Thermodynamics B/C

[arv101]

Definitely have a thermometer of your own to measure the initial water temperature inside of your beaker. For a 65 C water pot at 100 ml, the water decreased to around 58 C in my beaker, so at least make sure to account for a drop in initial temperature. At 100 C, between scooping the water then into the beaker, the 100ml went down to 86 C which then, after 30 minutes, decayed to 74 degrees.

For such a large time constant for your box, a linear or quadratic or exponential curve works. I know for my box, an exponential curve fit right along Newton's law of cooling derivation(mostly due to conduction). I advise using excel or a similar spreadsheet for data collection because your data is then stored in a more secured location without risk of accidentally deleting it.

Your results look impressive.. What have you used for constructing the box?

A medicinal styrofoam box with cottonball stuff around teh beaker with a cap: a very simplistic design for now.

Wait inside the box, is the beaker resting on cotton balls? Because don't you have to elevate the beaker to meet the 12 cm requirement? You can choose not to answer totally fine.

[Justin72835]

For those of you dying to get your hands on a challenging test, I can assure you one will be created imminently, (over Winter Break). If you wish, I can even develop rankings for scores on the tests for all to see. Let me know how you would like this to be done and importantly, what topics you think I should test on. I have more information than I can handle.

Any word about the test?

[takuramen89]

Hello!
I just want to check if im doing my stuff correctly.
Right now i'm doing multiple test for different amounts water/temperatures. (aiming for 20 total different combinations). So, am i doing this correctly? since I'm halfway done and im getting skeptical that im doing this completely wrong.
Also, right now im averaging about 1.5 - 1 degree drop per 5 mins, is that good?
Thanks.

[ClaireAndreasen]

Hello, I am new to this forum and had a few questions

1. The device must be made to keep radiation in (right?). But I read that radiant barriers are supposed to have a space of air in front of the reflective part. If they have a space of air in front of the reflective part, isn't that extremely conducive for convection? Additionally, most radiant barriers are mad out of metal-like materials. So basically, how is one supposed to make a radiant barrier that isn't also a really good conductor and convector?

2. I am having a hard time finding good polyurethane foam to purchase online. Does anybody have good links or should I call a foam provider? Also, is it best to use a pourable foam, spray foam, or foam sheets?

3. To create the layer that fits to my beaker, would it work to use a flexible spray foam and spray it on my beaker covered in foil?

4. Would a mylar blanket work as a radiant barrier?

[Justin72835]

Hello!
I just want to check if im doing my stuff correctly.
Right now i'm doing multiple test for different amounts water/temperatures. (aiming for 20 total different combinations). So, am i doing this correctly? since I'm halfway done and im getting skeptical that im doing this completely wrong.
Also, right now im averaging about 1.5 - 1 degree drop per 5 mins, is that good?
Thanks.

At least for me, that seems like a pretty solid way to test. After doing all those tests, I would then plug the numbers into a calculator or something to find a good regression function for the data.

As for the 1-1.5 degree drop every 5 minutes, I think your results are actually really impressive.

[Justin72835]

1. The device must be made to keep radiation in (right?). But I read that radiant barriers are supposed to have a space of air in front of the reflective part. If they have a space of air in front of the reflective part, isn't that extremely conducive for convection? Additionally, most radiant barriers are mad out of metal-like materials. So basically, how is one supposed to make a radiant barrier that isn't also a really good conductor and convector?

Rip double post

For your device, you actually have to worry about both conduction and radiation, although I would say conduction is a little more important (don't worry about convection).

Anyway, radiation is usually solved using metallic materials (like you were saying) since they are able to reflect incoming radiation. If you were to use blocks of metals, then, of course, the heat would just leave the water through conduction. This is why reflective insulation is done using multiple thin sheets of metal and spacing them out with either stagnant air or a vacuum. The spacing in between is what prevents conduction. All this may sound pretty hardcore but it can be done pretty easily with a ton of aluminum foil with small pockets of air in between.

Obviously, convection isn't really an issue here since the pockets are so small (couple millimeters), but if you want you could use bubble wrap in between or other insulative materials (which most of the time also have stagnant air pockets) to completely mitigate any convective effects.

Not too sure about your other questions though.

[Alex-RCHS]

Hello!
I just want to check if im doing my stuff correctly.
Right now i'm doing multiple test for different amounts water/temperatures. (aiming for 20 total different combinations). So, am i doing this correctly? since I'm halfway done and im getting skeptical that im doing this completely wrong.
Also, right now im averaging about 1.5 - 1 degree drop per 5 mins, is that good?
Thanks.

At least for me, that seems like a pretty solid way to test. After doing all those tests, I would then plug the numbers into a calculator or something to find a good regression function for the data.

As for the 1-1.5 degree drop every 5 minutes, I think your results are actually really impressive.

The temperature should drop a lot more in the first few minutes than near the middle or end, so the “average” isn’t a very good way to compare. The standard, based on what others have posted, is 100 mL at 90C for 30 minutes (I believe).

Hello, I am new to this forum and had a few questions

1. The device must be made to keep radiation in (right?). But I read that radiant barriers are supposed to have a space of air in front of the reflective part. If they have a space of air in front of the reflective part, isn't that extremely conducive for convection? Additionally, most radiant barriers are mad out of metal-like materials. So basically, how is one supposed to make a radiant barrier that isn't also a really good conductor and convector?

There are some options out there that are only part metal. Also keep in mind that most substances used as radiation barriers are extremely thin. They don’t increase conduction rates much at all.

[JoeyC]

Hello, I am new to this forum and had a few questions

1. The device must be made to keep radiation in (right?). But I read that radiant barriers are supposed to have a space of air in front of the reflective part. If they have a space of air in front of the reflective part, isn't that extremely conducive for convection? Additionally, most radiant barriers are mad out of metal-like materials. So basically, how is one supposed to make a radiant barrier that isn't also a really good conductor and convector?

2. I am having a hard time finding good polyurethane foam to purchase online. Does anybody have good links or should I call a foam provider? Also, is it best to use a pourable foam, spray foam, or foam sheets?

3. To create the layer that fits to my beaker, would it work to use a flexible spray foam and spray it on my beaker covered in foil?

4. Would a mylar blanket work as a radiant barrier?

In response, yes the device should be made to keep radiation in, and while radiant barriers do allow convection, the heat loss from convection does not matter as much in this event. To find PUR foam, just go to Lowe's or Home Depot, they have plenty of foam insulation there, board and spray. Make sure to find boards with good R-value, and make sure the boards are faced. This means that they have vapor protection, so they won't deteriorate due to the moisture. Plus, some facing is reflective and functions partly as a radiant barrier.

[CurryMuncher]

So I'm a pretty big noob to all this but just for clarification in simple terms, we are building a box which is going to hold a hot thing. We need to make sure our box can hold in the maximum amount of heat possible and we are going to be judged based on the amount of heat we keep in? A basic example is cardboard box with cardboard box stuffed? Plz dont judge, im really bad with english

[Unome]

So I'm a pretty big noob to all this but just for clarification in simple terms, we are building a box which is going to hold a hot thing. We need to make sure our box can hold in the maximum amount of heat possible and we are going to be judged based on the amount of heat we keep in? A basic example is cardboard box with cardboard box stuffed? Plz dont judge, im really bad with english

That's all true and correct, but the prediction of the internal beaker's final temperature is weighed more than the heat retention.