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Active Heat Pipe

Move heat downhill
  [vote for,

Firstly, I'll mention that I've used this idea in the two most recent ideas I've posted, and thought that it merit's it's own page.

The idea is relatively simple, but I haven't found anything very much like it on google.

There are two heat exchangers (HXs), one at at some high location, and other at a low location.

At the bottom of the lower HX is a liquid sensor, and a pump (probably hermetically sealed, like the pump in an air conditioner system). Whenever liquid is sensed, the pump turns on.

The top of the upper HX is connected via a pipe to the top of the lower HX, and allows gas to flow from the upper HX to the lower HX.

The whole system is vacuum purged, and filled with a refrigerant. The amount of refrigerant is enough so that the pump, the pipe from the pump to the upper HX, and the upper HX, can all be filled with liquid refrigerant, with the rest of the system filled with gaseous refrigerant.

When heat is added to the upper HX, the refrigerant boils there, raises the pressure in the system, and causes some of the gaseous refrigerant in the lower HX to condense, giving off heat. The condensate moves (by gravity) down to bottom of the lower HX, triggers the liquid sensor, and activates the pump. The pump of course moves the liquid back to the upper HX.

As with a regular heat pipe, heat is moved by evaporation and condensation. The only real difference is that condensate is moved from one end to the other by a pump. The pump is only working against gravity, and is not doing any compression, so little energy is needed to run it.

Efficiency can be maximized by selecting a refrigerant such that the latent heat of vaporization, divided by the difference in density between liquid and gaseous refrigerant, is maximized.

Water has a fairly high latent heat of vaporization, so it's probably best for this application.

goldbb, Oct 01 2009

My first idea with a powered heat pipe Solar_20Steam_20Cooling
[goldbb, Oct 01 2009]

My second idea with a powered heat pipe Solar_2fAntisolar_20Heating_2fcooling
[goldbb, Oct 01 2009]

Loop heat pipes https://en.wikipedi...wiki/Loop_heat_pipe
work exactly as was described, but without a pump! [justin_case, Oct 21 2021]

Swept Boundary Layer Heatsink Swept_20Boundary_20Layer_20Heatsink
[bs0u0155, Oct 22 2021]


       My understanding is that regular passive heatpipes generally work just fine for moving heat downward, as long as they're built with wicking structures inside to convey the liquid back up by capillary action.
notexactly, Oct 04 2019

       Strange this idea went completely un-annoed for ten years.   

       [notexactly]'s annotation makes me wonder if a piezobuzzer attached to a heat pipe would increase its capacity with the continued appearance of no moving parts.   

       Another use for a piezovibrator is to vibrate the external heat shedding coils at a household fridge; they could see if microwiggles disrupt boundary layers and cause better cooling. This could also benefit air conditioners and heat pumps.   

       piezoelements are 1/10 of 1 cent at alibaba...
beanangel, May 10 2021

       If we're in the business of annotating old ideas...   

       I get the idea, the biggest problem with heat pipes is the liquid return. Normally, they use a sintered porous structure and rely on capillary/wicking type movement. This doesn't scale well and isn't fast.   

       Pumping liquids around is the standard solution to move thermal energy around, so an obvious choice. But, you're necessarily dealing with a liquid that's very nearly, or very actually boiling. This is a problem. In this situation, any type of pump will behave horribly. For example, a centrifugal vane type pump will have the liquid boiling in the low pressure areas on the back side of the blades, you'll have endless gas-void/cavitation/priming problems.   

       If you want to move heat downhill, and you're OK with moving parts, just use a pressurized water cooling loop like a car/house.   

       //Another use for a piezovibrator is to vibrate the external heat shedding coils at a household fridge; they could see if microwiggles disrupt boundary layers and cause better cooling. This could also benefit air conditioners and heat pumps.//   

       A sound (get it?) theory that would do exactly as you say and improve the efficiency of the liquid/air heat exchanger component of fridges/AC units. The problem, as usual, comes from the inconvenient nature of the real world. Aluminum, and it's alloys do not behave like steel for example. They undergo "work hardening", or another way of putting it, they have no fatigue limit. You can't make a spring out of it, well, you can, but it only works once, which is a crap spring. So if you subject aluminum to repeated deformation it becomes progressively brittle and then fails.   

       I have a practical demonstration of this, I occasionally make fluorescent liposomes, essentially a fluorescent dye in a lipid sphere suspended in aqueous solution. To make them involves a lot of vibration/shaking over 12-24hrs. To protect the fluorescent dye from light exposure I wrap the tubes in aluminum foil, and shake the tubes at ~60Hz. After 24hrs of this, the foil is practically dust. The same would happen to piezo-wobbled radiator fins.   

       I had an idea a while back for solving boundary layer heat problems <link>
bs0u0155, Oct 22 2021

       ^Non light transmissable laboratory tubes and flasks is not a product? Must be.
wjt, Oct 23 2021


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