Experimental Assessment of a Reverse Brayton Cycle Based on Automotive Turbochargers and E-Chargers for Cryogenic Applications

Abstract

The utilization of automotive engine components for the development of a reverse Brayton cycle is shown in this study. The well-known characteristics of turbochargers and electrical centrifugal compressors commonly used in the automotive industry is a starting point for developing an experimental cycle configuration of a reverse Brayton refrigeration cycle with the ability to achieve up to 115K after a multi-stage compression with intermediate cooling and a single-stage expansion in a radial turbine using air (R-729) as working fluid. The use of a variable nozzle turbine allows to evaluate the optimum rack position for each operating point, as well as having control over refrigeration capacity. Studies over the minimum cycle pressure at the inlet of the first stage of compression have been performed to assess the possible benefit of creating vacuum or pressurize the working fluid. A 1m3 cooling chamber was attached to the installation to test the ability of cooling different thermal loads working under different operation ways, open or closed cycle, this is, letting the working fluid to interact with the thermal load or cooling it through a heat exchanger. The evaluation of thermodynamic parameters allows to obtain the coefficient of performance (COP) of the installation as well as the efficiency of each component. The analysis of turbomachinery performance will allow identifying weak points to improve cycle performance, and to improve the coupling model between the rotatory machines as well as to adapt the size of the installation to the refrigeration capacity required for different applications.