Numerical investigation of low mass flux flow boiling in high aspect ratio microchannel subjected to constant temperature

This document presents a simulation-based study to understand flow boiling of water at low mass flux in a high aspect ratio microchannel subjected to constant wall temperature. In addition, numerical investigations are done to understand the influence of mass flux, at low mass fluxes, on flow boiling in high aspect ratio microchannels subjected to constant wall temperature. The dimensions of the microchannel under consideration are 1 mm (width) and 70 mm (length) while the mass flux is 30 kg/m 2 s. Studies help identify the flow regimes associated with flow boiling in high aspect ratio microchannel as well as the associated flow boiling parameters such as vapor fraction, vapor quality, temperature, heat flux, heat transfer coefficient, velocity, and pressure. The flow regimes are bubbly, bubble-slug, slug and semi-annular. The findings indicate that bubbles form and coalesce slowly, resulting in the production of low-quality vapors in bubbly flow. As the boiling progresses, this flow transforms into slug flow to annular flow characterized by higher vapor quality with reduction in heat transfer rate, drop in pressure and increase in velocity along the length of the microchannel. The increase in mass flux, from 30 to 90 kg/m 2 s, delayed the occurrence of flow regimes as well as significantly affected the flow boiling parameters.