Half a croissant, on a plate, with a sign in front of it saying '50c'
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Eutectic water heater

Solve water temperature consistency with phase change.
  [vote for,

There are many types of water heating systems. The most common in the US is the tank type <link>. This is a simple beast, a water tank, heating elements and a thermostatic switch. The water in the tank is heated to a target temperature and maintained by the thermostat switching the heating element on and off. When hot water is drawn off, cold water enters to replace it. The only nod to sophistication is that this cold water enters at the bottom, in an attempt to prevent the hot and cold water mixing and cooling the outflow. This doesn't work. The result is a declining water temperature in times of peak demand.

The standard solution is to buy a bigger one. More water, larger heating element. It ameliorates but doesn't solve the problem. Worse, the larger tank leaks heat for all the time of the day it isn't being used, only a little more, proportional to the extra surface area, but more.

The solution, is phase change. When solids melt, they absorb a huge amount of heat energy for no real change in temperature. Conversely, when liquids freeze, they give out a tremendous amount of heat energy while the temperature stays the same. This is the principle behind ice in drinks, and the coffee cup I invented <link> that someone inconsiderately invented before me* <link>.

So, water heater, tank style. Water in the tank. Tank has chamber inside filled with a wax that melts at say 50 Celsius. No need for double walls or any such sophistication. Even a couple of sealed metal tubes of reasonable volume would do it. Now, the heating elements heat up the water and as it approaches maximum regulated temperature, the wax starts to melt. As the thermostat clicks off, the wax is liquid. Now, water is demanded, hot water leaves and cold water rushes in. The temperature drop is detected and the heating element turns on. Simultaneously the wax begins to solidify transferring huge heat capacity to the water.

A kg of standard hydrocarbon wax will melt with 220kJ energy given off, which will be enough to heat 52 liters of water one degree. So 10kg would provide very significant heat buffering capability, in a package 1/60th the volume of water. So you could have a much more stable tap temperature without a bigger tank leaking more heat.

Now, if someone would kindly make one and send it over, perhaps I could have a shower unimpeded by the ancillary bath/laundry demands.

*My invention lacked the leaky lid feature.

bs0u0155, Nov 06 2017

Tank Type Water Heater https://www.onecomm...014/06/Picture3.jpg
[bs0u0155, Nov 06 2017]

Eutectic Coffee Cup Eutectic_20Cup
[bs0u0155, Nov 06 2017]

Real Eutectic Coffee Cup https://joeveo.com/
[bs0u0155, Nov 06 2017]

US 20110081134 https://google.com/patents/US20110081134
Water heating unit with integral thermal energy storage (containing a phase change material) [xaviergisz, Nov 06 2017]


       "Dystectic" should be a thing. I'm just not sure what sort of thing yet.
pertinax, Nov 07 2017

       As soon as it's decided on, they can begin work on an appropriate ointment..
bs0u0155, Nov 07 2017

       I'm struggling to think of a reason why this wouldn't work - which is unusual for an idea here
hippo, Nov 07 2017

       It turns out there are a few specialist binary materials with latent heats over 330 kJ/kg. I can imagine you could make some pretty energetic chain events, perhaps a liquid that binds water and releases it on solidification, a second liquid with a lower melting temperature binds the water in an exothermic manner. And so on, in a dreary chemical type way.
bs0u0155, Nov 07 2017


       One wonders, does one, why such isn't commonly used as passive solar thermal mass, instead of a rock or cement wall [edit: one has just found ou that they do]. More expensive of course, but not by much... in fact you could pour the stuff into the holes in breezeblocks for some random amount of effectiveness.   

       Also, "Lavalamp Water Heater".
FlyingToaster, Nov 07 2017


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