Building A DIY Heat Pipe

Once the secret design tool for aerospace designers, the heat pipe is a common fixture now thanks to the demands of PC CPU cooling. Heat pipes can transfer lots of energy from a hot side to a cold side and is useful when you need to cool something where having a fan near the hot part isn’t feasible for some reason. Unlike active cooling, a heat pipe doesn’t require any external power or pumps, either.

[James Biggar] builds his own heat pipes using copper tubing. You can see a video of one being made, below. There’s not much to it, just a copper pipe with some water in it. However, [James] gets the water boiling to reduce the pressure in the tube before sealing it, which is an interesting trick.

One limitation of his technique is that there is no internal wick. That means the tube can only be installed vertically. If you haven’t looked at heat pipes before, most of them do have a wick. The idea is that some working fluid is in the pipe. You select that fluid so that it boils at or below the temperature you want to handle. The hot vapor rushes to the cool side of the pipe (carrying heat) where you have a large heatsink that may have a fan or active cooling system. The vapor condenses and–in this case–drops back to the bottom of the tube. However, if there is a wick, capillary action will return the fluid to the hot end of the tube.

You might think that using water as the working fluid would limit you to 100°C, but remember, [James’] technique lowers the pressure in the tube. At a lower pressure, the water will boil at a lower temperature.

We’ve seen heat pipes and wine chillers used to cool a PC before. In fact, we’ve even seen them in builds of completely fanless PCs.

69 thoughts on “Building A DIY Heat Pipe

  1. Cool! Interesting proposal – if someone could figure out how to fill a tube with refrigerant without too much leakage… (higher performance, generally lower temperatures they’ll work at, someone who’s less rusty with thermo should explain) protip, most canned air dusters are actually just refrigerant

    1. There are a lot of compounds that can be used as refrigerants, including propane (R-290), N-butane (R-600) that are sometimes used in small refrigerators to get away from HFCs that most people think of as “refrigerant”. Big commercial factory systems use ammonia (R-717) and lots of it. Typically the choice is based on application, flammability, temperature range and pressures involved. Water/steam (R-718…yes it has a number) systems are great until you try to make ice cubes or work in extraordinarily hot environments.

      https://en.wikipedia.org/wiki/List_of_refrigerants

      The builder’s method of creating steam to provide low pressure is mimicked in the canning industry that injects steam into the headspace of cans prior to lidding to evacuate oxygen and provide the familiar vacuum, but he could make it much more predictable/controllable by using a relief valve set to a predetermined pressure on a vent stub then crimping and soldering it shut – you could reliably drop the pressure to the vapor pressure of water at room temperature (about 2.5 kPa / 0.33 psia) that way and have a very efficient low-temperature heat exchanger.

      1. People should ALWAYS be reminded that using explosive gases like propane and butane can be incredibly dangerous. Those propane/butane systems have been known to actually explode when the compressor kicks the bucket or a leak is developed. I’ve heard stories from my buddies at work(I moved from IT to HVAC a few years ago)

          1. Indeed, I never heard of any exploding fridges. This is the kind of stuff that would end up directly at 21h news and repeated for the next weeks as a big “story”.

        1. I suspect that those stories are either complete bunk, or an exceptionally rare exception due to an improperly filled system. There is no oxygen in the system, and therefore it cannot explode no matter what. A leak is unlikely to cause an explosion, and is more likely to make a flame jet for a brief period of time. Funny how people worry about a pound or two at most of flammable refrigerants in cars and houses, but think nothing of having gas plumbed in the walls or sitting on top of a 10-40 gallon tank of gasoline…

          As a side note, even if burned, a propane or butane system is wayyyy safer than R-134a or even worse, R1234yf both of which contain fluorine, and release hydrofluoric acid when burned. HF is nothing to joke about, it has such a strong affinity for calcium, that sufficient exposure will strip the calcium out of your blood and cause cardiac arrest due to the lack of calcium channel needed for proper cardiac function. The worst you get with a butane system is a flame jet at the breach for a minute or two, similar to what happens if you tear a hose on your propane grill, or if it fails to light immediately.

