Transferring heat from hot body to water.

Question

Transferring heat from hot body to water.

asimpson (Mechanical)

(OP)

18 Jul 11 05:31

I am working on an idea of boiling drinking water from a metal heat store at +500C.

Assuming the heat store is replinished how would I go about the messy buisness of heating water from about 5C to 100C at about 2L per min. to a nice cup of boiling water? Water supply about 0.25 bar or more.

Thinking about traditional heat exchangers I would guess there would be a lot of steam, noise and pressure generated when cold water comes into contact with 500C. As well as scale buildup.

Are there any techniques out there already that address this problem without going into high pressure?

Thanks in advance.

ornerynorsk (Industrial) · Answer 1 · 2011-07-18 09:24:26

Try looking at a point-of-use water heater. These devices do precisely what you are trying to accomplish. Either that or an espresso machine :>)

Good luck!

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

asimpson (Mechanical) · Answer 2 · 2011-07-18 10:03:59

Thanks.

But point-of-use devices usually have a store of heated water which is drawn off and replenished.

I wish to avoid this water store and instead store heat in metal device at much higher temperature then boiling point of water.

macmet (Materials) · Answer 3 · 2011-07-18 10:40:19

I would suggest red flagging this post and posting again in the heat transfer or the HVAC forum. I imagine those forums are more popular to the site visitors than this one.

ornerynorsk (Industrial) · Answer 4 · 2011-07-18 11:07:57

There are flow-through POS water heaters that provide the heated water instantaneously, with no storage other than the supply line. 500C is probably in the range of those heating elements. Just a thought.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

davefitz (Mechanical) · Answer 5 · 2011-08-01 09:17:16

At 500 C, the liquid water would never "wet " the surface, because the surface is well above the "liedenfrost" temperature. So the 500C body would instead be located inside a cooling jacket- the empty space between the body and the jacket would be engineered for controlled rate of thermal radiation heat transfer, by specifying the surface emissivities of teh body and the jacket and/or adding a radiation screen between the 2 bodies.

This design would avoid the thermal stress associated with direct contact with the 500 C body

chicopee (Mechanical) · Answer 6 · 2011-08-06 06:35:31

You could explore the idea of having the cold water pass thru the annular spaces of several concentric short tubes heated by electric current. Obviously the metal tubes would need to be resistant to corrosion from water and be able to get hot just as the filaments of an electric stove.

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Transferring heat from hot body to water.