Questions About Materials And Heat

[paulecia]

Hello, I am a designer working on a project where I need to find a material of relatively easy access that is good absorbing heat.

The project is about making an object meant to absorb the extra heat of a lamp, or a heater (any home appliance that radiates heat), to become warm and later serve for warming the body.

 

It should be dry, so water is not an option.

It should easily absorb heat, and hopefully retain it for a considerable amount of time.

 

In my research, I have seen some people talking of rocks as a second good option for this. Or even sand.

 

Would they?

If so, which kind of rock?

Could it be some kind of gravel?

How about sand?

 

I have been looking at specific heat capacities for different elements but I wonder if this the number I need in order to decide.

I have understood that it defines the amount of head needed to raise the temperature of a material in one degree.

I am a bit confused with this since in my case, the speed in which the material heats is also very important, it cannot be too slow, for it would not heat enough, or not too fast for it would loose heat too fast.

Is this also true? If a material heats at a certain speed, does that mean it will also lose temperature at the same speed?

 

I am pretty confused with this.

Any comments will help

Thanks!

[modest]

Hi, Paulecia

 

It should be dry, so water is not an option.

It should easily absorb heat, and hopefully retain it for a considerable amount of time.

 

So, you're looking for 3 factors.

1. 
    
   
2. You want something that is solid and will remain solid at the temperature of the lamp or heater or whatnot.
   
3. You want something that easily absorbs heat (ie something that has a high thermal conductivity)
   
4. You want something that holds a lot of heat per temperature change per volume (ie something that has a high volumetric heat capacity)
   

 

A further factor, as you say, is that the material is relativity accessible and cheap.

 

Some random and non-inclusive materials which would satisfy these requirements are brick, rock, and iron. Scrap iron actually has a volumetric heat capacity nearly as high as water and it easily conducts heat. Brick and Rock (and probably ceramics) have about half water's value. They would probably hold the heat longer than iron, but absorb it less readily.

 

You should probably remember that absorbing heat quickly can easily mean losing it quickly if the storage material is not well insulated.

 

~modest

[Qfwfq]

Waxes typically have a considerable latent heat and their melting point is usually reasonable for your purpose, which enhances the effect compared to a material that doesn't melt. Look up the melting properties of waxes; maybe there are suitable materials of other kinds but wax is what comes to my mind.

 

Basically, the advantage is that it can absorb and later release quite a bit of heat at the melting point, instead of by increasing and then decreasing its temperature. For body warmth, you don't want a temperature too high but you need it to be sufficient, so the right kind of wax would give you the required effect in a suitable, narrow range.

 

I am a bit confused with this since in my case, the speed in which the material heats is also very important, it cannot be too slow, for it would not heat enough, or not too fast for it would loose heat too fast.

Is this also true? If a material heats at a certain speed, does that mean it will also lose temperature at the same speed?

You certainly want the material per se to be a quick absorber, but it works both ways unless you surround it with insulation until the heat is needed, as Modest already suggested.