The Naked Scientists

The Naked Scientists Forum

Author Topic: The "thing" with the best heat retention  (Read 25604 times)

dentstudent

  • Hero Member
  • *****
  • Posts: 3146
  • FOGger to the unsuspecting
    • View Profile
The "thing" with the best heat retention
« on: 15/08/2007 10:18:11 »
What element, product or, er, thing best retains heat? It would have to be something that doesn't generate it's own, and it should be a solid.

I'm expecting a harsh winter, and want to make a decent hand-warmer ;)

Let me just quantify it a bit - if there were a series of these "things" all heated to say 100°C, which would retain the heat the longest?
« Last Edit: 15/08/2007 11:27:49 by dentstudent »

syhprum

  • Hero Member
  • *****
  • Posts: 3333
    • View Profile
The "thing" with the best heat retention
« Reply #1 on: 15/08/2007 15:19:53 »
I don't think 100°C would be a very suitable materiel for a hand warmer, what you want is some materiel that undergoes a phase change from solid to liquid at about 30°C giving up its latent heat.

lyner

  • Guest
The "thing" with the best heat retention
« Reply #2 on: 15/08/2007 16:03:54 »
A small amount of heat output and a lot of insulation around your hands is the most ideal. You have plenty of energy available in your body. The problem is your surface capillaries shutting off  and this makes your fingers cold.  If you just warm them up a bit and then insulate them - there are some brilliant gloves, these days - your own blood will keep them warm.
I remember being told by an experienced diver that  putting your hands into warm water  just before a cold dive was a really effective way of keeping them feeling warm for the next half hour as long as you had good gloves.
Of course, if you are in really extreme conditions, cold hands is the least of your worries.

another_someone

  • Guest
The "thing" with the best heat retention
« Reply #3 on: 15/08/2007 18:29:40 »
Going back to the specific question (rather than the perfectly valid alternative solutions to the underlying problem that have been suggested).

I don't know what would actually be the best materials as such, but there are as I see it 4 possible ways of retaining heat (not necessarily mutually exclusive).

Firstly, simply using a material with a high specific heat:

http://en.wikipedia.org/wiki/Specific_heat_capacity
Quote
Factors that affect specific heat capacity
  • Degrees of freedom: Molecules are quite different from the monatomic gases like helium and argon. With monatomic gases, heat energy comprises only translational motions. Translational motions are ordinary, whole-body movements in 3D space whereby particles move about and exchange energy in collisions (like rubber balls in a vigorously shaken container). These simple movements in the three X, Y, and Z–axis dimensions of space means monatomic atoms have three translational degrees of freedom. Molecules, however, have various internal vibrational and rotational degrees of freedom because they are complex objects; they are a population of atoms that can move about within a molecule in different ways (see animation at right). Heat energy is stored in these internal motions. For instance, nitrogen, which is a diatomic molecule, has five active degrees of freedom: the three comprising translational motion plus two rotational degrees of freedom internally. Not surprisingly, nitrogen has five-thirds the constant-volume molar heat capacity as do the monatomic gases.[2] See Thermodynamic temperature for more information on translational motions, kinetic (heat) energy, and their relationship to temperature.

  • Molar mass: When the specific heat capacity, c, of a material is measured (lowercase c means the unit quantity is in terms of mass), different values arise because different substances have different molar masses (essentially, the weight of the individual atoms or molecules). Heat energy arises, in part, due to the number of atoms or molecules that are vibrating. If a substance has a lighter molar mass, then each gram of it has more atoms or molecules available to store heat energy. This is why hydrogen—the lightest substance there is—has such a high specific heat capacity on a gram basis; one gram of it contains a relatively great many molecules. If specific heat capacity is measured on a molar basis (uppercase C), the differences between substances is less pronounced and hydrogen’s molar heat capacity is quite unremarkable. Conversely, for molecular-based substances (which also absorb heat into their internal degrees of freedom), massive, complex molecules with high atomic count — like gasoline — can store a great deal of energy per mole and yet, be quite unremarkable on a mass basis

