Erik_MagAir cooled engines as the name implies, are cooled by convective heat transfer between the fins and the air along with some radiative heat transfer. For large engines with a lot of air flowing through the fins, e.g. airplane engines, paint on the fins would be detrimental to cooling as almost all of the cooling is convective heat transfer. For a small engine with little or no induced airflow, e.g. lawnmower, the cooling would mostly be radiative heat transfer, so paint may actually help if it increases emissivity. I suspect heat loss from rail would mostly be radiative heat transfer, so paint might help with increasing emissivity. The main effect is decreasing the amount of solar energy absorbed by the rail.
I suspect heat loss from rail would mostly be radiative heat transfer, so paint might help with increasing emissivity. The main effect is decreasing the amount of solar energy absorbed by the rail.
Most lawnmower type engines have a fan that is integral with the flywheel to provide air flow to the cooling fins - the cowling on the engine hides this fan and is also the inlet for the air the the fan dispenses to the cooling fins.
In racing there are two forms of Formula V cars - Vintage and Current. The vintage cars are required to utilize the fan, fan shroud and generator from the 36 hp Bug engine; vintage cars also use a Z-bar rear suspension set up. The Current cars DO NOT use the fan, fan shroud and generator - instead they have external ducting to provide air to the cooling fins on the pistons; additionally they use what is termed a Zero Roll rear suspension.
Never too old to have a happy childhood!
EuclidThere are people advocating laws requiring urban roofs to have white shingles to stop climate change. That too is dubious as to its effectiveness, I think. So this painting things white to keep them cooler seems to be a bit of a fad.
Admittedly the value in mitigating AGW is comparatively slight ... especially if the surface is not 'white' reflective in IR ... but it's very easy to see the difference between a white roof and, say, a black tarred one if you're up on the trusses under it on a good bright hot day. I suspect there's an interesting comparison between something like titanium-dioxide white and aluminum powder (perhaps more specular?) for what the 'best' roofing surface coat will be.
Of course, you also see these people putting white shingles on roofs and then installing ridge vents, destroying much of the actual value: it's not just the relative lack of thermal gain, it's the insulating value of the dead air underneath the reflective surface. Anyone who has owned a Land Rover with safari roof knows the rather surprising effectiveness, but they may not recognize why.
The safari roof is a simple panel of white-painted metal, curved down at the edges to follow the roof, attached with standoffs so it 'floats' an inch or two above the actual top of the vehicle. No insulation, no vents, no 'through circulation' to "cool" the area under the reflective panel. What it does is limit the amount of heat capture in the roof while trapping a layer of heated but still air between the two panels. This is just the opposite of the approach touted in the 1930s with 'dome' manufactured housing, where air from 'under the foundation' was supposed to be carried up through the double walls by convection and exhausted through a roof vent. It works astoundingly well, even when there is a fair amount of dirt and mold on the white paint.
Myrick's Railroads of Arizona had several mentions of double roofs for houses to cut down on the heat. I had a similar experience when having the house remodeled a while back, for a couple of weeks the attic was essentially open to the breeze and the house was noticeably cooler.
The ultimate coating for roofs would be something that folks at Stanford U came up with. The material is highly reflective where the atmosphere has high IR attenuation (e.g. water vapor lines) and highly emissive where the atmosphere is transparent.
Erik_MagMyrick's Railroads of Arizona had several mentions of double roofs for houses to cut down on the heat. I had a similar experience when having the house remodeled a while back, for a couple of weeks the attic was essentially open to the breeze and the house was noticeably cooler. The ultimate coating for roofs would be something that folks at Stanford U came up with. The material is highly reflective where the atmosphere has high IR attenuation (e.g. water vapor lines) and highly emissive where the atmosphere is transparent.
If we are to believe the 'Green Movement' using the roof surface as a garden is the ultimate solution - growing plants in soil on the roof would minimize the solar energy that would work its way through such a roof as well as providing additional insulation in winter - how strong the support structure of such a roof would need to be is a entirely different conversation.
BaltACD Erik_Mag Myrick's Railroads of Arizona had several mentions of double roofs for houses to cut down on the heat. I had a similar experience when having the house remodeled a while back, for a couple of weeks the attic was essentially open to the breeze and the house was noticeably cooler. The ultimate coating for roofs would be something that folks at Stanford U came up with. The material is highly reflective where the atmosphere has high IR attenuation (e.g. water vapor lines) and highly emissive where the atmosphere is transparent. If we are to believe the 'Green Movement' using the roof surface as a garden is the ultimate solution - growing plants in soil on the roof would minimize the solar energy that would work its way through such a roof as well as providing additional insulation in winter - how strong the support structure of such a roof would need to be is a entirely different conversation.
