|
painting tubes black for heat disposal???
Dull, black, heat resistant paints
have been used to help cool engines for ages. It would be cool (literally) if one could spray and heat-cure unshielded tubes and improve their heat-shedding Is there any indication that such paints, or some vacuum-tube specific types, would help keeping tubes cool by improving heat radiation? I'd love some factual info, if it exists, or educated guesses, rather than uninformed blind guesses, as I am awfully good at doing uninformed blind guesses already! :-) |
painting tubes black for heat disposal???
spamhog wrote:
Dull, black, heat resistant paints have been used to help cool engines for ages. It would be cool (literally) if one could spray and heat-cure unshielded tubes and improve their heat-shedding Is there any indication that such paints, or some vacuum-tube specific types, would help keeping tubes cool by improving heat radiation? No, but don't let that stop you from trying it anyway. -Chuck |
painting tubes black for heat disposal???
On Jan 17, 12:48*pm, Chuck Harris
No, but don't let that stop you from trying it anyway. -Chuck :-) What keeps me is the fact that I have no idea how I could measure the core temperature in a tube! Is heater current temperature-dependent enough as to provide a proxy? Hints anyone?? |
painting tubes black for heat disposal???
On Jan 17, 12:49 pm, spamhog wrote:
On Jan 17, 12:48 pm, Chuck Harris No, but don't let that stop you from trying it anyway. -Chuck :-) What keeps me is the fact that I have no idea how I could measure the core temperature in a tube! Is heater current temperature-dependent enough as to provide a proxy? Hints anyone?? This test was done using a Raytek laser digital thermometer. Temperatures were taken from a 6BZ6 1st RF amp tube on a John R. Leary SP-600JX no suffix number, serial number 1262. Ambient room temperature was 75°F. I'm not a scientist nor should this be misconstrued as a scientific test. I have always been curious as to whether the IERC tube shields "actually" prolong tube life. As noted there were several different tube shields used in this "test." Also note there are several different types of inserts inside these tube shields. The bare tube bulb temperature was "shot" immediately after removing the tube shield. The "Real McCoy" IERC Tube Shields have a finger grip type of insert that acts as a heat sink and the test results show that the temperature difference between the shield and the tube itself is little. That should tell us that that type of shield is the "Standard." For your information, I don't use tube shields and my tubes seem to last a long time. Take this information as it's meant to be, strictly informational. 1.. Shiny metal Eby tube shield no insert. 94°, bare tube 124°F. 2.. Shiny metal Eby tube shield with seven-sided black aluminum insert. 96°F, bare tube 127°F. 3.. Dull metal Elco tube shield no insert.108°F, bare tube 135°F. 4.. Black heat resistant painted Eby tube shield no insert. 104°F, 126°F bare tube. 5.. Black anodized Eby tube shield with "waveform, nine ridges" aluminum black heat shield insert. 107°F, bare tube 127°F. 6.. Collins black anodized tube shield with "waveform, nine ridges" aluminum black heat shield. 100°F, bare tube 122°F. 7.. W.P.M. tube shield with five-sided aluminum insert. 106°F, bare tube 118°F. 8.. IERC tube shield with "finger grip" type beryllium insert. "The Standard." 102°F, bare tube 104°F. ( has to be the insert) 9.. Bare tube, no shield. 6BZ6 114°F. YMMV |
painting tubes black for heat disposal???
spamhog wrote:
On Jan 17, 12:48 pm, Chuck Harris No, but don't let that stop you from trying it anyway. -Chuck :-) What keeps me is the fact that I have no idea how I could measure the core temperature in a tube! Is heater current temperature-dependent enough as to provide a proxy? Yes, it is rather temperature dependent. What I might do, is put two identical tubes with their filaments in series into a bridge configuration with two identical resistors, and measure the voltage between the junction of the two filaments, and at the junction of the two resistors. Then paint the one tube, and leave the other unpainted. If the paint causes any change in the tube's internal heat, it should cause the bridge to move one way or the other. Tungsten's resistance rises as its temperature rises, and lowers as its temperature lowers. ~ +12.6V(REG) ~ | ~ +---------+-----------+ ~ | | ~ FIL-A R ~ | | ~ +--------DVM----------+ ~ | | ~ FIL-B R ~ | | ~ +---------+-----------+ ~ | ~ -+- ~ /// The inside of the tube is a hard vacuum, so the only way heat will pass the void is by conduction (through mica, and leads...), and direct radiation. Direct radiation is where the lion's share of the heat goes. Since the filament is surrounded by the plate, it should see as much radiant energy as the tube radiates out through the glass. -Chuck |
painting tubes black for heat disposal???
