Energy Matters Forums

[Gordon-Loomberah]

The short answer is No


Each substance will have its own specific latent heat of fusion, which occurs at the melting point. They also have their own specific latent heat of vapourisation -at their boiling point. There are tables of these constants online, such as here: http://en.wikipedia.org/wiki/Latent_heat
Paraffin wax's latent heat of fusion is around 200kJ/kg (varies a bit, according to the mix of wax)

notable is how much energy it takes to boil water, a LOT!

[munter]

I would guess that the energy input would be different. Just as each material has a different specific heat, each material would probably have a different "heat of phase change". Wikipedia probably has an answer or listing for these though I can't remember the correct technical term at the moment.

There aren't many existing applications in the domestic environment - the latento wax capped hot water tank is the only one I can think of.

[120ThingsIn20Years]

cool, thanks

so much to learn

[120ThingsIn20Years]

was this a phase change thing going on here?

I had some curds (lumpy stuff) and whey (runny stuff) in a double boiler (pan inside a pan of water). The curds and whey were at 31 deg C and the water in the outside pan was at 31-32. This was normal as there is some heat lost because the inside pot sticks up in the air above the outside pot and thus vents a bit of heat.

When it was time to add rennet (rennet is used to set the curd) The temp dropped a little so i added heat to the out side pot. Normally there is some delay before we see a rise in temp of the inside pot, but for the first time I noticed just how much more heat I was putting in to get a 1 degree increase. In the end the water in the outside pan was at around 50 to get a one deg c change in the curds and whey. Then the curd set and the temp when up, even though I had turned the heat off for the last 5 minutes.

So for the entire time it took for the curds to set I just kept jamming energy into it with no increase in temperature.

final temp was 34 in the outside pot and 34 in the curds and whey.

[Gordon-Loomberah]

Its a bit hard to say whats going on in an uncontrolled scenario like on your stove
Phase change really only refers to melting/freezing or boiling/condensation of a substance.

The setting of something is not the same thing, its a chemical reaction between the various compounds in the pot, although I admit to having no idea what compounds might have been in there The heat being added to the water bath is going to be delayed in getting into the inner pot, water isnt a very good conductor, so you would expect to have to get the water significantly hotter than the inner pot needs to be.

Also, chemical reactions can be exothermic ie they give off heat - such as oxidation in a flame, or endothermic, which takes heat from the surroundings... which may be what's going on with the curd setting.

[120ThingsIn20Years]

ok cool . thanks

pitty I would have liked it to have been

[Red]

Curds would be endothermic being proteins and acids.

Phase change is what makes global warming such a threat.