Hey Bruce, Your answers seem somewhat 'mechanical'.
Are you a 'bot? Not a joke... REAL question. -John ============== > Rex wrote: >> Hal Murray wrote: >> >>> p...@phk.freebsd.dk 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 -- time-nuts@febo.com >> 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 -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
