Wednesday, March 30, 2011

What Can Ice Cream Teach Us About Fluid Transfer?

Tony Cantone, President
The Hope Group

Here’s an interesting challenge for you fluid control experts. If you hold an ice cream cone out the window of a moving vehicle, will the ice cream melt more quickly or more slowly than if you keep it inside the vehicle? Keep in mind the issue of insulation and you may come up with the answer. If you want to know the answer, you can skip to the bottom of this post. Or, you can read a great article that I found in Cold Facts, a publication of the Cryogenic Society.

The article addresses the issue of sweating and frosting of vacuum insulated cryogenic fluid transfer. It explains the basics of heat transfer and its effects. It also addresses the control options for heat transfer. It describes the science and theory, but it drills down to explaining practical applications. The article concludes with a review of its topics:
  • Forced air flow can reduce or eliminate sweating and frosting under the right environmental conditions
  • Both an excellent and a poor thermally performing vessel will sweat and frost under the right environmental conditions
  • De-humidification can reduce or eliminate sweating and frosting under the right environmental conditions.
  • A vessel that has decreased vacuum quality, has a thermal short circuit, or no resistance to radiation will frost or sweat in nearly all environments.
  • Adding foam or fiberglass insulation to a vacuum insulated vessel is usually ineffective.
And that last point brings me back to the ice cream question. So which is it? The answer is the ice cream melts more rapidly outside than inside the vehicle in slow moving air. Inside the vehicle the ice cream creates a boundary layer of cold air, insulating it from air that contains a greater amount of heat.

With that lesson learned, read the article to learn more about fluid transfer and storage. Let me know what you think.