Rex wrote: > Hal Murray wrote: > >> [email protected] said: >> >> >>>> Can I get reflections without some inductance? >>>> Is there any inductance in a system of alternating >>>> layers of insulation/storage? >>>> >> >> >> >>> I think you are overstretching the badly chosen nomenclatures >>> parallels to electricity. >> >> It was actually a (somewhat?) serious question on several grounds. >> >> Can I get reflections from a lumped circuit model of a transmission >> line made out of just Rs and Cs? If so, I can probably do the same >> in the thermal world. >> >> Can I get reflections in a thermal context? Bruce's URLs say yes, >> but my math is rusty enough that I can't quickly understand what's >> going on. >> >> If a thermal problem can generate reflections, does that mean it also >> has something corresponding to inductance? If so, what is it? >> >> It's possible that the key idea is time-delay. In the electrical >> world, a delay is a transmission line which has both C and L. I'm >> not sure what the one-dimensional equivalent in the thermal world is. >> >> What's the speed-of-light equivalent in the thermal world? >> >> >> >> >> > > Why were you somewhat serious about this? > > If you want to extropolate heat into electromagnestic waves, what > would be the analog of frequency? There are a few parallels in the two > realms by analogy but that doesn't mean they map in all aspects. > Sometimes, to help learning ohms law, the analogy of water is used > with pressure = voltage, flow = current, resistance = narrow pipes. It > sort of makes the concepts easier to grasp, but when you get to AC and > wave reflections I think one has to struggle to make the water analogy > useful. For heat, I think the water analog might be more useful than > trying to map the EM waves to heat. > > The reflection idea did remind me of something that occurred to me, a > gallows-humor joke from years back. I'm sure most of you remember > hearing about the 1989 San Francisco earthquake. The earthquake > epicenter was between Santa Cruz and San Jose, about 40 miles south of > San Francisco, but a lot of the serious damage and fires occurred in > San Francisco near the tip of the penninsula at the bay shore. There > was a lot of discussion about this localized damage so far away, and > how that could happen. San Francisco is at the tip of a peninsula that > forms the Bay. I immediately thought that the problem was obvious. The > penninsula was excited at its bottom end and was left improperly > terminated at San Francisco. I couldn't tell this joke for two > reasons, one: it was in bad taste, but two: I only knew a few people > who would get it -- the mismatch/termination joke. > > Now, back to the subject of heat, I have a strange observation that I > posted on the web a few years ago. A few people thought they had seen > the same thing, but most thought what I noticed was not real. I posted > because, if it was true, it seemed unexpected and I had never heard > anything that could explain it. > > I was welding or heat treating steel. Imagine a steel bar about 1 inch > (2.54 cm) in diameter and a foot to 18 " (30-40 cm) long. The bar is > clamped in a vise and with a torch one end is quickly brought up to > red heat. The other end is still cool enough that with my bare hand I > can hold the bar by the cool end and carry it into the next room. I > carry it there to cool it in the sink. A stream of cold water turned > on, I quickly cool the hot end in the water. My observation, from > doing this several times, is that the cold water quickly absorbes heat > from the red end, but also seems to chase a lot of the heat quickly up > toward the cold end, making the bar rapidly uncomfortable to hold. So > that's my observation. I think the sudden cooling of the very hot end > has somehow chased a glob of heat toward the cool end. If true, I have > no explanation. I don't think it is related to steam; it seems to me > to be something happening inside the bar. > > Most people thought it was coincidence of heat propagating up the bar > just at that time, or steam. Could be, but I still think it is real. > The cold end of the bar was slowly getting warmer as I carried it, but > after the sudden cooling of the hot end, the cold end seemed to get > hot fast. > > I meant to try an experiment with two bars and dual thermocouples, but > I never got around to it. The main problem is getting things close > enough to compare without questioning the heated states. My plan would > have been: attach two themocouples to the cold end of two identical > bars. Heat the two other ends rapidly to red heat (that is the very > hard part to get right and balanced) and then just cool one bar > rapidly while recording both temp profiles of the cold ends. If I > figure out how to do the heating quick and balanced, I may still try > the experiment. > > So I started with a bit of complaining about the rambling of the > thread, and now I've rambled it in a whole nother direction. Sorry, I > guess. > > > > > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > Rex
your experience with the hot bar is quite common. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
