A hybrid immersed boundary-lattice Boltzmann method for flow and heat transfer within a fluid heat exchanger

This study extended a hybrid immersed boundary-lattice Boltzmann method (IB-LBM) to analyze the hydrodynamic and thermodynamic behaviors of a fluid heat exchanger (FHE) with an asymptotic tube configuration. The effects of Reynolds number (Re), superheat levels, porosity, and cylinder arrangements on temperature and flow velocity were primarily examined. Several thermodynamic parameters were introduced as metrics to evaluate the thermal efficiency of the FHE. The results revealed that the Re significantly influenced the hydrodynamic and thermodynamic behaviors of the FHE. Pressure drops increased with higher Re, while the rapid decline in average heat flux was attributed to reduced conductive heat transfer caused by decreasing temperature difference. Moreover, superheat levels directly impacted the outlet temperature but primarily affected the frequency of flow velocity fluctuations. The average flow frequency, determined through the fast Fourier analysis, helps avoid resonance with the structure's natural frequency, thereby preventing potential structural failures. Additionally, five different porosity and cylinder configurations were analyzed to evaluate their impact on thermal performance of the FHE. The findings from this research provide valuable insights for enhancing the thermal efficiency of the FHE.