Preventing fatigue failure of copper refrigerant lines that connect compressors to condenser coils is a critical aspect of designing a new scroll compressor chiller configuration. Traditionally, R&D teams use a combination of physical testing and conventional finite element analysis to qualify the lines, especially to identify and correct resonances that could cause a reliability problem. But this approach is too slow to address chiller designs that have more than 100 refrigerant-line configurations. Trane has developed a new automated workflow capable of developing robust designs. The methodology combines design of experiments, response surface modeling and numerical optimization algorithms to configure refrigerant lines to minimize stress at running speed. The automated workflow uses ANSYS® software combined with Optimus® parametric optimization tools to evaluate 10 design alternatives and tune the refrigerant line geometry until operating stresses are below the endurance limit — all in the time once required to analyze just one design.
Existing Manual Process
Trane is the world’s leading producer of commercial and light commercial scroll air-cooled chillers that are used for air conditioning, process cooling, refrigeration, dehumidification and other applications. The company’s line of chillers includes single-scroll compressor configurations under 15 tons up to tandem compressors over 60 tons. The refrigerant lines are sized to survive long periods of near-continuous operation in an environment that teems with strong vibrations generated by compressor cycling. Lines that are configured with a resonant frequency away from the operating frequency of the compressor have a substantially longer fatigue life. Each line’s resonant frequencies depend on the details of its geometry, such as overall length, bends and bend radii. The geometry of each line is, in turn, constrained by the need to avoid obstructions, such as equipment and other lines.