Common Water-Insoluble Powders to Use as Wick

Flour won't withstand the temperature criterion. One would be making pancakes with it at those temperatures...

Hello, sugarandfat.

Well, I would offer Sphagnum Moss as a candidate for consideration.

It absorbs and wicks very well (has been used for diapers, wound dressing), is ubiquitous and inexpensive, insoluble in water and organic. While I do not know, I suspect it can be run thru some type of food processor to powder it (probably do not want to do more than a fine chop), and it will retain at least some of it's wicking properties.

Withstand the heat... again a guess, but probably, if kept moist. Another guess, but I suspect it would not clump or harden like chalk dust, talcum powder, etc. It may be worth an investigation to see.

If, after investigation, discarded from consideration, it could be used as pancake topping???

Sphagnum's awesome, we've got quite a little industry going on it back in New Zealand.

It needs to be something most people are going to be able to get their hands on fairly easily tho. The heat pipe's for an open source solar energy device which people will ideally be building themselves from scrap and basic materials.
Sphagnum would be ideal if you live near it, otherwise a little tricky to procure.

Tho this does open up the field of organic fibres...
Will think on it.

OOOoooo....

You know what I just thought of (and this is weird):

Tampons.
Quite a few of them, stuffed into a tube or sleeve.

That's one of the more unsettling thoughts I've had, but it just might work. Need quite a few tampons tho, probably about 40.

Sintered copper may be used as a best wick material. It can take a very high heat and it does not dissolve in water. the heated water may lack oxygen and hence a little chance of oxidation. Copper cools and heats up faster making one of the best material for wick.Its availabilty is with anyone who deals in non ferrous material. Let me know in which country youlive and i can help you to get the vendor.

I think that- since you are trying to develop a product that "average" folks can make for themselves- you should consider poly-styrene beads (like the ones in bags used to fill up bean bags).

According to Dow Chemical, styrofoam melts at 464F, so you are fine there. It is relatively small and can be packed tightly into a nylon or aluminum window screen "tube" that will fit into the heat pipe tube. It is waterproof and essentially non-reactive. AND- most importantly- it is cheap and readily available.

Try blotting paper - I do not know of the temperature it can withstand but is an excellent absorber. Also cotton cloth.

"talcum powder, chalk dust and sand."

Hi,

these are good, but you need a possibility to select the optimum grain-size and to mix different grain sizes to get the wanted combination of pore size and connectivity.

Any mineral grains are suitable: glass grit, crushed and milled stones...

But: these are not at all optimum!

Optimum structure would have defined pore size together with tube-like structure of pores.

These shall have low flow resistance with defined soaking/wetting characteristic.

I would try stretched plastic (Nylon or else) filaments (very thin ones), bundled together to form ribbons and soaked in wet clay, dry and slow fire at low temperature to burn the organics and hard fire above 800 to 1000°C depending on clay type.

Also cold forming with "water-glass" will be possible.

RRHABE

we used to use sand in a paint gallon can with kerosine on it with a rise on the middle. Made a long burning heat source. Make sure it is out when you add more kerosine. Works with gasoline as well, but burns more vigorously.

Couple of 100DegC?

You do not have much choices. Sintered Copper powder in the required granule size is the best or you can try fine wire mesh of either Cu or SS.

Hi,

"sintered Copper powder" very likely undefined oxidation and or corrosion, needs acidic pH to be stable, will corrode severely in presence of chalk.

"fine wire mesh" of SS or Titanium will be great - but paralleled wires will be much better - but this is a low price application, so I would stay with clay and sintered wicks.

Can be done everywhere (a pottery or brick factory should exist). Local material can be used, everything is low cost.

RHABE

Hi RHABE,

We regularly produce these Heat pipes with sintered copper powder that are sintered in an inert atmosphere. Your concern on oxidation and corrosion is well founded - but the transporting liquid used is De-ionized water that too in absence of air.

