Can stones in a pot conserve energy?

democrates

I'm boling two eggs right now, and have two large stones in the pot to take up much of the rest of the space (I haven't got a smaller pot, yet).

My theory is that lot's of heat energy going into water is lost as it evaporates, so replacing much of it with stones which reach a temperature and stay that way means less heat loss. Thoughts?

Wishbone Ash

democrates wrote:

I'm boling two eggs right now, and have two large stones in the pot to take up much of the rest of the space (I haven't got a smaller pot, yet).

My theory is that lot's of heat energy going into water is lost as it evaporates, so replacing much of it with stones which reach a temperature and stay that way means less heat loss. Thoughts?

Would it not take a fair bit of energy to bring the stones to the optimum temperature? Get a tiny saucepan for boiling the eggs or throw them into the kettle when you are making the tea. If you really want to be really economically, don't store them in the fridge.

SolMate

Interesting. I've no idea whether you're right, but one passing question is whether the presence of the large stones slows up the boiling of the water and so use up more energy that way...?

I think the most important benefit of your strategy though is that, so long as you eat plenty of eggs, you will always have a good supply of hot rocks - an excellent in-law deterrent (as I'm sure you know, the main difference between in-laws and outlaws is that outlaws never promise to pay you back!)

S.

damiand

It would appear that all the stones are doing is taking up space and at the same time absorbing some of the heat of the water. The stones will release their heat back into the water as it cools down.

Dont know enough about science to be able to help but cleaver way of taking up space in the pot...:)

CJhaughey

What do the stones taste like after they have been boiled?

bonkey

democrates wrote:

I'm boling two eggs right now, and have two large stones in the pot to take up much of the rest of the space (I haven't got a smaller pot, yet).

Interesting idea....

My theory is that lot's of heat energy going into water is lost as it evaporates, so replacing much of it with stones which reach a temperature and stay that way means less heat loss. Thoughts?

I think your theory is slightly wrong, but the idea is probably correct.

The heat energy thats "lost" is the effort required to boil the water and keep it boiling long enough for heat-transfer to boil your eggs. Consider - if you used a 10-gallon saucepan to do a single egg, it would obviously be far more wasteful than a 1-pint saucepan! All you want is enough water to cover the eggs, with as little spare width in the pan as possible.....in otherwords, the less water you use, the more efficient it will be.

By adding stones, you are decreasing the volume of water you need to heat, and replacing it with stone. Whether or not this is energy-efficient will depend on how quickly the stone absorbs heat (and perhaps also how quickly it releases it again).

I would guess that its more energy efficient, but its not going to save the planet. I'm not sure the same logic would necessarily hold for longer cooking times (e.g. a stew).

jc

ircoha

Interesting post this.

To boil eggs u really need very little water, just enough to cover the bottom of the pan for the whole process.

'The specific latent heat of vaporization is the amount of heat required to convert unit mass of a liquid into the vapour without a change in temperature."

For water at its normal boiling point of 100 ºC, the specific latent heat of vaporization is 2260 kJ.kg-1. This means that to convert 1 kg of water at 100 ºC to 1 kg of steam at 100 ºC, 2260 kJ of heat must be absorbed by the water. Conversely, when 1 kg of steam at 100 ºC condenses to give 1 kg of water at 100 ºC, 2260 kJ of heat will be released to the surroundings.

Assuming an airtight lid and no water vapour escaping, the eggs will absorb the most of the heat released when the steam condenses. If u ever got scalded by steam, [not water vapour] u will know what I mean..
My point here is that we specify that the water must be boiling, so we are using the hugh amount of enegy to boil the water but the steam when condensing is nowhere near the eggs if they are covered with water.

The stones are a waste of energy, as already intimated above

http://www.physchem.co.za/Heat/Latent.htm

Eddiethehill

ircoha wrote:

Interesting post this.

To boil eggs u really need very little water, just enough to cover the bottom of the pan for the whole process.

http://www.physchem.co.za/Heat/Latent.htm

So! What would be the best way to cook two eggs? We need to transfer the energy to the eggs in a controlled manner - raise the temp of the eggs close to 100 degrees slowly enough so as not to crack them, but wasting as little energy as possible in the process. Do we really need to boil water at all? Maybe there is some other way to do this.
Would putting them in the microwave at a low setting use less energy? Or maybe putting the eggs on top of the toaster when toasting the bread would use otherwise wasted heat.

Is Mise...

I KNOW this won't save the planet, but it is interesting to think about.

CJhaughey

Eddiethehill wrote:

Would putting them in the microwave at a low setting use less energy?

Whatever anyone does to experiment with this question PLEASE do not microwave eggs.
It is highly dangerous and has resulted in at least one person being blinded by an exploding egg lacerating and scalding the eyeball.
Google it if you doubt me, but whatever you do microwaving eggs is not to be laughed at.

conzy

Trying to find a new way of boiling eggs to save 500ml of water is a bit silly when your Toilet, shower, dishwasher....... are using several hundred litres a day......

Gurgle

democrates wrote:

My theory is that lot's of heat energy going into water is lost as it evaporates, so replacing much of it with stones which reach a temperature and stay that way means less heat loss. Thoughts?

Absolutely right.

Its not so much the loss due to evaporation as the energy required to raise the temperature of water.

Liquids have generally a much higher heat capacity than solids, and water is higher than almost any other liquid (its about the most un-natural substance we have on this planet. It never does what you would scientifically expect it to do.)
Water has a heat capacity is 4.186 joule/gram °C, much much higher than e.g. granite with 0.71joule/gram °C, or basalt at 0.84joule/gram °C.

Thats why water is the best medium for storing heat.

Capt'n Midnight

if you fill the pot to the same level the one with stones in it will take less heat to the temperature.

but most of the heat lost is though evaporation / boiling the water. if all the stones are below the surface then you still have the same surface area so probably the same heat loss. (though very small stones are used as boiling chips to stop large bubbles forming so less "blop blop" )

having a lid on the pot is more important than stones.

Re microwaves - use a pin to put a hole in the egg first, and wait a minute to let the egg cool down before taking it out of the microwave.

ircoha

conzymaher wrote:

Trying to find a new way of boiling eggs to save 500ml of water is a bit silly when your Toilet, shower, dishwasher....... are using several hundred litres a day......

RTFP:( this is not about saving water

ircoha

Gurgle wrote:

Absolutely right.

Water has a heat capacity is 4.186 joule/gram °C, much much higher than e.g. granite with 0.71joule/gram °C, or basalt at 0.84joule/gram °C.

Thats why water is the best medium for storing heat.

No issue with the science, can u please put the
"Thats why water is the best medium for storing heat" comment in context
thanks

Capt'n Midnight

ircoha wrote:

No issue with the science, can u please put the
"Thats why water is the best medium for storing heat" comment in context
thanks

wikipedia.org wrote:

Water also has the next highest specific heat capacity of any known chemical compound, to ammonia, as well as a high heat of vaporization (40.65 kJ/mol), both due to the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large swings in temperature.

http://en.wikipedia.org/wiki/Specific_heat_capacity

water is also cheap and can be pumped from a to b so you can move the heat easily. the main disadvantage is that it boils at 100c and sometimes you might prefer a solid to a liquid

Gurgle

ircoha wrote:

No issue with the science, can u please put the
"Thats why water is the best medium for storing heat" comment in context
thanks

It takes more energy to heat water than most things.

If you want to store a lot of heat, then you're better off using a sealed insulated container of water than e.g an insulated lump of iron or an insulated stone. You can store more thermal energy per kg in the water.