Amy bought me a thermoelectric cooler as an early birthday present. I saw a couple for sale in a Target a little farther north. We went to the Target in Cocoa Beach, but the only coolers they had ran on AC current. This seems a little pointless to me. If you have unlimited AC current, you probably should just run a regular refrigerator. They're a lot more efficient under those conditions.
I was bummed, but we went to Walmart, and they had a couple 12 volt DC coolers to choose from. I could go on a tangent here about how Walmart has upped it's game, and Target seems to be slacking, but I'll curtail that. Let's just say that I've visited a bunch of both stores on my trip south and I'm impressed with Walmart's newer stores.
If you're interested in how a thermoelectric cooler works, here's a Wikipedia link. Basically, it's a solid state device which when powered, cools on one side and heats on the other. I'm thinking that it is the same type of device which Grampa said powers outer planet space missions. I imagine that the degrading Plutonium on the spaceship heats the device and causes electricity to flow. I think it's the same device, but used in reverse. But I'm sure Grampa can clarify that.
This is one of the cool things I've learned from my limited engineering experience. A lot of devices work backward or forward. A generator is just a motor in reverse. A microphone is just an amplifier in reverse. You can take your ipod earbuds, plug them into your computer microphone jack and use them as a microphone. The sound quality won't be great. Probably because of design to make them work best as an amplifier. But they will work.
But anyway, so far I've been powering my new refrigerator only while I have the generator running. Cooling the stuff inside even for an hour or so makes a big difference over having no refrigeration at all. But I'm looking to get a solar panel to dedicate to the cooler.
Here's a photo of a radio shack thermoelectric device connected to some old solar cells I have aboard. If you place your fingers on it, you can feel one side cold, the other hot.
Monday, March 24, 2008
The New Cool
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11 comments:
Scott,
I'm on the ship tomorrow and Wednesday, off Thursday. But, we have a vehicle! Could go by truck for a cocktail this evening if you want. Paul's going to Tampa tomorrow for a hockey game. Let me know. I'm doing canvas repairs (ugh) on our Oday 272 today, but I'll be heading over to Merrit Island later, looking for a counter top icemaker. We used to have one that we ran into the ground, and I miss it. I'm thinking it'll be nice on the Gemini too as long as we have AC power.
Right you are Scott. When you put heat in you get electricity out and when you put electricity in you get cooling out (or heat rejection as another term). Thermoelectrics operate when there is a temperature difference across them.
In the spacecraft application, the plutonium produces the high temperature and space radiators reject the heat (minus the fraction converted to electricity) to space.
In the refrigerator application, pumping electricity in produces the temperature difference between the legs of the thermoelectrics, and the inside of the refrigerator is on the cold side while the outside of it is on the hot side. The difference between the two is equivalent to the energy of the amount of electricity you are pumping in.
Thanks for the confirmation Grampa!
Now my question is about efficiency. Of course there is a "conservation of energy". Energy in, energy out, whether that is electrical energy, motion, heat, light, etc.
What I've read is that a traditional fridge is 40% efficient, whereas a thermoelectric cooler is 10% efficient. I'm not sure what this means. I'm assuming that somehow the electrical energy is being used less efficiently for cooling. Perhaps it's being turned into more heat?
In the case of the space application, the efficiency of conversion of heat to electricity is about 8%. That means that about 92% of the plutonium generated heat is rejected to space.
In the case of your refrigerator, it's a little worse. Your solar collector is fairly inefficient in converting solar energy to electricity (this is one reason that nuclear RTGs are used for outer planet missions; however, there has recently been a dramatic increase in efficiency due to technological improvements, so maybe it would be smart to either wait or look for products using the new technology).
Beyond that, due to the about 8% efficiency of the thermoelectics, only about 8% of the electrical energy is translated to the temperature difference you see. The remaining 92% is rejected as heat.
You are dealing with the second law of thermodynamics, which is essentially the law of conservation of energy.
Of course, us nuclear folks must deal with a more modern concept due to Einstein, which says that the total of energy plus mass is conserved. We use the equivalency of E = mc 2 or mass times speed of light squared.
As usual, Grampa, I'm left thinking that your science is much cooler than my science.
I am glad that maybe I'll get to have some dairy products on my next trip! Real milk in my instant coffee!
That's only if I don't convert my fridge for space exploration before then.
There's a huge fire to the west of the Cocoa Village anchorage. I've got the boatcam pointed towards it. It's been spewing a tremendous amount of smoke for the past hour or so. Anyone know what's going on. I've searched the web, but haven't been able to find any info. Fortunately, the fire is downwind. Otherwise, I'd be hightailing it out of here.
Your comment about the benefits of being able to cool something down, albeit temporarily when low on power sources, is something I'd never considered. I'd always operated from the limited perspective that refrigeration required a more or less permanent committment and was therefore something to be wary of unless all the arrangements for an on-going power source had been met. I now recognize how being able to 'make' a cold beer, if only occassionally, can be a good thing even if you can't continue to keep things that way.
Along those lines, you can also use this cooler to extend the life of any ice you may take on-board.
It was interesting to read the e-mails of the couple who had spent the winter in the Abacos. I wonder if they ended up getting any lobster?
Hey Ross,
I suppose that is "inside the box thinking". We're all used to plugging things into a socket and getting a bill at the end of the month.
I'd think solar power and a thermoelectric cooler might be a practical solution for a lot of sailboats.
But anyway, I'm a little under the weather today. Amy caught something on the plane on the way down here, and I think I might have caught it from her.
I'm trying to power my way through it. The weather is supposed to be right for sailing north this week. Hopefully I'll feel better tomorrow.
Oh no. I'm sorry you're sick. At least I only took some of your sudafed. If it's any comfort, my cold hung on for a while but never got very severe.
Not what I want to hear. Couldn't you tell me that it hit you like a ton of bricks, but was over in 24 hours?
Found out what the smoke was yesterday. They were doing a controlled burn of some marshland. Whoa that was a lot of smoke!
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