          On R1234yf
          http://uk.reuters.com/article/uk-europe-cars-refrigerant-idUKBRE8BB0HE20121212
          http://www.r744.com/articles/span_style_color_rgb_255_0_0_updated_span_daimler_video_claims_1234yf_is_dangerous-vw_says_co_sub_2_sub_is_best_refrigerant

          1. With you on that one! These “stories”, which should more accurately be called “fairy tales”, are deliberately propagated by the likes of DuPont and other large corporations with a vested interest in selling their proprietary gasses – profit before environment. Does the CEO not have children? No matter where you were on the Titanic, you still got to the bottom just as fast as the rest. *NO* amount of money can buy you off this planet mate.

          2. Not everyone from the titanic died… If you could position yourself to be one of the people who gets the lifeboat you’ll do relatively ok. The logic is if the world is going down, be the one with enough money/power to survive, so what if it goes down faster.

          3. And yes you can’t leave the planet, there will be a time when we can no longer deny climate change once mass starvation and extreme climate events become common, but it will not kill people off instantly. The planet might look awful and virtually uninhabitable but we are very good as a species at adapting, hell I’m sure we could survive on Mars if we could just get enough people and equipment there. And I bet that the richest and most influential people will be among the rarer ones who get the live in the underground shelters and remaining safe outdoors areas.

          4. Yeah, because propane explosions never happen, right? Seriously, you’re right that it requires oxygen but you make a lot of assumptions that I have learned to never make in this line of work. When propane goes from liquid to gas it expands about 200 times its liquid volume, and sparks don’t always happen right next to the compressor so there’s plenty of time for oxygen to mix. Just do a simple search and you’ll see these things do indeed happen enough to be concerned, OR continue thinking the way you are and maybe I’ll read about you on one of our HVAC horror story sites(I have about a dozen over the past 3 years that would make your skin crawl as to how dangerous they were).

          5. ehrichweiss – Did a lot of reading out of curiosity on the topic (I’m one of those folks that easily gets lost down “click holes” see Ben Bailey Accidental Ornithologist https://www.youtube.com/watch?v=buKbdETQrxM)

            You’re right about the expansion part, but wrong about them occurring “often enough to be concerned” unless of course you live in a house with no gas or electrical setup, because those two utilities cause far more issues than flammable refrigerants ever have. Properly set up and maintained systems don’t leak or explode, just like proper natural gas installs don’t burn houses down, outlets don’t catch on fire, and people live with a 250 gallon tank of diesel fuel in their basement all their lives with no issue (home heating oil) which really SHOULD be far more concerning than a pound or two of propane. Hell, people have multiple 20 lb tanks of propane for their grills, and hundred pound or more tanks hanging around for pool heaters or home heating where there is no natural gas available.

            Just because the working gas is flammable doesn’t mean it shouldn’t be used. Its safer when burned than current refrigerants, much more environmentally friendly to produce, more friendly if released, and much less expensive. Not to get too tin foil hat theorist on this, but it would come as no surprise to me if the reason we have laws against propane/isobutene as a refrigerant in residential applications in the US comes down to chemical companies lobbying to keep it that way to prevent profits from evaporating (also add in fear induced lack of fact checking and lawmakers who don’t understand actual risks).

            Also, it wouldn’t surprise me if refrigeration professionals (not trying to point the finger at you specifically, since I’m inferring that you are) also lobby against such things. Not on the basis of safety (though that would be the method of argument) but on the basis of job security. Propane systems are less problem prone than R134 or R410 systems since propane/isobutene molecules are larger, and don’t leak as easily. Additionally systems running propane rather than R134 are much more tolerant to variations in fill volume, allowing a pressure based rather than mass based fill, while still maintaining acceptable performance.

            Even IF such systems posed a statistically significant risk (which I am pretty sure they don’t, anecdotal single point issues being excluded) we have an obligation to explore the option, given that the global warming potentials of various refrigerants are:
            R-134a = 1430
            R-410a = 1725
            R-22 = 1810 (also depletes ozone)

            Obviously those are bad from a global warming standpoint, so lets look at low ones

            R-1234yf = 4 (but its flammable and releases Hydro-Fluoric acid when burned)
            R-1270 = 1.8 (Propene, aka MAPP-Pro torch fuel)
            R-744a = 1 (CO2, requires the construction of a system to hold over 800 PSI, raising price of parts)
            R-600 = 4 (butane)
            R-600a = 3 (isobutene)
            R-290a = 3.3 (Propane)

            In fact, most of the very low GWP refrigerants (all that will be available soon, like it or not) are flammable (data pulled from https://en.wikipedia.org/wiki/List_of_refrigerants )

            Also of interest is that Australia, one of the historically largest opponents to HC based refrigeration, seems to now have companies such as http://www.engas.com.au/about/about-hydrocarbon-refrigerants/the-future-of-refrigerants/ involved with conversions for static use (homes/businesses).

