Yield wood stove and flue gas temperature

[Christophe]

Delicate question: what is the "maximum admissible" temperature measured on the outlet nozzle of the heating body of a wood stove or boiler which indicates that the efficiency of the latter is "correct"?

Question valid when the stove is hot and in the "embers" phase, that is to say between phase 4 and 5 according to this classification:



Measurements made on this small boiler stove deom which here is the assembly plan https://www.econologie.com/forums/chaudiere- ... t4589.html



Linked Topic: https://www.econologie.com/forums/rendement- ... t6977.html

[bernardd]

Below 100 ° C is ideal because it means that there has been condensation of water vapor and thus recovery of the heat of vaporization.

It also seems that the cooling of the fumes from 600 ° C to 100 ° C must be fast enough to avoid leaving them at 250 ° C, because it is the temperature zone that allows the formation of dioxins around the chlorine.

[Ptilu]

In his type of stove (the top of the top), we recover condensates?

[Christophe]

Ptilu, it's not funny to make fun of our deom !! Yeah we get them back: it's bistre in the chimney but it's not wanted

Less than 100 ° at the outlet nozzle? It's hugely low ...

Well, here are the measures that I have just realized with a infrared thermometer of that type: https://www.econologie.com/shop/thermome ... p-132.html

At the level of the heating body:

Maximum T °:

left:

Right (the gas exhaust nozzle added for "increased efficiency" is below this measuring point so I would have thought it was hotter than on the left ...):


Nozzle temperatures:

Exit:

After about 1 m:
After about 2 m:


Attention the emissivity is not corrected (fixed on this model of thermometer to 0.95) so I think that it is necessary to increase (a little) the measurements made on galvanized steel compared to the cast iron (emissivity very close to 1.0 I think) ... or lower that of cast iron?

If anyone has a correction suggestion?

[Ptilu]

No no, it was a non-ironic and legitimate question;)
If not, what do you mean by DEOM?

I must however contradict you, the metals have a very low emissivity, from 0.05 for polis to 0.65 for diffuse ...
Which makes them very good insulators for radiative transfers.
Ideally, an aluminum foil, and you have excellent insulation. This is the principle of the survival blanket !!!

Well, it's diffuse stainless steel, so I do not know ...

[Christophe]

Deom is the brand of the stove boiler it is noted above on the photos

Uh, are you sure about emissivity? For aluminum yes (0.1, principle of thin insulators) but for the cast, black, it must be very high right?

It's not stainless steel, it's galvanized steel (not the means to take stainless steel ...)

[Ptilu]

The relationship between ratiative fux and temperature is:

flux = emissivity * sigmma * T ^ 4

where T in Kelvin and sigmma = 5.67 e-8

for your temperature of 54 ° C:

flow = 617 W / m²

and thus taking real emissivity of 0.65

T = 86.6 ° C

goes up to 132.9 ° C for an emissivity of 0.4!

We are not far from 100 ° C

[Ptilu]

The chord font
it has a very good emissivity, 0.81 unpolished:

http://www.fluke.co.uk/comx/show_produc ... &pid=37822

Either for an indicated temperature of 296 ° C, an actual temperature of 592 ° C ...

I do not have eyes in faces of holes, dsl. I was just wondering where the condensates came out;) (thirst for technology)

[Christophe]

Super, thank you for the method, it's nice to be able to find the heat flow as easily thanks to an infrared thermometer ...

Would you have a table with the different emissivity of metals because in the doc of the thermometer there is no metal ...

[Ptilu]

And it's not because these black that it has a good emissivity ... The white paint is very reflective in the visible range, but very absorbent in the IR range ... between 0.9 1!

So in the usual temperatures (from 300 to 700K) it is an excellent absorbent and radiative emitter.