Author Topic: Heat Pipes  (Read 7388 times)

Offline buffalow bill

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Heat Pipes
« on: August 04, 2011, 08:35:41 AM »
Hi,
Most of my workshop is in storage and the house is up for sale so at the moment all I can make are plans. Being of retiral age, my aim is to reduce all house/shop running cost. I’m thinking about solar heating and came across this
  
 


 but it raises several questions;-
How critticle is the 8ml and the volume in the pipe.?
How critile is it that all the air is out of the pipe.?
If all is sucessfull what temperature will the hot end attain – would it be better to braze the pipe work?

Bill

Sorry but my attemps to make the youtube thingy a link fails me!!!
« Last Edit: August 04, 2011, 12:37:58 PM by Bernd »
Helensburgh, Argyll & Bute

Offline David Jupp

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Re: Heat Pipes
« Reply #1 on: August 04, 2011, 10:10:36 AM »
Probably not too critical on volume of solvent, though there is likely to be an optimum for particular sizes/conditions.

The method shown won't remove all the air, but will drive some out - this will reduce the internal pressure and lower the boiling point of the solvent.

Hot end temp will depend on the heat input - the pipe will merely 'shunt' away some heat to the cooler end (where hopefully it is removed if you have sufficient cooling capacity).  Ignoring the fact that a thermal gradient is needed to get heat into the tube, the hot end will to some extent be limited by the boiling point of the solvent (assuming some liquid solvent remains).  So reducing the internal pressure helps to hold down the hot end temperature.

Offline Bernd

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Re: Heat Pipes
« Reply #2 on: August 04, 2011, 12:38:22 PM »
Fixed the link for you Bill.

Bernd
Route of the Black Diamonds

Offline buffalow bill

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Re: Heat Pipes
« Reply #3 on: August 08, 2011, 05:46:41 PM »
Thanks for the reply David.
From your reply I take that it would be better for a slight increase in volume of solvent than a decrease.

My thoughts for home heating,
1, using the heatpipes to collect solar heat.
2, transfering this heat into a transfer medium that will cope with low winter night temperatures
3, when in use does not consume any external energy

So the system---
Heatpipes 500mm long (because that’s how long the thermal vacuum tubes are) fitting these into a manifold, through wich antifreeze is passed. All this is outside and low down on the roof. After feeding the supply and return into the building. The hot pipe will rise up into a small heat exchanger to warm DHW then down into the under floor heating pipes, to rise up into the manifold return pipe. All circulating pipes to be a minimun of 22mm, the DHW heat exchanger at this moment in time is just another unknown. The under floor heating will be several 15mm pipe loops. My thoughts are that this system is only to provide background heating, so no pumps or thermostates will be used, may be or may be no!!!

Bernd thanks for the fix!
How are you at fixing other things ie my depleating number of brain cell s ?

( still make a balz trying to put them thar icons in ?)
Helensburgh, Argyll & Bute

Offline Bernd

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Re: Heat Pipes
« Reply #4 on: August 08, 2011, 09:15:50 PM »
Bernd thanks for the fix!
How are you at fixing other things ie my depleating number of brain cell s ?

( still make a balz trying to put them thar icons in ?)

Quite OK there Bill.

As far as the brain cells go, can't help you there, but the icons are easy. Once you've written your sentence do a space and then click on the icon of your choice. 

Take a look at what I have written back to you here by clicking on quote and you'll see the format of the message.  :nrocks: Look at the banna holding the madmodder rock sign you'll see how I added it in to the sentence. Hope this is helpful.

Sorry about the  :offtopic: reply here, but we aims to please.  :beer:

Bernd
Route of the Black Diamonds

Offline David Jupp

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Re: Heat Pipes
« Reply #5 on: August 09, 2011, 03:18:36 AM »
Heat pipes like this may not be very good collectors - the vacuum tubes that you mention are.

Heat pipes like this are more akin to the processor coolers in some PCs - they are good at removing heat from a hot area and transfering it along the tube.

Offline buffalow bill

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Re: Heat Pipes
« Reply #6 on: August 10, 2011, 04:48:56 PM »
David,
Thanks again for the info.

I think it may be an idea to try one to start with and see if it’s worth proceeding

:nrocks:

Bernd, very helpful

:beer:

Bill
Helensburgh, Argyll & Bute

Offline fatal-exception

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Re: Heat Pipes
« Reply #7 on: September 23, 2011, 06:55:21 PM »
Unless you really want to build your own, they can be found very cheap with the evacuated tubes if you find a supplier that gets them directly from China.

I've played around with these systems for a few years now. Its quite impressive at how much energy can be harvested from the sun, but this type of system will NEVER save you money. The cost of the system alone will eat up any savings you will potentially see for years to come. Maintenance is a big consideration, component replacement, replacing broken tubes (hail and kids are the big factors there), and god forbid your system freezes and you lose your expensive glycol.

Dont get me wrong, when a system is properly installed and working, they are fantastic, they just aren't for everyone.

Offline mechanicalmagic

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Re: Heat Pipes
« Reply #8 on: September 24, 2011, 12:12:34 AM »
Bill,
In a previous lifetime I made some heatpipes, still remember some of the design issues.  But first, answers to your questions.
Quote
How critical is the 8ml and the volume in the pipe.?
  Both can be changed without problems, leave about 1/3 of the bulb on the end empty.
Quote
How critical is it that all the air is out of the pipe.?
  With air in the pipe it will not function, or very poorly.
Quote
If all is successfull what temperature will the hot end attain.?
The boiling temperature of the "working fluid".

A little explanation of heat pipes. 
The "bulb" at the end is like a kettle or boiler, provides "working fluid" and a place to deposit heat.
The "tube" simply carries the heated vapor to the cold end, and back again as a liquid.
The "bulb" must be at the lowest point of the heat pipe.
The working temperature of the heat pipe is determined by: the vapor pressure of working fluid and the pressure in the heat pipe.
A well designed heat pipe can achieve supersonic vapor flow, moving lots of heat.

A quick analog (on a large scale, is a single pipe) steam home heating system.  bulb=boiler, pipe=pipe, cold end=radiator.

However, with a heat pipe, the temperatures can be designed for the application, but the fluid still travels downhill, and steam up.

Dave J.