          6. I know an AC repair guy. I forget the name of it, but there is one now illegal to produce but still legal to resell refrigerant. According to my friend, this stuff sells for it’s weight in gold, and it is in high demand by people who work on AC units, apparently it works much better, transfers more heat, cools the house down faster, etc. That’s all secondary markets beyond the chemical company; I think absolute performance is still the driving factor in these things. When it comes down to it the AC is probably the number one energy drain in most people’s houses and small differences in efficiency equals less electricity cost, I see no reason why energy ratings and consumer interests would not be the major driving factor in using the more obscure chemicals.

            Unless I am wrong and a propane system would cool a house down just as well with no extra electricity cost?

          1. Right, you can die from inhalation. and before internal combustion engines became common, there were industrial and transportation explosions due to it …. …

          2. …. and on 15th April 1912 a lethal double whammy combination of solid phase and liquid phase dihydrogen monoxide resulted in the deaths of more than 1500, with possibly around a hundred being killed instantly due to a vapor phase explosion during the event.

    2. Easiest: solder a valve designed for the refrigerant onto the pipe and fill after sealing other openings. Somewhat harder: form a bottleneck at one end of a pipe, fill it through that, compress the neck and then weld it together quickly using a spot welder. That seem to be the standard for professionally manufactured devices.

  2. This has been on my “to do” list for a quite a while, I have been waiting to have some leftover glass cloth or roving for wicks, because I would find them most useful in other than vertical configs.

    1. There are solar adsorption refrigerators working on methanol and charcoal out there.

      I have always wanted to make one, but they are bulky and methanol is not the thing I want to touch. Not that I can buy it legally without a licence and a government-approved storage facility anyway.

  3. Most heat pipes have wicking-ALL heat pipes have some sort of wick, either small internal fins or s loose, sintered metal powder inside piece. It’s essential to how the heat pipe works, along with a low boiling point liquid and reduced pressure. Without those they become either inefficient or just a tube that is a ticking bomb as it starts to heat up and pressure builds.

    1. I agree that all that I have seen do, but with the caveat that these operate vertically, I don’t see what the problem is. The wick isn’t magic. It just returns condensate from the cold end back to the hot end via capillary action. As long as the cold end condenses and the condensate returns, I don’t see the issue. I’d need some math to figure out if it is more or less efficient to return hotter condensate faster (I assume falling down the tube takes less time but gives the liquid less time to cool). As for bomb, wicking doesn’t prevent that from happening. Poor choice of working fluid or insufficient heat transfer at the cold end can do that, but otherwise, I have to disagree.

      In fact, the first heat pipes were Perkins tubes that had no wick and were used in railroad and commercial ovens. It was 1942 before someone at GM suggested capillary wicking and then 1963 before someone at Los Alamos actually built one and coined the phrase heat pipe.

      From Wikipedia:
      Most heat pipes use a wick and capillary action to return the liquid from the condenser to the evaporator. The liquid is sucked up to the evaporator, similar to the way that a sponge sucks up water when an edge is placed in contact with a water pool. The wick allows the heat pipe to operate in any orientation, but the maximum adverse elevation (evaporator over condenser) is relatively small, on the order of 25 cm long for a typical water heat pipe.
      Taller heat pipes must be gravity aided. When the evaporator is located below the condenser, the liquid can drain back by gravity instead of requiring a wick. Such a gravity aided heat pipe is known as a thermosyphon.[20][21] (See also: Perkins tube, after Jacob Perkins.[22]) Please note that a heat pipe thermosyphon is different than a thermosiphon, which transfers heat by single phase natural convection heat transfer in a loop.
      In a thermosyphon, liquid working fluid is vaporized by a heat supplied to the evaporator at the bottom of the heat pipe. The vapor travels to the condenser at the top of the heat pipe, where it condenses. The liquid then drains back to the bottom of the heat pipe by gravity, and the cycle repeats. Thermosyphons also act as diode heat pipes. When heat is applied to the condenser, there is no condensate available, and hence no way to form vapor and transfer heat to the evaporator.

