Talk:Heat pipe

Erroneous Originator

The original patent for heat pipes was granted in 1942 to Mr. R. S. Gaugler of the General Motors Corporation. Grover and his team made extremely important mathematic advances to heat pipe theory, proposed several key applications and coined the term "heat pipe." However, these advances occurred over 20 years after the original patent.

Clarification needed

An anon made the following edit to the article, probably because they couldn't make a new page, (this Talk page.)

Internally, a wick structure overcomes gravitational forces (or because of their absence in the case of space applications - huh? what does this mean? Can someone clarify?).

I have reverted the edit, but the statement seems reasonable. --Charles Gaudette 07:51, 27 July 2006 (UTC)

It should mean that if the heat pipe is tilted with the evaporating end higher than the condensing end, the capillary force exerted by the wick on the liquid is able to drag it higher, contrary to the gravity force, but it's wrong. Almost all heat pipes used in space application cannot work against gravity, unless the inclination is limited to very few mm/m. Heat pipes able to work against gravity do exist, but they have other limitations and are not used on satellites. I have changed the sentence, do you mind fixing my word usage? i am not mothertongue and my english is far from perfect. Thanks, Andrea.gf 10:30, 29 July 2006 (UTC)

I believe it may be referring to heatpipes used in computer cooling? In certain instances, heatpipes as used in computers may be working against gravity... Nil Einne 17:07, 21 October 2006 (UTC)

Article lacks comparitive technological context

This is an article about a cooling technology yet it lacks any citiations of actual SI units with which to measure performance - eg: Thermal conductivity. It also lacks any comparison to other cooling technologys, save for one sentance with an ad-hoc comparison of heat pipes to solid copper (- a typical example instance of where some SI units would be helpful for comparison). How do heatpipes compare with watercooling? Roidroid 06:10, 2 August 2006 (UTC)

You need a physicist to swing by. It's tough to write about it scientifically if you don't know how. :) I'd suggest doing some google searches for better information. But, with regards to water cooling vs. heat pipes, I'd say it's similar but a lot different. Both are relocating the heat to another location. However, heat pipes use evaporative cooling (phase change) whereas water cooling is just moving heat from one place to another via water's impressive heat capacity (relative to air). Been a long time since I had physics though so don't ask for more! --Swaaye 17:04, 2 August 2006 (UTC)

Both heatpipes and watercooling have their advantages and disadvantages. But I think water cooling is better. Heatpipe's efficiency greatly drops when all the working fluids are evaporated and converted to vapor, while water cooling doesn't have this problem. Also, heat pipes work with earth's gravity, so it matters in the direction that you install it and water cooling don't have this problem. However, water cooling has its own problems. Like potential leaking and algaes growth inside the system. However both of these problems can be minimized with proper installation and selection of coolent. Lightblade 23:47, 13 May 2007 (UTC)

Actually, gravity is not that much of a concern. Wicking inside of the tubes allows orientation to be perpendicular to gravity, or even against it. Otherwise PC coolers using heatpipes wouldn't work well at all, which is definitely not the case. The range of temperatures at which the heatpipe is useful is determined by internal pressure and/or choice of the fluid. And, heatpipes have zero maintenance requirements. The article covers each of my points. --Swaaye 02:43, 14 May 2007 (UTC)

Standard Enthalpy Change of Vaporization of water

The standard enthalpy change of vaporization of water is 540 calories per gram. It was originally listed in this article as 80 which is incorrect. I changed it to 540 then someone changed it back to 80. The correct value is 540 not 80 please stop changing it. 80 calories per gram per is the standard enthalpy change of fusion of water.

Gravity

I would be interested to know how gravity affects heatpipes. The 'hottest' part is rarely at the bottom of the system, and I would like to know how gravity affects this. —Preceding unsigned comment added by Blammermouth (talk • contribs) 03:48, 12 January 2008 (UTC)

Split article?

The picture at the top of the article is not a heat pipe as described in the article. It's just solid copper wire that CPU heat sink manufacturers call a "heat pipe". Should we split the article, one with the scientific concept of a heat pipe, and one with the colloquial definition? Or maybe just get rid of the bad picture? Gigs (talk) 21:00, 26 February 2008 (UTC)

The heat sinks shown in the mentioned picture are indeed heat pipes. —Preceding unsigned comment added by 70.231.246.208 (talk) 17:47, 25 August 2008 (UTC)

Yes, but entirely not the sort of heat pipe described in the article. There's no liquid in those, they are just copper wire. Gigs (talk) 10:45, 22 December 2008 (UTC)

amri sembil... dah la paka tali pinngan kecik,bajet ye kurus.... dah la kenang ke teh...bajet teh kenang ke ye dekpon..... —Preceding unsigned comment added by 210.48.156.51 (talk) 12:14, 3 September 2008 (UTC)

Can anyone translate? Gigs (talk) 10:45, 22 December 2008 (UTC)

The referenced picture shows a common style notebook cooling module using heat pipes. These are indeed heat pipes, likely flattened 6mm diameter with a 0.5mm wall, 0.4mm wick and water as the working fluid. — Preceding unsigned comment added by Gameyer4 (talk • contribs) 19:02, 13 January 2011 (UTC)

