Your trying to measure the infrared emission of a mirror that reflects infrared???
jn
Scott, the issue was we really aren't in a major disagreement. When I get a chance I'll paint 1/2 of a sheet (say 2" x 12") of aluminum black and place a resistor in the middle. You can predict the difference at the edges, I'll do a measurement.
Right, the walls and ceiling radiate at the same temperature as the black half (everything in the environment is relatively at equilibrium). The instrument just picks up the thermal reflection of the ceiling. The difference arises when you actually heat the plate well above the local environment.
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What about if they are not being heated? I just took mine into the bathroom and scanned acroos the vanity mirror to the pitch black frame, less than .1 degree change. Couple of degrees on the stove black glass vs polished stainless, far, far less than the emissivity difference.
EDIT - more importantly from your viewpoint should the temperature of a very refective surface (emissivity < .05 or so) always measure almost negligable? This is not my experience.
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Zeroth Law. Doesn't seem to be well known or at least not well appreciated.
Your IR temperature device is at the same temperature as everything else. How could it pick up a difference?.
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You are on to it!
Answere this one - something any one can experience - and then 'connect the dots':
you are standing around an outdoor pit fire... no breeze/wind. The smoke rises straight up. But as you stand closer to the fire, the smoke is drawn over to you. You move around to the other side and soon the smoke is drawn towards you and in your face again. Why is the smoke drawn to you??
Thx-RNMarsh
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Mr Wurcer,
welcome to the hot club.
Once a week, I prepare my own chili paste ration. Once a month, an occasion to spend emotional quality time with madame Jeanette.
A word of warning, there's another vital part not to touch after a rub-down.
(you have no idea how stray-minded some capsaicin users can be, time and again. sometimes I long back to the times of bumping my head on a daily basis)
In order for the heat sinks to work efficiently there needs to be air movement allowed, right? Cool air entered from the bottom side and open area above it for the hotter air to escape. The effeciency is a litttle higher when black. But if you have enough forced air past the fins, they dont need the extra cost of being black treated. and....
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What caused a draft?
The temp difference from the front side to your back side has a temp differential thus the draft.
Thx-RNMarsh
Not quite the point the shiny part reflects the same power as the black part radiates. If you heat the plate the plate to 300C you will measure a difference. Stefan's estimate of the sun's temperature was a brilliant experiment (so to speak), we forget how smart these guys were.
And I thot hot air from the fire rose, causing the draft....
You mean it's not because I created a low pressure area in front of me?
You mean it's not because I created a low pressure area in front of me?
You cause a pressure drop on your side away from the heat (cooler on the back side).
-RNM
suppose my body occupies 10 degrees of circumference around fire but the air sweeps in from the whole 360, except where i'm standing facing the fire.
am i wrong in thinking there will be a low pressure area in front of me, like down stream side of a rock in the river?
the air doesnt sweep in from the whole 360. Its already there. the air temp diff betwen the front of the body and the cool back causes the draft to come towards you... the pressure drop on the cooler side draws the hotter air towards you.
Though I suppose there is some diff from the middle of the fire to your front side... the smoke would go straight up if your body wasnt there ... -->
I was with a group of guys about 100-150 miles north of LasVegas. In the middle of that Keep out under penalty of Death or worse... the No Fly zone seen on the maps. A few of us were around a fire someone built to keep warm in the evening; A beer party after or before our nuclear underground 'event' occured. All the instrumentation, installation and controls were completed. One of the nuclear physicists there explained it to me/us as I stood around and I and others kept getting smoke drawn to us when we approached the fire. he said... go over to the other side - the air isnt going that direction. Sure enough.. I go stand over there and soon the smoke would follow me and be in my eye/face. Then he told me why it happens. I have no reason not to believe him....so passing it along.
Thx-RNMarsh
Though I suppose there is some diff from the middle of the fire to your front side... the smoke would go straight up if your body wasnt there ... -->
I was with a group of guys about 100-150 miles north of LasVegas. In the middle of that Keep out under penalty of Death or worse... the No Fly zone seen on the maps. A few of us were around a fire someone built to keep warm in the evening; A beer party after or before our nuclear underground 'event' occured. All the instrumentation, installation and controls were completed. One of the nuclear physicists there explained it to me/us as I stood around and I and others kept getting smoke drawn to us when we approached the fire. he said... go over to the other side - the air isnt going that direction. Sure enough.. I go stand over there and soon the smoke would follow me and be in my eye/face. Then he told me why it happens. I have no reason not to believe him....so passing it along.
Thx-RNMarsh
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Richard, I'm not sure you're correct with your explanation.
When the hot air (and smoke) from the campfire rises it is replaced by the cold air from its surroundings (360 deg). When you stand near the fire facing it, your body is an obstruction, disrupting airflow, and vortex forms in front of you. This vortex begins to circulate and draws some of the smoke towards you. Something like that. I don't think it has anything to do with the body temperature.
(Google for "sea breeze" for some pictures)
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