Without sand, forced air and being electric you have just made a muffle heat treat oven. You have to have air forced through the sand from the bottom to fludize it as well as create the even temps. The "boiling" effect of the sand is what creates the even temp. By even temps I'm talking within +- 3°C. The tricky bit is injecting the gas "air" just right so it creates and even bubble matrix. The other real tricky bit is as the bubbles forum at the gas ports aka jets or bubblers you don't want a pressure drop in the air supply. This causes problems with the sand chugging which is the sand going up and down and pulsing. The. After that you need to design the jet so the sand can not get into it and weep back into the manifold. This is actually rather tricky to do and even proper systems that use bubble caps that are shealded can weep. It has to do with the drop in pressure when a bubble forums and the surface collapses and kinda shoots sand twords the zone of low pressure. I was looking at X-rays last night of bubblers that had this problem. Was cool to actually see the sand in action and caught in a picture. Any way I have a few ideas on how to deal with these things in a sand pot. I hope to be back on build soon.
Oh and about the heating rate of sand vs salt, it's rather quick. MUCH faster then just a atmospheric heated forge. According to the chart a 1" round steel bar will heat to 1830° in around 6min from ambient temp. But the same bar heats to the same temp in salt in around 4min. Compare those to a atmospheric furnace and that is 14min. If your wanting actual numbers here is what the experts hav to say. "Relative heat-transfer coefficient range for various furnaces"
salt bath = 500-1200 W/m²·K
fluidized bed = 500-700 W/m²·K
Forced circulation furnace = 150-200 W/m²·K
So as you can see salt is fast but so is sand when compared to a normal furnace.
I work on electric sand pot JT .On picture is also with AO sand and with forced air . Air regulation was not a problem, I have a precise tool for that. Little tricky was to find how much jet and size of jet ..... I think I've experimented enough and that the electrical will turn out properly .Without sand, forced air and being electric you have just made a muffle heat treat oven. You have to have air forced through the sand from the bottom to fludize it as well as create the even temps. The "boiling" effect of the sand is what creates the even temp. By even temps I'm talking within +- 3°C. The tricky bit is injecting the gas "air" just right so it creates and even bubble matrix. The other real tricky bit is as the bubbles forum at the gas ports aka jets or bubblers you don't want a pressure drop in the air supply. This causes problems with the sand chugging which is the sand going up and down and pulsing. The. After that you need to design the jet so the sand can not get into it and weep back into the manifold. This is actually rather tricky to do and even proper systems that use bubble caps that are shealded can weep. It has to do with the drop in pressure when a bubble forums and the surface collapses and kinda shoots sand twords the zone of low pressure. I was looking at X-rays last night of bubblers that had this problem. Was cool to actually see the sand in action and caught in a picture. Any way I have a few ideas on how to deal with these things in a sand pot. I hope to be back on build soon.
Oh and about the heating rate of sand vs salt, it's rather quick. MUCH faster then just a atmospheric heated forge. According to the chart a 1" round steel bar will heat to 1830° in around 6min from ambient temp. But the same bar heats to the same temp in salt in around 4min. Compare those to a atmospheric furnace and that is 14min. If your wanting actual numbers here is what the experts hav to say. "Relative heat-transfer coefficient range for various furnaces"
salt bath = 500-1200 W/m²·K
fluidized bed = 500-700 W/m²·K
Forced circulation furnace = 150-200 W/m²·K
So as you can see salt is fast but so is sand when compared to a normal furnace.
Good idea on the PVC. I've picked up the components to wire it 240v, but I still have to do a bit more reading on how it all goes together before I pour the liner.That should work as long as it's stiff enough to hold form when you pour. I'd probably want to do a cardboard tube wrapped around a PVC pipe or something to be sure as the cardboard is going to suck up some moisture and lose rigidity. But then you could slide the PVC out easily and burn the cardboard out like you planned.
ETA also I don't know if you planned 120v/240v but figure that out so you can plan coil starts/stops or whether you want a 2 lead spiral, etc.