DougPaul
Well-known member
Correct.
Keeping a liquid at a constant temp requires no energy if there is no heat flow to or from the outside world. And since the bladder is surrounded by flesh at the same temp, so there is no such heat flow.
Doug
Requesting Advice on Winter backpacking
- Thread starter ADKnBVI
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Keeping a liquid at a constant temp requires no energy if there is no heat flow to or from the outside world. And since the bladder is surrounded by flesh at the same temp, so there is no such heat flow.
Doug
Oldsmores
New member
Hmmmm, this would be true if the thermal system ended at the skin. However, the body (including the bladder) is constantly losing heat to the outside world. It's been a long time since thermodynamics, but I think that the amount of energy required to keep a body at a constant temperature in a fixed ambient temperature environment is proportional to the mass of the body. IF that's correct, then losing the mass of the pee (maybe a pound at most) would make a very slight change (1/150 for a 150 lb. person) in the energy you burn to stay warm.
delta-q = mc delta-t
peeing lowers your m (mass). c is the constant for the mass, where water is 1. delta-t is the change in temperature. delta-q is the change in the amount of thermal energy transferred (thanks, Doug!)
http://en.wikipedia.org/wiki/Heat_transfer
Tim
peeing lowers your m (mass). c is the constant for the mass, where water is 1. delta-t is the change in temperature. delta-q is the change in the amount of thermal energy transferred (thanks, Doug!)
http://en.wikipedia.org/wiki/Heat_transfer
Tim
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DougPaul
Well-known member
Your skin and breathing system are losing heat to the outside, but the urine in your bladder has no direct contact with the outside and therefore cannot lose or gain heat directly from the outside.
Your memory is misleading you. An object (or container of liquid) will stay at a constant temp unless heat is added or removed.
A net addition of heat will raise the temp of the object, a net loss of heat will lower the temp (assuming there are no phase changes or chemical reactions). The "specific heat capacity" is the ratio of the amount of heat energy required to increase the temp of a specific mass of a substance by a specific amount. http://en.wikipedia.org/wiki/Specific_heat_capacity
As noted above, the premise is wrong so the conclusion does not follow.
If we model the human body as 150 lb of water in an idealized (perfectly insulating, no thermal mass) container and add the appropriate amount of heat, the temp will go up 1 degree. If we use 149 lb of water, it will take 149/150 amount of heat to raise the temp 1 degree. This, however, is the energy required to change the temp. In either case, the temp will stay constant if no heat is added or lost.
Doug
DougPaul
Well-known member
Missing a definition:
delta-q is the change in the amount of thermal energy transferred.
Thanks,
Doug
Chip
Well-known member
For us dummies: Needing to pee prevents decent sleep. The sooner you take care of it, the better your chances of a night's rest. Same thing with being cold: put a hat or fleece hoodie on, add a layer. Being cold prevents good rest.
Pee to Sleep ! Hike to Live !
Pee to Sleep ! Hike to Live !
Oldsmores
New member
It doesn't have to. There's a constant transfer of heat from your body, assuming ambient temperature less than 98.6°. The heat loss is from the body as a whole, and the bladder is part of that system.
[/QUOTE]Your memory is misleading you. An object (or container of liquid) will stay at a constant temp unless heat is added or removed.
A net addition of heat will raise the temp of the object, a net loss of heat will lower the temp (assuming there are no phase changes or chemical reactions). The "specific heat capacity" is the ratio of the amount of heat energy required to increase the temp of a specific mass of a substance by a specific amount. http://en.wikipedia.org/wiki/Specific_heat_capacity[/QUOTE]
My point exactly: heat is removed from the body (as you pointed out above) through the skin and breathing. It isn't removed from the skin and lungs only, but from the body. Otherwise, you'd never get hypothermic, your skin would just freeze.
[/QUOTE]As noted above, the premise is wrong so the conclusion does not follow.
If we model the human body as 150 lb of water in an idealized (perfectly insulating, no thermal mass) container and add the appropriate amount of heat, the temp will go up 1 degree. If we use 149 lb of water, it will take 149/150 amount of heat to raise the temp 1 degree. This, however, is the energy required to change the temp. In either case, the temp will stay constant if no heat is added or lost.
Doug[/QUOTE]
I think that's what I said. What I don't understand is why you think that no heat is lost. We lose heat anytime the ambient temp is less than body temp. The goal is to produce sufficient heat through metabolism to maintain a constant temperature. Our bodies have to produce (marginally) less heat to maintain 149 lbs. at 98.6° than to maintain 150 lbs. at 98.6°.
OK, I never did figure out how to put multiple quotes in a post.
Now we can toss in surface-to-volume ratio. Or, why smaller people get cold faster than larger people. Or, why you curl up when you're cold (decreasing the surface area.) If you've ever owned a cat, you already know how this works. Sprawled in the summer, curled up in a ball (over a hot water pipe in the floor) in the winter.
Tim
Tim
But the rate of heat loss varies with surface area (as bikehikeskifish implied), not with the volume or mass. Heat is lost from your skin and lungs only--it's just then heat is taken from elsewhere in the body to rewarm those points. Unless emptying your bladder reduces your surface area (in which case you've waited way too long), it won't affect the rate of heat loss. Since it decreases your mass, it will (slightly) increase the rate at which your temperature drops. It's the same reason a full refrigerator lasts longer in a power outage.
