Instead, the bubbles that do form coalesce into one large bubble that sits on the heated surface. As the heated fluid reaches its boiling point, the bubbles do not rise to the surface. Meanwhile, the remaining water further away from the heat source stays relatively cool. The warmer water cannot rise instead it remains near the heat source, getting hotter and hotter. Without gravity, the effects of buoyancy and convection are absent. In space, however, bubbles behave differently. In fact, so effective that ultimately it leads to more complex boiling called transition boiling-the highly turbulent bubble flow that indicates the water is now hot enough to cook your pasta. This bubble formation is called nucleate boiling a far more effective way to transfer heat than natural convection on its own. This motion not only helps to move the water around more quickly (think stirring), but the bubbles themselves transfer heat energy as well. When the boiling point is breached, you finally begin to see the tiny bubbles of water vapor you’ve been waiting for! The bubbles rise, due to buoyancy, and then collapse as they reach the denser, relatively cooler water at the surface of the pot. To get those bubbles, you have to wait long enough for the bottom of the pot to get hotter than the boiling point of the water. Without buoyancy or convection, boiling fluidsīut natural convection is not enough, as it does not yet provide those bubbles you need for your pasta.
This is known as natural convection-the movement of molecules through fluid-which is a primary method of heat (and mass) transfer. The water molecules in your pot continually exchange in this way, thanks to gravity, eventually warming the entire pot of liquid. The rising hot water is replaced by the cooler, more dense water molecules. First, the liquid on the bottom of the pot closest to the heat source starts to get hot as it does, it rises. It seems straight-forward enough here on Earth: you turn on the burner, wait a few minutes, and when all those small bubbles appear, you’re ready to get cooking.Īs you wait for your pot of water to boil, there is a complex process going on in there. To simplify a bit, boiling is actually a very efficient heat transfer process and, in this case, boiling transfers the heat from the fire on your stove to the water that will cook your pasta. (Image courtesy of Markus Schweiss via Wikipedia) On Earth, water boils via natural convection. But what do those bubbles tell you and what makes them the key indicator of perfect pasta water temperature? You’re anxious to see the bubbles that signify that you can put your pasta into that water. You are staring impatiently at the pot when the water looks like it’s starting to swirl. Your pot of water is on the stove, you’ve turned on the maximum heat, and the wait for boiling begins. If you don’t think of yourself as the type of person who could ever be interested in physics, let’s boil this down. This week, comments from guest blogger and International Space Station Associate Program Scientist Tara Ruttley, Ph.D., as she reflects on the physical science of boiling in space.
0 kommentar(er)
