[Stoves] flames touching pot

[Crispin Pemberton-Pigott]

Dear Frank

 

It will be difficult to get the temperature of the inside of the pipe with an IR device because the surroundings are going to swamp the outside, given that background of the furnace walls. Note that the one I recommended has a 1:50 beam spread which is a very narrow viewport, which is in your favour.

 

The idea of sticking a fairly long probe into a second hole is a good one. You will need to get a probe long enough to not be affected by the heat conducted back to the handle. There are wire thermocouples that can handle the temps you are using. The longest I have in a 3mm rod is 12 inches I think. It might not be long enough for oven work L .

 

Regarding the emissivity of the outside of the pipe – yes it matters. If you were to open the door and get close enough for a 2 second read at a distance that the eye was not picking up background IR, the tube could conceivably be read without a thermocouple inserted into it. The colour matters. Note that the colour matters even if it is glowing bright red. Emissivity is emissivity. So you need to establish what the ɛ value is before you start. It will give off the radiation it is able to throw off. It is true the emissivity changes a bit with temperature but it is not much between 0 and 700. What you view as black or glowing red is just your eyes picking up (or not) radiation in certain frequency ranges. The IR camera sees at different frequencies (hence false-colour photos taken in the IR radiation range. When we look with bare eyes we see nothing, perhaps (like at night). I write this to point out that ɛ remains the same.

 

The ɛ f black pipe is about 0.9-0.95. Something as low as 0.25 is very shiny like polished aluminum. 

 

Complicated? Well, yes but at least it is possible when a few years ago it was not! Gotta be happy about that!

 

Regards

Crispin

 

From: stoves-bounces at lists.bioenergylists.org [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Frank Shields
Sent: 15 September 2011 19:07
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] flames touching pot

 

Dear Crispin,

 

I’m using pipes to char samples for testing.  The furnace the pipes are in is temperature controlled. I want to check the temperature to make sure the furnace temp reading is accurate to the temperature of the pipe.

I like the fact the IR detector also has a probe. I am thinking I can ‘read’ the outside of the pipe using IR and have a blank pipe with a larger hole in one end to insert the K-probe to get a reading inside the pipe. 

 

In this case the heat is outside and inside the pipe (in the furnace) so does emissivity come in to play? There should be no lost of heat at the surface as I see it. Should I set it at 1 to get the real temperature?

 

Why is something so simple always become so complicated. : )

 

I have more questions but will read your email again to see if it answers it. I am using a ‘black’ steel pipe that has an e of ~0.23. How would I set the IR meter to read the temperature of the pipe surface while it is in the furnace (open door and read quickly)? 

 

 

Thanks

Frank

 

 . 

 

 

 

 

 

 

 

Frank Shields

Control Laboratories, Inc.

42 Hangar Way

Watsonville, CA  95076

(831) 724-5422 tel

(831) 724-3188 fax

frank at compostlab.com

www.compostlab.com

 

 

  _____  

From: stoves-bounces at lists.bioenergylists.org [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin Pemberton-Pigott
Sent: Thursday, September 15, 2011 1:52 PM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] flames touching pot

 

Dear Frank

 

There is a marvellous product available from ThermoWorks. It was not very expensive compared with earlier technologies. We have two of these in Ulaanbaatar.

http://www.thermoworks.com/products/ir/irpro.html

 

It comes in that very nice box on the right.

 

Because it was quite new I had to have them shipped to my regular supplier E&E Process and take them to UB.

 

Make sure to get a K-band thermocouple to go with it that is long enough to get into places the supplied one can’t reach. It is not wrong to have a 5 foot long one 8mm in diameter. They are not very expensive.

 

Note that the emissivity can be set from 0.1 to 1.0 – an amazing range. This is a new generation machine. $225!

 

Regards

Crispin

 

 

 

++++++++

 

Dear Crispin,

 

 

I’m surprised the paint color on the outside would make much difference. 

Lets see if I have this right. As the goal is to keep the heat inside the stove body we want less radiation to the outside off the paint. So more heat on the outside surface the more loss from the inside stove unless the loss is greater than the heat being supplied from the stove (not likely(?)). So its not the thickness of the paint and insulating material of the paint but the color of the surface that makes a big difference(?) as to how fast the heat will radiate to the outside air(?). 

 

And thanks for the info on purchase of an IR thermometer having an emissivity setting as I am about to purchase one. Any suggestions?

 

Again - lots of great information. 

 

Thanks

Frank

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