DougPaul
Well-known member
The original conjecture was "Holding it in does consume some energy and does cool you down.". This is basically saying that you lose heat directly from the urine in your bladder, which is incorrect. (This says nothing about other avenues of heat loss from your body.) Another way of saying the same thing is that your total heat loss rate is greater when your bladder is full than when it is empty, again, false.
Chip is correct about what to do in the field: if you need to pee, then pee. If you are cold, put more insulation on.
Doug
Oldsmores
New member
ADKnBVI
New member
Wow... I can't believe where this thread has gone... LOL
Thanks Chip for the common sense approach! I have to say that running outside for just a few seconds is my preferred way of dealing with this situation. The down sleeping bag is still warm when I get back, and as a woman, I'm UNWILLING to try the pee bottle in the tent despite the description of "how to do it" in Allan and Mike's Backcountry Winter Adventure book.
I was a ChemE once, before 20 years in IT fried my brain. I don't remember enough of my thermodynamics classes to help me with backcountry winter camping.
Valerie
For us dummies: Needing to pee prevents decent sleep. The sooner you take care of it, the better your chances of a night's rest. Same thing with being cold: put a hat or fleece hoodie on, add a layer. Being cold prevents good rest.
Pee to Sleep ! Hike to Live !
Thanks Chip for the common sense approach! I have to say that running outside for just a few seconds is my preferred way of dealing with this situation. The down sleeping bag is still warm when I get back, and as a woman, I'm UNWILLING to try the pee bottle in the tent despite the description of "how to do it" in Allan and Mike's Backcountry Winter Adventure book.
I was a ChemE once, before 20 years in IT fried my brain. I don't remember enough of my thermodynamics classes to help me with backcountry winter camping.
Valerie
J.Dub
Active member
If it wasn't glowing yellow already, it would be after you used it!
I'll have to try the duct-tape-marking-trick to differentiate the pee bottle from the bottle of hot Gatorade I usually take in the bag at night. (That way I can go by feel and not have to flip the headlamp on in the middle of the night.)
Definitely! My other Nalgenes either have no tape at all or a ring of tape around them (to keep them from falling out of my mittened hands in the winter). For the bottle of doom, I took about a dozen layers of tape and made a vertical stripe on the bottle. Even half-asleep, it can't be mistaken.
As a side note to the duct tape, I always wrap some tape several times around the bottle to use in a pinch. It has helped to mean a broken tent pole, snowshoe, ski skin, and ski pole before. I'm sure you could use it to help make a splint if needed.
Chip
Well-known member
Can't blame you there.I'm UNWILLING to try the pee bottle in the tent despite the description of "how to do it" in Allan and Mike's Backcountry Winter Adventure book.
My simple point is: as opposed to rolling over and hoping it'll go away, I find it's better to deal with the situation ASAP, whatever it is, if you hope to actually sleep. This is true for 1 nighters or the first night. By the second night I usually sleep well regardless.
KayakDan
New member
and as a woman, I'm UNWILLING to try the pee bottle in the tent despite the description of "how to do it" in Allan and Mike's Backcountry Winter Adventure book.
Valerie
It's entirely possible,and Mrs KD has it figured out-no accidents in 10 years. Just make sure your sleeping bag is clear if there's a "mishap".
Heck,I don't even get out of my sleeping bag! Hey,it's cold out there!
As for killing time before you go to sleep. I have "The 9 o Clock Rule". Nobody sleeps before 9,cause you'll be wide awake at 4AM,and I'm not gonna break camp in the dark! Mrs KD just loves this rule
We just spend a lot of time eating. Hot soup as soon as camp is set up,then snacks,then the main event. Play electronic Yahtzee for a while,take a short hike sometimes,then it's time for dessert and tea before bed.
Another vote for down booties too! We snagged 2 pairs of MH SubZeroes before they were discontinued.Toasty!
Another trick that works nicely in deep snow is digging a "boot pit" at the end of the tent in the vestibule area. Now you can sit to put boots off/on,and I put the stove (propane/butane-NOT white fuel!) in the bottom of the pit so we can cook from the tent(lots of ventilation) and it takes a bit of the chill out of sitting in the tent.
DougPaul
Well-known member
Try practicing in the shower to learn/check out the technique without risk of consequences if you miss.I'm UNWILLING to try the pee bottle in the tent despite the description of "how to do it" in Allan and Mike's Backcountry Winter Adventure book.
Doug
wardsgirl
Active member
as a woman said:
DougPaul
Well-known member
Certainly consider non-Nalgene containers/bottles. Perhaps a wider mouth will make aiming easier. 500-1000ml (8-16oz) is probably a reasonable size. Just make sure it has a reliable lid so it doesn't leak in your sleeping bag. As I suggested earlier, just try it out in the shower to make sure that it will work in the field.
Booties are a lot faster to put on and off than are boots. And you can wear them inside your sleeping bag on cold nights.
Doug