  4. > One limitation of his technique is that there is no internal wick. That means the tube can only be installed vertically.
    Incorrect
    While many heat pipes will be installed with a vertical orientation, any heat pipe, including bare tube heat pipes, can also be installed horizontally. The heat pipe will work to equalize temperature across it’s area, in the case above this is its length. The water vapour is higher in pressure and will shoot to the cool area of the heat pipe due to its lower pressure, where the vapour will condense. What is required is that there be enough liquid (or wicking function) in the heat pipe to ensure that there’s always liquid in the area it is absorbing heat, or the efficiency drops drastically to largely that of heat conducting along the wall of the pipe. Take a look at flat plate heat pipes.

    Wicking or sintering is required if you need to ‘lift’ the condensed liquid back to the evaporator section. Surface wetting of ribbed designs has some minor lift capability.
    BUT, where you’re moving a lot of heat with a heat pipe, you can also have a situation where the velocity of the vapour flow is high enough that it impedes the flow back of the condensed liquid. So some applications without a lift requirement, may require a heat pipe with a protected path for the flow-back, provided by wicking, sintering, mesh, ribs or in some cases even a separate gravity flow-back pipe (typically of a smaller diameter than the main heat pipe). With DIY, watch if your pipe is too narrow to allow unimpeded bi-directional flow of vapour vs. liquid.

    > You might think that using water as the working fluid would limit you to 100°C, but remember, [James’] technique lowers the pressure in the tube. At a lower pressure, the water will boil at a lower temperature.
    Where the water boils isn’t important in the way you seem to think. A heat pipe does NOT work by boiling the water inside it, but by latent evaporation. Liquids suitable for use in heat pipes have a high latent evaporation pressure, as does water. (Note: it doesn’t require a refrigerant) A heat pipe utilizing water is efficient between 5C and 95C. Use a different liquid, then the temperature ranges changes. There are tables showing liquids for heat pipes with their effective temperature ranges. Some items in the table are powders, as their heat pipes are assembled with powders but within their operational range melts the powder and that liquid’s latent evaporation drives the heat pipe across its operational range.

    > ALL heat pipes have some sort of wick, either small internal fins or s loose, sintered metal powder inside piece. It’s essential to how the heat pipe works, along with a low boiling point liquid and reduced pressure.
    Not quite.

    Better quality heat pipes will have something (for the reasons described above), but not all. If it’s not required for the application, why pay for it.

    In fact, some applications require that the heat pipe NOT have any means of the liquid lifting, as they are installed with the condenser higher than the evaporator, with the application requiring that the heat pipe function as a Thermal Diode, providing heat-pipe quality heat transfer in one direction only. There can of course be some heat transfer in the opposite direction (if the application has a condition where the condenser is warmer than the evaporator), but that is limited to the rate of heat transferring through the length of the pipe wall.

    Not a low boiling point liquid: a liquid with high latent evaporation pressure.

    The evacuation of atmosphere from the heat pipe is to maximize the liquid’s vapour having free and full access to the inside surface of the heat tube. Contaminants in the pipe can go to gas and limit performance, or even stop it. Cleaning and rinsing the pipe before assembly is a very good idea. RO/DI water works well for the heat pipe’s water, as it’s not introducing contaminants that can go to gas and interfere with vapour access to the condenser section pipe surface. Some of the early Evacuated Solar Tubes had this issue, with contaminant gasses blocking the condenser section that was in contact with the collecting manifold. One way of addressing this, is to have the condenser section be below the top of the tube, with the top insulated; over time, any contaminant gasses are welcome to occupy the very top without affecting efficiency nor requiring re-evacuation, as that’s not where the vapour is being condensed.

    Puzzle: Two water tanks for heat storage. One is heated in its top half by a solar heated heat exchanger. How would you arrange heat pipes such that once the first tank has been heated, heat pipes will automatically start storing excess heat in the second water tank? As heat is removed from the first tank, how would heat pipes get that heat back to the first tank?

