Modeling of S-RAM energy recovery compressor integration in a transcritical carbon dioxide cycle for application in multi-temperature refrigerated container systems.

With recent growth in awareness of the environmental impacts of hydrofluorocarbon (HFC) refrigerants, efforts towards the use of natural refrigerants as a replacement have increased dramatically. With these efforts has come the development of system components designed and optimized for the unique challenges surrounding these working fluids. The natural refrigerant carbon dioxide (CO2) has spiked particular interest for military application due to its global warming potential (GWP) of 1, low cost, high energy density, being non-flammable, and ease of maintenance. This research focuses on the development of a simulation model of a transcritical CO2 cycle for use in a U.S. Army Multi-Temperature Refrigerated Container System (MTRCS). The MTRCS has two compartments, each with variable cooling capacity and temperature. The core technology for the proposed transcritical CO2 cycle is a novel Energy Recovery Compressor (ERC) that utilizes the Sanderson-Rocker Arm Mechanism (S-RAM). The ERC is a two-stage compressor combined with a single-stage expander in one unit. This paper discusses the inclusion of the volumetric flow ratios of the ERC compression and expansion stages into the transcritical CO2 cycle model and presents results on the effects they have on the system operation and performance. The model is able to predict over and under-expansion at various operating conditions, considers these effects on overall system performance, and captures the effects of expander isentropic efficiency variation on the entire system performance. In addition, the next steps for further model improvements and the validation of model predictions through experimental results are provided.