In reply to daWalt:
My understanding of thermodynamics is virtually nil. I'm not totally getting the 'more mass == more energy usage' thing. Here's my thinking:
If you have the following layers:
Skin: 33° in a toasty sleeping bag?
Inner tissues: 37°
Bag full of fluid inside body: 37°
The cooler skin is 'trying to make' the the inner tissues colder. Those tissues are actively expending energy to stay 37°. The bag of 37° fluid is contained within the tissues which are actively maintained at 37°, so there's no net loss/gain between the liquid and the container,
irrespective of the mass of the liquid.
If the body temperature were to drop to 36°, then the tissues would actually be heated slightly by the warmer liquid, until they reached equilibrium (tissues now slightly warmer, liquid cooler). In this case, a larger mass of liquid would heat the surrounding tissue more (and itself, cool less) before reaching equilibrium. (This equilibrium may never occur if the skin were cooling the tissues faster than the liquid - and tissues themselves - were heating the tissues.)
There is no direct gain or loss of heat from the liquid to the skin, without first heating or cooling the intervening tissues.
Assumption here is that your bag of liquid is already 37°. If you're drinking Ice Cream Smoothies, then it's going to need heated. Here, I can see that more smoothie mass = more energy needed to heat it up. In terms of
keeping something at a given temperature, as long as you're putting in heat as fast as it's being lost, I don't see how mass is a primary factor. I don't see how greater mass would cool quicker. Given similar insulation, surface areas etc. I'd expect a greater mass to retain heat better/longer.
(I suspect there are large parts of my thinking here which are totally incorrect, but I'd be interested to know which bits, and why, thus possibly gaining some understanding of thermodynamics.)
Post edited at 16:39