Archive for the 'Thermal IR' Category

Tiny Bubbles

My trip home for Christmas gave me my first shot at using my thermal IR camera in quasi-freezing conditions — it ended up being warmer than usual, but still dropped to freezing, or close to it, when the sun was down. I did a survey of my mom’s and a neighbor’s house (confirming for the neighbor that the section of roof where the snow melts fastest is warmer than the rest). Not surprisingly, the warmest parts were the windows, and we have lots of windows. The largest ones are now double- or triple-pane, so it used to be be worse.

Several basement windows, though, are still single-pane. The whole idea of insulation is to trap dead air, i.e. it won’t convect and it also conducts poorly, so I tried a little experiment: putting some bubble wrap up against the window, wrapped in some thin packing foam. I left a slice of it uncovered as a control.

You can see that the left side is noticeably warmer than the insulated part. I went online to see if anyone made insulation made specifically for glass, and ran across a site that had done pretty much what I did — just using two layers of large-bubble packing material so I went out and bought some. The basement windows are now no warmer than the rest of the cinder-block walls. The bubble wrap is translucent, so most of light still gets through.

I used the last of the wrap on some windows on the north side of the house, so I’m not blocking any incoming light that helps heat during the daytime. In my test, I blocked off one section

The window I tested is the one on the left. It’s slightly cooler than the rest. I used one of the other FLIR programs to confirm it’s about 1 ºF cooler than its neighbors (those pictures don’t get saved to the camera roll, though. Not sure why). These are multi-pane windows so the effect isn’t as dramatic, but every little bit helps, so I ended up covering up a few more windows to use up the bubble wrap I had bought. They’re in a part of the room that’s partly blocked anyway, so it doesn’t really impede looking out. This could be re-used from year to year (the basement windows probably left up permanently) and only took a few minutes to do.

I Can See Right Through You

Having some more fun with my thermal camera (after a cold kept me from it for a bit). I had noticed that my lunch did not show up while being microwaved, because long-wave IR generally doesn’t pass through glass — here’s another image confirming this

You can’t see the thermal signature of my hand that’s behind the window. This is, of course, responsible for the greenhouse effect — visible light goes in but thermal IR does not leave, making the greenhouse (or your car, or, with a more wavelength-selective effect, the planet) get hotter.

I wanted to see if I could find anything that was transparent. I checked the transmission of sapphire and discovered it was a possibility — the transmission cutoff is out at 5 microns. Alas, the windows were opaque, meaning either that the windows I looked at were antireflection-coated (a distinct possibility), or that the bolometer sensors aren’t sensitive at the shorter wavelengths. But the plastic bag this window is in transmits just fine!

It’s probably made of polyethylene, which has good transmittance in much of the thermal range — just a few absorption lines (at about 3.5, 6.5 and 13 microns). We happen to have some 1/16″ thick poly sheets, we use for our air sled to allow it to work over porous surfaces, and are opaque to visible light. But not to thermal IR!

You can see a couple of spots where I touched the sheet with my fingertips and warmed it up, but in the picture my hand is behind the sheet and not touching it.

That's So Hot

Finally got my FLIR One thermal-IR camera working (the issue was with the phone to which it’s attached), and it’s amazing.

This is my kitchen sink, with a bowl full of room-temperature water in it, along with some utensils, and the water on hot, aimed so it hits the basin rather than going straight into the drain.