Analysis of a compact heat exchanger using porous media cooling for use in a SCO2 rankine cycle

This paper presents the analysis of a compact heat exchanger design for application to a supercritical CO₂ (SCO₂) Rankine cycle waste energy conversion cycle. In this paper a compact heat exchanger using a multi-pass wavy channel configuration with surface area density β = 1222 m²/m³ and overall surface efficiency of 50% is analyzed using the NTU-ϵ method. Due to the high pressures used in the SCO₂ Rankine cycle (high side of 20 MPa low side of 12.4 MPa) the variability of the specific heat of SCO₂ leads to thermal pinch which must be accounted for in the modeling. Heat transfer augmentation is accomplished using porous media Silica particles on the low-side (12.4 MPa, a.k.a. hot fluid stream) of the SCO₂ heat exchanger. Results for heat transfer area versus duty, temperature approach versus heat transfer area, and, effectiveness versus duty are presented. Parametric results for entropy generation and Second Law considerations are presented in order to place a realistic bound on the analysis. Effects of porous flow on exit temperature, temperature approach and effectiveness are summarized. Results of this study can be used to guide design and development of compact heat exchanger selection for renewable energy waste heat recovery applications.