Expansion Valve........? Also general design Q.....

[postaldudeleo]

Do I really need an expansion valve on the capillary tube for safe measure or sould I do some other design precausion, Im not too sure.

In fact also, where do I place acces valves and why?

[froudeg]

Will need more info on the setup to answer first question properly...but TEV's (thermionic expansion valves) tend to be used in variable high load situations - such as the first stage of a cascade setup. They are rarely used with single stage direct cpu die setups - as the TEV needs to be connected directely to the evaporator, which can be a problem as its very bulky and hard to insulate and mount on a cpu evaporator.

Access valves are, at the very least, brazed onto the access port of the compressor (which is just another suction line), or onto the suction line itself via a T connector. This used both for initial vacuum pull down, and for charging the system with chosen refrigerant....usually via a manifold hose and guage set which lets you monitor pressures.

I tend to also braze in a T piece access valve on the discharge (high side) line, the main reason is for a much faster vacuum pull down - but it also lets you monitor high side pressures.

[gclg2000]

interesting

[buffarilla]

yes very

[postaldudeleo]

Thanks, but im using a very high load cascade system using helium. So ill probably have to use a TEV. Problem is that, which one should I use, do you know any sites that sell one or can you get them in a hardware store? Secondly , dont you need to just connect a capiilary tube through one end and the continuing cap tube ont he other end or do you literally have to attach the cap tube to it then attach the actual valve to the evaporator top.

[JSU]

im could you post some info on the cascade you intend on building? Helium needs alot of pressure to condense + has a VERY low heat capacity.

[froudeg]

Helium???? - um, i dont think so! To make a helium based cascade will be basically pointless....to get helium to condense requires a temperature so low that there is just no point making a cascade with it...the maximum temperature that helium will condense at is -268 celcius (critical temperature), yet its boiling point is -269 celcius. In other words you will need loads of stages, using various exotic gases to get down to -268 celcius, just so you can use helium to get a further 1 celcius cooler.

A liquid helium creating system is both not possible or practical with traditional cascade cooling system design that we have seen on XS forums. In order to liquify helium you must first precool it below its maximum inversion temperature - which is 43K (-230 celcius), so you would need a cascade setup that could get down to -230 celcius (which has yet to be achieved by anyone here), then you will need to expand the compressed gas through a throttling device which will further cool it due to the Joule-Thomson effect, producing droplets of liquid helium..this can be seperated and the remainder refed back round the system. The amount of liquid helium produced will be small, and for it to have enough thermal capacity to cool a cpu, you will need to produce a heck of a lot per minute.

With regards to the TEV, the valve has to be directly attached to the evaporator...as its output will effectively be an evaporator.

Cap tube is not used with a TEV - the liquid line (output of condensor) is connected directly to it - you can have a fairly long length of tube from condensor to it tho.

[chilly1]

The TEV (TXV) can be connected through a metering device to the evaporator in fact most if not all evaporqtors used commercially have a metering device. The use of a capillary tube to connect TEV to an evap is not really workable, Once the valve is connecterd to the tube the pressure will rise on its discharge raising the pressure on the backside of the bollows causing the valve to restrict teh valve more than normal, Sometime this is used to better meter teh coolant, I have done this in a HX for a cascade. I used 2 inches of .060 as a metering device it was done to better regulate the flow of refrigernat into teh system,.