    Since the bulk density of a solid chemical element is strongly related to its molar mass, generally speaking, there is a strong, inverse correlation between a solid’s density and its cp (constant-pressure specific heat capacity on a mass basis). Large ingots of low-density solids tend to absorb more heat energy than a small, dense ingot of the same mass because the former comprises more atoms. Thus, generally speaking, there a close correlation between the size of a solid chemical element and its total heat capacity (see Volumetric heat capacity). There are however, many departures from the general trend. For instance, arsenic, which is only 14.5% less dense than antimony, has nearly 59% more specific heat capacity on a mass basis. In other words; even though an ingot of arsenic is only about 17% larger than an antimony one of the same mass, it absorbs about 59% more heat energy for a given temperature rise.

  • Hydrogen bonds: Hydrogen-containing polar molecules like ethanol, ammonia, and water have powerful, intermolecular hydrogen bonds when in their liquid phase. These bonds provide yet another place where kinetic (heat) energy is stored.

Substance Phase cp Cp Cv
  J g-1 K-1  J mol-1 K-1  J mol-1 K-1
Air (Sea level, dry, 0 °C)  gas  1.0035  29.07
Air (typical room conditions)  gas  1.012  29.19
Aluminium  solid  0.897  24.2
Ammonia  liquid  4.700  80.08
Antimony  solid  0.207  25.2
Argon  gas  0.5203  20.7862  12.4717
Arsenic  solid  0.328  24.6
Beryllium  solid  1.82  16.4
Copper  solid  0.385  24.47
Diamond  solid  0.5091  6.115
Ethanol  liquid  2.44  112
Gasoline  liquid  2.22  228
Gold  solid  0.1291  25.42
Graphite  solid  0.710  8.53
Helium  gas  5.1932  20.7862  12.4717
Hydrogen  gas  14.30  28.82
Iron  solid  0.450  25.1
Lead  solid  0.127  26.4
Lithium  solid  3.58  24.8
Magnesium  solid  1.02  24.9
Mercury  liquid  0.1395  27.98
Nitrogen  gas  1.040  29.12  20.8
Neon  gas  1.0301  20.7862  12.4717
Oxygen  gas  0.918  29.38
Silica (fused)  solid  0.703  42.2
Uranium  solid  0.116  27.7
Water  gas (100 °C)  2.080  37.47  28.03
  liquid (25 °C)  4.1813  75.327  74.53
  solid (0 °C)  2.114  38.09
All measurements are at 25 °C unless otherwise noted.
Notable minima and maxima are shown in maroon.

The other option is to rely on phase changes (such as storing energy in some substance that melts at around 60°C).

Thirdly, using a reversible chemical reaction to store heat.

Fourthly, simply use a thermos flask (have a small surface of the material protruding from the flask, the material might be heated to well above 100°C, but since only a very small amount of the substance is exposed, so the rate of heat loss to the surrounding environment will remain low.

lyner

  • Guest
The "thing" with the best heat retention
« Reply #4 on: 21/08/2007 16:44:19 »
Electric, off-peak night storage heaters nearly all use some sort of refractory material which gets very hot and is kept in an insulating jacket. But I did come across one sort that used water. They were a bit bigger but had the advantage that, because the temperature difference between hot water and the room was relatively small, the actual heat transfer was less when the room got warmer - a sort of automatic regulating system.
Water does have a very handy specific heat capacity for something so common. But it's a bit special in a lot of  ways; it only needs a few trace chemicals to turn it into BEER - or US, for a start. And it's hardly at all poisonous.

