Sun 22 Jul, 2018 1:52 am
Orion wrote:
So you're going to double down on this?
Orion wrote:
I didn't misquote you. You stated something that is physically impossible, not something that "usually" doesn't happen. You'd need to rejigger the laws of thermodynamics if you want a hotter body to emit less energy than a colder one.
jdeks wrote:Increase the insulation even more, and you can potentially hold so much heat that the bag skin will then warm, even with the consequent increase in radiant heat loss. In this case,you will indeed be losing more heat energy, but youd want to be - or you'd probably overheat.
Sun 22 Jul, 2018 2:52 am
jdeks wrote:Orion wrote:
So you're going to double down on this?
On what - reality?
It's all there in black and white, champ.Orion wrote:
I didn't misquote you. You stated something that is physically impossible, not something that "usually" doesn't happen. You'd need to rejigger the laws of thermodynamics if you want a hotter body to emit less energy than a colder one.jdeks wrote:Increase the insulation even more, and you can potentially hold so much heat that the bag skin will then warm, even with the consequent increase in radiant heat loss. In this case,you will indeed be losing more heat energy, but youd want to be - or you'd probably overheat.
Second time I've had to repeat myself, and spit out the words you're trying to put in my mouth. Quit trying to turn this thread into a p155ing contest
Sun 22 Jul, 2018 8:06 am
Orion wrote:jdeks wrote:Okay I'm goinna lay this out in a bit more detail. Whether folk read it is up to then, but dont come back at me unless you get to the bottom.
Heat energy creeps from the body outwards through the insulation, warming it as it goes. The speed of this is pushed by temperature difference, at first between the warm body and the inner skin of the bag, then between the warming inner skin and the first 'layer' of down, then between this layer and the next, and so on, right up to the outer skin.
So you're going to double down on this?
I didn't misquote you. You stated something that is physically impossible, not something that "usually" doesn't happen. You'd need to rejigger the laws of thermodynamics if you want a hotter body to emit less energy than a colder one. I thought you'd recognize that but instead you came back with a painfully long hand waving attempt to explain it all away. It was hard to read all that as it just dug the hole deeper.
Sun 22 Jul, 2018 8:10 am
Sun 22 Jul, 2018 8:28 am
Sun 22 Jul, 2018 9:47 am
Orion wrote:So a really warm bag will result in faster heat loss?
jdeks wrote:Takehome message here is that it's an interlinked multivariable system. It's not just "more x = more y".
Sun 22 Jul, 2018 9:54 am
Warin wrote:
The system can be simplified ... and modelled as one thermal path from the bags outer to one heat sink. At that point the argument falls down. No amount of argument by trying to make the model on the inside of the sleeping bag more complex changes the outside model.
The statement stands that an increase in the bags insulation will lead to an in the bags skin temperature is correct.
Warin wrote:
However, I think, jdeks argument is about the moisture/humidity in the bags insulation...
Sun 22 Jul, 2018 10:39 am
Huntsman247 wrote:Warin wrote:Neo wrote:Full bladder, better to get up and pee as the body puts it's heat to the bladder and extremities get cold.
Better to pee into a bottle .. and then use the bottle as a hot water bottle untill it cools.
This way you relieve the bladder, don't waste heat getting out of the bag cooling your body, bag and tent, and make use of the heat in your pee.
As long as you don't recycle it further I won't judge
Sun 22 Jul, 2018 3:04 pm
jdeks wrote:You're not getting 'sweaty' because you're cold. You're constantly perspiring and emitting water vapor, you're in a cold alpine environment with high relative humidity, and your bag is too cold to keep your sleep zone warm enough to keep your perspiration as vapor. Bags, jackets and everything else is only breathable if the water is evaporated. When the whole bag, and well as you and your pants, are under dew point, that goes out the tent door.. Hence it's gathering as 'clammy' condensate on you and the inside of your bag.
Go try it somewhere REAL cold like Majura, and you'll get to wake up with the wonderful experience of having your own clothes frozen to the inside of your bag., while you're still wearing them.
Cinching the bag closed, in this case, isn't the main problem. It's just not helping, and if anything, hindering moisture evacuation. As neilmny's story illustrated, if you're warm enough but the rel humidity is high enough to make your feet sticky, a bit of air circulation fixes it.
