I can see from some recent threads that the cooling of VW engines has been a 'hot' topic.
For the devotees of VWs: Are you aware of folks using heat pipes to assist with cooling?
As many folks may be aware, a "heat pipe" can transfer heat very efficiently from one place to another. They typically are comprised of a hollow tube with a working fluid inside (water, ammonia, freon, etc--chosen to work best at the temps encountered). The liquid boils on the hot end of the pipe, the vapor travels very quickly (typical velocities=100s of M/sec) to the "cool" end, where the vapors condense. The liquid flows back to the hot end via capillary action through a wick on the inside surface of the pipe and the cycle repeats. The heat transfer is very rapid, very efficient (they can move hundreds or thousands of times more heat than a similar sized copper rod), and entirely passive (the pipes are sealed--no pumps or external energy needed. Very reliable). They don't weigh much: just a little bit of fluid is needed and there is typically very little pressure difference between inside and outside, so the walls can be thin.
Many consumer computers now have tiny heat pipes to take the heat away from the CPUs.
Anyway, this IS experimental aviation. If VW engines have increased in output to where it's becoming hard to remove all the heat from the heads (there's only so much real estate for fins, and their efficiency decreases with fin length) I could see a heat pipe with a large finned evaporation end brazed to the fins of the head and carrying heat off to some purpose-built heat exchanger inside the cowl, or even to a finned exterior plate on the outside of the aircraft (under the nose bowl, in the prop blast?). This might be especially useful for turbo-normalized applications: Cooling an 80HP engine at 2000' MSL is a lot simpler than cooling it at 12K' (the cooler air up there doesn't come close to making up for the lower air density as far as cooling effectiveness goes).
Well, there are no new ideas under the sun, so I'm sure this would be being done already if needed/practical. Anyone know?
For the devotees of VWs: Are you aware of folks using heat pipes to assist with cooling?
As many folks may be aware, a "heat pipe" can transfer heat very efficiently from one place to another. They typically are comprised of a hollow tube with a working fluid inside (water, ammonia, freon, etc--chosen to work best at the temps encountered). The liquid boils on the hot end of the pipe, the vapor travels very quickly (typical velocities=100s of M/sec) to the "cool" end, where the vapors condense. The liquid flows back to the hot end via capillary action through a wick on the inside surface of the pipe and the cycle repeats. The heat transfer is very rapid, very efficient (they can move hundreds or thousands of times more heat than a similar sized copper rod), and entirely passive (the pipes are sealed--no pumps or external energy needed. Very reliable). They don't weigh much: just a little bit of fluid is needed and there is typically very little pressure difference between inside and outside, so the walls can be thin.
Many consumer computers now have tiny heat pipes to take the heat away from the CPUs.
Anyway, this IS experimental aviation. If VW engines have increased in output to where it's becoming hard to remove all the heat from the heads (there's only so much real estate for fins, and their efficiency decreases with fin length) I could see a heat pipe with a large finned evaporation end brazed to the fins of the head and carrying heat off to some purpose-built heat exchanger inside the cowl, or even to a finned exterior plate on the outside of the aircraft (under the nose bowl, in the prop blast?). This might be especially useful for turbo-normalized applications: Cooling an 80HP engine at 2000' MSL is a lot simpler than cooling it at 12K' (the cooler air up there doesn't come close to making up for the lower air density as far as cooling effectiveness goes).
Well, there are no new ideas under the sun, so I'm sure this would be being done already if needed/practical. Anyone know?
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