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measuring air velocity through rocket.  RSS feed

 
                            
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I would like to tinker with rocket stoves, without the fire. 

In otherwords, experiment with various notions without have the light up a fire, or require testing parts be fireproof, or keep at a distance for observations and measurements.

For example - I'd like to test out a venturie to recirculate some smoke for a reburn.  Without fire, I can make test shapes with paper and plastic pipe, and stick my head right in the pipe to see how it's working if I can avoid the fire part of the rocket stove but still have the draft effect.

So far, I've gotten an infinitely variable-speed leaf blower which I want to blow into the wood feed.  What I'm trying to do now is figure our what speed best approximates the normal draft of the rocket stove while burning.

I figure I need to run and typical fire and measure the flow - probably at the top of the stack (simple cooker design - no bench).  Then match that measurement by playing with the blower speed switch. 

Problem is, how to get first measurement in the fire?... any ideas?
 
pollinator
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Location: Vancouver Island
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Scott911 wrote:
I would like to tinker with rocket stoves, without the fire. 



Stoves or heaters? You need to measure what you are planning to test.


In otherwords, experiment with various notions without have the light up a fire, or require testing parts be fireproof, or keep at a distance for observations and measurements.

For example - I'd like to test out a venturie to recirculate some smoke for a reburn.  Without fire, I can make test shapes with paper and plastic pipe, and stick my head right in the pipe to see how it's working if I can avoid the fire part of the rocket stove but still have the draft effect.

So far, I've gotten an infinitely variable-speed leaf blower which I want to blow into the wood feed.  What I'm trying to do now is figure our what speed best approximates the normal draft of the rocket stove while burning.

I figure I need to run and typical fire and measure the flow - probably at the top of the stack (simple cooker design - no bench).  Then match that measurement by playing with the blower speed switch. 

Problem is, how to get first measurement in the fire?... any ideas?



I would measure at the air intake... taking into account that there would be a load of wood partly blocking that opening. Then remember that the volume of the flue gasses changes as it  heats and cools and so would the speed of the flue gas.
 
                            
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because the gas expands, and speeds up significantly, I think I do need to measure at the exit of the stove.  I would be feeding cold air into the inlet with my blower at a higher than normal input speed to componsate. 
 
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I work for a company that makes airflow measurement devices and to do it accurately in high temps is expensive.  We use inconel or hastelloy probes (for high temps - up to about 1900 deg F) that utilize Pitot Averaging technology in conjunction with ultra-low dp transmitters.  For a system that is set up correctly you can expect 2-3% accuracy.  The problem is that you need a measurement location that has a uniform air velocity profile.  This is easier with small ducts, but you still need about 4 diameters of straight duct run upstream of the measurement location.  Also you need to consider the losses with venturi type devices. 

The more I study these rocket stoves and other similar rocket stove type applications, the more I am convinced that the simpler approaches give the most bang for the buck.
 
I'm THIS CLOSE to ruling the world! Right after reading this tiny ad:
Would you replace your oven with a rocket oven?
https://permies.com/t/90099/replace-oven-rocket-oven
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