Other angle is just get warmer, so the moisture evaporates effectively. In which case, cinch away!
neilmny wrote:My mat is an Exped Synmat UL 9. This is a review I found http://backcountryskiingcanada.com/Expe ... L-9-Review
The specs -
Weight: 795g / 1.75lb
Dimensions: 197× 65cm / 78 × 26"
Packed Size: 27 × 13cm / 10 × 5"
Thickness: 9cm / 3.5"
R-value: 6.0
Colour: Yellow
Franco wrote:The Therm A Rest XTherm is rated at 5.7
The Exped Downmat UL Winter M is rated R7.
There are others but those two are a bit lighter.
Warin wrote:Huntsman247 wrote:Warin wrote:
Better to pee into a bottle .. and then use the bottle as a hot water bottle untill it cools.
This way you relieve the bladder, don't waste heat getting out of the bag cooling your body, bag and tent, and make use of the heat in your pee.
As long as you don't recycle it further I won't judge
You did ask ?
Read 'Skeletons in the Zahara' (note the Z rather than an S) for a comparison of the taste and usefulness of human, camel and horse pee. An interesting read.
Tells the story of an American ship wreck on the Moroccan coast ~1815.
Sun 22 Jul, 2018 3:32 pm
Sun 22 Jul, 2018 3:58 pm
north-north-west wrote:Thanks to the physics geeks from here too.
And thanks to Huntsman for raising this one. It happens to me sometimes when I sleep in the car and I've always assumed it was due to sweat from overheating, even though I've felt chilled. It's great to finally understand what's going on.
Sun 22 Jul, 2018 4:12 pm
neilmny wrote:north-north-west wrote:Holy crap can someone explain in dumarse terms what all this means.....we cretins need to understand too.
Sun 22 Jul, 2018 4:43 pm
In summary our bodies constantly create vapour (sweat if our bodies overheat).neilmny wrote:north-north-west wrote:Thanks to the physics geeks from here too.
And thanks to Huntsman for raising this one. It happens to me sometimes when I sleep in the car and I've always assumed it was due to sweat from overheating, even though I've felt chilled. It's great to finally understand what's going on.
Holy crap can someone explain in dumarse terms what all this means.....we cretins need to understand too.
Sun 22 Jul, 2018 5:14 pm
Huntsman247 wrote:neilmny wrote:north-north-west wrote:Thanks to the physics geeks from here too.
And thanks to Huntsman for raising this one. It happens to me sometimes when I sleep in the car and I've always assumed it was due to sweat from overheating, even though I've felt chilled. It's great to finally understand what's going on.
Holy crap can someone explain in dumarse terms what all this means.....we cretins need to understand too.
if you push the sleeping bag past is thermal rating
Sun 22 Jul, 2018 5:31 pm
Just trying to simplify it. But in my case its not the breathability of the bag. Not that it isn't the reason in some cases. But for the breathability to really be a factor the perspiration has to remain as a vapour. Otherwise it could be the most breathable bag in the world but your not addressing the root cause and would still be wet. So I don't think it should be 'past it's breathability'. I'm certainly not steaming when I sleep if it was breathability then this would occur even in warmer temps. I'm not using a bivvy sack. But yes it could be better written as 'past what its rated or designed for'.Warin wrote:Huntsman247 wrote:neilmny wrote:
Holy crap can someone explain in dumarse terms what all this means.....we cretins need to understand too.
if you push the sleeping bag past is thermal rating
Strictly speaking the thermal rating is its R rating.
And that says nothing about its 'breathablity'.
For that you need g/m2 per 24 hour period. That is grams per square meter per 24 hours.
So the above should read "if you push the sleeping bag past it's breathablity "?
Beyond the R rating you simply get cold.
Beyond the breathability you or the bag gets wet .. and then you 'll get colder.
Sun 22 Jul, 2018 8:09 pm
Huntsman247 wrote:In summary our bodies constantly create vapour (sweat if our bodies overheat).
I figured that this moisture would pass through the bag as sleeping bags are breathable. But as has been brought out by the way that the sleeping bag works, if you push the sleeping bag past is thermal rating it is unable to keep the area directly around you warm enough to keep the vapours coming out of your body vapours. These vapours condensate on and around you. Leaving you damp as I and others have experienced. You survive and I could probably push the bag in even colder temps but it leaves you uncomfortable.
