New methodology for CFD simulations of compact evaporators used in automotive ORC systems

Abstract

Waste heat dissipated in exhaust systems of a combustion engine represent a major source of energy that can be recovered and converted into useful work. Waste heat recovery systems based on the organic Rankine cycle (ORC) have already proven their efficiency in recovering energy from different heat sources, thus, achieving a significant reduction in fuel consumption and exhaust emissions. This study aims to evaluate an engine's main component, an evaporator, using computational fluid dynamics (CFD). This study implements a coupling methodology between a one-dimensional discretised model of a working fluid (WF) and a three-dimensional solution for the gas and metal sides in the CFD software ANSYS Fluent. Computational results were compared with experimental test-bench data and with wall temperature contours registered using infrared thermography, which elicited good agreement regarding the evaporator performance, outlet temperature responses of the gas and WF, and wall temperatures. The evolution along the evaporator for all the parameters of interest, such as vapour quality, Reynolds or Nusselt numbers, and local thermal properties, were also predicted. The presented methodology represents a valuable tool for aiding the design and enhancement of compact evaporators used in automotive ORC systems.