RD

  • Neilep Level Member
  • ******
  • Posts: 7347
    • View Profile
The "thing" with the best heat retention
« Reply #5 on: 22/08/2007 17:34:46 »
I'm expecting a harsh winter, and want to make a decent hand-warmer ;)

Quote
Self-Heating Electric Gloves

• Heats up to 40 degrees in 5 minutes
• Water resistant
• Great for the active outdoor person
• Safely concealed heating element warms the upper palm and radiates out to the fingers
• Cosy lining provides extra warmth and eliminates heat loss
• Requires 3 x AAA batteries in each glove (Order Code: L29BJ for high-capacity rechargeable batteries)
• Constructed using the most advanced heating wire
• Batteries stored in a discrete pouch
• Available in two sizes

These water resistant heated gloves are great for hiking, skiing and hunting. The safely concealed heating element in the gloves is designed to warm the upper palm area and radiate out to the finger area. They have a cosy lining for extra warmth which also helps to eliminate heat loss. These would make an fabulous gift for the active outdoor person!
Requires 3xAAA batteries in each glove (not supplied) Order Code: L29BJ for high capacity rechargeable batteries
http://www.maplin.co.uk/Module.aspx?ModuleNo=47714&&source=14&doy=search

Soul Surfer

  • Hero Member
  • *****
  • Posts: 3347
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
The "thing" with the best heat retention
« Reply #6 on: 22/08/2007 22:05:37 »
Water is by far the material with the highest thermal capacity no other solid or liquid comes near.  For pedants lithium metal is almost the same as water. Hot water bottles have been used for years.  The reason for this anomalously high specific heat is that water has a very low molecular weight and is in effect a polymer to it stays a loquid to quite a high temperature.

The figure of 228 for gasoline in the table above must be wrong.  22.8 is more likely.

Water is just about the most amazing chemical there is but very few people realise this.

« Last Edit: 22/08/2007 22:16:46 by Soul Surfer »

neilep

  • Withdrawnmist
  • Too Much Free Time Level Member
  • **********
  • Posts: 20589
    • View Profile
The "thing" with the best heat retention
« Reply #7 on: 22/08/2007 22:10:53 »
Forget all the above !!

BAKED POTATOES !!



bake em, wrap em, stick em in your pocket !!...then...ewe can eat them !!

Karen W.

  • Moderator
  • Too Much Free Time Level Member
  • *****
  • Posts: 31545
  • "come fly with me"
    • View Profile
The "thing" with the best heat retention
« Reply #8 on: 22/08/2007 22:49:44 »
OOOOOOOH I love baked potatoes.. But Hand warmers eh?? LOL I actuall heard my grandma talk about doing just that as a young girl!

another_someone

  • Guest
The "thing" with the best heat retention
« Reply #9 on: 22/08/2007 22:56:46 »
Water is by far the material with the highest thermal capacity no other solid or liquid comes near.

Does not liquid ammonia exceed the specific heat of liquid water (but then, ammonia has a lower molecular weight than water, it simply also has the problem of having a lower boiling point).

syhprum

  • Hero Member
  • *****
  • Posts: 3333
    • View Profile
The "thing" with the best heat retention
« Reply #10 on: 23/08/2007 07:54:50 »
Although water is a very good heat storage materiel surely the best way to store heat is by means of a liquid to solid phase change.
Again water is very good but it occurs at the inconveniently low temperature of 0°C, what we need is some materiel where this phase change occurs in the 30-50°C region, any suggestions?.
My great grandmother (born 1855) used to recommend a quantity of decayed wood (touch wood) smouldering in a tin can.
« Last Edit: 23/08/2007 08:22:15 by syhprum »

another_someone

  • Guest
The "thing" with the best heat retention
« Reply #11 on: 23/08/2007 11:14:37 »
Although water is a very good heat storage materiel surely the best way to store heat is by means of a liquid to solid phase change.
Again water is very good but it occurs at the inconveniently low temperature of 0°C, what we need is some materiel where this phase change occurs in the 30-50°C region, any suggestions?.
My great grandmother (born 1855) used to recommend a quantity of decayed wood (touch wood) smouldering in a tin can.

You mean like this: http://www.thenakedscientists.com/forum/index.php?topic=9619.msg118015#msg118015
or this: http://www.thenakedscientists.com/forum/index.php?topic=8763.msg103883#msg103883

OK, not quite the phase change you probably had in mind, but a pertinent phase change at around the right temperature.
« Last Edit: 23/08/2007 11:17:32 by another_someone »

 

SMF 2.0 | SMF © 2011, Simple Machines