So even if you sleep somewhere dry, whether it be under an overhang or a night with 0 humidity if your bag isn't up to the ambient temp you'll still get clamy from your body vapours when cold enough.
I'm thinking you could probably get away with pushing the limits of a bag by throwing a couple hand warmers in the bag that can last the night. That they would produce enough heat possibly to keep the bag heated enough to keep the body vapours as vapours.
Warin wrote:So the above should read "if you push the sleeping bag past it's breathablity "?
Beyond the R rating you simply get cold.
Beyond the breathability you or the bag gets wet .. and then you 'll get colder.
Wed 25 Jul, 2018 8:15 am
Wed 25 Jul, 2018 9:25 am
north-north-west wrote:All this sciencey stuff has got me thinking (never a good idea) about the 'wet foot' phenomenon with the sleeping bag.
Now, the idea of it being from vapour emitted by the feet overnight, passing through the bag and collecting on shell doesn't make sense to me. Maybe thatt's because I doon't know enough about the science but . . . with poor peripheral circulation especially, wouldn't the majority of the vapour be from the torso and, therefore, the outer dampness (and I'm talking about those mornings with the shell wet when the inside is dry) should be more on the upper area than around the foot.
So . . . but with warmth being transmitted (for want of a better word) ing through the inner lining and the insulation into the shell material, if the feet are colder and the torso/head area warmer (and this could be exacerbated by the greater dead air space around the feet), could there be a sufficiently significant temperature differential between the material of the outer shell in those areas for vapour inside the tent to condense on the foot rather than elsewhere?
It seems logical to me, but I don't know enough about how this works. Does the science contradict that?
Wed 25 Jul, 2018 9:38 am
Wed 25 Jul, 2018 10:16 am
Wed 25 Jul, 2018 10:20 am
north-north-west wrote: would the lower surface area lead to less perspiration and thus less vapour . . . )
Wed 25 Jul, 2018 10:34 am
jdeks wrote:Its complex stuff! Essentially weather forecasting for your own microclimate. Just be thankful you don't have to do.it for a 60000ft column of air! And then have everyone complain that the fog cleared by 10 am but 'YOU said it'd clear by NINE Am!!!"....
What problems are you having, and with what sleeping rig?
Mon 06 Aug, 2018 3:02 pm
Tue 07 Aug, 2018 3:49 pm
Huntsman247 wrote:Just got a new upgraded sleeping bag. Shout out to jdeks. He had a few new sleeping bags from a trip that never got off the ground. Just got it today, an unused, tags still on it, mountain hardware phantom flame. Trying to get out and try it in the next week and will report how on how the claminess goes.
jdeks has a few more sleeping bags and mats if anyone is interested.
He's got bags from about 5+ to -12 and a -7 quilt but its 2nd hand...
DM him if you're interested.
Anyways I received my bag in excellent condition and thought to give others some peace of mind if anyone's looking to buy a new sleeping bag.
Cheers jdeks.
Tue 07 Aug, 2018 4:46 pm
Huntsman247 wrote:I've never really noticed this before but last couple of trips I've slept in around -5 and have had to cinch up the bag around my head. I was warm... just but not hot. I'm a cold sleeper. But I woke up each time around 4.30am feeling cold and clammy needing to drape my jacket over my body and seem to feel slightly cold and rather damp till I wake up...
...
I've researched this a bit and most people say that your too hot and therefore sweat but I'm just feeling warm.
Wed 08 Aug, 2018 4:42 pm
GPSGuided wrote:Huntsman247 wrote:... a sudden change in one's ability to adapt to the cold is suggestive of some body changes ...
Sun 12 Aug, 2018 7:15 pm
Sun 12 Aug, 2018 8:54 pm
Huntsman247 wrote:Ok. Just got back from a trip. Jdeks was spot on. Conditions wasn't quite as cold but it still was well below zero, really windy and raining all night. Rather miserable actually.
Anyways, woke up dry and not clammy! However I did notice a little bit of condensation on the inside of the outer fabric. Although I suspect that it was more due to how much moisture was in the air. Or the fact that I had the bag half unzipped till I woke up in the mid morning a bit nippy and zipped it up. Either way the original bag was definately not warm enough for the conditions and my body temps. Thanks to everyone's thoughts!
© Bushwalk Australia and contributors 2007-2013.