What is a heat pipe?
A heat pipe is a sealed tube, usually metal, containing a small amount of a working fluid and a porous lining called a wick. It gathers heat at one end, carries it to the other, and releases it there — with no moving parts and no external power. Because it uses boiling and condensing, it can move heat far faster than a solid rod of the same material.
Why look inside?
From the outside a heat pipe is just a featureless metal cylinder, so it is impossible to guess how it works. Opening it up shows the three ingredients that make it special: the open core that the vapour races along, the wick that quietly pumps the liquid back, and the two ends where heat is taken in and given out.
1. Heat boils the liquid at the hot end
The hot end, called the evaporator, is where heat enters. It warms the working liquid until it boils, turning it into vapour. Because boiling takes in a lot of energy, this end draws heat away from whatever it is attached to.
2. The vapour flows along the core
The vapour is free to move and the core down the middle is an open channel. A tiny difference in pressure sends the vapour rushing along the pipe from the hot end to the cold end — no valve or fan is needed to push it.
3. The vapour condenses at the cold end
The cold end, called the condenser, is cooler, so the vapour gives up its heat and condenses back into liquid. That released heat passes through the wall and warms whatever the cold end touches, which is how the heat is actually delivered.
4. The wick returns the liquid
Now there is liquid at the cold end but it is needed back at the hot end. The porous wick lining the inside wall draws it along by capillary action — the same force that soaks water up a paper towel — so the liquid travels back against the flow of vapour.
5. The cycle repeats
As long as one end is warmer than the other, the loop keeps running: boil, flow, condense, return. A heat pipe has no pump and no moving parts, so it can quietly move heat for years as long as it stays sealed.
What is a heat pipe?
A heat pipe is a sealed tube holding a small amount of a working liquid and its vapour, lined with a porous wick. Because it moves heat by boiling and condensing, it can carry heat along its length far faster than a solid bar of the same metal.
What is the wick for?
The wick is a thin, porous lining on the inside wall. Once the vapour condenses at the cold end, the wick draws that liquid back to the hot end by capillary action, the same effect that pulls water up a paper towel.
Does a heat pipe need a pump or electricity?
No. It has no moving parts and needs no power of its own. The loop is driven entirely by the boiling and condensing of the working fluid and by capillary action in the wick, so a heat pipe can run for years without maintenance.
Why is a heat pipe better than a solid metal bar?
Moving heat by boiling and condensing is very effective, so a heat pipe can conduct heat hundreds of times better than the same metal solid. That is why it is used to cool laptops, spacecraft and electronics.
Which way does heat flow in a heat pipe?
Only from the hot end to the cold end. The evaporator must be warmer than the condenser for the loop to run. Orientation matters too: gravity can help the liquid return, but a long or steeply tilted pipe can reach the wick's capillary limit.