Incorrect formulation

"By limiting the quantity of working fluid in a heat pipe, inherent safety is obtained. Water expands 1600 times when it vapourizes. In a water containing heat pipe if the water is limited to a 1600th of the volume of the heat pipe, the pressure within the pipe up to 100 C is limited to one atmosphere. Calculations can be made to ensure that the pressure is within the limits of the pipe strength at the highest possible working temperature of the device." This suggests that the pressure in the heat pipe is related to the mass of the fluid within the pipe. Actually the pressure only depends on temperature. Excess mass of fluid will merely remain liquid and occupy some of the inner volume to no use. Of course, in case of explosion, the larger the quantity of liquid, the more expansion of the gas upon pressure release and the farther the debris will be propelled. So it is not in terms of pressure limitation that it is required to limit the mass of the fluid, but to limit the blast in case of an overpressure. —Preceding unsigned comment added by 62.161.229.37 (talk) 09:16, 5 June 2009 (UTC)

Confusing references to vacuum

The interior of a heat pipe is not evacuated - it contains a liquid and its vapour, at a pressure equal to the liquid's saturated vapour pressure, which is a function of temperature. While one could use a vacuum pump to make a heat pipe, that seems to me to be an unnecessary complication. The obvious method (especially with water) would be to boil the fluid in the unsealed heat pipe to expel the air and then seal it off while still hot - is this not how they actually do it?Moletrouser (talk) 20:01, 24 September 2011 (UTC)

Not necessarily. The liquid will condense at the coldest spot of the tube, meaning the whole tube has to be at least 100°C when dealing with water. I imagine most technicians would prefer a vacuum pump to the handling of steaming hot pipes. Boiling the liquid may be the best DIY solution, and have some use in specific industrial applications, but I doubt it would always be an option. However, this only applies to systems with low working pressure. Is there any reason why one would prefer to use water, methanol or acetone instead of for example propane or butane? I made an improvised heat pipe with copper piping and gaslighter refill; seemed to work fine. Wouldn't higher pressures allow faster heat transfer, or is the specific heat of evaporation and the liquid flow rate the limiting factor? Ssscienccce (talk) 09:55, 4 June 2012 (UTC)

agreed, a heat pipe indeed does not contain a vacuum. i wish contributors would get a clue and stop talking about vacuums so much. all that is happening is that all the air is evacuated, leaving only the vapor of the working fluid, and a temperature/pressure relationship depending on the chemical used. certainly you can remove the air with "vacuum", but if you have access to youtube you'll see that it's quite common for people to make heat pipes by heating the pipe and sealing the end — Preceding unsigned comment added by 110.175.57.184 (talk) 15:23, 8 June 2012 (UTC)

Pressure versus boiling temperature

I would be interested to see discussion about how the change in mass of vapor-phase liquid affects the pressure and hence the boiling temperature. I haven't thought it through, but it seems like that relationship will be interesting. In particular, the heat pipe will not be effective below the boiling point and when all of the fluid is in gas form. For example, as you raise the temperature, in that temperature range, does a fixed volume force it to follow the liquid-gas curve of the phase diagram, or is something more interesting going on? Also, it seems like the total mass of fluid for a given volume is a design parameter that will affect performance... —Ben FrantzDale (talk) 17:33, 10 January 2012 (UTC)

Vapour pressure diagrams of water; data taken from Dortmund Data Bank. Graphics shows triple point, critical point and boiling point of water.

It looks like Vapour pressure of water is relevant. The left curve at right shows the saturation vapor pressure of water across temperatures. If the heat pipe has some mass of liquid water in it and is sealed, then (I think) the relative humidity is 100%, so as you heat one point, the relative humidity there goes down (moving right from on the curve to below it). That frees water molecules as it's locally above the dew point, this increases the volume of gas, raising the pressure everywhere, so at the other end of the pipe, the state moves up from the saturation-pressure line, causing condensation. So I think at all points in the pipe the multi-phase state is "trying" to stay on that 100% humidity curve. —Ben FrantzDale (talk) 14:33, 25 April 2012 (UTC)

in a heat pipe the liquid is always at boiling point, because the pressure adjusts with temperature. however, a pipe won't work when the liquid freezes (which is why water wouldn't work at zero kelvin, even though ice does have vapor pressure), and the upper temperature limit of any fluid is due to the bursting pressure of the pipe (among other things) — Preceding unsigned comment added by 110.175.57.184 (talk) 15:33, 8 June 2012 (UTC)

Trademark?

