Analysis of the heat transfer characteristics of supercritical CO2 microchannels considering heat transfer with the surroundings

• A numerical simulation process for heat transfer with surroundings is proposed. • Boundary heat flux is used as the initial condition for calculating heat exchange in outer layer microchannels. • Heat transfer with surroundings decreases the heat exchange efficiency of the S-CO 2 working fluid in outer thermal channels. • A heat exchanger model with ≤5 % error, suitable for high heat transfer prediction. The unique microchannel and structural characteristics of printed circuit heat exchangers (PCHEs) make numerical simulations of the total heat exchange difficult. The overall performance is often represented by heat transfer between a pair of cold and hot channels, without considering heat loss of the heat exchanger. On the basis of experimental data for the thermohydraulic performance of PCHEs, in this study, the deviation between the effective heat transfer obtained via the heat loss analysis method and the heat transfer rate obtained via the heat transfer correlation method is examined. A boundary condition treatment method accounting for heat transfer with the surroundings is proposed. Under the assumption that the outermost layers of PCHEs serve as thermal channels, the influence of heat transfer to/from the surroundings on heat transfer of the outer-layer microchannels is investigated. The results reveal that the presence of external heat exchange leads to insufficient heat exchange of the work mass in the outer hot channel, whereas heat absorption in the adjacent cold channel increases. Finally, a one-dimensional heat exchanger model is developed through the finite difference method under certain assumptions, and the mathematical model is improved by considering the differences in heat transfer in the outer microchannels in terms of flow cross-sectional dimensions. Notably, a heat exchanger model with a relative prediction error not exceeding 5 % is obtained, which is extremely suitable for predicting performance under high-temperature heat transfer conditions.