Project 210K: the journey to -63C
Page 1: Introduction

Before describing the details of Project 210K, I would like to thank the wonderful AC/R engineer known on the Internet as 'Haeg'. He provided me much of the components used in this project, and he has proven to be a good sparring partner. He belongs to the top 5% of engineers in the realm of refrigeration. It is absolutely necessary to have backup in the form of such a person to successfully design and build a cascade refrigeration system.

Also, amongst all the good guys at the phase-change.com and refrigeration-engineer.com there is one person who provides invalueable information and excellent teaching: Gary, so I would like to thank him also before writing anything else.

After the death of my R507 liquid chiller due to the calcium chloride eating away the copper, I decided not to fix it, but instead move on to the next phase. Chilled liquid is great for cooling PC components due to it's flexibility, but below the -30 °C/-22F mark many problems rise. Standard aquarium pumps as used by many overclockers do not like these low liquid temperatures. Special pumps are very expensive and hard to obtain. The transfer fluid becomes a problem if you don't like poisonous and flammable liquids in your system (personally I don't like to have enough fuel in my PC to run a car for 10 kilometers).
These problems can be solved by evaporating the refrigerant in an evaporator directly on top of the CPU, skipping the secondary coolant loop entirely. The drawback: it is much harder to chill various components.

I already envisioned problems with using secondary coolant, so I already got myself an evaporator suitable for direct CPU use. Thus, switching the evaporator could be a simple job, and it would give me about -50 °C/-58F temperatures

But I never go the easiest route since the hard route provides more fun (usually). Therefore, I decided to experiment with a cascade refrigeration system. These systems use one stage to go from ambient to a lower temperature of, say, -20 °C. The second stage goes from that -20 °C to an even lower temperature. Rinse & repeat until the desired temperature is reached.

My final goal is -100 °C / -150F, but this step is too large to complete succesfully. Therefore, I will split the final goal of going to -100 °C evaporation temperatures into two separate projects. This is the first one with a goal of -63 °C / -81F. It will use fairly common refrigerants, which eases experimentation. To reach -100 °C, special exotic refrigerants are needed.