Graphene heat pipe

Does it actually claim to dissipate heat? I thought heat pipes just conducted heat to be dissipated elsewhere.

ates

I'm a bit puzzled by the claims. They talk about the working fluid just li ke in any other heat pipe. In those pipes it is the working fluid that car ries the heat. So why does anyone care about the pipe casing? Is this hea t pipe just a thermal conductor with a working fluid to lubricate the non-m oving parts? How is the graphene actually helping the thermal properties, by adding to the working fluid?

I didn't read all of it, but it looks like the 3.5 times better is in terms of weight. It's only 'better' 'cause it's lighter.

George H.

Many times.

Exactly. And the mechanism isn't thermal conduction, it's vapor transport.

Heat pipes are usually skinny, so the radial heat flux is large at their active surface. Graphene only conducts heat well in-plane, and the planes are microns thick.

They also talk about allowing a higher power density, so my impression was that the gains came both from better conduction of heat from the outside wall to the fluid inside, and perhaps better conduction of heat up the wall until it could get transferred to the inside. I'm no expert on this, I just thought it was interesting. It's graphene, it has to be better :-). I'm sure some PC overclocker will be bragging about upgrading from water cooling to them within a year :-). Think how much lighter your laptop could be - at least a couple of grams.

You can buy pyrolytic graphite sheets from Digikey. They have high thermal conductivity, but only in the plane axis, and are thin, so are basically useless.

The rules of thermodynamics don't allow heat to be conducted elsewhere without dissipating it. There has to be a thermal gradient or there's no conduction, and that's what dissipation is.

If heat is transported in a highly conductive rod that is well insulated, where is it dissipated?

Dissipated, to me, means dispersal into the ambient environment. That's what heat sinks do. Transport doesn't do that.

but the heat is not dissipated in heat pipe (ideally) it is dissipated in the sink on the other end

What part of the Second Law do you (and JL) have difficulty understanding?

Heat surely is dissipated in the heat pipe, or it could not be conducted. There is no thermal superconductor, last time I looked. Even the carbon nanotubes that are touted for the role aren't so "super".

So it comes down to non-zero thermal resistivities and time constants. Of course.

What happens if I carry a thermos of hot coffee upstairs? Does that create dissipation?

Heat pipes transport heated mass.

There has to be a thermal gradient or there's no

Transportation doesn't need a gradient. It can work against a gradient.

We seem to have different definitions of "dissipated."

An insulated truck carrying a load of hot tar at 75 MPH: is that transportation dissipation?

A heat pump requires dissipation elsewhere.

All thermal flow requires dissipation, because that's what dissipation is.

We live in different worlds. I design electronic things with parts that need to be cooled, and I need to get rid of the heat.

What do you do?

I try to avoid prevarication, which seems to be your #1 pastime. I also use words that have meanings other people recognise, instead of my private meanings.

Your tar truck and your carrying coffee upstairs are both examples of heat pumps. The graphene heat pipe is passive, not a pump. Your heat pump examples are pure prevarication, nothing more. We weren't talking about heat pumps, and you tried to change the subject... your favorite thing to do when you discover you're wrong.

If the passive pipe works, it dissipates heat. Perhaps the heat it dissipates is transported to something that dissipates it further, but heat pipes do not "just" conduct heat to be dissipated elsewhere. Thermodynamics doesn't allow that.

OK, you don't design electronics.

You have a very fragile ego too. That makes me sad for you, because you clearly know what you're doing, except where it comes to projecting your personality.

Here's my work for this week, a HomeBus/WiFi thing with LCD. It uses something like the gyrator I mentioned here a while back. Thanks to those who helped. This is off to JLCPCB shortly.

CH

DISSIPATION n Scattering, dispersion, disintegration; wasteful expenditure of;... [The Concise Oxford Dictionary of Current English]

Heat energy flowing through a channel is conducted or transported by the channel. Heat energy coming out of the end of a channel and flowing to waste would be dissipated by the act of flowing to waste. Alternatively, the energy could be collected in an area of lower energy or used to do physical work; it would still flow through the channel but there would be no dissipation.

The channel is not dissipating heat energy, the dissipation, if any, takes place after the energy has left the channel.

A heat pipe connecting a CPU chip to a heat sink: 20 watts goes into the hot end of the pipe, 20 watts comes out of the cold end; no dissipation there. If the heat sink is 2 K/W, the sink dissipates 20 watts and rises 40C.

The delta-T in the heat pipe will be small, roughly 1 c, and its surface dissipation small too.

Don't need a lot of thermodynamics to do that math.