Chuck Harris ) writes:
spamhog wrote: Dull, black, heat resistant paints have been used to help cool engines for ages. It would be cool (literally) if one could spray and heat-cure unshielded tubes and improve their heat-shedding Is there any indication that such paints, or some vacuum-tube specific types, would help keeping tubes cool by improving heat radiation? No, but don't let that stop you from trying it anyway. -Chuck Of course, there were tube shields that seemed intended to act as heat sinks. I can't remember if I merely thought that, or if I knew that somehow. But they real contact with the tube glass and certainly seemed as if they could draw heat from them, the same way heatsinks dissipate heat from semiconductors. Michael VE2BVW |
painting tubes black for heat disposal???
spamhog wrote:
Dull, black, heat resistant paints have been used to help cool engines for ages. It would be cool (literally) if one could spray and heat-cure unshielded tubes and improve their heat-shedding Is there any indication that such paints, or some vacuum-tube specific types, would help keeping tubes cool by improving heat radiation? I'd love some factual info, if it exists, or educated guesses, rather than uninformed blind guesses, as I am awfully good at doing uninformed blind guesses already! :-) One might think that the metal shields would "catch" the radiated heat after it has left the tube. I feel that the black paint would act as a heat insulator, preventing efficient transfer of the filament heat to the outside. Unless you can put a thermocouple in the tube, it will be hard to know how hot it gets Inside. (Yes, it can be done, despite the "how to build a triode" nonsense. Tubes were fabricated and evacuated with mercury pumps by amateurs in the 19 'teens and 20's). And will it make any difference? Most equipment was designed to operate over a rather wide range of ambient temperature. Heat dispersion might be important with power tubes (rectifiers, audio/rf amplifiers), but most of that is due to the power inefficiencies of operating the tube,(see the red or white-hot plates!), not from mere filament heat. In that case fans or liquid cooling would be a better alternative. Try painting a 3-500 tube black and fire it up! --afcsman |
painting tubes black for heat disposal???
On Thu, 17 Jan 2008, spamhog wrote: Dull, black, heat resistant paints have been used to help cool engines for ages. It would be cool (literally) if one could spray and heat-cure unshielded tubes and improve their heat-shedding Is there any indication that such paints, or some vacuum-tube specific types, would help keeping tubes cool by improving heat radiation? I'd love some factual info, if it exists, or educated guesses, rather than uninformed blind guesses, as I am awfully good at doing uninformed blind guesses already! :-) I'm not sure that a layer of black paint (as in exploiting what physicists call "black body radiation" [or rate of heat transfer is proportional to wavelenght raised to a power greater than one, and I don't remember the power]) of is going to help you very much. Yes, mirrors, white surface, black surface reflect, respectively, high, medium, or low amounts of impinging radiation but at some point down the time scale, it will all come to equilibrium anyway. Several additional thoughts: 1. The layer of paint probably won't act as much of an insulator (silicon grease, an insulator at high thicknesses, is used in thin layers between computer CPUs and heatsinks and nobody gets worries about this). 2. A question about heat dissipation would have to involve knowing that most heat is dissipated (from the plate) as infra red (unless the tube plate is warm enough to start glowing red). Black paint would have to be examined in terms of its spectral absorbtion as a function of visible-IR wavelengths and compared with how well glass (which, IIRC, passes IR but not UV) passes a given quantity of heat at the same operating temperature. The passband and transmission spectrum may also be dependent on any doping (dyes with bandpass absorptions, etc) but I certainly recall no writings about this in terms of tube cooling. 3. Some tube sheilds were shiny, some were blackened. Good question as to whether the difference helped or hurt temperature, but some tube sheilds were advertised as helping with heat transfer (had some kind of slots). However, all of the metal enveloped tubes had a dull black surface and there may have been a minor component of contribution to surface cooling through black body radiation, or it was simply the cheapest surface to make. 4. Personally, an opaque tube envelope means I can't tell by looking at the tube if the filaments are lighting up when I turn on the power. Its not clear to me that you need to worry much about running tubes at a lower bulb temperature since glass (and even the metal covered glass tubes) won't melt until you get a way much quite a bit hotter than they usually run. If you are worried about heat causing a variety of accellerations of temperature-based aging processes in other components (transformers, capacitors, etc), then put a small fan somewhere to draw out the heat or blow in cooler air. If you are thinking about pushing tubes beyond spec limits, then I'd suggest just not doing that (or, to get more power, or whatever, put more tubes in parallel or use bigger tubes, but that did not seem to be part of yor goal). |
painting tubes black for heat disposal???
