In this work, a discontinuous airfoil fin printed circuit heat exchanger (PCHE) was used as a recuperator in a micro gas turbine system. The effects of the airfoil fin geometry parameters (arc height, maximum arc height position, and airfoil thickness) and the airfoil fin arrangements (horizontal and vertical spacings) on the PCHE channel’s thermo-hydraulic performance were extensively examined by a numerical parametric study. The flow features, local heat transfer coefficient, and wall shear stress were examined in detail to obtain an enhanced heat transfer mechanism for a better PCHE design. The results show that the heat transfer and flow resistance were mainly increased at the airfoil leading edge owing to a flow jet, whereas the airfoil trailing edge had little effect on the thermo-hydraulic performance. The airfoil thickness was the most significant while the arc height and the vertical spacing were moderately significant to the performance. Moreover, only the airfoil thickness had a significant effect on the PCHE compactness. Based on a comprehensive investigation, two solutions NACA-6230 and -3220 were selected owing to their better thermal performance and smaller pressure drop, respectively, with horizontal spacings of 2 mm and vertical spacings of 2 or 3 mm.

Flash evaporation processes are widely adopted in the desalination, food processing, waste heat recovery and other industries for heat extraction or product separation. In this paper, a pressure-driven phase transition model is developed by improving the Lee model and combined with the VOF (Volume of Fluid) method to numerically simulate the flash evaporation process. In this modified Lee phase transition model, the driving force for the rates of the local phase transition is calculated using the local temperature and static pressure magnitude. Numerical simulations are carried out in a water-circulating flash chamber and compared with the experimental results to obtain the values of the time relaxation parameters. And the non-equilibrium fraction of the outlet water can be effectively obtained under different conditions of flow rate, inlet temperature and initial liquid level height. The time relaxation factor takes values from 0.195 to 0.43 (P_out,v = 19.9 kPa) and from 0.31 to 0.92 (P_out,v = 31.2 kPa) with increasing superheat. In addition, the model can effectively represent the evolution of the unstable flow flash evaporation from the initial rapid boiling state to dynamic equilibrium.

To study the influence of the spatial configuration of two tandem ground-effect hydrofoils on the power-extraction efficiency, this paper uses the overset grid method to establish a two-dimensional numerical calculation model based on the STAR-CCM+ software. The comparison of the numerical results of the single hydrofoil verifies the validity of the method. This paper systematically analyzes the influence of ground effect on the energy extraction performance of the hydrofoil, and further studies the changes in the hydrodynamic performance and energy extraction efficiency of the hydrofoil when two ground effect hydrofoil are tandem. The results show that: compared with a single ordinary hydrofoil, the energy extraction efficiency of the ground-effect hydrofoil is slightly improved. When the hydrofoil is close to the wall, its lift will be significantly increased due to ground effect. When two ground effect hydrofoils are tandem with a phase difference of 180 deg, the vortex generated by the upstream hydrofoil will significantly increase the absolute lift of the downstream hydrofoil, but the energy extraction efficiency will be reduced significantly.