Erik_Mag Myrick's Railroads of Arizona had several mentions of double roofs for houses to cut down on the heat. I had a similar experience when having the house remodeled a while back, for a couple of weeks the attic was essentially open to the breeze and the house was noticeably cooler. The ultimate coating for roofs would be something that folks at Stanford U came up with. The material is highly reflective where the atmosphere has high IR attenuation (e.g. water vapor lines) and highly emissive where the atmosphere is transparent.
The double roof is more in line with what Overmod was describing, a relatively light roof that minimized radiative heat transfer - helps both in summer and cold clear winter nights. To get the most effectiveness, the underside of the upper roof needs to be a material like polished aluminum. Nothing as heavy as the rooftop garden to moderate heat.
The Stanford development was a coating to put on roofs or other outdoor surfaces. Its working principle relies on the effective sky temperature being at a much lower temperature at certain wavelengths than others (e.g. it is 3K (-455F) at 20 centimeters). Sky temperature at wavelengths associated with water vapor absorption is typically the dew point which can be 80F (or higher) along the Gulf Coast.
The visitor center for San Elijo lagoon has one of the garden roofs and it does a fairly good job of moderating the indoor temperature on hot days, though weather report for this time of year is low of 65, high of 75.
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Erik_Mag... To get the most effectiveness, the underside of the upper roof needs to be a material like polished aluminum. Nothing as heavy as the rooftop garden to moderate heat.
Part of the 'secret' is to use channelized insulation with reflective faces in the space between the joists.
Part of the fun in the past 40 years has been to watch engineers in one discipline forget all about practical implications from other disciplines. A hundred years ago, the point of a whole-house fan was well recognized in the South; part of that involved venting trapped heated air under the roof for reasons that didn't involve the insulating value of hot still air very much. The issue with 'ridge venting' is to provide channelization that accomplishes as much as possible of what a whole-house fan or turbine vents do 'actively' with natural circulation, while maintaining low heat rejection or 'gain' transfer to the 'inside.' It can be almost as simple as a reflective (or at least low-e) barrier on the inside of the decking and more on the formed-foam channels...
Meanwhiile, of course, the whole point of a roof garden is transpiration cooling from the vegetation, and this has been the principal stated reason for implementing the idea to reduce urban 'heat islanding' since at least the early '70s. Before anyone asks the next dubious question: the water is supplied via something like soaker hoses, proportionally, and not with sprinklers out the wazoo or methods that allow secret ponding, channelizing, or leaks.
The Stanford development was a coating to put on roofs or other outdoor surfaces.
What materials did they use to get the variable reflectance and re-emission?
Interesting parallels with good low-e glass (as distinct from the approach used for the Hancock building!) and with Besler tubes in power boilers (where you want to preferentially absorb in the excitation bands for CO, CO2 and H2O and then re-emit in broad spectrum for radiant absorption across the enclosing flue or tube wall)
BaltACD zugmann BaltACD When it is the only thing you can afford in a TIMELY fashion it is the only play you can make. Doubt it's effectiveness, but if it saves one derailment it will have more than paid for itself. I'm thinking that someone on this side of the pond tried that a few years ago. I believe you are right and I believe there was no definitive evidence that it worked.
zugmann BaltACD When it is the only thing you can afford in a TIMELY fashion it is the only play you can make. Doubt it's effectiveness, but if it saves one derailment it will have more than paid for itself. I'm thinking that someone on this side of the pond tried that a few years ago.
When it is the only thing you can afford in a TIMELY fashion it is the only play you can make. Doubt it's effectiveness, but if it saves one derailment it will have more than paid for itself.
I'm thinking that someone on this side of the pond tried that a few years ago.
I believe you are right and I believe there was no definitive evidence that it worked.
The problem was that after they tried this stunt under controlled conditions, the real world application (on the old SP in AZ ???) did not go so well.
mudchickenhttps://www.fra.dot.gov/Elib/Document/15600 The problem was that after they tried this stunt under controlled conditions, the real world application (on the old SP in AZ ???) did not go so well.
Funny how theory and reality seem to have differing results.
Overmod Part of the 'secret' is to use channelized insulation with reflective faces in the space between the joists.
I've wondered about whether solar panels could help with cooling - where the panels are on racks a few inches above the roof itself. A strong incentive for a free air space underneath the panels is that performance drops with increasing temperature.
The Stanford development was a coating to put on roofs or other outdoor surfaces. What materials did they use to get the variable reflectance and re-emission?
