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Teachable Moment #2

Outta Control

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Alight gents. Let's talk about Thermal Science specifically Heat Transfer.

If you could remember back in college or even high school there are three methods of transfer.
1. Conduction
2. Convection
3. Radiation


We are going to cover Radiation and Convection.

Let's take at look at Radiation. Radiation is what every object (living or not), particle, or substance emit. This radiation is what makes up the Electromagnetic Spectrum.


1. Now let's take a look at this photo:


It is an RGB photo of 2 glasses resting on top of a table. The ambient temperature is within the 50F, but should not matter for this example.

As you can see, there is a light source coming from the left side, and casting a shadow of the glasses on the table. This is a great example of what Radiation heat transfer looks like. If I were to take a thermal image of those glasses, at the current condition, we would see the left side of the glass glow warmer than on the right side.

The light source's radiated heat flows from the lighting element through the air, and is being absorbed by the glasses' material and is being emitted out.

2. Now take a look at photo #2:


This now is a thermal image of the same glasses, on the same table, but now is being subjected through Thermal Convection from a propane patio heater, coming from the right side and out of the thermal image frame.

As you can see, there is the larger amount of thermal radiation being emitted from the patio heaters, forcefully being
absorbed by the glasses' right side. See the photo below.



Conclusion:
What this experiment shows are some of the ways heat transfers occurs and based on objective observation we can logically identify each of the different ways heat is transmitter.

Thank you.
 
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ArrUnTuS

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Thanks to you for sharing your knowledge, and with examples and everything, which is as best understood. This, at least for me, helps me to put my feet on the ground and understand that it's not just taking a thermal camera and flying, you have to have a good base to be able to provide the customer good results.
 

AH-1G

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Alight gents. Let's talk about Thermal Science specifically Heat Transfer.

If you could remember back in college or even high school there are three methods of transfer.
1. Conduction
2. Convection
3. Radiation


We are going to cover Radiation and Convection.

Let's take at look at Radiation. Radiation is what every object (living or not), particle, or substance emit. This radiation is what makes up the Electromagnetic Spectrum.


1. Now let's take a look at this photo:


It is an RGB photo of 2 glasses resting on top of a table. The ambient temperature is within the 50F, but should not matter for this example.

As you can see, there is a light source coming from the left side, and casting a shadow of the glasses on the table. This is a great example of what Radiation heat transfer looks like. If I were to take a thermal image of those glasses, at the current condition, we would see the left side of the glass glow warmer than on the right side.

The light source's radiated heat flows from the lighting element through the air, and is being absorbed by the glasses' material and is being emitted out.

2. Now take a look at photo #2:


This now is a thermal image of the same glasses, on the same table, but now is being subjected through Thermal Convection from a propane patio heater, coming from the right side and out of the thermal image frame.

As you can see, there is the larger amount of thermal radiation being emitted from the patio heaters, forcefully being
absorbed by the glasses' right side. See the photo below.



Conclusion:
What this experiment shows are some of the ways heat transfers occurs and based on objective observation we can logically identify each of the different ways heat is transmitter.

Thank you.
Architecture 101, it's been awhile.
 
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Outta Control

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Thanks for taking the time to create this series. Very informative.

When you have more than one heat source, say the sun (radiation) and a leak or poor insulation. How do you determine what's happening? Or is that a subject for future thread?

That is a great question.

I will respond to your questions with not much detail but may consider this cover is the near future.

So what we have is 2 heat sources (Sun and leak). The super quick answer is as long as we can #1 eliminate reflections/refraction and #2 there is a heat differential between the sun's radiated heat and the potential leak you could spot the weak point. The other quick answer and the solution I would do is eliminate the variable, which is the Sun, out of my total equation. This means as the leak will generate heat, I could operate at night to have larger ambient temperature environment and eliminating most or all of any external heat source.

Hope this makes sense.
 

Sojourner60

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Yes it does. Thanks. Don't you have to get a waiver to fly at night? Or am I over thinking it? I suppose if ya took the photo in the morning, you could retake in the afternoon so you don't have direct sunlight on the part of the roof in question., Or vice versa. Wait till close to dusk and make a quick flight could be another option.
 

Outta Control

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Yes it does. Thanks. Don't you have to get a waiver to fly at night? Or am I over thinking it? I suppose if ya took the photo in the morning, you could retake in the afternoon so you don't have direct sunlight on the part of the roof in question., Or vice versa. Wait till close to dusk and make a quick flight could be another option.

Yes you would need a Night Waiver but you do have the 30 minutes before civil twilight. So I would do the test during early morning. ;)
 

ArrUnTuS

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Yes you would need a Night Waiver but you do have the 30 minutes before civil twilight. So I would do the test during early morning. ;)

Interesting, so you guys have a deadline of 30 minutes from the official time of dusk and dawn?

Here the condition is "optimum visibility conditions". Then as in an open condition to interpretation like this one you have to hold on to..... it is not a total night, there is still some light....... :rolleyes:
 

Outta Control

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Yeah there is incoming radiation but such as the example I made. Early morning is most advantageous since the ambient air is cooler and the surrounding object and structure should be cool enough to detect a heat transfer.
 

Dave Pitman

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ArrUnTuS

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It's called "civil twilight" by the FAA. They have used it for years to define when "night" starts and ends with regard to full scale pilot ops. Only natural they use what they already have.

Night flying: Sort through the different definitions of night - AOPA

"civil twilinght" -> is the "period beginning one hour after sunset and ending one hour before sunrise.". If I understand correctly, 30 minutes before is 30 minutes of darkness after dark and just before dawn? Would that be correct?
 

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