High-performance computing to enable next-generation low-temperature waste heat recovery

The Oak Ridge National Laboratory (ORNL), in collaboration with Eaton Corporation, has performed computational research and development to design an innovative, direct-contact heat exchanger (DCHE) that is optimized for a low-temperature organic Rankine cycle. A computational fluid dynamics (CFD) model of DCHE was developed in STAR-CCM+ which was later calibrated and validated against the experimental data from literature. The validated CFD model was used to develop an industry-relevant liquid-liquid direct-contact heat exchanger system with water and pentane working fluids. This work heavily relied on highperformance computing (HPC) resources to investigate multiple designs and to identify a baseline design. The innovative design consists of two chambers connected by a converging-diverging nozzle. Phase change for pentane, from liquid to vapor, occurs in the first chamber, whereas the second chamber serves as a separator. Outlets in the second chamber are staggered to prevent entrainment of the liquid water by the gaseous pentane. CFD results confirm that the design behaves as expected and the addition of baffles enhances mixing and heat transfer for higher flow rates while preventing entrainment of gaseous pentane by the liquid water.