A waste heat recovery system, based on a Brayton cycle, comprises a heater configured to circulate carbon dioxide vapor in heat exchange relationship with a hot fluid to heat the carbon dioxide vapor. An expander is coupled to the heater and configured to expand the carbon dioxide vapor. A compressor is configured to compress the carbon dioxide vapor fed through a cooler and a heat exchanger is adapted to circulate the carbon dioxide vapor from the expander to the cooler in heat exchange relationship with the carbon dioxide vapor from the compressor to the heater, wherein the expander and the compressor are mechanically coupled volumetric machines.