The helium compressor that drives a cryocooler has to effectively reject the heat it’s removing from the helium stream to prevent itself from overheating, and keep the cryocooler cooling efficiently. In most cases, this means running a heat exchanger with a cooled water loop to keep everything cool. This can be very effective when you’re running high purity, clean water through the heat exchanger, but dirty, rusty, or impure water can reduce performance and foul the heat exchanger tubes. In the lab, we use a cooling loop independent from the building water paired with a water filter to help keep water as clean as possible in the loop. Unfortunately, our water pump in the loop had a cast iron casing and impeller, which began to rust and dirty the water. During the process of cleaning out the water and rebuilding the system, we’ve learned a few things about our cryocoolers and keeping them clean.
Sumitomo (SHI) Cryogenics:
The heat exchanger built into the SHI HE-4 cryocooler is a 1/2″ flattened copper tube, and pretty robust. It’s unlikely for anything to get stuck in the tube, although fouling on the surface is possible. Calling Sumitomo, they recommended reversing the water flow through the heat exchanger while the compressor is off to ensure the heat exchanger is free of obstruction. Running vinegar solution through the lines will help remove fouling.
Similar to the Sunitomo cryocooler above, the Cryomech cryocoolers also use copper tube in their heat exchangers. The technical representative from Cryomech recommends reversing the flow on the heat exchanger and to flush the system with a standard strength Calcium, Lime, and Rust (CLR) Remover solution. In the event of sludge build up, a 50 wt. % solution of hydrogen peroxide (H2O2) is a viable option in extreme cases.