Thermodynamics B/C

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Re: Thermodynamics B/C

Post by WhatScience? »

I am currently looking ways to make a detachable lid for the device that is close to airtight. Any suggestions?
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Re: Thermodynamics B/C

Post by retired1 »

A round oatmeal container could be cut down as needed to meet the height requirement and the lid fits snugly and easily. (It is also easy to cut the required hole in the top. If you do a lot of testing, I would spray the upper portions with a clear spray like lacquer to keep it from getting soggy. A second unit would be nice. Note that it weighs very little and is thin cardboard so it will not suck up much (if any) heat.
The last time this event was done by one of our schools we made a plug that fit into the beaker .this was done with scrap balsa and a plastic bag from a food store. The plug needs a hole in it also. Anything that does not suck up a lot of heat and cuts down the convection currents will help if it is easy to use.

We used air as an insulator by using mylar bags ( with a silvered surface) from coffee or chips about 1/4" apart. 3 layers.
Got a cup of coffee that was hot yesterday and they had the foam holders to keep the heat from transferring to your hand. A couple of these cut to fit and scotch tape taped together very probably help. If nothing else, you could bring the beaker of hot water back to your station. 60 to 90 C is HOT. I would actually recommend using a rubber dish washing glove for safety.

We made a grid to fit under the beaker. Minimum contact with the beaker. We used 1/8" wood but cardboard might work just as well.
Aero gel is great stuff, but it might not be needed as layers of air will work well.

For the very talented with shop resources, you could make a vacuum container out of larger plastic beakers. Hot glue a ring lid onto it and evacuate the air with a vacuum pump, either an electrical or hand manual one will work. Check with your chemistry dept to see if you can borrow a valve. The drawback to this is the amount of heat that the inner plastic beaker would absorb.
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Re: Thermodynamics B/C

Post by WhatScience? »

Thanks retired. Don't know if I will end up using this but definitely worth a couple tests.
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Re: Thermodynamics B/C

Post by Ashernoel »

The smaller 250 ml beaker I linked above has a lower base diameter of 5.60 cm, a height of 9.00 cm and an upper diameter of 7.00cm
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Re: Thermodynamics B/C

Post by wzhang5460 »

I think there isn't an advantage of plastic or glass beakers as the beakers in the insulator and the beaker without the insulator are the same, so the insulating properties of the beaker cancel out. Correct me if I'm wrong but I don't think plastic or glass beakers will make a difference in score.
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Re: Thermodynamics B/C

Post by retired1 »

The HRF is interior temp divided by exterior. A glass beaker is about 130g and a plastic one about half of that. with a 20C lab temp and 80C water temp, the water is going to give up wt x delta t or 130 x 60 (7,800)calories for the glass beaker. The plastic one will take a while to do that but that beaker will only absorb 65 x 60 (3,900) calories. If everything else was equal, the exterior water would be warmer which would yield a lower HRF value. You want the HRF value to be as high as possible for the HS score.

Now with a good design "box" the remaining water temp will lose temperature much slower with a plastic beaker as it is a relative insulator. The ability of the plastic beaker to transfer heat to a well insulated material (Air is my choice) will be even slower than a glass beaker. So the plastic wins this portion. Now look at the PE ---- Final interior temp minus predicted temp over the final interior temp. Hopefully the top portion of this would be close to zero. for example it is 2 degrees. That divided by say 70C would be a smaller number than if it were 60C. Since this final number is subtracted from 1, you would like the subtracted value to be as small as possible since it is 1 minus ? is times 25 for the PE.

Note that the interior temp will be higher by 3,900 calories with the plastic beaker (from the first portion of the example)

The test score is the most important part of this event. But, You would like the lab portion to be as high as possible as it is a tie breaker.

So, The plastic is slightly better if you are going to do precision lab work.
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Re: Thermodynamics B/C

Post by wzhang5460 »

I thought that since you are using the same beaker for both the outside temp and insulated temp, the insulating properties of the beaker itself would cancel out. Let's say you have a plastic beaker, which is a better insulator than a glass one. Although the final temperature of the insulated beaker would be higher than if you used a glass beaker, the final temperature of the outside beaker would also be higher than a glass one. So when the Interior is divided by the Exterior there will be no difference in the final HR score since they are both increased by a factor of x, canceling each other out.
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Re: Thermodynamics B/C

Post by Ashernoel »

Plastic breakers are thinner to allow a higher r value of insulation? You can have the insulating material closer with a thinner beaker.
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Re: Thermodynamics B/C

Post by BasuSiddha23 »

Has anyone tried a vacuum? Would you suggest using that rather than using the mylar bags mentioned earlier? Our plan was to use a vacuum on the outer layer of the device, and on the inner layer, use aerogel which surrounds the beaker. Also, would 3-D printing any parts be more efficient?
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Re: Thermodynamics B/C

Post by wzhang5460 »

I think the aerogel itself is enough for insulation, I don't really think the vacuum on the outside will have any difference since the aerogel should be able to keep in most of the heat.
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