Free 7 Day Trial RV GPS App RV Trip Planner Campground Reviews RV Maintenance Free 7 Day Trial ×
RV Trip Planning Discussions

Go Back   iRV2 Forums > MOTORHOME FORUMS > Class A Motorhome Discussions
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
 
Thread Tools Search this Thread Display Modes
 
Old 12-16-2016, 06:13 PM   #71
Senior Member
 
ModestMonk's Avatar
 
Outdoors RV Owners Club
Join Date: Oct 2016
Posts: 1,804
Quote:
Originally Posted by MN_Traveler View Post
ModestMonk - I suspect (emphasize "suspect") your propane company had good reason to recommend the larger tank. What I believe is missing from this conversation (and several of the posts below this one quoted) are the issues of "heat transfer."

We all know that propane tanks get cold when propane is drawn out of them. this is because it takes energy (heat) to convert the liquid propane into the gas form. That heat comes from the remaining "liquid" molecules immediately around the ones that vaporize. So the surface of the liquid gets cold and then that cold liquid would sink (with warmer liquid from below rising to replace it). That warmer liquid rising is necessary to supply heat for more (i.e. additional) molecules to go into the vapor phase.

Do the "thought experiment" of a "tank" that is really a very very tall, but very very small diameter cylinder (oriented in the vertical dimension). As molecules evaporate at the surface, the remaining liquid at the surface gets cold. Two things: with very small cross sectional area for the "cold" liquid to sink, the exchange of cold for hot is slowed. Second, even if that exchange does happen ... all you get is a slightly thicker layer of cold liquid ... and the system needs to "reach" further down the tube to find the heat to evaporate more molecules from the surface. If this goes on long enough, you will have warm liquid **way** down low in the tube, and really, really cold liquid at the surface ... and not enough time for the warm liquid down low to be transported to the surface to supply heat for more evaporation .... and so the rate of evaporation slows down (or virtually stops in an extreme case).

That "thought experiment" is an extreme case ... but hopefully leads one to conclude that a "short-wide" tank allows for faster evaporation than does a tall-thin tank. I would think that the tolerance for just how "tall and thin" depends on the expected rate of draw of vapor.

The OTHER thing regarding "area" is the total surface area of the tank. When that remaining liquid in the tank gets cold .... more heat needs to come from somewhere to allow evaporation to continue. That heat comes from the world outside the tank ... and needs to pass through the surface of the tank material to get to the liquid inside. In general, bigger tank = more surface area of the outside of the tank = faster replenishment of the heat in the tank lost to evaporation (for a given total rate of vapor generation that is).

I am skipping over some fine points ... but hopefully that generally makes sense?????
Thanks, yes that is how I understood that concept. You explain it better than I remember hearing it the first time 12 years ago. The concept in my head related across the board and into RV tanks. As I was building this house and adding more devices and running out of vapor, they kept adding more or larger tanks. The need for more sq inches of surface area to replenish the vapor was their battle cry. The real issue is how it applies to RV's...it doesn't; and this next level conversation is essentially over the top.

Thank you all for you patience and help!
__________________
2018 ORV 24KTS 30,000+miles
2017 Ford 3.5 TwinTurbo w/MaxTow
640 Watts solar/600 Ahr
ModestMonk is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 12-16-2016, 09:07 PM   #72
Senior Member
 
Ray,IN's Avatar
 
Join Date: Aug 2001
Location: North America somewhere
Posts: 21,993
Quote:
Originally Posted by Mr_D View Post
Actually, in some areas you will get butane. Problem is that it takes a higher temperature to off gas which can cause problems if you buy it where it's warm and travel to a colder area. It happened to my parents years ago.

If one has their LP tank refilled in the RGV/S. Texas you either get butane or a mix of butane and propane. Both are LP=liquefied petroleum gas.
__________________
2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy
Ray,IN is offline   Reply With Quote
Old 12-17-2016, 09:09 PM   #73
Senior Member
 
Ray,IN's Avatar
 
Join Date: Aug 2001
Location: North America somewhere
Posts: 21,993
Quote:
Originally Posted by ModestMonk View Post
Thanks, yes that is how I understood that concept. You explain it better than I remember hearing it the first time 12 years ago. The concept in my head related across the board and into RV tanks. As I was building this house and adding more devices and running out of vapor, they kept adding more or larger tanks. The need for more sq inches of surface area to replenish the vapor was their battle cry. The real issue is how it applies to RV's...it doesn't; and this next level conversation is essentially over the top.

Thank you all for you patience and help!
Liquid surface area is the key to supplying large demands for LP gas. Ever see a 20# cylinder with frost on the outside? The top frost line is the liquid level. What creates that frost is temperature conversion-when liquid boils/converts into a gas so quickly it chills the steel tank enough to condense water from the atmosphere then freeze it into frost/ice.

