Onset of nucleate boiling and pressure drop for subcooled flow boiling in a microchannel
摘要
The onset of nucleate boiling (ONB) and pressure drop during subcooled flow boiling in microchannels are key parameters for various applications, especially for the design of high-performance evaporators. However, available experimental data are limited, and existing correlations often show significant deviations. This work presents new ONB and pressure drop data obtained in a microchannel test section with an internal diameter of 1.1 mm, using R514a and R123 as working fluids. Experiments were conducted under high heat and mass flux conditions, ranging from 90 to 1808 kW/m2 and 1500 to 7300 kg/m2s, respectively, with saturation temperatures between 40 and 55 ° C. Results show that both heat and mass flux influence the wall superheat required to initiate ONB. Comparisons with existing predictive methods reveal that traditional ONB correlations tend to underestimate the superheat, consistent with previous microchannel studies. A new ONB predictive method is proposed, incorporating effects of surface tension, viscosity, inertia, evaporation momentum, and turbulence. Additionally, a new microchannel threshold criteria based on ONB observations is introduced. The subcooled flow boiling pressure drop results indicate that the pressure drop increased with the increasing of mass flux, heat flux, and vapor quality, while predictive models could predict this data with mean absolute errors as low as 9.0%.