Hi - I am teaching a thermodynamics class (remote to Beijing!). I would like to use my rocket mass heater as an example. I am wondering if anyone can suggest a useful thermometer for measuring temperatures at various positions along the burn tunnel, J-tube chimney, barrel....
One thought was to make an open air J-tube with small holes in the side - and seeing different - but I would also like to be able to get more accurate and precise measurements of the complete closed system.
Hi Karl; Way to go using your RMH to teach! I Like it!
A simple candy thermometer is perfect for inserting into stove pipe to read true gas temperatures. Quite a bit different from external pipe temps.
The probe on them is apx 6-8" long so one could be inserted at a brick joint. They are maxed out anywhere close to the core, above 400F .
There are wireless temp senders but again the burn tunnel and riser are 1300 F and up I don't know of any that could take that heat.
If you did find high temp wireless senders, cost's would be high.
Of course an IR external temp gun, would give you barrel temps and external mass temps.
Hi Karl, Using a RMH to explain thermodynamics sounds like a wonderful idea! Most people probably have not seen a RMH before so it will be an education in permaculture as well as heat flow.
A thermometer for the high temps inside the core can perhaps can use something like this one rated up to 2372 °F 1300 °C: K-Type Thermocouple. I have not used any thermometer inside the core so I don't know how long it would last in such harsh conditions as Thomas pointed out.
I have seen a few people who have made a core with a side high temp glass window installed to see the fire and its flow for demonstration purposes.
This video at the 30 second mark shows an example of this: intro from RMH DVD
Most of the time the digital thermometer can withstand and measure 2370 ºF or 1300 ºC, but the K-type thermo coupler can be used up to 1000 ºC or 1830 ºF. Above that temperature they'll die silently, I've seen that happen multiple times, much to my dismay. There's another thermo coupler that will survive 1300 ºC, unfortunally I forgot which one. And I might add: the thermometer need to be ready to accept those higher specc'd couplers.
Mine is a simple two-channel type only useful for K-types from Conrad Electronics. At some point I could borrow a higher specc'd instrument with couplers, highest recorded temperature using that one was 1172 ºC or 2140 ºF, close to the theoretical maximum of 1200 ºC or 2190 ºF for an atmospherical aspirated wood fire as I was led to believe.
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