You are right, what I have been mentioning is for industrial application. For a low cost of manufacture, I may be wrong with these suggestions.

Still, for 200DegC application?

And what about the longevity?

Anyway! I will be more concerned with the adhesion of the wick material to the inner wall of the container and their compatibility and the compatibility of the transporting liquid.

What you need is porous ceramics, these will stand the temperature and will not rot should last you a long time.

Here is a link that gives you specifications.

http://www.soilmoisture.com/PDF%20Files/Ceramics2000.pdf

Hope this helps.?

Wow, good response. Thanks yall.

Sintered copper: sounds good and seems in keeping with industrial production approaches. Would be concerned about corrosion and availability.

Poly-styrene beads: really? They wick? I'll try it out.

Paper: might not take the heat.

Cotton: see tampons.

Fired plastic ribbons in clay: wow. Now that sounds interesting. What role would the clay and the firing take? Is it to do with the microstructure of carbonised organic material?
Kilns might be slightly beyond the easily practical tho.

Sand: thinking the pore size might be too large. Would certainly work for smaller distances.

Wire mesh: as above.

I was also recommended fiberglass, particularly in the form of the rope used to line fireplace doors and similar.
And apparently carbon fibre is about the best thing around, but obviously pretty tricky to get your hands on.

This is really helpful, thanks guys.

I always knew that common news print will dry (absorb fluids) quite well. The task is to trap newsprint fibers in an otherwise porous sack. There is a product (looks like a long legging) used in a water drainage system (flexible tubing). The sock is pulled over the tubing & acts as a barrier against entry of small stones/sediment & plant roots but allows for fluid flow. Stuff this 'sock' with old newspapers & make sure that the far end is below the level of the 'receiving' end of the that sock. Carlos

SugarandFat:

Hi,

I live in wyoming and we have been blessed/cursed with this stuff called Bentonite, it is all over the place and there are many uses for it one of which I read is to filter things under unique conditions, maybe that will help.

I say blessed/cursed because on one hand it is mined in great quantities which helps the state keeping us income tax free and cursed because you never know where this stuff will turn up and if you are driving down a dirt road in a rain storm and hit a patch of this stuff it seems like God just pulled the rug out from under you, it is very slick. I have never seen it disolve as they use it to seal the bottoms of lakes and ponds, some people make filters out of it to filter certian things.

Amoroso82

Call me Guest Joe for an ID. Try InsoLute, which is a ceramic adhesive which will stay together at temps up to 800 degrees C. Very impressive stuff. I've used it in hot, wet, foul post-combustion gas streams. It is somewhat porous to gas & liquids. To increase porosity I think you could add some powdered glass to the mix. Its made by Saueriesn (forgive my spelling of that company name). Use distilled water to mix the paste for best results, and you should try to cast your wick in a stainless steel molding sleeve. Instead of removing the molding sleeve, retain the sleeve in the wick as it is used. There may be a ceramic shop or hobbyists near you that have a similar product that is not too pricey. For a couple of wicks you don't need much material. Good luck. Joe

Hi,

the company name is "Sauereisen".

RHABE

Some more good suggestions. What about charcoal?

I've started experimenting with different materials. My apparatus is just a 12mm internal diameter clear PVC tube, taped to a wall, packed with the various materials, with a container of fluid at the base (2-3 cm immersed, yellow food colouring added)

The results so far:

Sucrose + saturated H20 -- 1-2 cm vertical

Salt + saturated H20 -- 7.5 cm

Salt + Ethanol -- 7.0 cm

Talc + H20 -- hydrophobic (very)

Talc + Ethanol -- pending (some wicking but turns to sludge)

Cotton (tampons) + H20 -- 29 cm (in looser plastic sleeve)


Still to try. fibreglass, metal powder, charcoal, chalk, fine metal mesh, plant capillaries.

Hi,

not the material is generating the sucking height but the size of the pores.