    1. First I’d try using a single bi-directional heatpipe from the bottom of the first tank (A) to the top of the second tank (B), with the hope that the temperature gradients in the tanks is enough to ensure that tank B only gets heated once the bottom of tank A is hot, and loses it’s heat to tank A as soon as soon as the base of A begins to cool.

      If that doesn’t work (or if the contents of the tanks are subject to mixing) I would try using a bi-directional heat pipe with a high operating range (so it kicks in only once tank A is sufficiently hot) to take excess heat from A to B, along with a lower range heat pipe arranged as a thermal diode to conduct head from B back to A (but not vice versa). To achieve the diode effect I would arrange this second heat pipe such that the condensate travels (inside the pipe, under gravity) to the end of the heatpipe in contact with tank B only.

      Am I close?

      1. My take is to use bare heat pipes as thermal diodes.
        Easy to DIY too.
        Heat is supplied to the top half of Tank A by a heat exchanger: some convection occurs within the range of the heat exchanger, layered water below. As the top of Tank A gets heated, the lower portion heats more slowly by conduction through the water. Over time, the lower portion of Tank A becomes heated.

        So run a thermal diode from low on Tank A over to slightly higher on Tank B, where the heat brought into Tank B will rise to the top of Tank B.
        Then run another thermal diode from near the top of Tank B to slightly higher in Tank A. When the temp in the top of Tank A is less than in the top of Tank B, the heat in Tank B is transferred over to Tank A.
        This keeps Tank A as the hot tank, hence a good single source to pull the stored heat from. And we can store additional heat in Tank B, (Tank B can store additional heat in Tank C, etc.).

        Of course the length of heat pipe outside of the tanks would be insulated. Thermal Diode can be improved: heat conducting ‘the wrong way’ along the wall of the heat pipes can be reduced by having the heat pipe constructed as two lengths of copper joined by a piece of appropriate plastic (plastic for a thermal break).

        While the above keeps Tank A hot while providing for additional storage capacity, overall this isn’t ideal. The efficiency of the transfer from the heat exchanger into Tank A reduces as the temp in Tank A rises, as the rate of transfer depends on temperature differential (hot heating less hot vs. hot heating cool). So this reduced rate of heat transfer into Tank A can occur even when we have cooler water in Tank B, which would be more efficient to pull heat from a heat exchanger.

        So while interesting, there has to be a better way to do it.
        Right away, putting the heat exchanger lower in Tank A (instead of the top) will have Tank A absorbing heat faster, getting to its temp faster, so you can optimize the position of the heat exchanger and the lower Thermal Diode, but eventually heat transfer slows down as in the example above. A lot more to do.

  5. I good friend of mine some years back recharged his air conditioning with Propane and it worked a lot better than the original gas. I was a little worried about the flammability side but the actual volume of gas is so insignificant even if it did rupture a line the change of an explosion was prety low.

      1. Here in Europe household refrigerators are often filled with R600a (Iso-Butane) and in One Superamrekt I have seen a Label on the freeze-box “R290” (Propane) with a Flame-Symbol. So this is common.

  6. I have Propane in my AC and it works like a champ, R134 never worked a damn so I found alternative refrigerants on the web. The temp gauge in my vent sometimes goes down to 28deg F sometimes. I’ve heard anecdotal stories of explosions but nothing based on fact.

    1. Assuming that your thermometer is accurate, your A/C is functioning a bit improperly. The coils should be limited to operation above freezing to avoid ice build up which will eventually stop them from functioning. You should see if you have a temperature probe in there that has gone bad, or maybe the thermally compensated expansion valve is stuck (if the car is equipped with one) Lots of budget cars, like my old Ford Escort, have no such controls and are based on hoping the coils don’t ever ice.

  7. I was thinking about building something similar, but filling it with water, not s heat pipe but a liquid thermal convection tube. Only works vertically, but is simpler. Effectively just a substitute for a large chunk of copper.

  8. Why do people find it necessary to stick musical diarrhoea on instructional videos.

    If there is no sound I can leave the speakers on, if there is sound I am unsure whether I can turn them off or not and have to listen to the tripe in case a commentary starts. It’s the same on TV now, close up and noise all the time. (Rant over)

  9. Can someone explain to me why the fluid is necessary? Doesn’t water have a high resistance to absorbing heat? Wouldn’t solid copper work better, or is this just a cost effectiveness thing?

