Mechanistic modeling of the liquid film shape and heat transfer coefficient in annular-regime microchannel flow boiling

Abstract

A methodology is proposed for predictive modeling of the liquid-gas interface shape and saturated flow boiling heat transfer coefficient in two-phase microchannel flows within the annular regime. The mechanistic model accounts for the effects of surface tension and interface curvature, gravity, and shear stress in determining the liquid film shape; one-dimensional conduction is assumed to occur across the variable-thickness film to calculate wall heat transfer coefficients locally along the channel length. Model performance is benchmarked against 251 experimentally measured heat transfer coefficient values taken from the literature for annularregime flow boiling in microchannels of a rectangular cross-section. These data are successfully predicted with a mean absolute error of 21.7%, and 72.1% of the points lie within an error band of ±30%. The match to data is poorest at lower vapor qualities corresponding to the onset of the annular regime, for which the heat transfer coefficient is underpredicted; an experimental investigation is performed to better understand the disparity under these operating conditions. Liquid film shapes are measured during adiabatic annular flow through microchannels of square cross-section for a range of channel hydraulic diameters (160 µm, 510 µm, 1020 µm) and operating conditions, so as to control the void fraction and Weber number of the flow. Using air and water as the working gas and liquid, respectively, trends in film behavior are identified and 2 compared against model predictions. The experimental findings reveal the non-negligible impact of capillary pumping on the interface morphology at the onset of the annular regime.

Novel Research on CuONPs/MWCNTs Effect on the Properties of Na-Bentonite Water Based Drilling Muds with Experimental Study

“…Filtration properties of CuONPs/MWCNTs added water based drilling muds.-Filtration of drilling fluid is its liquid phase being forced into a permeable formation by differential pressure. 50 It is the amount of filtrate (free water) passing from the drilling mud into a porous permeable formation. 51 In this study filtration loss and drilling mud cake thickness analyzes were performed in accordance with API standards.…”

Characterization of liquid film thickness in slug-regime microchannel flows

“…The experimental facility shown in Figure 1 is briefly described here; additional details are available in Patel et al [16]. The schematic diagram in Figure 1b fraction; the working gas is compressed air.…”

Two-phase flow morphology and local wall temperatures in high-aspect-ratio manifold microchannels

“…Depending on the channel geometry and flow characteristics, flow regimes present in microchannel systems typically include bubbly, slug, and annular flows. Inside each regime, mechanistic models specific to the flow morphology yield improved predictive capabilities [21].…”

“…Flow visualizations in microchannels are used to monitor the transitions between flow regimes [22][23][24][25][26], measure film thicknesses [21,27], determine nucleation sites and location of the boiling front [28][29][30], and match transient thermal data with flow characteristics [31,32]. The data collected in these studies provide vital information necessary to develop models used to predict system performance.…”