: 6713





Ignore
« Reply #17 on: February 23, 2011, 10:52:03 PM »
ReplyReply

Gasoline evaporates instantly.  Shortly after someone consumes way too many beers and says, "Hey y'all, watch this!"
Logged

Its a fair cop, but society is to blame.
Pages: [1]   Go Up
  Print  
 
Jump to:  


Want to ride some great roads amongst stunning scenery?
Take a gander around New Zealand on a Guzzi from Guzzi Gander Ltd.
http://www.guzzigander.com
Advertise Here
Powered by MySQL Powered by PHP Wildguzzi.com © 1998 - 2013
Powered by SMF 1.1.19 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Valid XHTML 1.0! Valid CSS!


Further info on echo and along with currentaction
The Fastest SFTP on the planet Go FTP FREE Client