Thursday, 29 May 2008

The science bit...

The advantage in having lots of thermocouples is that you can spend inordinate amounts of time watching how your oven heats up and cools down. Here's the results of the first large fire I had - temperature scale is degrees C. The dome surface got up to about 500 C in this burn.
The second large fire was earlier in the day, so easier to measure for longer without staying up half the night. The dome surface (red line) got up to 600C, while the hearth brick only got up to 400C. The vermiculite was still steaming on this burn - it's absorbed lots of water from the mortar. You can see how the temperatures rapidly drop after the fire is finished (about 4h on this graph below), then soon even out to a more steady decline. At present, the oven dome surface takes about 4 hours to drop from 300C to 200C. Most of this heat will go out of the open oven front - there's no door on this yet.
Here's the same graph with a Farenheit scale for those who prefer it in old money...

You can see how all the heat is locked up deep in the clay dome - the 2" deep probe is always the hottest, and gives up its heat to the dome surface and outer surface. The temperature below the thermalite blocks never goes above 45C. I need a door!

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