1. Bryant Mueller M.S. Student Mechanical Engineering Room: 1335 ERB Email: bwmueller@wisc.edu Hometown: Two Rivers, WI

2. Modeling of a cold cycle 3He-4He dilution refrigerator Motivation and applications: -Sub-Kelvin cooling for space applications -Increased reliability over conventional dilution refrigerators due to the elimination of moving parts in the pump -Continuous cooling possible by using check valves to maintain 3He flow in one direction -Closed cycle allows conservation of the helium mixture Overview: -Dilution refrigeration cools by mixing two isotopes of helium -3He is circulated by a magnetic pump, with no moving mechanical components, that leverages the fountain effect of the superfluid 4He to increase the pressure of the mixture by raising its temperature. -Phase separation and superleaks allow the normal fluid 3He to be preferentially circulated through the superfluid 4He in the cycle -Operates as a superfluid Joule-Thomson refrigerator at startup to achieve temperatures low enough to allow phase separation

3. Refrigerator design and cycle description Refrigerator schematic Objectives: -Models of individual refrigerator components -System-level model -Parametric study of key variables to optimize the overall refrigerator design Cycle on a temperature – 3He concentration plot