If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #1526
Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216
See, that was my initial reaction too, it`s just that when I re-focussed I considered again what we know: that a heatpipe of size definitely has much higher thermal conductivity than a piece of coppper of size, despite double the number of material interfaces => there is room to manoeuvre.
From looking again at the XtremeSystems thread I see that someone mentioned `vapour chamber` blocks on some GPUs. I think now that this is what I`m arriving at maybe...?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
That's true, but the point is that a long, thin copper rod has pretty lousy thermal conductivity, so it's not hard to beat.
A heatpipe works by vapour phase cooling: the alcohol boils at the hot end and condenses at the cold end, where a wick carries it back to the hot end.
Because the heat is carried by moving alcohol vapour, the delta-T and hence the effective thermal resistance hardly depends on the length and shape of the pipe. The heat just has to get from the pipe wall into the liquid at one end, and then from the vapour back into the pipe wall at the other end. In between, there is essentially no temperature difference except what's required to drive convection.
To sum up: The "Heatpipe beats solid copper" assertion really only holds for long, thin, heatpipe-shaped things that wouldn't be any good if they were made of solid copper. For a large enough cross-sectional area and short enough distance of heat travel, a solid copper slab will beat a hollow copper box full of alcohol vapour, and a slab with fins will beat a separate heatsink connected by a heatpipe. The main use of heatpipes is to cater for odd-shaped scenarios like inside laptops, where the heatsink can't be bolted right to the top of the CPU.
Registered Member #1526
Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216
I think that`s where my thoughts are - in that nether region where we define what `heatpipe-shaped` means. I guess the proper empirical research in this area has been done already though. I`m happy right now, no more niggling :o)
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Water directly on the CPU is probably not the best idea, the waterproofing of the die interconnects is never 100% so if you are using say one of the newer hybrid chips with bare die it could have reliability problems long term.
I had this happen once, had a dead laptop which did the 3BOD ie CPU/RAM fail. As no CPU was available I oven cooked the CPU for an hour at 125 Celsius as this procedure is recommended for SMDs prior to rework. I'll be damned, it worked!
Had previously reseated CPU, RAM and even did a low temp reflow of the GPU, no workie.
EDIT: Another approach might be to vacuum evaporate copper directly onto the core as serpentine patterns.
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
Threadsurrection!
wrote ... but what I`m thinking is that it`s the interface to the water that`s the problem, that`s why the direct to die doesn`t work because below a certain limit of area, the water just won`t take up the heat fast enough. So then you increase the area as discussed until you reach the sweet spot where the water can pick up the energy fast enough, in return for moving the water further from the die. Once the energy is in the water it`s problem solved.
It's not just an interface problem, it's also a flow-rate problem. The temperature rise in the water is the heat power / (volumetric specific heat * flow rate). If you bring the water closer to the die you're pumping it through a smaller cross-section. To keep the same temp in the water you need the same flow rate which requires higher pressure due to the smaller pipe area. Bringing the water closer to the die means you can reduce the flow rate a bit since you don't have the deltaT over the heat spreader, but I'm guessing the require pressure will still be very high.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
CPU waterblock idea...
For a large enough cross-sectional area and short enough distance of heat travel, a solid copper slab will beat a hollow copper box full of alcohol vapour, and a slab with fins will beat a separate heatsink connected by a heatpipe. The main use of heatpipes is to cater for odd-shaped scenarios like inside laptops, where the heatsink can't be bolted right to the top of the CPU.
