Thermodynamics B/C

[Alex-RCHS]

What we did at our invitationals was bring a thermometer to measure the temperatures ourselves.

Also, we tried using Newton's Law of Cooling for predictions, and when we did this, it was off by many degrees. Am I doing something wrong or is everyone having this problem?

I have not tried using Newton's Law of Cooling to predict temperature but I can tell you with certainty that the setup for thermo is far more complex than Newton's Law of Cooling is able to predict. Other factors such as evaporation, condensation, convection, the varying thermal properties of the materials of your beaker and device, etc., play important roles.

Newton's Law creates a constant (k) for the device that is used in the equation to predict the temperature. As a result, those factors that you have mentioned earlier are accounted for in the constant.

The equations for Newton's Law of Cooling is T(t) = Ts +(T0 - Ts)e^(-kt)

where:
t = time taken for the cooling
T(t) = the temperature of the given object at time t
Ts= the surrounding temperature
T0 = the initial temperature of the object
k = decay constant

Still, that’s very much theoretical. There may be other methods of estimating that work better in practice. It’s best to experiment.

[kendreaditya]

Still, that’s very much theoretical. There may be other methods of estimating that work better in practice. It’s best to experiment.

I strongly agree.

[Pizzacats]

Are there other equations or laws to predict, or should we just use whatever temperature the graphs we made usually say?

[kendreaditya]

Are there other equations or laws to predict, or should we just use whatever temperature the graphs we made usually say?

I mean the past couple of pages have been about Netwons Law of Cooling . But other than that I am pretty sure there aren't any other equations. However, I strongly suggest creat a funtion for each water amount, this is alot more accurate.

[CookiePie1]

Are there other equations or laws to predict, or should we just use whatever temperature the graphs we made usually say?

I mean the past couple of pages have been about Netwons Law of Cooling . But other than that I am pretty sure there aren't any other equations. However, I strongly suggest creat a funtion for each water amount, this is alot more accurate.

What I do is, using past data, logically estimating what the end temperature will be. It's not very mathematical, but it works very well and my predictions are on average 1-2 degrees off.

[kendreaditya]

Are there other equations or laws to predict, or should we just use whatever temperature the graphs we made usually say?

I mean the past couple of pages have been about Netwons Law of Cooling . But other than that I am pretty sure there aren't any other equations. However, I strongly suggest creat a funtion for each water amount, this is alot more accurate.

What I do is, using past data, logically estimating what the end temperature will be. It's not very mathematical, but it works very well and my predictions are on average 1-2 degrees off.

Thats what I do, but I wonder what is affecting the device, I think it was the ambient temperature, but I have not got around to test that out.

[superpenguin666]

This is off topic,
but does anyone have any recommendations for sites to buy aerogel from and the amount needed? State is coming up, and I want to make sure I bring a good box to competition.
Thanks!

[CookiePie1]

See this quote from cuber.

Could any of you share some reputable links for buying aerogel?

You can get 250cc of granular aerogel from this website: http://unitednuclear.com/index.php?main ... ucts_id=89 for only $13.00 (Have made successful purchases from that site in the past).

250cc might be enough, with a custom shell, to create a 1-2cm thick gel barrier around the beaker, plenty considering how well aerogels insulate. Then again, if you wanted to fill up the entire 3,375 cm3 space it would cost you about $160.

This is also where I got mine from.

[kendreaditya]

See this quote from cuber.

Could any of you share some reputable links for buying aerogel?

You can get 250cc of granular aerogel from this website: http://unitednuclear.com/index.php?main ... ucts_id=89 for only $13.00 (Have made successful purchases from that site in the past).

250cc might be enough, with a custom shell, to create a 1-2cm thick gel barrier around the beaker, plenty considering how well aerogels insulate. Then again, if you wanted to fill up the entire 3,375 cm3 space it would cost you about $160.

This is also where I got mine from.

Same with me, but I recommend using something different because aerogel is very messy and unreliable. If water is dropped into the aerogel, the R-value immediately changes. And most teams put a barrier between the aerogel and beaker to make sure the aerogel does not stick to the beaker. This defeats the purpose of using aerogel, as the barriers now conductions most of the heat from the beaker. In my option, aerogel is not necessary, as many other great insulators exist.

[IDon'tKnowMyName]

See this quote from cuber.

You can get 250cc of granular aerogel from this website: http://unitednuclear.com/index.php?main ... ucts_id=89 for only $13.00 (Have made successful purchases from that site in the past).

250cc might be enough, with a custom shell, to create a 1-2cm thick gel barrier around the beaker, plenty considering how well aerogels insulate. Then again, if you wanted to fill up the entire 3,375 cm3 space it would cost you about $160.

This is also where I got mine from.

Same with me, but I recommend using something different because aerogel is very messy and unreliable. If water is dropped into the aerogel, the R-value immediately changes. And most teams put a barrier between the aerogel and beaker to make sure the aerogel does not stick to the beaker. This defeats the purpose of using aerogel, as the barriers now conductions most of the heat from the beaker. In my option, aerogel is not necessary, as many other great insulators exist.

I agree with kendreaditya.

We initially used aerogel to surround the beaker and we lost a decent amount of our aerogel. I think simple foam sheets that are topped with aluminum should be enough to insulate the beaker and only have a small temperature loss. Anyways, prediction is much more important and aerogel makes your prediction off because of its unpredictability. At the invitationals I went to, the top ranking teams had a simple design and scored well on the prediction.