| Published: July 11, 2010 – 8:05 pm
Can it be so hot you can fry an egg on the sidewalk? Is a hot sidewalk evidence of global warming?
This week, I was asked to comment on the big heat wave along the east coast of North America and the resolution of the scandal that came to be called âClimategate.â Along with these serious subjects, an egg got fried on a sidewalk.
As you may know, I strongly believe humans are making our world warm. The egg on the sidewalk provided me with a chance to talk about the fundamentals of heat transfer and about our changing climate.
I commented briefly that indeed Climategate was much ado about very little. The scientists were proven to not be hiding anything, and so on. Unfortunately it nearly derailed the real climate conference in Copenhagen. Several minutes later at the end of her show, journalist Campbell Brown showed some video of one of her CNN producers taking a shot at cooking an egg on a New York sidewalk. Â He had a bit of trouble, but I think he got the idea across. Itâs hot back east, very hot.
Using my radiant thermometer (pyrometer, such a word!), I satisfied myself that an egg on a griddle cooks well if the griddle is around 125 Celsius (260 Fahrenheit). Doing a bit more messing around, I found that an egg will cook on a surface thatâs only 55 Celsius (130 Fahrenheit). It just takes time â almost 20 minutes. So indeed, it can be hot enough to fry an egg on the sidewalk.
I can tell you from experience in the airplane electronics industry that you can, for just a moment, put your hand on a metal surface thatâs around 65 Celsius, about 150 Fahrenheit. Much above that, and you canât leave your hand there for more than an instant. You may have found yourself walking on a hot sidewalk or on hot sand, and you can just barely stand it (pun intended). Thatâs the temperature weâre talking about.
If you want to try this, please do. Post a picture on my Facebook page. Some more advice: use a little olive oil or butter on the sidewalk or street. This allows more heat to flow into the egg. This is âconductionâ of heat. Then, use an egg âringâ to keep things under control while the egg gets hot. You get your egg rings (if you donât already have âem) in the gadget section of a grocery store or cooking specialty shop.
The science to discover or keep in mind is that the sidewalk can get hotter, much hotter, than the air. The air this week was around 40 C (a little over 100 F). But the egg cooking area was a bit hotter than that because itâs not only heated by the air, itâs heated by sunlight, or sun-heat. It was heated by convection with the air, and by radiation of the sun. Black surfaces do indeed get hotter than not-so-dark surfaces. Asphalt gets hotter than cement. Hot enough to fry an egg. Oil helps conduct heat into the egg.
For me, this has everything to do with climate change. Everyone should keep in mind that if we made every black street a pale color, like white, or close to white, the world would indeed cool off. If we did indeed embrace solar hotwater systems for our houses and buildings, we would pump out much smaller amounts of greenhouse gasses.
If youâre a young or young-at-heart engineer or entrepreneur, consider coming up with an economical pale pavement material and getting rich! Same with a standardized solar hot water system. Rich! I tell you!
Two more good ideas. Think about it over fried egg, your poached egg, your egg salad sandwich, and your soufflĂ©.
Letâs change the world,