If you have tubes of diameter D then you have a circumference of 3.14*D.

If you suck up water and your material is clean you will have sigma= 0.07 N/m of sucking force per length of wetted-to-nonwetted surface.

If you suck up oil or similar or your surface is not clean, then you will have typically 0.03 N/m sucking force.

So if you suck against gravity - that will pull back with density (ρ) times Volume (V).

So upwards force is Fup= 3.14*D*0.07N/m = π*D*sigma

and down-wards force is Fdown=ρ*π*D²*H*g (g=9.81m/s²)

these Forces shall be equal at final height: π*D*sigma = ρ*π*D²*H*g

or solved for final height H = sigma/(ρ*D*g)

if water and D = 1 µm then H = 0.07N/m/(1000Kg/m3*10^-6m*9.81m/s²)= 7.1 m

So if you have measured some height with any material you will only measure efficient porosity (equivalent diameter to tubes). Grind this material to finer grain size - and you will have a higher height but a smaller flow rate.

Final height is going up by 1/D but flow rate is going down by D³!

Reaching final height may thus take considerable time.

In my experiments in realising a capillary-driven lubrication system for high precision ball-bearings some oils needed up to 30 days in reaching the final height.

Materials as you try (powders) are good in sucking as the effective capillary diameter is small but are pretty bad in flow rate as the path is much longer than necessary and there are many very small passages to overcome.

Have success!
RHABE

Thanks Rhabe, good info. I've been using Wolfram Alpha to do all the working out for me

http://www.wolframalpha.com/input/?i=capillary+action

which for a 1 meter column of water gives a pore radius of .014 mm. I have no idea what real world material that would correspond to, but that's what I'm aiming for.

Flowrate is one of the things which greatly affects heat pipe efficiency, yes, but keeping in mind that the gas expansion ratio of water is about 1600, I shouldn't need to be getting a huge amount through.

I got some chalk, but fibreglass rope and metal powder, sintered or otherwise, are proving tricky.

btw, below should be corn syrup, not cornstarch.

Whilst working on a laser development project once - we used molecular seive to abosorb moisture. I am not sure if this would help but the capacity of this product was better than anything that we had come across. These are beads with very long and controlled size small pores. They can be dried out by heating - I have not checked if these would do the job but may be worth investigation.

I had a further idea, what about a liquid wick? ie cornstarch, which water floats on. If I could somehow introduce water into a tube of a denser liquid it should rise indefinitely.

Problems with this would include but not be limited to: it would take some initial force to introduce the water, ie to lift the column above it. Also that corn syrup boils at 110ºC, so would need to be insulated or something. On the plus side it's a lot more viscous, so there would be membranes that water would pass through but it wouldn't.

Some more results, for anyone interested (all with water):

Toilet paper (loose): 15 cm

HEPA filter from vacuum cleaner bag: 10 cm

chalk stick/powder : 0 cm

Kitchen sponge / chamois : 2 cm

Paper coffee filters (in tube or loosely rolled) : 41 cm

The last one being actually fairly impressive, considering. I would still like to try ground charcoal and ceramic.

I think tho there doesn't seem to be a really simple and nice way of getting a heat pipe to operate 1 meter upwards. Instead I guess I'll have to not go against gravity and just jack my boiler up two meters vertically, fed into by wickless heatpipes.
Not the end of the world.

But now I possibly have another problem. If I'm trying to boil water with the heat from the device, via the heatpipe, then the 'cold' end of the pipe would be 100º, if it's plugged into a reservoir of boiling water. But with the near vacuum in the pipe, the boiling point of the water inside will be 0-30º. Does this mean the water won't condense and drop it's heat, thereby making the pipe not function and me have to find another working fluid?

What other fluids would be workable?

For a high temp water insoluble power you might try abrasive powders like silicon carbide, emery & alum oxide. Abrasive powders come in a very large range of grain sizes.

Doug