    1. Yes copper has better thermal properties than water. However the advantage of a working fluid is that is directly carries energy as it moves (convection), whereas the rate of conduction through a solid medium is inversely proportional to its length.

      Couple a working fluid with evaporation and condensation and you can achieve exceptionally high rates of heat transfer (significantly more than straight conduction) unless your distances are very short.

  10. Acetone is also an excellent refrigerant, we sometimes use acetone sprayed onto bushings with a fan blowing across it to quickly drop the temperature to shrink the bushing for easy insertion. You’d be surprised by how effective this is.

    1. That’s evaporative cooling, it isn’t acting as a refrigerant.

      (its also a rather health dangerous and environmentally awful practice and can’t drop the temperature as far as a freezer)

  11. >However, [James] gets the water boiling to reduce the pressure in the tube before sealing it, which is an interesting trick.

    It should be noted that getting the water boiling before sealing is not an “interesting trick” but is absolutely necessary for the heat pipe to function. They only work when the tube is filled entirely with the liquid and gas phases of the working fluid. Merely filling the pipe with water and capping will barely function better than an empty pipe by itself.

  12. 50 posts. Only 2 posts mention METHANOL (aka Wood Alcohol).

    Are you telling me not one soul here thought Isopropyl alcohol?
    http://en.wikipedia.org/wiki/Isopropyl_alcohol (damn interesting)
    Denatured Alcohol WOULD be viable?
    http://en.wikipedia.org/wiki/Denatured_alcohol

    Or Triple Distilled Moonshine for that matter.

    https://www.americanelements.com/boiling-point.html

    Honestly it seems like Dry Ice would be ideal, PRESUMING you’d somehow calculate the EXACT amount of Atmospheres dry ice generates AND the container can handle. Safest bet, go with the 190 proof Grain Alcohol.

    Funny folk tale, Married couple bickering, Man promises to quit drinking. Well a heavy winter hit and snow had built up, spent his energy and cabin fever hit with it being something like -40 the previous night outside. He had squirrel away a bottle of Triple Distilled in his barn, clears the path well enough to get to barn and tractor. Inside he was amazed that the Moonshine didn’t freeze. Then. He died.

      1. Methanol (aka Wood Alcohol) =/= Ethanol (aka Grain Alcohol aka Bacardi 151, Everclear or Golden Grain). One of the recommenced treatments for Methanol toxicity and Ethylene-Glycol toxicity is Ethanol. Conversely if you read about Denatured alcohol you’ll find they add Ethanol to prevent poisoning and other nasty stuff to prevent drinking.

        Yet, no one mentioned Ethanol. That isn’t a good why.

  13. Have no experience with that. Looks very effective way of cooling. How dangerous is pressure rising during heat of such pipe? If cooling system get punctured or malfunctioning? Does system needs safety valve? Any other safety measures?
    Thanks for answering these questions.

  14. according to someone on a forum who i trust to know what what he is talking about says chemical level cleaning. not just a quick brush y is necessary as already pointed out. and just a few grams of water calculated from the area of the tube. on my 100 things to do before i get too old to care.been on the list for a round 5 years now. better get on with it……..

    1. I love the simplicity of water heat pipes. Simple to make by boiling and crimping and a great demonstrator of mean free path length in low pressure. The reason the work so well isn’t the fact water is pretty much the best working fluid for heat absorption phase change, but the simple fact the vapour molecules get to the hot side in practically one bounce. This is why other gases getting in causes major problems as higher pressure doesn’t just mean less evaporation, it also means shorter mean free path, until the pipe is useless.

      Anyone who questions heat pipe performance against solid copper, get one out of an old laptop or something and dip it in a hot cup of coffee, you won’t hold it for more than a second! You could stir your coffee with any size of copper bar no problem.

  15. The fluid in the pipe is not the important bit. Changing to 134a or anything else does not capitalize on the mechanism that is actually doing the work here in a wicking heat pipe. Please understand the theory and thermodynamics before trying to redesign something that…well, doesn’t need to be redesigned.

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