Advice on DIY heatpipes

[VsUK81]

Hi guys, looking for a bit of advice. I'm experimenting with heating solutions for my outdoor potting shed & workshop & I'm putting together an electric tube heater connected to copper heat pipes. Now I'm starting off small just as an experiment to see if I can do it & then upscale if needs be. So my question is about the heat pipe itself. I'm wanting to start off by making a 50cm length of copper piping, sealed at both ends eventually, but I'm trying to work out how much water to use to create the right amount of evaporation with still a small amount of water left to keep the cycle in the vacuum. I assume I create by heating the bottom with the water & having a fixing at the top loosely fitted so steam starts to push out & then I would seal it. And water comes to boil much lower than 100c when in a strong vacuum?
I was thinking about having multiple pipes cut at 50cm with the same fixings at 1 end & then pour in different amounts for each pipe & then seal when its boiling & a vacuum has been created & see which transfers heat the best & then repeat. But I thought I would ask first in case any of you wise people have already done this & know the amounts needed to save me the time testing.
I plan on using standard 15mm piping as it seems to be cheaper per meter than 10 or 8mm piping.
Thanks in advance.

 

[Knappers]

I don't understand what your trying to do here.
I've tried...?

 

[oz-plumber]

What do you wish to achieve by lowering the boiling point of water?

If you want to heat your potting shed, why would you want to lower the temperature of the water to reduce the heat output of the system you are trying to design.

Lower water temp = lower heat output.

Lower pressure = lower boiling point.
Higher pressure = higher boiling point.

eg: Water boils on Mt Everest at 68C. Water boils at sea level at 100C.

 

[Enthalpy]

How much heat do you want to transfer?

Here is an example of an 8 x 350mm heat pipe that uses water:

SF-08-350-S | Heat Pipe, Heat Pipe, 8 x 350mm | RS - https://uk.rs-online.com/web/p/heatsinks/8670950

The rated heat is 32 W which may be useful for cooling electronics but is not much for heating.

‘The performance of a heat pipe is mainly determined by its wick structure, which performs 3 primary functions: First, to allow the backflow of the liquid from the condenser section to the evaporator section; Second, to allow the heat transfer between the inner wall and the fluid; Third, to provide room for the fluid to change phase.’

Standard Heat Pipes | MyHeatSinks - https://myheatsinks.com/heat-pipe-solutions/standard-heat-pipes/

Without a suitable wick the heat transfer between the water vapour and copper tube will be small making the heat pipe ineffective.