I don't remember, my vague recollection was that secret sauce may have been the size of the particles in the coating as opposed to the specific material. ISTR that there was hope that the coating could be made cheaply and that it would last. In light of the dirty feathered guy's post, I am not sure how well this would work on track.
Erik_MagI've wondered about whether solar panels could help with cooling - where the panels are on racks a few inches above the roof itself. A strong incentive for a free air space underneath the panels is that performance drops with increasing temperature.
We should probably work a bit more rigorously through what's actually going on with thermal gain, shielding, and reflection effects from these 'standoff' panels.
There appears to be little question that the panels run and 'live' better when stood off from the roof a few inches. It also appears obvious (although I haven't measured directly) that the thermal gain to the roof underneath is greatly reduced by shadowing, at least across a wide range of visible and UV radiation.
Part of the question then becomes what the characteristics of re-radiation from the panel back to the underlying roof shingles is, perhaps with cavity-radiation-like multiple 'passes' with decreasing frequency, with the panel at a particular ambient temperature. Seems to me you would want emission from the panel to be as high as possible, with much of this effective heat then dissipated by the vertical air circulation via the air space; I expect there will be some 'best standoff distance' and perhaps aerodynamic considerations for the channelization of space behind the panel optimizing the airflow and perhaps surface turbulence. One thing that comes to mind is the Babcock & Wilcox discussions (in the '50s versions of Steam: Its Generation and Use) of boiler insulation in 'cavities' and the need to duct airflow through them to prevent unexpected heat rise.
More fun with the heat gain from the 'attic' space through to the shadowed face, as you might want to limit emission (or the re-emission above) from the 'shingle' faces to the back face of the panel. That has implications if you want to 'float' the roof deck as a kind of thick shield between foil-backed insulation channels inside and shingles outside; you might want to try increasing heat transfer to the channelization inside the deck, perhaps even darkening the shingling under the panel to increase radiant uptake at IR.
I don't think anyone has studied coordinating the airflow up the inside of the deck to the ridge vent (or turbines) with the airflow behind the panels. Perhaps there is little effect to be gained (or other practical considerations in panel fabrication, installation and connection render it relatively insignificant).
The Stanford development was a coating to put on roofs or other outdoor surfaces ... my vague recollection was that secret sauce may have been the size of the particles in the coating as opposed to the specific material.
Would this be like Ironball, but at IR wavelengths? Seems like the element size would go down as you went from radio to THz and then into IR, so without doing any analysis I'd say a mix of tuning might well work -- although for them to optimize a combination of actual reflectance vs. absorption rather than just selective one or the other is kinda nifty. The immediate question I'd have is whether the coating would have to be in layers, a bit like Kodacolor process, and whether common-sense characteristics like UV stabilization would impair the 'action'. Heaven knows there's a market for sophisticated 'smart paint' formulations; didn't we discuss some interesting ones for the Navy here circa 2012?
In light of the dirty feathered guy's post, I am not sure how well this would work on track.
Ah, this brings us back to reality with a bang. As far as I can see, nothing that doesn't enhance first reflectivity, then re-emission will do any good, and it would have to work over a fairly wide angle of incidence (for reflection) and relatively high dispersion (for re-radiation) so something that looks visibly white but not specular seems a reasonable thing. Meanwhile you want any emission from the 'shadow' side to be optimized ... this immediately raises the same red flag that black Shuttle tiles in high-heat regions does. It does not help the situation with ribbon rail to have the heat dissipate more quickly or directly when the problem with heating is from incident radiation complicated by high ambient temperature, so I'd predict the 'action' would work best on stretches of track where one side of the rails regularly faces the sun; in fact I'd think you'd get some advantage from reflective shields stood off from the 'sun' side of the rail, and enhanced emission from the back side and perhaps the front side into the 'cavity' between the rail web and shield. Of course I can hear the laughter now at the thought of installing shielding strips that are vertically high enough to shadow up to the railheads on what may be long stretches of east-west track...
The UP has a line of trees with drip irrigation along parts of their Mojave Desert crossing, although I think it is for blowing sand. Has anyone thought of planting trees on the south side of ROW for shading.
MidlandMikeHas anyone thought of planting trees on the south side of ROW for shading.
I suspect that there are some variables there - what kind of tree, how close, does it add anything to the cost of operation (or more than the potential savings).
We run on jointed rail, so kinks aren't a factor. We also run through plenty of "tree tunnels" in the Adirondack forest. We're talking deciduous trees.
This is actually a problem - leaves on the tracks in the fall are like grease, and can very nearly overwhelm the sanders.
