A Different Kind of Thermostat
CHAPTER 37 - Stuff That Melts and Freezes
In the morning, my wife normally drinks hot tea, which she enjoys even when it becomes lukewarm. However, on Sundays during the summer and fall, we both have coffee and freshly baked blueberry scones from a nice young couple, vendors at our weekly farmers market. We have this repast while watching Sunday Morning on CBS with Charles Osgood. Unfortunately, my wife, who drinks very slowly, does not like lukewarm coffee and I typically miss part of my favorite program going downstairs to heat up/replenish her cup.
Understandably, I was intrigued by an article titled "Running Hot and Cold Forever" in the HOT TECH section of the September 2013 issue of Discover magazine. The article shows a picture of what resembles a typical commuter coffee cup except that the cup has embedded in it a coil containing a "phase change material" (PCM) that serves to maintain the coffee at what the article says is the ideal drinking temperature of 140 degrees Fahrenheit.
Lest you think that a PCM is some sort of exotic material, one example of a phase change material is H2O, which exists in at least three phases: solid ice, liquid water and vapor (it's not the heat, it's the humidity). Consider the phase change from water to ice, or vice versa, freezing or melting. When water freezes to form ice, heat is given off. It takes heat to melt the ice, so heat is absorbed. When you have a mixture of ice and water, the temperature is normally maintained at 32 degrees Fahrenheit, the freezing point of water (or the melting point of ice).
In our aforementioned coffee cup, the PCM is some sort of (unidentified) compound made from vegetables by a Minnesota company called Entropy Solutions, using what it calls PureTemp technology. By using vegetable oils as starting materials, the company has managed to isolate from the veggies compounds that melt/freeze at temperatures ranging from 40 to 300 degrees Fahrenheit. So, you want your coffee at 140 degrees. There's a PureTemp compound melting at that temperature and you incorporate some of that compound in the coils of your cup. Pour your freshly brewed coffee into the cup when it's hot, perhaps around 200 degrees F. The hot liquid melts the PureTemp compound, which absorbs heat from the coffee and in a minute or two the coffee has cooled to 140 degrees, just right for drinking. Now, if you're like my wife and sip your brew slowly, the coffee would normally cool down. However, as it cools the PureTemp compound freezes, releasing heat and keeps the brew at an enjoyable 140 degrees. Voila!
So, a PCM in this case is simply a material that has a melting/freezing point and a significant amount of heat absorption/emission on melting/freezing. Actually, I'm reminded that my first publication after joining Bell Labs was on just such a material, germanium. Francis Hassion, Carl Thurmond and I published a paper in 1955 in the Journal of Physical Chemistry on the melting point of germanium. We measured both melting and freezing of various germanium samples prepared under a range of conditions and got values in the range of 937.5 + 2 degrees Centigrade. We concluded that the most reliable value was 937.2 + 0.5ᵒC, obtained by other colleagues at Bell Labs. At the time, values in the literature ranged from 926 to 975ᵒC, with the most widely quoted value in handbooks being 958-959ᵒC, significantly different from our value.
Just for the heck of it, I decided to Google "melting point of Germanium" and was pleased to see that our 1955 paper was one of the references that came up. Disturbing, however, was Wikipedia's value of 947ᵒC as the melting point. Most other sources Google turned up that I checked had values in the range of 936 to 938ᵒC, which are consistent with our Bell Labs results. Should I edit the Wikipedia entry? If so, how do I do it?
So much for the complex science of a PCM. I wish everything was that simple. I couldn't post this column without expressing my sadness at reading a recent NASA press release stating that the Kepler spacecraft, premier discoverer of planets outside our solar system, will no longer be able to continue its planet-seeking mission. Two out of its four spinning reaction wheels have failed and without them the spacecraft can no longer be pointed at its targets in space. NASA is trying to find some other use for the mission with only two wheels working. Fortunately, there's still a large backlog of Kepler data to be analyzed and the hope is that hundreds more planetary candidates will be added to the thousands already spotted by Kepler. What a fantastic job it's done.
I've mentioned before that I'm signed up to get NASA press releases and am bombarded with emails from NASA telling of findings on black holes, galaxies formed soon after the Big Bang, collisions of galaxies, discoveries by our rovers on Mars and the like. As a space nut, most of these are of interest to me. Occasionally, a press release deals with findings related to climate change or other matters of relevance to our own planet, Earth.
One such NASA releases this past week blew my mind. I had just watched an old BBC program with David Attenborough on the natural wonders of our planet in which he traveled to every continent. In North America he visited the Grand Canyon and I recalled sleeping in a sleeping bag near the edge of that canyon when four of us grad students from Pitt drove out west on a two-week jaunt. One would think that, after all these centuries of exploration and discovery and of viewing Earth from space, the topography of our planet has been thoroughly mapped out. Certainly something as large and spectacular as the Grand canyon would be hard to miss.
Well, NASA announced last week that decades of airborne radar data and work by NASA and researchers from the UK and Germany piecing together all that data and data collected by a multiyear NASA program on polar ice, Operation IceBridge, has yielded a startling finding. They've found a bedrock canyon in Greenland that's at least 460 miles long, longer than the Grand Canyon! In places, this canyon is 2600 feet deep, making it comparable in depth and general characteristics to portions of the Grand itself. How come we didn't know about such a natural wonder? It's buried beneath a mile of ice covering Greenland.
Let's hope that no human is able to set foot on that canyon in the next hundreds or thousands of years. That would mean that global warming has truly run amok; all that Greenland ice will have melted and sea levels will have risen to catastrophic levels. As it is, I keep seeing more articles on how we should be taking action now to counter global warming and to make plans to deal with rising sea levels already likely to occur in the years to come. In my view, we've already passed a tipping point and I shudder to think of more Sandys hitting our Jersey shores. As I recall, it was in a recent National Geographic that there was a map showing what the future shorelines of the world will look like, with so many major cities likely to be under water and goodbye to much of Florida.
Oh well, I personally won't be here to see all that happen. I have enough to deal with what with my hip replacement, acting as care giver for my wife and learning how to drive a rental Nissan Altima, with Florida license plates! Recently, there have been media accounts of a measles epidemic due to failure of some parents vaccinate their offspring. I think there's a StocksandNews disease, rear-ending, which seems to be contagious. Our editor, Brian Trumbore, has had his car rear-ended twice within the past few months. The second time he was parked in a parking lot and someone backed into him. This past week I parked on the street to attend a meeting. Emerging from the meeting, I wondered why a police car was parked behind me. The car was banged up with a smashed left stoplight and fender panel and broken side mirror. The officer explained to me that the fellow who hit the car was parking to attend the same meeting and his car had to be towed.
Before posting this column this morning, I decided to first go to the farmers market for my scones. On the way, I was listening to WNYC, our New York area public radio station, and a woman was being interviewed who was associated with the Kepler mission. I don't know her name but she was talking about the initial launch of Kepler and the time when they first "turned on" the telescope for a trial 10-day run. She described how extremely excited she was when, in that trial run, they found their first evidence for a planet orbiting another star. (OK, I just Googled WNYC and found that the woman's name is Natalie Batalha, a mission scientist at NASA Ames Research Center.) I can't help thinking how satisfying it must be to be associated with such a wonderfully productive project.
Oh, I almost forgot, PureTemp technology doesn't just keep coffee warm, according to the Discover article. Another PCM is used in a baby warmer and a "Cool Vest" uses a PCM to prevent overheating in both our human and canine troops in Afghanistan.
Next column should be posted on or about October 1.
Allen F. Bortrum