I will be reconfiguring our first AutoCascade (a two phase-separator with no auxilary condenser) into a single phase-separator with an auxilary condenser. The first design was a great learning experience and it will be very useful data to help me select proper captube lengths and refine the exact "design-point" cycle I will try and match. I now have a general idea of the heat-transfer performance of the HX's I have to use (and have incorporated this knowledge into my simulation model). Based on the test results with our first AutoCascade, I am confident the cycle performance measured will be quite close to my simulation model.
Refrigerant mass fractions are 58% n-butane 38% ethylene (at compressor inlet). Note in the "Compostion" table that only about 5% n-butane (mole fraction) is present in the evaporator.
I am going to tweak this cycle for CPU cooling duty (target -80C, 300W duty) and will post cycle details for "over-clockers" that my be interested.
Kevin, Matt, and Joe