Now, put exactly the same gas demand on a 40# cylinder, and it will not accumulate frost on the outside of the tank. Reason_ the increased surface area of the LP liquid and tank material.
__________________
2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy
Ray,IN is offline   Reply With Quote
Old 12-19-2016, 05:57 AM   #74
Senior Member
 
Join Date: Jun 2015
Posts: 234
I have a 2016 Winnebago journey 40 r. We have now had it about 6 weeks. We have 2 propane furnaces that work sometimes. Local RV shops can't get it in for warranty work ( lots ) until the end of January. Both will rarely produce heat at the same time. Either one by its self will work for hours and then just shut down. I'm thinking that when they first filled my tank they did not do the purge and I have air in my tank. My question now is how do I get the air out? When the furnaces stop working it is like they are running out of fuel. Thermostat is calling for gas but they are not running. I replaced the thermostat so I don't think that's the problem.


Sent from my iPhone using iRV2 - RV Forum
gcamper is offline   Reply With Quote
Old 12-19-2016, 06:23 AM   #75
Senior Member
 
MN_Traveler's Avatar
 
Join Date: Apr 2012
Location: Minneapolis, MN
Posts: 630
Quote:
Originally Posted by gcamper View Post
I have a 2016 Winnebago journey 40 r. We have now had it about 6 weeks. We have 2 propane furnaces that work sometimes. Local RV shops can't get it in for warranty work ( lots ) until the end of January. Both will rarely produce heat at the same time. Either one by its self will work for hours and then just shut down. I'm thinking that when they first filled my tank they did not do the purge and I have air in my tank. My question now is how do I get the air out? When the furnaces stop working it is like they are running out of fuel. Thermostat is calling for gas but they are not running. I replaced the thermostat so I don't think that's the problem.


Sent from my iPhone using iRV2 - RV Forum

I would think the hat any air in there initially would pretty quickly be carried out with the outgoing LP. especially after "hours". I would look elsewhere for a problem. Could the regulator be frosting? If you have a gas stove, when he furnaces stop working can you still get gas flow at the stove?
__________________
- 2012 Fleetwood Expedition 36M -
MN_Traveler is online now   Reply With Quote
Old 12-19-2016, 06:36 AM   #76
Senior Member
 
Join Date: Jun 2015
Posts: 234
Regulator doesn't seem to be frosting. Hard to tell when they are shutting down. They will run fine all day and then I will wake up during the night noticing the temp drop. I get up to find they are not working but the thermostat is calling for gas. Sometimes I can shut them off and restart them sometimes they will restart and sometimes only run for a short period of time.


Sent from my iPhone using iRV2 - RV Forum
gcamper is offline   Reply With Quote
Old 12-19-2016, 06:57 AM   #77
Senior Member
 
Join Date: Jul 2014
Posts: 26,782
Most likely any air is long gone.

Moisture in the propane may be your problem. They can add some stuff to fix that. Call a propane dealer and discuss it with them.
twinboat is offline   Reply With Quote
Old 12-19-2016, 07:01 AM   #78
Senior Member
 
Join Date: Nov 2005
Posts: 3,826
Quote:
Originally Posted by Gary RVRoamer View Post
There is nothing "fraudulent" about that. You are buying LP (Liquified Petroleum) gas, not "propane" or "butane". In warmer climates, the LP blend typically contains a higher percentage of butane because that performs better at higher ambient temperatures. Butane-rich LP, however, may not work well if you move to a cold climate because it doesn't vaporize as well at low temps. The bottom line is that the LP blend is a regional difference, not malfeasance on the part of the retailer.
As mentioned earlier all "LPG" is not the same. Technically to be legally sold as HD-5 "liquid propane gas" the mixture must contain at least a minimum of 90% propane gas and less than 5% butane and ethane.

The term "LPG" is used for 2 commercially available gasses. It can be either Liquid "Petroleum Gas" which can contain as little as 60% propane, or Liquid Propane Gas which must contain at least 90% propane. Liquid Propane Gas will vaporize down to -44*F. Liquid Petroleum Gas may not vaporize below 33*F depending on the amount of Butane in the mixture.

To be sure you're getting Liquid Propane Gas as opposed to Liquid Petroleum Gas ask the dealer if it meets the HD-5 standard.

Here's a little more information on the subject.
https://en.wikipedia.org/wiki/Propane
__________________
Hikerdogs
2013 Adventurer 32H
Hikerdogs is offline   Reply With Quote
Old 12-19-2016, 07:36 AM   #79
Senior Member
 
ScottyBye's Avatar
 
Join Date: Jul 2013
Location: Calgary, Alberta, Canada
Posts: 596
Quote:
Originally Posted by gcamper View Post
Both will rarely produce heat at the same time. Either one by its self will work for hours and then just shut down.

