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  1. rumborak

    Fluid going through pipe: what is the influence of speed on exchanging heat?

    I'm doing a fun home project, and it involves water flowing through a metal pipe, where the surrounding is significantly lower temperature than the water in the pipe. The point of the exercise is to cool the water in the pipe as it flows through it. The question is, what influence does flow...
  2. rumborak

    Straight line plot of bipolar transistor - temperature?

    Is there a reason why you think you can transform it into a straight line?
  3. rumborak

    One stroke engine

    Classic designs wouldn't work, but if you incorporated some kind of "flywheel" that gets accelerated on the downstroke and whose inertia would carry it through the upstroke, I don't see why that couldn't work at least theoretically. It would be like riding a bike but only ever pushing on one of...
  4. rumborak

    Logarithm in entropy shows irreversibility of the Universe?

    I think that author's interpretation of why the logarithm is used massively understates the rationale that went into the derivation. I don't know the derivation of physical entropy, but the formula for Shannon entropy (which uses the same logarithm) comes directly as a mathematical consequence...
  5. rumborak

    Why does stretching a rubber band increase its temperature?

    You shouldn't think of it like "releasing heat", as if heat detached itself from the object. Rather, think of it as a process of equalization: the rubber band heats up because of the work you put into it, and now the band is out of thermal equilibrium with its environment. Your tongue gets to...
  6. rumborak

    Most efficient temperature to evaporate water?

    Based on this thread I read the Wikipedia article on the subject. Very cool, I had no idea that desalination by freezing is actually a thing.
  7. rumborak

    Most efficient temperature to evaporate water?

    There will essentially be no other way than to do testing, since it depends on so many factors. For example, while physical formula do exist for vapor pressure in equilibrium, your scenario is decisively not in equilibrium, since the point of desalination is to transport away the vapor to a...
  8. rumborak

    Most efficient temperature to evaporate water?

    It's really a question of how exactly you pose the energy question. I mean, if you have water and just leave it at whatever temperature it already is, you will expend no energy, but there will always be a certain amount of evaporation. So, when posed that way, you already have perfect efficiency...
  9. rumborak

    Most efficient temperature to evaporate water?

    Isn't the rather obvious answer here, the hotter the better? I mean, people boil water to create steam after all.
  10. rumborak

    Thermal velocity of a soccer ball

    Totally agree of course :smile: Shoot the ball high up in the air, then use a camera to analyze the speed.
  11. rumborak

    Thermal velocity of a soccer ball

    Mythbusters actually did this several times, to measure terminal velocity of objects. They would have a long plastic tube that they pushed up air in upwards, and then they dialed up the air speed until the object was suspended. Might be a bit difficult with a soccer ball though because of the...
  12. rumborak

    Could one build "thermal power lines"?

    Yeah, and when you look at an effect that doesn't rely on delocalized electrons, like dielectric constants, those also only have a spread of 3 orders of magnitude.
  13. rumborak

    Could one build "thermal power lines"?

    Interesting comments, thanks. This one struck me as the key. I actually looked a bit at tables of thermal conductivity of different materials, and they all seemed to hover with maybe 3 orders of magnitude. Looking at a table of electrical resistance of materials, that spans about 30 orders.
  14. rumborak

    Has anyone studied Equilibrium thermodynamics by CJ Adkin?

    I have not, but I have to make the comment here ... Isn't "Equilibrium Thermodynamics" a bit of an oxymoron?
  15. rumborak

    Could one build "thermal power lines"?

    It just occurred to me that akin to electric power lines, which in the end just connect a voltage differential over a long distance and facilitate power exchange between the two end points, one could build "thermal power lines". That is, a well-insulated cable that internally consists of a...
  16. rumborak

    Wire temperature control

    Hmm, I don't think I see how you would use the Wheatstone Bridge for his purpose of drastically changing the current through the wire though. The bridge has no direct connection between the two arms, instead there's a voltmeter. So you can detect deviations from the operating point (which...
  17. rumborak

    Wire temperature control

    Well, as I said, you likely won't be able to control the current in the wire without majorly overheating the current-controling component as well. However, what you can *can* do is to switch on and off the current very fast with a transistor. Because you are essentially switching between...
  18. rumborak

    Wire temperature control

    I think your biggest problem will be the current needed to heat up the wire. Now, if you wanted to smoothly regulate that current to achieve any temperature in that 100-300C range, you will need a component that does so by varying its resistance (I.e. a transistor). However, now you have the...
  19. rumborak

    Temperature as a measure of thermal energy

    As you point out yourself, it's about the thermal energy per particle. If you have 10 particles instead of one, your denominator is also 10. If you have only one particle, you divide by just one. Either way, the energy per particle will be the same. This is assuming you are disregarding the...
  20. rumborak

    Heat transfer of a hot plastic thread in a cold water bath

    I'll leave better answers to others here, but it's probably also worth pointing out that the matter will be confounded by the convection effects of the water. The water will heat and thus rise up, causing turbulences and pulling cooler water from below. Calculating that on paper, not sure it can...
  21. rumborak

    Temperature and Average kinetic energy of moleces

    Is the assumption here that the average speed of all the molecules is 1980 m s/-1? Because if it is not, the answers could be anyone's guess. Also, what do you think the answer should be?
  22. rumborak

    What temperature actually means?

    When looking at the definition of heat through the entropy of the system, it also becomes obvious that a uniform motion won't change the entropy, and thus the heat.
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