I’ve had the good fortune to be on the Outer Banks of North Carolina this week. To redeem myself in the eyes of those still working away back in the office, I’ve done a bit of “Thinking Thermally” while here.
Surprisingly, it’s not been hard! The beach is one thermal event after another. Here are a few that just beg to be mentioned:
- Sea breezes: when I get to the beach early, the breeze is from the land toward the sea, but by late morning it has reversed itself. The sun is the power source, and the differences in temperature between the land and the water drive the breeze in one direction or the other from cooler toward warmer. And the wind, of course, is one of the most powerful heat transfer forces thermographers must deal with, but more on that another time.
- Hot sand: by afternoon it is nearly impossible to walk more than about twenty paces on the dry, hot sand! The first few steps are warm, the next few uncomfortable, and then it becomes painfully hot even if you hop and run. Years ago we named this phenomenon, in jest, the “Sarducci Effect,” after a local restaurant by that name where we first “discovered” the impact of accumulative conductive heat transfer when rubbing a finger across a sun-warmed table. Although thermographers don’t often encounter it, this “effect” is important to understand and anticipate.
- White car/black car: you don’t need an infrared imager to know that full spectrum sunshine is absorbed more efficiently by dark surfaces. But for anyone who is using an imager out-of-doors—even in overcast sun—the “zebra effect,” as it is also known, is powerful and influential as you can see from the attached thermal image of “Old Glory” in the sun.
- Heat islands: the town I’m staying in has consistently been 10-15oF warmer than the beach. This is because there is more convection and evaporative cooling at the beach, and less absorption of the sun’s energy by high capacitance materials like black pavement. The ocean is also a vast “heat sink”—though perhaps not as vast as we once imagined! It would be interesting to see a graph trending the temperatures of the two different areas over time.
- Condensation: the surface of my cold drink container is obviously below the dew point—not hard considering it is close to air temperature today! I wonder what is happening inside the walls of the house I’m staying in, given that the air-conditioner has been running all night long?
Next week we’ll talk specifically about heat transfer—more specifically, radiation. For now, I have to go enjoy the electromagnetic energy being radiated 94 million miles through space by our star and the thermal capacitance of this marvelous strip of beach!
John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner