Heat sand to 400f

[veggie]

*** PROJECT CANCELLED ***

After modeling the idea, the numbers do not make sense for a micro system.

Summary....
==========

Specific Heat:
Water = 4182
Sand = 830
Sand holds only 20% of the BTU content of water.

Raising a 50 gallon tank of water from 68f --> 180f requires ~46,725 BTU's
To store the same amount of heat in 50 gal of sand would require a temperature rise of approx. 900f

Heat transfer factor
Water = 13
Sand = 0.06
Roughly 200 times slower transfer rate in sand. (It holds heat very well ! )
But heating the sand bed would take a considerable amount of time.

So how do the new commercial sand heat storage systems get around these obstacles.
1] They heat the sand to 1800f or more by circulating molted nickel or molten salt through exchanger tubes in the sand bed.
2] With super high differential temperatures, they can rob heat from the bed at greater rates than my proposed 400f project.

For smaller heat reservoir systems water in king. It has the highest specific heat value and storage properties of any readily available media.

[HWEW]

I was just thinking about a low pressure steam system. If I remember, steam gives out more Btu's per pound. Wow, it's been 33 years since I worked on my last steam boiler. Cap a hopper off an S195. A couple cast iron radiators...

Added:
After thinking about it, the best way for steam is a heat exchanger for the exhaust.

It would be different.