Homebrewed Electricity > Storage

Sand Batteries

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Mary B:
Saturate the sand with a liquid that works well to transfer heat... if it is a closed system you could even use waste oil from changing it on the car/truck/SUV...

SparWeb:
Hey, that's the same video I just saw, Bruce.  The Youtube algorithm knows we know each other now.

I've been mulling over the usefulness of water, just like Mary suggested.  I think the ability to heat the sand up above 300F, or higher than boiling water is an advantage that you can't use if you add water.  If it's a closed loop, some glycol in the water would help use higher temperatures.  The mixture of sand and water might also be a problem if it needs filtering, silt traps drains, etc., to work for a long period of time.

Tube-in-tube heat exchange is the standard, taught to every mechanical engineer in thermodynamics class.  If you build one, remember to include temperature sensors on inlets and outlets.  A simple feedback control makes a big difference in the efficiency, worth the effort.

To keep it as KISS as possible, what can be done with a simple tank of sand with an electric heater in it?  One thing is to just use it like an old-fashioned cottage stove - it heats the room by radiating its heat through the sides.  Careful not to touch it though.  For a small insulated building, this could make a big difference.

Another way is to pass the ductwork in your house through a sand tank.  This sounds like it would work, as long as the sand makes lots of surface contact with the duct, or else the air will blow by without picking up much heat.  Think of a basement air duct about 8 inches diameter and you fit a 12" duct around it, filled with sand and some lengths of nichrome wire encapsulated.  Wrap the outside of the 12" duct with insulation so that the sand doesn't just heat the basement.  When the central heating blows air from the furnace, it will be heated a second time by the sand heater.  The central thermostat will detect the house warming up faster, and will shut off the furnace sooner.  The furnace would not run as much, saving on heating.  If the sand heater is driven by PV, the electricity is free.  It would take some math to figure out if the amount of energy collected this way and the heat-exchange process would add up to a noticeable effect.

Bruce S:
SparWeb;
He's pretty good at details and generally answers emails and posts.
Having played around with this tin can and using heat from a few different sources, I think I'm going to stay away from any liquid addition to the sand.
In fact I'm working on  cooking the sand as dry as possible, since I'm leaning towards as close to a closed loop system as possible, along with a pressure gauge & relief valve of some sort.

Back when I had my Mercedes 5cyl 300TD I got around to "remembering" how to build a tube-in-tube system and found that the cooling system worked great  to pre-heat the Bio-D. I of course added a few extra temp probes (Both digital and analog) Analog cause I'm nostalgic for swing needles  ;D as I was curious about the returning fuel's temps.
I also remember the disaster here when a steam boiler failed and launched itself killing two onsite and two people who had just started a new job 60+ meters away.
The video liked below gives a very good recreation of what happens.
https://www.youtube.com/watch?v=3Bs6W19cLcY
I know from reading a bunch of your posts and answers to other posts, you understand THE DANGERS when doing these sort of tests and I know JW is a steam guru, BUT anyone else reading these needs to watch the video so they are aware of how quickly things can get deadly  :-[.

I'm also remembering surface contact is vital to extracting the stored energy in an efficient way. OF course all this Mechanical engineering math gets my brain to hurting again and I need to take libation breaks often  8). I still have an old 1M satellite dish that I may setup as a sorta of heliostat to gain a few extra temps.
I've also done some of handed testing of capturing waste heat from our gas dryer by using a few soldered together tins to pump a little warmer air into the house , I borrowed a few surplussed air monitors to make sure there wasn't any nasty un-burned hydrocarbons trying to give me a headache.

I do like the use of tin cans, as they are free, can take a pretty high heat and solder together nicely too. Using the surface area of them I can do these trails pretty cheaply. Also when I ran out of solder I tested a few connections using the Flex-Tape, that worked surprisingly well for a short term test.

Sorry for the disjointed reply;
It's been a busy week  :o

Bruce S

Mary B:
Tube in tube I would use oil as the heated medium... minimal expansion that could be handled by an expansion chamber keeping working pressure low to non existent...

Just a thought. Could even recycle used motor oil as the heated medium, filtered to get rid of particulates. Oil is a pretty decent heat exchange medium, better than air./sand would be. Downside is any leaks would make a mess...

Bruce S:
Mary B
With the flash point of new motor oil being above 200C , I'm now inclined to give it a try :-) too.
I think I might take the dog out for a walk and give that an extra thought.
Any leak will certainly help in during the discovery part  ;D.

I'll keep moving forward on the sand stuff since I already have a little bit of working knowledge with it. AND I was smart enough to grab a decent pair of FF gloves!!
My other concern is insulating the external tin can. 

Bruce S

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