Training Day 3, Part 2

Did you know that hot always flows towards cold? Knowing this can be of huge help to a thermographer. A flow of thermal energy will occur when there is a difference in temperature between two objects. Heat transfer is a big deal in the infrared thermography world, and we talked a lot about it today. We, as professionals in the thermal imaging world, must understand how this works in order to accurately analyze what is going on in an image. We also must understand the difference between convection, conduction, and radiation and the concept of heat capacity. To the left is an image that can help you visualize the difference between some of these concepts.

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Conduction- The transfer of heat energy through a material (solid, liquid, or gas) by the motion of adjacent atoms and molecules.

Below, the heat from the burner to the pan is an example of conduction. Also, the walls of a home that are insulated or not insulated show up in an infrared camera because of conduction.

Convection- Heat transfer due to bulk movement of a fluid.

Below, the bluish streaks below the window you see under the window is caused by convection. We also have seen convection occurring when balloons are let go at a football game and are carried aloft as a result of warm air rising.

Radiation-The process of transferring energy by electromagnetic waves. No medium required!
- Heat is transferred by emission & absorption

- Both objects emit and absorb radiation

- Radiation occurs from all object above 0 degrees Kelvin (That’s really cold!!)

On the right, heat is being emitted by the coals of the grill and radiating to us and any food that would be held over them.  This is also how the sun heats us and the earth. 
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The hard thing here is to remember that even cold things emit and absorb infrared radiation. It isn’t just only the warm stuff that we see when using the infrared camera as shown by the images taken from a freezer shown below. 

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Roof Scan, water trapped colored orangish-yellow.

Heat Capacity is the ability to store heat. Objects with high thermal capacity react slower to temperature changes, meaning they require more energy to change their temperature. Water has a pretty high thermal capacitance, and knowing this can help us with a few things. Watching  a target when it is heating or cooling may offer diagnostic clues. For instance, with water being of high thermal capacitance, it tends to be easy to see when their are leaking problems on a roof. After a long day in the sun, water that is on the roof soaks up the sun (called solar loading) and keeps that energy longer. When an IR inspection is done, the water shows up easier on a scan because it does not cool down as quickly as its surroundings. You can point out where the water is as long as the temperatures allow for it...which may mean you have to go inspect in the middle of the night!

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The rest of the day we talked about using infrared for electrical applications, but I will talk more about these in a later blog post. We ended the class with more labs and practice with our cameras. We had time to ask questions and get familiar with everything that we were taught. We also went through a study guide for the test that was coming up on us very quickly! Oh..did I mention I didn't miss any on the quiz? Woo!

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This was the last full day of training. In class on the last day, we go over a few more applications and then review for the test. This week has flown by! I cannot believe how much stuff we have gone through. Here is to getting a good grade on the test! Cheers!


Christina


P.S.- Come back next week and hear how my last day went!