Eutectic water heater

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.