Last weeks I've been quite busy with finding solutions for clamping those micro parts and it's almost certain that ice chucking is the most desirable solution for this kind of application. Knowing this, it was just a question how to make a cold plate.
There are, in my eyes, different possibilities to develope this cold plate, like using technology based on refrigerants, vortex- or venturi-effects.
Looking at sites who use extreme cooling for cpu's gave me the idea to use another technologie based on THE PELTIER-effect, or TEC's (thermo electric cooler's). An application based on a peltier can be found on the next link, and it looks like the ice chuck I need to make myself.
http://www.melcor.com/mpa.html
Principle:
DC current flows through the TEC causing heat to be tranferred from one side of the TEC to the other, creating a cold and hot side. The sides can be inverted when you change the direction of the DC current, so it's easy to change from "cold-mode" to "heat-mode", and temperatures are easy adjustable by changing the amount of current through the peltier cell.
Other advantages of this technologie are that it takes little space to implement a peltier-cell (I've got room for a plate of 100mm x 100mm) and it's cheap technologie. This almost sounds like a commercial but is just a big introduction to my next problem.
I find it rather difficult to chose the right peltier cell. The danger excist in chosing the wrong cell, which causes to heat your chuck and not cooling it, because the hot sides really becomes hot
For example, I could use a high powered peltier cell so cooling will happen quite fast, but if you can't get lost of all the watts the peltier cell creates himself, the hot side becomes to hot and you'll end up heating everything and your cell will be ready for the dump.
So I'm searching someone who has experience with peltier technologie.
The goal is to reach a temperature of maximum -15°C at the cold side of the peltier, so a piece of aluminium with dimensions of 100mm x 100mm x 10mm shall cool down (between -10°C and -15°C) in a maximum of 10 minutes.
The maximum ambient temperature Ta will be a 30°C and a heat sink with a ventilator is prefered. (I know I ask much, sorry for that
Perhaps knowing this, someone with the experience of peltier could tell me if it will be possible to cool down with a single stage unit, or multistage has to be applied because the temperature difference is to big, or the time is to short. Or if it will be possible at all to use a peltier...
I already said that a heat sink with a ventilator is prefered, watercooling of the heatsink is perhaps a solution if there is realy
no where else to go. I would rather wait another extra 10 minutes, then use watercooling.
Cooling down the heatsink by injecting the coolants who are already available in the CNC machine (95% water) to improve the efficienty of the heat sink sounds like a good idea to me.
Here are some calculations I tried myself, but I changed the order in which they usually happen, tell me if I'm wrong somewhere:
Ta = 30°C
Tc = -15°C
Th = Ta + (P+Qc) (°C/W)
P: the power of the module
°C/W: the efficiënty of the heatsink, or thermal resistance
Ta: the ambient temperature
Th: the hot side temperature of the module
Tc: the cold side temperature of the module
Qc: the heat input to (or heat pumped by) the module in watt
the most difficult part here is to estimate Qc. There is no active load, only a passive load. I used a program from some site to estimate which load there has to be transported. It gave me about 20 watts, but I would like to see some calculations about this Qc.
Knowing most the elements have a dTmax of 65°C I estimated Th at max 50°C
deltaT = Th - Tc
65°C = Th - (-15°C) => Th = 50°C
Th = Ta + (P+Qc) (°C/W) => 50°C = 30°C + (P+20W) (°C/W)
I think it should be possible to get an heat sink of 0,20°C/W, so
20°C = (P+20W) 0,20°C/W => 100W = P+20W => P=80W
Following calculation I made to estimate the time it takes to cool down the piece of aluminium.
The amount of energie needed to transport, to assure a piece of aluminium will cool down from example 30°C to -15°C is according to me:
Q = m.c.dT where
c = 960 J/kgK
dT = 45K
m= 2710 kg/m³ . 0,0001m³ (100mm x 100mm x 10mm)
= 0,271 kg
=> Q=0,271kg . 960 J/kgK. 45 K = 11,7 kJ
so if my peltier with power 80 W has a Qmax of 50W, I would take 11700 J/ 50 W= 234 s to cool down the piece of aluminium.
Am I right now to think that I can order a peltier element with deltaT = 65°C and a power that shouldn't necessarrily exceed the 80 W,
for example the TEC1-12705T125 with
Umax = 15,2
Imax = 5 (=>P max=76W)
dT=67°C
Qmax = 52,1W
Hopefully my assumations where right and I didn't make to much faults, because I'm new peltier. A lot of information I found on sites for computermodding, but they always calculate with their known active load of the cpu which I have to estimate.
I have to thank all that have had the courage to read this post
and those who will reply with any kind of information.