When the furnaces stop working it is like they are running out of fuel. Thermostat is calling for gas but they are not running.


Sent from my iPhone using iRV2 - RV Forum

Have you checked the outlet pressure at the regulator. This is essential for proper LP vapor supply to the appliances. Pressure should be at 11" WC when at least 50% of gas appliances are running.
__________________
2008 Fleetwood Southwind 36D
8.1L Vortec Gas with 5SP Allison Tranny
W-24 Workhorse Chassis
ScottyBye is offline   Reply With Quote
Old 12-19-2016, 03:27 PM   #80
Senior Member
 
Join Date: Jun 2015
Posts: 234
They ran fine all day today. I guess I'll wait and let the experts work on it.


Sent from my iPhone using iRV2 - RV Forum
gcamper is offline   Reply With Quote
Old 12-19-2016, 04:39 PM   #81
Senior Member
 
ScottyBye's Avatar
 
Join Date: Jul 2013
Location: Calgary, Alberta, Canada
Posts: 596
Intermittent problems are the hardest to fix because the issue usually has to be present in order to fix it. Usually,,,,
__________________
2008 Fleetwood Southwind 36D
8.1L Vortec Gas with 5SP Allison Tranny
W-24 Workhorse Chassis
ScottyBye is offline   Reply With Quote
Old 12-20-2016, 05:10 AM   #82
Senior Member
 
Join Date: Jun 2015
Posts: 234
It's 12 degrees outside and both of the furnaces have now been working correctly for the last 24 hours. I'm wondering if they did not purge my tanks when then first filled them and I have just now worked all the air out. We had a really bad dealer. That's another topic!


Sent from my iPhone using iRV2 - RV Forum
gcamper is offline   Reply With Quote
Old 12-20-2016, 06:00 AM   #83
Senior Member
 
Murf2u's Avatar
 
Join Date: Aug 2011
Location: Near Toronto, Canada
Posts: 1,842
Filling Butane to 80%

Quote:
Originally Posted by firedoc View Post
Does surface area of the exposed fuel come into play?
Quote:
Originally Posted by select55 View Post
no and that's my point all u need is the same volume area to accept the same expansion

That's completely false, unless you misspoke and are talking strictly about physical expansion and not the quantity of vapour produced.

Expansion and evaporation are two completely different issues and one really has nothing to do with the other.
__________________
Ted 'n' Laurie, plus Jackson (aka Deputy Dog, the Parson Russell Terrier 'fur kid') and, Rylie (who crossed the Rainbow Bridge June 14, 2012).
Murf2u is offline   Reply With Quote
Old 12-20-2016, 08:30 AM   #84
Senior Member
 
Join Date: Apr 2015
Location: Rogers, AR
Posts: 1,421
gcamper, a couple of things you might want to think about in relation to how your furnaces are operating.
If one of the furnaces will run for hours, there's probably no air in the lines. The liquid vaporization rate can be affected by the outside temperature. If it's warmer outside, the liquid may vaporize fast enough to supply vapor to both furnaces, then as it gets colder, the rate could slow down to a point both furnaces can not be run at the same time, and it could continue to slow to where one furnace would require more than what will vaporize. Have you compared the temperature changes in relation to how the furnaces are operating?

Another thing to keep in mind is that the available vapor is dependent on the liquid surface area available to evaporate. Since the tank is round and laying on it's side, that's an assumption, and was filled at the dealer, the liquid level in the tank will be high and results in a smaller liquid surface area to evaporate. As you have used some of the gas, the liquid level will drop and as it reaches the center (1/2 full) point of the tank, the liquid surface area will increase resulting in more surface area to evaporate.

You last said both furnaces are working. It could be a combination of the temperature and liquid level in the tank.


I love this kind of thread and feel like I've learned a lot about LP gas. There is also some "crap" posted here (as in many threads) but if you just sort through it all, much good information has been provided.
Than you to all that has participated.
__________________
2019 Fleetwood Discovery LXE 40M w/2012 CRV toad
alank is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Butane bottles Tench MH-General Discussions & Problems 2 09-09-2016 03:29 PM
filling butane jamescook RV Systems & Appliances 4 04-17-2014 06:20 AM
Refrig.Runs on Butane only BLUEDOG MH-General Discussions & Problems 4 09-29-2010 06:12 PM
Trailer has Butane Appliances Can I Use Propane? MarvinD Vintage RV's 5 06-08-2010 07:26 AM
LP filling Ol'Joe RV Systems & Appliances 8 01-24-2009 04:44 AM


All times are GMT -6. The time now is 05:50 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.