Is "Heat Pipe" a registered trademark? --Jidu Boite (talk) 19:39, 21 February 2012 (UTC)

Computer usage citation

As someone who takes computers apart every day for a living, does the statement

Heat pipes are extensively used in many modern computer systems, where increased power requirements and subsequent increases in heat emission have resulted in greater demands on cooling systems. Heat pipes are typically used to move heat away from components such as CPUs and GPUs to heat sinks where thermal energy may be dissipated into the environment.[citation needed]

really need to be cited? I also ask this as someone who doesn't know too much about wiki etiquette. However, to me at least it is a fairly obvious observation. -- Rosseloh (talk) 18:31, 21 January 2013 (UTC)

As to your question, Sure it does! Just think of all us butchers and bakers and candlestick makers out there who come across the mysterious term "heat pipe" in our general reading and need all the help we can get. We probably even have laptops but no clue about what keeps them cool, since we don't hear a fan. Best regards to an expert from an utter layperson --Remotelysensed (talk) 16:11, 26 July 2013 (UTC)

Tidy-up

I've just done a fairly comprehensive tidy-up. Apologies if any of your favorite bits got axed in the process, but please think very carefully before reverting them - the article as a whole is (I believe!) significantly improved by my changes. Snori (talk) 09:39, 31 July 2013 (UTC)

Variable Conductance Heat Pipes

I have extensively modified the Variable Conductance Heat Pipe section. I've corrected two errors:

1. "Active control of heat flux can be effected by adding a variable volume liquid reservoir to the evaporator section" This is incorrect. VCHPs control heat pipe temperature, not heat flux. There is no liquid reservoir, but a reservoir for the non-condensable gas. 2. Immiscible gas - the gas actually mixes with the heat pipe working fluid vapor - it is not immiscible.

I've added a background paragraph, discussing why VCHPs are used, and provided a typical example of their thermal control. I've also added a few sentences on Pressure Controlled Heat Pipes, which are a variant of Variable Conductance Heat Pipes

Bill Anderson — Preceding unsigned comment added by BillAnderson71 (talk • contribs) 00:59, 22 October 2013 (UTC)

Structure, design and construction

I've corrected some errors in the first two paragraphs of the Structure, design and construction section. First, the primary selection criteria for the envelope material is that it is compatible with the working fluid, not that it has high conductivity. Copper/water and aluminum/ammonia heat pipes have a highly conductive envelope, but many heat pipes at higher or lower temperature ranges use stainless steel for compatibility (The thermal conductivity of stainless steel is only 20 W/m K.

Second, the mass of working fluid added to the heat is chosen so that both vapor and liquid exists under normal operating conditions.

Third, the text stated that water heat pipes start working near 0 C. While strictly speaking this is true, significant power is normally carried above 20-25 C (as the paragraph correctly states)

Finally, the text said that mixtures of ammonia/water/alcohols could be used. While all of these fluids are commonly used, they are normally not mixed (water in an ammmonia heat pipe will cause severe corrosion).

BillAnderson71 (talk) 23:12, 3 December 2013 (UTC)

Active or passive?

Is a heat pipe considered an active heat-transfer device or a passive heat-transfer device?

I understand that a simple heat sink, with no moving parts, is a passive device, and a system that uses a pump to circulate a coolant is an active device. But what about the heat pipe; is it in a grey area halfway between active and passive? 174.24.50.139 (talk) 01:10, 27 January 2014 (UTC)

That seems to depend on who you ask. Some people think heat pipes are active, since the working fluid is moving inside the heat pipe. On the other hand, the Spacecraft Thermal Control Handbook state that Heat Switches are passive, even though they have have internal movement, caused by the melting and freezing of a phase change material. From this, I would argue that heat pipes are passive, because there is no electrical power source required, and no moving mechanical components. BillAnderson71 (talk) 19:46, 8 February 2014 (UTC) On the other hand, NASA TFAWS (Thermal and Fluids Analysis Workshop) classifies heat pipes as an active heat transfer device, so I guess that the correct answer depends on the phases of the moon. BillAnderson71 (talk) 22:20, 3 July 2014 (UTC)

Removed a paragraph about heat pipe maximum vapor velocity

I've cut a paragraph that discusses heat pipe maximum vapor velocity in /* Structure, design and construction */, since it had several errors. First, it said "Due to the partial vacuum that is near or below the vapor pressure of the fluid, some of the fluid will be in the liquid phase and some in the gas phase." The heat pipe must have saturated liquid and vapor, and is by definition at the fluid vapor pressure. It makes no sense to talk about a partial vacuum below the vapor pressure of the fluid.

Second, it says "In this sense, the only practical limit to the rate of heat transfer is the speed with which the gas can be condensed to a liquid at the cold end" This is only one of the heat pipe limits, and only controls at temperatures near the triple point (sonic limit). At higher temperatures, the heat transfer is limited by the capillary limit, or the ability to transfer heat into and out of the heat pipe.

BillAnderson71 (talk) 02:37, 10 April 2014 (UTC)

Opening sentance

I'd say that the opening line should be:

"A heat pipe is a heat-transfer device that uses phase transition to efficiently manage the transfer of heat between two solid interfaces."

i.e. drop the current reference to thermal conductivity.

While it's certainly true that the pipe itself generally has some ability to conduct heat, this is simply to efficiently trasfer the heat locally to the liquid, at one end, and to dissipate heat from the vapour at the other end - not for the transfer between. Heat pipes would surely work just as well normally if the majority of the pipe between both the ends was of made of a very poor conductor of heat? Snori (talk) 00:04, 13 March 2017 (UTC)

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