afcsman wrote:
spamhog wrote: Dull, black, heat resistant paints have been used to help cool engines for ages. It is not done to cool the engine, it is done to make the engine look cool. It would be cool (literally) if one could spray and heat-cure unshielded tubes and improve their heat-shedding Is there any indication that such paints, or some vacuum-tube specific types, would help keeping tubes cool by improving heat radiation? I'd love some factual info, if it exists, or educated guesses, rather than uninformed blind guesses, as I am awfully good at doing uninformed blind guesses already! :-) One might think that the metal shields would "catch" the radiated heat after it has left the tube. I feel that the black paint would act as a heat insulator, preventing efficient transfer of the filament heat to the outside. Empirical evidence that most everyone has witnessed, shows that black objects absorb light from the sun, and get hot. So, that is exactly what you should expect to happen with painting a tube's envelope black. The paint will absorb the radiant heat from the plate, and conduct it to the glass envelope. The glass envelope will then get much hotter than it would have if the radiant heat had been allowed to escape through the glass and radiate out into space. The black EMC tube shields cool the tube envelope by conducting the glass's heat to the metal shield. This is done not to make an unshielded tube cooler, but rather to make a tube that must be shielded less hot than it would be in a conventional shield that lacks the heat conducting structure. Unless you can put a thermocouple in the tube, it will be hard to know how hot it gets Inside. It is a hard vacuum, vacuum doesn't get hot or cold. You could measure the temperature of some of the tube's elements, but why would you care if they get hot? As long as they don't get hotter then the yellow heat they were heated to when they were evacuated, there is nothing to be concerned about. (Yes, it can be done, despite the "how to build a triode" nonsense. Tubes were fabricated and evacuated with mercury pumps by amateurs in the 19 'teens and 20's). True, but I would bet that you can't do it! Building a triode requires a wide variety of knowledge and capabilities. The French guy that did it in one of the videos built every piece of equipment that he used in making the triodes, and successfully built a nice little hard sealed glass triode too. It was impressive, whether or not it impressed you. And will it make any difference? Most equipment was designed to operate over a rather wide range of ambient temperature. Heat dispersion might be important with power tubes (rectifiers, audio/rf amplifiers), but most of that is due to the power inefficiencies of operating the tube,(see the red or white-hot plates!), not from mere filament heat. In that case fans or liquid cooling would be a better alternative. Try painting a 3-500 tube black and fire it up! It would melt the pyrex glass envelope, particularly around the already highly stressed filament pins. -Chuck |
painting tubes black for heat disposal???
