Numerical Thermohydraulic Analysis of Flow Boiling in GeometricalModified Microchannels

Abstract

One of the major issues of flow boiling in microchannels is ensuring adequate management of thermohydraulic instabilities which can severely impact the system’s efficiency in terms of pressure drop and heat transfer coefficient. Focusing on microchannels with geometric modifications, varying inlet conditions and geometry dimensions, this study follows a novel approach on how to mitigate thermohydraulic instabilities and improve overall performance. This study uses Computational fluid dynamics (CFD) simulations in ANSYS Fluent with Volume of Fluid (VOF) model. The flow was kept transient and laminar in a 3-D domain with water (H2O-liquid) as working fluid and saturation temperature at 373.15 K analyse the flow and heat transfer characteristics in baseline rectangular, and compared with constricted inlet-, and expanding inlet- and diverging inlet of 0.2 o – 1 o microchannels. Pressure drop, heat transfer coefficient (HTC), Nusselt number, and frictional factor are studied and visualized across varying mass fluxes 3000 – 7000 kg/m2 s (for all microchannels) and angle of divergence 0.2o – 1 o (for the expanding inlet), with a mesh independence study ensuring accuracy. The expanding and diverging inlet microchannel showed a better thermohydraulic performance, having a 63.25% increase in HTC and a 64.16% reduction in pressure drop compared to the baseline design, highlighting its potential for enhancing thermohydraulic stability in flow boiling. Also, the angle of divergence gave more insights to the optimal specifications of the expanding inlet microchannel with 0.2 o having a better performance. These findings solidify the critical role of geometric modifications in optimizing microchannel performance, with the expanding and diverging inlet design resulting as the most effective configuration for a better heat transfer performance and pressure stability, thus giving valuable insights for future advancements in microchannel design and in the applications of flow boiling.