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A Bunch of Hot Air

I know readers have enjoyed Michael Stuart’s wonderful Teaser Infrared Images posted every week in the blog. While I may have infected him with the “IR Bug,” the “fever” he caught has taken him places I can’t be responsible for (even if I’ve been with him some of the time).

I was particularly intrigued by the image of the hair dryer. This is not an easy subject for imaging as the range of temperatures is so wide and of course I loved the “back story” about Yul B.. As Vermont’s own ice cream geniuses, Ben & Jerry, say “If it ain’t fun, why do it?”

Ice cream is great anytime of year but warm summer weather definitely makes it taste and feel special. Maybe it is time to do some basic thermal research with your imaging system, some neighborhood kids and some cones!

Thermographers image so many different things, ice cream included. I once worked inside the Ben & Jerry’s freezer plant and was shocked see to cartons of “warm” ice cream coming from the production side into the freezer side. Temperature is relative, right?!

On the cold side of the freezer, I had fun imaging the recently made pints as they spiraled up a quick freeze unit that took them to -20F/-29C over the course of an hour. The main heat transfer mechanism was a 50mph/80kph “breeze” of cold air blowing over them as they made their way to the top of the unit. While I could see them coming in “warm” at the bottom, they were virtually invisible by the time the exited “cold” at the top. I’m sorry I no longer have images as those were from the pre-digital age!

I also remember being shocked the first time I saw hot air coming out of a hair dryer. How many times had I blithely told students in my classes “You can’t see air.” But I was, or it appeared I was seeing air!

The invisible portions of a flame of a burning match are visible thermally because we are actually seeing small hot particles rather than just “hot air.”

I quickly got on the phone with my colleague (and mentor) Greg McIntosh (Snell Infrared Canada). He reminded me that the air I was seeing was both quite warm and humid enough that I was probably seeing hot H2O vapor and possibly CO2 as well. I had intended to duplicate the experiment in a very dry environment but never did. Any volunteers? He also suggested I was using a midwave imaging system that was pretty darned sensitive to seeing water vapor; in the past the imagers I’d used has probably simply not been sensitive enough to see what was actually there. So all my hot air ended up being a good learning experience for the class.  You may not be able to see the hot air from a hair dryer with your imaging system, but you will probably be able to see the hot gases from burning match, candle or gas flame.

Speaking of learning from Greg, I can also highly recommend to you one of his papers, 10 Reasons Why a Temperature Rise Should Be Reported As “At Least,” available at no cost from the Knowledge Center at The Snell Group’s website.

So have some ice cream and have fun taking images of anything (even hair dryers) and everything you find around (at least if it is safe to do so!). If you come up with some good ones, I’m sure Michael would welcome a week off the routine of Thinking Thermally and provide a platform for a guest Teaser IR Image or two!

Thinking Thermally,
John Snell—The Snell Group, a
Fluke Thermal Imaging Blog content partner

5 comments to A Bunch of Hot Air

  • Michael Stuart

    John,

    I’m not really sure how I should feel about being the first thing mentioned in a blog post titled “A Bunch of Hot Air”…. but I can say that I pretty much blame you for the majority of my “infrared affliction / fascination”. Personally, I’d love to see some of the infrared images that all of our readers could come up with.

  • Gene

    Hi all,
    Newbie here to the blog. Wondering how do I get accurate temp readings from my camera when the environment I’m shooting in has many different types of materials-both organic and inorganic and thus potentially countless emissivities? If, for example, I walked through a super market would I find one ‘average’ emissivity, or do I really need to adjust the image for 25 different types of materials such as plastic, foil, cardboard, etc?

  • The juxtaposition of the two was purely accidental, my friend! But now that you mention it…

  • Michael Stuart

    I learned from the best! ;)

  • “Newbie here to the blog. Wondering how do I get accurate temp readings from my camera when the environment I’m shooting in has many different types of materials-both organic and inorganic and thus potentially countless emissivities? If, for example, I walked through a super market would I find one ‘average’ emissivity, or do I really need to adjust the image for 25 different types of materials such as plastic, foil, cardboard, etc?”

    Great question Gene! In many cases we simplify into two categories. First there are higher emissivities (.8 and above) with reasonable backgrounds; this includes nearly all non-metals and most of the time we can measure temperatures pretty accurately even if we are not 100% accurate in our corrections. Second are uncoated metals and there we must be much more precise and accurate or we’ll get very, very poor results. Even when we are accurate with our corrections, it is easy to get poor results! So mostly I stay away from making those sorts of measurements.

    If our need for precision is very high, then, yes, we should adjust for emissivity and background for each and every single spot we are interested in measuring! Clearly that is a challenge. Being able to make these corrections after the image has been saved in the software makes life much simpler.

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