24 Nov
1999
24 Nov
'99
4:19 a.m.
According to my numbers: AL 210 Cu 380 Ag 408 - just
I have no expliciet
temperature named (and I'm somewhat confused, since I belived that lambda
is not depending on any temperature, but rather a coefficient(?) to
determinate
the conductance (?) - otherwise you'd have to
integrate lambda over the
temperaturerange within the object (remember, its w/mK, where K is dT))
For really accurate studies you do indeed have to do just that. Thermal
conductivity varies with temperature in much the same way as electrical
conductivity - and is (AFAIK) similarly infinite in superconductors, which no
doubt helps in cooling them...
> Anyway, it seems to me that the way to go is:
> 1. Peltier chip between CPU and heatsink. Heatsink is a large block of
copper.
Adds more and more heat - an infinite loop, where you have to add a bigger
part to the 'interchange' on the hot side, hust for transporting the
Yes, but not much more. I have never seen a figure for efficiency of peltier
chips, but I have always assumed around 200%, i.e. removes about twice as much
heat as it generates. (YMMV - Efficiency varies with temperature difference)
Peltiers own heat. I found it better to optimise the
transport within the
interchange element (as with using Cu or Ag, and mor efficient flow
structures) than just adding a Peltier. It's not about geting the
Possibly true in a lot of applications ...
target temperature as low as possible, but rather
transporting away
ad much (thermal) power as possible - that will inherently keep the
target from overheating.
I have not much experience with cooling CPUs, but with other semiconductors
(mainly power transistors) I have found that the biggest thermal resistance in
the circuit is almost invariably semiconductor to package exterior. The amount
of heat you can remove depends therefore mainly on maximum allowable temperature
of semiconductor and temperature of package surface. Getting the package
surface down another few degrees will in a lot of cases more than make up for
the extra heat the peltier chip produces. It may even do so without extra
cooling on the water (etc.) side - a few degrees lower on the IC balanced by a
few degrees higher on the water may transport all the extra heet you need.
Especially if your cooling is decent (low thermal resistance) between water and
ambient.
Also, if we just remove the heat to keep the device
(and all parts)
not below environment temperature we avoide all probems with
condensation (word?). We don't have to isolate all cooled parts
wathertight. Saving again a lot of recurces.
Condensation could be a problem, although it didn't seem to be in project
EUNUCH. Some sort of drying arrangement for the ventilation should be
sufficient though - this too can be done with cooling...
2. Use a
refrigerant cycle similar to a domestic freezer, but connect the
refrigerant circuit directly to holes bored in the heatsink block. No
intervening water circuit.
3. Of course, keep the refrigerant radiator well
away from the system, and
supply it with plenty of fans...
Or just use water and a real _big_ radiator to expell the heat.
After all, it's again about radiation a specific amount of
thermal power - and this can be done by either a high delta-T
or just a biger surface (phi = lamda * S * delta-T / delta). Conclusion: I belive that a 'soft' aproach can
give the same
result in most situation without spending endless resources
to push a single idea solution (brute force).
Perhaps. But your solution is limited by the ambient temperature, the maximum
chip temperature and the thermal resistance within the IC. For any better heat
transfer than that, you _have_ to cool below ambient. I was simply exploring
ways of doing this.
Philip.
This E-mail message is private and confidential and should only be read
by those to whom it is addressed.
If you are not the intended recipient, you are hereby notified that any
dissemination, distribution, copying, reproduction, modification or
publication of this communication is strictly prohibited. Please delete
the message from your computer and destroy any copies.
This message is not intended to be relied upon by any person without
subsequent written confirmation of its contents. This company therefore
disclaims all responsibility and accepts no liability of any kind which
may arise from any person acting, or refraining from acting, upon the
contents of the message without having had subsequent written
confirmation.
If you have received this communication in error, or if any problems
occur in transmission please notify us immediately by telephone on
+44 (0)2476 425474