All this is very interesting.... There's a bunch of things I find
confusing. 1) Radiation vs conduction On one hand it's obvious that a layer of dull, IR-black paint has a thermal insulation effect. But the same may be said of ANYTHING surrounding a tube. Even one of the "good" IERC shields must have an insulating effect of sorts. Moreover, the copper "fingers" are metal- shiny, obviously designed to sink heat by conduction, not by absorbing radiation. 2) Terminal filament temperature The issue here isn't avoiding failures as much as increasing tube life. The heat issue in low power devices was much disregarded till close to the end of the tube era, due to engineering, commercial, and I believe psychological effects. In the end, microtubes used in the NORAD systems reached 500k h MTBF, and even before that, repeater amps in transatlantic underwater phone cables had already made major advances in reliability. There is a DoD or Collins study on the matter, claiming that IERC shields improved MTBF over unshielded tubes, if I remember correctly. As in all stable thermal systems, once equilibrium is reached the terminal temperature of cathode and filament can't be independent of what happens at the tube surface. I know how to scrounge up a Wiener bridge or a shunt and measure small deltas in heater current - but where do I look up some ideas on how current is related to temperature, whence what deltas to expect, at least in order of magnitude? Without a theory, even a rough one, as Popper pointed out, there's not much to test.... :-( 3) Cooling effect of going black-body in the IR range Granted, if 90% of the exchange surface eg in an aircooled engine faces . . . itself (think deep cooling fins facing each other) most cooling must come from conduction to a moving ambient medium (aka air). So blackening should not make much difference there. But what about situation where there IS open space around a hot device? Right now, I remember that I know a guy who makes heating systems, including a successful line of radiation heaters: http://www.sabiana.it/download_pubblici/catgen_en.pdf, see the 1st product, called Duck-Strip. The name's an inside joke: they were designed by a Mr. Anatrella - Italian for "cute duckling". The things run on hot water. At a Volkswagen plant those radiators heat people from a vertical distance of over 20m. From an economic standpoint I am not sure it's totally in the company interest to maximize per- surface-unit radiation, but I believe they took a look at paints. They also used to have a gas-fired radiation heater running at a much higher temperature than the water type. I'll ask him... stay tuned. Moreover, some things I found by googling words that came up in this thread: overclocking & paints (uh...) http://www.overclockers.com/tips684/ irrelevant but funny http://members.optusnet.com.au/mcdjim/100_4062s.jpg http://forums.bit-tech.net/showthrea...2a61& t=53048 read what Dampney writes on improving IR absorbtion with "visible and IR" black paint http://thurmalox.com/Upload/Products/Products28.pdf teacher's guide to experiment :-) http://www.ed.psu.edu/ci/Papers/STS/gac-3/in05.htm (no word on measuring temperatures in unreachable recesses) |
painting tubes black for heat disposal???
On Thu, 17 Jan 2008 04:27:06 -0800, spamhog wrote:
Dull, black, heat resistant paints have been used to help cool engines for ages. It would be cool (literally) if one could spray and heat-cure unshielded tubes and improve their heat-shedding Is there any indication that such paints, or some vacuum-tube specific types, would help keeping tubes cool by improving heat radiation? I'd love some factual info, if it exists, or educated guesses, rather than uninformed blind guesses, as I am awfully good at doing uninformed blind guesses already! :-) What I know is that the glass will pass a proportion of the IR energy being generated by the outside surfaces of the plate. Depending on just how great a percentage, you may get more heating of the glass from the paint capturing the radiation from inside than you get cooling from the paint re-radiating it to the outside. What I don't know is what will actually be the case. -- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html |
painting tubes black for heat disposal???
spamhog wrote:
On Jan 17, 12:48=A0pm, Chuck Harris No, but don't let that stop you from trying it anyway. -Chuck :-) What keeps me is the fact that I have no idea how I could measure the core temperature in a tube! With an infrared thermometer or optical pyrometer. Auto parts stores should have a model in the $20 range. Is heater current temperature-dependent enough as to provide a proxy? No, because the plate temperature is very different than the cathode temperature, and the plate temperature is what you worry about. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
painting tubes black for heat disposal???
Scott Dorsey wrote:
spamhog wrote: On Jan 17, 12:48=A0pm, Chuck Harris No, but don't let that stop you from trying it anyway. -Chuck :-) What keeps me is the fact that I have no idea how I could measure the core temperature in a tube! With an infrared thermometer or optical pyrometer. Auto parts stores should have a model in the $20 range. The hand held infrared thermometers will end up measuring the temperature of the glass, not the elements inside. An optical pyrometer would be the way to measure the filament's temperature (quite crudely), but they are expensive. Is heater current temperature-dependent enough as to provide a proxy? No, because the plate temperature is very different than the cathode temperature, and the plate temperature is what you worry about. The heater temperature should be somewhat dependent on the plate temperature, half of the plate's radiation goes into the center of the tube, which is where the heater is. The heater temperature should vary slightly with plate temperature. A sensitive bridge might be able to measure it, but it would be down in the noise. The plate of a tube doesn't wear out, so it's temperature isn't by itself important. When the tube is evacuated, the plate is induction heated to a nice red/yellow temperature. This is done to remove any absorbed gases and other contaminants. As long as the plate is never heated above this temperature, it won't release more gas. The big reason to worry about the plate getting too hot is the heat it radiates will heat the glass envelope, and may cause it to crack, or melt. -Chuck |
painting tubes black for heat disposal???
