Hello everyone! I've finally completed my R290 cold trap project, and it's working pretty ok-ish, meaning that it can indeed reach temperatures below -35°C, which is what I needed. However, having designed the circuit myself and being somewhat of a newbie, I definitely think something could have been done better. First of all, I must say that I didn't seal off the two access ports for now, mainly because I might need to add or remove refrigerant, and also because brazing with the gas inside scares me a bit, but I know professionals do it this way. Anyway, I've tested extensively with an Inficon for HC and have detected no leaks.

When charging the gas, I evacuated the system down to 250 microns, but unfortunately, the stiffness of the charging hose affected the accuracy of the gas gram measurement. Therefore, I charged it considering the superheat temperature, so in the end, I have no idea how many grams I put in.

After about an hour of operation, here are my observations:

Liquid line: 27°C, 13.5 bar
Suction line: -31°C, 0.3 bar

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It's worth noting that this cold trap could operate under very low load conditions for the compressor, so I had planned for a liquid accumulator, and it seems to be doing its job because I'm not detecting any anomalies in the compressor, such as an increase in current consumption which could indicate the compressor is operating with insufficient lubrication. I've also added more thermocouples to the system, such as:

Ambient: 15°C
Compressor: 50°C
Just out of the compressor: 65°C
Evaporator inlet: -41°C
Evaporator outlet after hours with no load: -38°C

I used 3.5 meters of 0.9mm ID capillary tube as indicated by the charts to achieve -35/-40°C evaporator temperatures. However, either it's too long, or I made a mistake by coiling it around the suction line including the liquid accumulator, because the capillary freezes very visibly.

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The suction line is also very cold, and the liquid accumulator freezes as shown in the photo.

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However, I imagine that with a higher ambient temperature and a higher load inside the cold trap, the situation might improve, but I still need to verify this.