That said, some sort of evergreen (arbor vitae?) might work. The payback might take a while - my arbor vitae have gone from 4' to 8', but it's taken around 4 years to do so.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
tree68 MidlandMike Has anyone thought of planting trees on the south side of ROW for shading. I suspect that there are some variables there - what kind of tree, how close, does it add anything to the cost of operation (or more than the potential savings). We run on jointed rail, so kinks aren't a factor. We also run through plenty of "tree tunnels" in the Adirondack forest. We're talking deciduous trees. This is actually a problem - leaves on the tracks in the fall are like grease, and can very nearly overwhelm the sanders. That said, some sort of evergreen (arbor vitae?) might work. The payback might take a while - my arbor vitae have gone from 4' to 8', but it's taken around 4 years to do so.
MidlandMike Has anyone thought of planting trees on the south side of ROW for shading.
Welded rail is a technology that has yet to be 'mastered' in all kinds of weather conditions.
Have viewed several videos about how LNG trankers are constructed. The holds (tanks) that actually carry the LNG are constructed of Stainless Steel account of it's ability to withstand the ultra cold temperatures and high pressures that it takes to keep Natural Gass liquid.
I am not a metalurgist - Is their some alloy that will make rail more resistant to expansion during periods of increased temperatures?
BaltACDI am not a metallurgist - Is their some alloy that will make rail more resistant to expansion during periods of increased temperatures?
Well, you could make the base and web out of one of the Invars (look the theory up if you are interested), and use a technique like explosive welding to put a hardened head and gauge surface on it. (This would concentrate the stress of expansion/contraction in the weld zone and likely lead to head cracking under load, but not rail cracking). I suspect there would be little problem with forming or rolling Invar into the required shape.
The problem, of course, is the cost -- followed by availability of some of the metals in the alloy composition at the required tonnage.
Modern rails have to do many things simultaneously: absorb both weight and shock with minimal cumulative damage, be tolerant of emergent cracking, hold up with dramatic amounts of wear or abuse, have hardened heads for increased life, and ... be net cost-effective over their installed lifetime. Concentrating on optimizing one or a few of these can only make sense if the others aren't compromised.
BaltACDI am not a metalurgist - Is their some alloy that will make rail more resistant to expansion during periods of increased temperatures?
It does always seem, though, that if you find some good quality you want in something, you lose some other quality you want in the process...
selector caldreamer I know rails buckle during heat waves, but I do not understand why. Steel does not even start to get soft until he temperature is over 2000 degrees. Mainline rail these days is at least 136 lbs or more per yard so it is pretty heavy. The previous responders mean well, but they're quite wrong. The truth is that all matter has something called 'phlogiston' in it. It's sort of like the element we know as fire. When rails heat up, the phlogiston is released and the opposite element, water, moves into the interstices between the molecules. As you know, it's akin to dry and hard noodles in hot water; they eventually soften, and this makes the rails do all sorts of goofy things. You're welcome.
caldreamer I know rails buckle during heat waves, but I do not understand why. Steel does not even start to get soft until he temperature is over 2000 degrees. Mainline rail these days is at least 136 lbs or more per yard so it is pretty heavy.
I know rails buckle during heat waves, but I do not understand why. Steel does not even start to get soft until he temperature is over 2000 degrees. Mainline rail these days is at least 136 lbs or more per yard so it is pretty heavy.
The previous responders mean well, but they're quite wrong. The truth is that all matter has something called 'phlogiston' in it. It's sort of like the element we know as fire. When rails heat up, the phlogiston is released and the opposite element, water, moves into the interstices between the molecules. As you know, it's akin to dry and hard noodles in hot water; they eventually soften, and this makes the rails do all sorts of goofy things.
You're welcome.
I wonder how many of those reading Selector's post realize it's probably a joke (at least I hope that's how it was intended). The"phlogiston" theory of heat was developed by a German chemist named Georg Stahl around 1700. It was discredited long ago in favor of the modern view that heat is a form of motion. Credit James Joule and William Thompson (Lord Kelvin) for the latter insight.
Falcon48I wonder how many of those reading Selector's post realize it's probably a joke (at least I hope that's how it was intended).
Of course it;s a joke; that's not how phlogiston was supposed to work. Have ye no faith that this forum knows nothing about the history and philosophy of science?
Overmod Falcon48 I wonder how many of those reading Selector's post realize it's probably a joke (at least I hope that's how it was intended). Of course it;s a joke; that's not how phlogiston was supposed to work. Have ye no faith that this forum knows nothing about the history and philosophy of science?
Falcon48 I wonder how many of those reading Selector's post realize it's probably a joke (at least I hope that's how it was intended).
Who got degrees in science from Trump University?
BaltACDWho got degrees in science from Trump University?
Isn't that precisely the source you'd expect to (still) be teaching the 'correct' phlogiston theory???
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