• 2 Posts
  • 715 Comments
Joined 11 months ago
cake
Cake day: March 31st, 2025

help-circle

  • the thing you’re missing is scale. what you’re describing is overgrown car radiator type scheme, and it works up to some couple MW if need be. when you have access to sea, or large river, you can just use that water as a coolant and dissipate some couple GW this way. this is the reason why so many nuclear powerplants are on seashore. because sea is generally very big [citation needed] temperature increase is slight and mostly harmless in usual cases

    inland, in absence of large river, the other way to provide cooling is by evaporation of water. one form is to take that oversized car radiator and spray water on it, water evaporates taking away some heat. this arrangement allows for no-added-water operation in low load conditions. in principle this means that lowest possible temperature is not air temperature, but instead it’s wet bulb temperature, which is always lower, and difference is greatest when air humidity is low. in practice this doesn’t allow to reach this lower temperature, but the other approach does. for bigger scale still, instead of using heat exchanger, water is dripped in a tower of some shape and air is moved in some way against it. small part of water evaporates, and the rest, now cooled down, is collected at the bottom. this is how these large cooling towers near coal or nuclear powerplants work, but so do smaller towers that rely on fans instead of chimney effect. extra water is always needed, and temperature closer to wet bulb temperature is achieved in all load conditions. rarely used alternative is to make an artificial lake, and allow for evaporation from water surface

    notice that if water is evaporated, it’ll leave whatever is dissolved in evaporator part, which means it has to demineralized at all times. in practice it means that some part of evaporated water is treated continuously by reverse osmosis, and the less saline input water is, the easier and more energy efficient it is to do it

    the thing with heat exchangers is, without water evaporation, that they have some constant thermal resistance. if you want to dissipate more heat, you need more of heat exchanger, or alternatively have to allow for higher temperature. the former means more metal needed, the latter means limits to other parts of coolant loop, or using heat pump to cool down silicon, while increasing temperature of coolant. both of these mean extra capex and/or energy use, but evaporating water is cheap, so it’s done instead. it doesn’t help that one of dc ratings is ratio of how much energy gets into dc to how much energy powers actual silicon. evaporating water does not add to energy use, so designs chasing this rating are likely to use that solution












  • there was chrome (and firefox probably?) extension that went through your all fb liked pages and unsubscribed from them so that when it’s done timeline is gone entirely. fb went after its dev, removed that extension and banned him forever because it kept people off fb https://www.businessinsider.com/facebook-bans-unfollow-everything-developer-delete-news-feed-2021-10 doing this all manually still worked back then, not sure about today

    Facebook’s letter took him by surprise, he said, adding that Unfollow Everything had only 2,500 weekly active users and 10,000 downloads.

    “It was definitely growing, but it wasn’t huge,” he said.

    “Apart from that I just very much saw it as something that improves the Facebook experience for Facebook users,” he added, saying he got “amazing feedback” from people saying they “were using Facebook in a way that was much healthier for them.”

    slightly healthier relationship with attention devouring parasite in your pocket? not on zucc’s watch, ALL contents of your skull are to be sourced from and licensed to meta platforms inc exclusively





  • i was thinking more like, thin external plastic shell and empty cells inside, perhaps with another thin plastic shell on inside, and internal metal shell (on plastic support?) fitting in snugly, for mechanical stability, idk 3dprinting

    keeping leads short and nonmagnetic (dramatic reduction in skin layer depth) would be a good thing because of losses, but the longest object in capacitor would be just capacitor plates, and either way in wavelength terms it’s rather small. more precisely you can model it as open transmission line stub with some weird and low impedance, but it’s so small that you don’t have to. you can also make capacitor shorter and wider, or even add more layers like how vacuum variables are made. in nesting design you can get taper effect just by making inner layers longer



  • The dielectric between the plates in this case is 0.4mm of ABS plastics (+ a bit of air in the 3d print layer lines).

    in terms of losses, PP or PE is a bit better than ABS, teflon or FEP is a bit better than PP, but air is superior to either (this is part of the reason why foam coax is a thing). not sure which ones are printable, or whether it’s practical at this size, but try to introduce as many voids as possible (perhaps requires larger thickness of dielectric). it doesn’t matter much in your case, because of low power (warping of plastic because of excessive heat is probably not a problem). if your coax has solid dielectric, then by introducing enough air in 3d-print your variable might become less lossy than that

    The Capacitors allows my 80cm diameter loop to tune from 20Mhz to 37Mhz. Sweeping the whole range is a bit slow due to the low RPM of the motor and takes about 6min. But that is kinda nice when fine adjusting to a frequency.

    you have probably noticed that position vs resonant frequency relationship is rather nonlinear. you can get higher sweep speeds at lower end without losing much accuracy at higher end by tapering end of side plates into a triangle shape (it will get longer overall). it doesn’t matter much in your case, because it’s all approx monoband, but if you want to go multiband with this, then it’ll be a nice enhancement. similar effect happens when air variable capacitors have moving plates shaped in such a way that one end is longer than the other, and external edge has shape roughly like a section of logarithmic spiral. precise movement of variables like this is done by use of worm drive with large wheel

    I am not sure what is causing this, but i assume it could be due to increase of dielectric losses in the capacitor getting bigger when more of the plates overlap because then the electric field has to flow thru a bigger area of dielectric, increasing the potential for losses.

    loss tangent of dielectric is material property, that is ratio of equivalent loss resistance to capacitance should remain constant at given frequency. so i guess that losses should remain roughly the same, if dielectric is to blame, but at any rate lossy capacitor should make bandwidth broader and SWR lower. my guess would be that it’s a matter of coupling loop becoming wrong-sized or wrong-positioned at some point with change in frequency (try moving it up or down? there’s gotta be some optimum position for your entire range of interest)