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Thursday, December 8, 2011

CryoBUG Theory

So what is this Fuderer patent I talked about in my last post, and how does it relate to the CryoBUG chiller I'm building now?

Well let's begin with what Fuderer had developed in 1965. In this first diagram contained in his patent #3203194 he lays out the most basic version of his unique refrigeration system.

Identification of Main Components:
20 -- Compressor
30 -- Condenser (water cooled)
40 -- Flash Chamber (Liquid/Vapor Phase Separator)
50 -- Evaporator/Condenser (Cascade Condenser HXC)
60 -- Lower Boiling Point Refrigerant Super Cooler (Sub Cooler #2)
70 -- Higher Boiling Point Refrigerant Super Cooler (Sub Cooler #1)
80 -- Evaporator
90 -- 1st Expansion Valve
100 -- 2nd Expansion Valve
110 -- Auxiliary Condenser HX
120 -- Cooling Water Supply/Return


Although the concept is sound, in it's portrayed form it still seemed a bit complicated. So I decided to see if I could simplify things and came up with this idea...

CryoBug HX Stack / Cold Head Diagram

This diagram has a reverse orientation from Fuderer's, showing the coldest part at the right (the Cold Head), and the warmer stages at the left. I'm just used to drawing things this way, and as the saying goes, old habits die hard.

As can be seen, the basics of Fuderer's design have been retained (Aux Condenser, Cascade Condenser, Sub Cooler #1, Sub Cooler #2). Although the expansion valves have been replaced with cap tubes (shown as dotted lines), and are directly sub cooled either within the cascade condenser (for CT #1) or within the Cold Head and it's interconnecting return line (for CT #2). I have also implemented additional sub cooling within the colder portion of the cascade condenser.

To elaborate...
What is shown as Sub Cooler #1 in the Fuderer system (item 70), is actually being performed by sub cooling CT #1 in the first half of my cascade condenser.  And what is shown as Sub Cooler #2  (item 60), is actually the 2nd half of the cascade condenser in my system. Further sub cooling is also provided by the returning gases after evaporation in the Cold Head, as they continue to travel past CT #2. This additional aspect is not covered in the Fuderer patent, but should still provide some added improvement in ultimate temperature.


The Phase Separator, which is based on a Temprite 340 coalescing oil separator, should provide superior liquid/vapor separation, and hopefully keep the high boiling portion of the refrigerant mixture from passing on to the cascade condenser.

In concept, the idea is to separate the high boiling component (probably Freon R-134a) via the phase separator and then use this to condense the low boilers, which in my case will be Freon R-14 with a little Argon dissolved into it. the better the phase separation, the more pure will be the R-14 being evaporated into the Cold Head, and thus a lower temperature will be the result. The dissolved Argon just makes it boil even colder, and the left over gaseous Argon creates a partial pressure effect that simulates an even lower evaporation pressure, and thus makes things even colder still.

Unlike Fuderer's example, CryoBUG in it's first iteration will not be water cooled, and instead will employ an air cooled condenser as shown in the diagram below. Cooling will be active, utilizing fans to move air through the condenser's fins.

CryoBUG Condensing Unit Diagram

The prototype will start out with no expansion tank, and probably no safeties (these will come later in the more refined design -- I'll just have to keep an eye on things in order to prevent possible damage to the compressor). And my charging manifold will suffice for the gauges. I'll also be doing the first test runs with a simple coiled tubing evaporator, no sub cooled CT #2, and no fancy machined Cold Head.

Next chapter, complete assembly...


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