Numerical modelling and transient analysis of a printed circuit heat exchanger used as recuperator for supercritical CO2 heat to power conversion systems

The paper presents a modelling methodology for Printed Circuit Heat Exchangers (PCHEs) in supercritical CO2 (sCO(2)) power systems. The PCHE model can be embedded in models of the full sCO(2) power unit for optimisation, transient simulation and control purposes. In particular, the purpose of the study is to assess the potential and limitations of lower order models in predicting the overall heat transfer performance of PCHEs. The heat transfer processes in the channels of the PCHE recuperator are modelled in 1-D and 3-D using commercial software platforms. The results show that predictions from the two modelling approaches are in good agreement, confirming that the 1-D approach can be used with confidence for fast simulation and analysis of PCHEs. Using the 1-D approach, the model was validated against manufacturer's data for a 630 kW PCHE recuperator, and subsequently used to simulate the performance of the heat exchanger at design and off-design operating conditions. Performance maps produced from the simulations, enable visualization of the influence of operating conditions on the heat transfer performance and pressure drops in the heat exchanger. Dynamic simulations under transient operating conditions show that the thermal expansion of the working fluid caused by a fast reduction in density and increase in pressure in the system, can be a concem, requiring careful management of the start-up process to avoid sudden changes in temperature and thermal stresses.