On Sat, 19 Jan 2008, spamhog wrote: All this is very interesting.... There's a bunch of things I find confusing. 1) Radiation vs conduction On one hand it's obvious that a layer of dull, IR-black paint has a thermal insulation effect. But at very thin layers, it is negligible. Look at house insulation. R-30 is 1-1/2 feet thick plus. A single pane window (single strength) is more like R-1. Glass is a great insulator (compared to, say, copper) but at 1/8 inch thickness its almost not there. Vacuum tube glass is even thinner. But the same may be said of ANYTHING surrounding a tube. Even one of the "good" IERC shields must have an insulating effect of sorts. Moreover, the copper "fingers" are metal- shiny, obviously designed to sink heat by conduction, not by absorbing radiation. You have to compare conduction, convection, and all the mechanisms. 2) Terminal filament temperature The issue here isn't avoiding failures as much as increasing tube life. The heat issue in low power devices was much disregarded till close to the end of the tube era, due to engineering, commercial, and I believe psychological effects. In the end, microtubes used in the NORAD systems reached 500k h MTBF, and even before that, repeater amps in transatlantic underwater phone cables had already made major advances in reliability. There is a DoD or Collins study on the matter, claiming that IERC shields improved MTBF over unshielded tubes, if I remember correctly. As in all stable thermal systems, once equilibrium is reached the terminal temperature of cathode and filament can't be independent of what happens at the tube surface. I know how to scrounge up a Wiener bridge or a shunt and measure small deltas in heater current - but where do I look up some ideas on how current is related to temperature, whence what deltas to expect, at least in order of magnitude? Without a theory, even a rough one, as Popper pointed out, there's not much to test.... :-( There may be some small effects, and it might be more tied to how many times a tube is warmed up from cold, cooled off to cold than actual temperature (in many applications, folks would turn them on and leave everything running [eg. computer monitors, even today]). 3) Cooling effect of going black-body in the IR range Granted, if 90% of the exchange surface eg in an aircooled engine faces . . . itself (think deep cooling fins facing each other) most cooling must come from conduction to a moving ambient medium (aka air). So blackening should not make much difference there. But what about situation where there IS open space around a hot device? That black-body radiation works in both directions, not just absorption. And, it may also be spectrum-dependent so that would have to be measured with instruments, not our (human) eyes. Right now, I remember that I know a guy who makes heating systems, including a successful line of radiation heaters: http://www.sabiana.it/download_pubblici/catgen_en.pdf, see the 1st product, called Duck-Strip. The name's an inside joke: they were designed by a Mr. Anatrella - Italian for "cute duckling". The things run on hot water. At a Volkswagen plant those radiators heat people from a vertical distance of over 20m. From an economic standpoint I am not sure it's totally in the company interest to maximize per- surface-unit radiation, but I believe they took a look at paints. They also used to have a gas-fired radiation heater running at a much higher temperature than the water type. I'll ask him... stay tuned. Moreover, some things I found by googling words that came up in this thread: Its good that you did some google searching, but on the whole I think you are worrying too much about cooling. And, if you do manage to cool the cathode, then emmission would surely suffer. As the ultimate wacky suggestion, you could immerse the tubes in liquid air/nitrogen and really keep them cool (cost a lot of money), but then I'll bet you couldn't "light up the tubes" (with filament voltage) at all. ===== no change to below, included for reference and context ===== overclocking & paints (uh...) http://www.overclockers.com/tips684/ irrelevant but funny http://members.optusnet.com.au/mcdjim/100_4062s.jpg http://forums.bit-tech.net/showthrea...2a61& t=53048 read what Dampney writes on improving IR absorbtion with "visible and IR" black paint http://thurmalox.com/Upload/Products/Products28.pdf teacher's guide to experiment :-) http://www.ed.psu.edu/ci/Papers/STS/gac-3/in05.htm (no word on measuring temperatures in unreachable recesses) |
| All times are GMT +1. The time now is 08:34 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com